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Did Velociraptor and Archaeopteryx climb trees? Claws and climbing in birds and other dinosaurs

The views expressed are those of the author and are not necessarily those of Scientific American.


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In a North American woodland about 115 million years ago, the dromaeosaurid Deinonychus climbs a tree to avoid the attention of the gigantic contemporary predator Acrocanthosaurus. This reconstruction - produced by Matt Martyniuk - is, of course, extremely speculative. But does it depict a plausible piece of behaviour?

Two weeks ago I and colleagues published a new paper in the august open-access online pages of PLoS ONE. Led by Aleksandra Birn-Jeffery of the Royal Veterinary College, and co-authored by Charlotte Miller, Emily Rayfield, Dave Hone and myself, the paper is titled ‘Pedal claw curvature in birds, lizards and Mesozoic dinosaurs – complicated categories and compensating for mass-specific and phylogenetic control’ (Birn-Jeffery et al. 2012).

This study is the latest in a long-running series of contributions on the hypothesised relationship that seemingly exists between behaviour and claw curvature in birds and other tetrapods; though restricted to foot (or pedal) claws alone (we ignore manual – or hand – claws entirely), it represents the grandest of such studies in scope and amount of data. While we certainly have results that are worth talking about, one of the take-home points of the study concerns the ambiguity and overlap that exists when we try to match claw curvature with behaviour.

Incidentally, this is another of those studies that was achingly long in the making. Things started with Charlotte’s Masters thesis in 2004-2005 (produced under Dave’s supervision) and it grew in scope and content over the intervening years. I feel that we all brought something useful to the table and the end result, with Aleksandra at the helm, is a strong paper. It goes without saying that this paper represents another triumph as goes open-access publishing. I think this is the third paper I’ve published in PLoS ONE. I have two more in press or in review.

A history of ideas on claw curvature

Ostrom's (1974) diagram showing pedal digit III and I ungual curvature in diverse birds. Archaeopteryx is in the middle.

The idea that claw curvature might represent some sort of special and reliable indicator with respect to behaviour and lifestyle is a fairly old one, perhaps best known due to its mention in the literature on Archaeopteryx. In 1974, John Ostrom illustrated the pedal unguals of various perching, predatory, climbing and ground-running birds alongside those of four of the Archaeopteryx specimens (Ostrom 1974) [note to theropod nerds: I will skilfully avoid the thorny topic of archaeopterygid systematics in this article]. Note that Ostrom illustrated pedal unguals – the bones that support foot claws – and not the keratinous claws themselves.

Because the Archaeopteryx unguals look weakly curved and have weakly developed flexor tubercles (the convex lumps on the undersides of phalanges that anchor the muscles and ligaments involved in digit flexion), Ostrom (1974) argued that the ungual morphology of Archaeopteryx was most consistent with a cursorial lifestyle, not one involving perching or climbing. Yalden (1985) also illustrated claws from a variety of living animals (this time, mammals as well as birds). However, he argued that comparison with living animals showed that claw curvature in Archaeopteryx is more like that of climbers.

Foot of the azhdarchoid pterosaur SMNK PAL 3830 (a very familiar specimen), with arrows showing the discrepancy between ungual length (tip marked by black arrow) and keratinous sheath length (tip marked by white arrow). From Hone et al. (2009).

As just mentioned, Ostrom used pedal ungual shape, not the shape of the keratinous claws themselves. We can see from living animals and well-preserved fossils that keratinous claws typically represent horny ‘extensions’ of the underlying bony cores: they make the claw in the living animal longer, more curved, and more pointed than the ungual bone is on its own. In some living animals (fruit bats, apparently, are a good example) the keratinous claw is substantially different in form to the ungual.

However, there’s some uncertainty over whether this is universally the case, since there are other living animals where the keratin sheath isn’t that much longer, or that much more curved, than the ungual (examples: some crocodylians, some ratites). This raises an interesting question: are unguals and their overlying keratinous sheaths similar enough in shape that they provide the same ‘signal’ as goes behaviour? We were only able to test this relationship preliminarily and found a significant difference between unguals and keratinous sheaths. Unguals are shallower and less curved than keratinous sheaths (Birn-Jeffery et al. 2012, p. 10).

Anyway, as is obvious from Ostrom’s (1974) and Yalden’s (1985) comparisons and conclusions pertaining to Archaeopteryx, several generalisations can be made about how claw shape (both ungual shape and keratinous sheath shape) relates to behaviour and lifestyle. In general, animals that run or walk on the ground exhibit weak claw curvature, those that climb up or cling to vertical surfaces have laterally compressed claws with needle-like points, and those that perch in trees have strongly curved, conical claws. Markedly curved claws are also (typically) seen in animals that use their extremities in apprehending prey.

Feduccia's (1993) suggested technique for measuring ventral (or inner) curvature in a claw. Some authors have criticised this as being less reliable than outer (dorsal) claw curvature; inner curvature is also less frequently measurable in fossil specimens.

Making generalisations ‘by eye’ is one thing, but there’s an undeniable degree of subjectivity when it comes to deciding how ‘curved’ a given claw is. Feduccia (1993) added rigour to this area by introducing a measure of how curved a claw is: it involved measuring the degree of curvature present across the inner (or ventral) curve of the claw.

Feduccia (1993) included a sample of over 500 bird species, but deliberately excluded raptors*, long-legged birds and various other ‘unusual’ kinds, presumably because they might cloud the results. Birds grouped into ‘ground’, ‘percher’ and ‘climber’ clusters, and Archaeopteryx – the main focus of his study – grouped among ‘perchers’ according to its foot claw curvature and among ‘climbers’ according to its hand claw curvature (Feduccia 1993) [see the figure below]. The three categories overlapped extensively and a criticism is that his grouping obscured the continuum that exists between them (Glen & Bennett 2007): many ‘perchers’ are actually generalists that spend much of their foraging time on the ground, for example (Pike & Maitland 2004). Another criticism (Dececchi & Larsson 2011) is that Feduccia’s exclusion of predatory birds disallowed fossil taxa (like Archaeopteryx) from falling into anything other than the ‘percher’ or ‘climber’ clusters: raptorial birds overlap with perchers and climbers (Pike & Maitland 2004) in claw curvature yet the species concerned are not ordinarily specialised for perching or climbing.

* Yes, I mean proper raptors… how I so hate the fact that a perfectly good, oft-used name is now hopelessly ambiguous whenever birds and non-bird maniraptorans are referred to in the same discussion.

Feduccia's (1993) scatter diagram, showing how claw curvature was distributed across the behavioural categories he recognised. Archaeopteryx pedal claws are marked by the horizontal line in the 'perchers' category; manual claws by the line in the 'climbers' category.

Since the publication of Feduccia’s 1993 paper, other authors have argued that claw curvature of the sort seen in Archaeopteryx is not demonstrative of a scansorial or arboreal lifestyle (Peters & Görgner 1992, Chiappe 1997, Pike & Maitland 2004, Glen & Bennett 2007, Dececchi & Larsson 2011). Other workers have applied claw curvature analysis to non-birds, including dromaeosaurids (Xu et al. 2000, Manning et al. 2006, 2009, Parsons & Parsons 2009) and the Triassic archosauromorph Trilophosaurus (Spielmann et al. 2005) (there’s also a short paper out there on pterosaur claw curvature but, despite having seen it once and allocated its existence to memory, I cannot find it today, nor does anyone I know own it). And interest in the claw anatomy of lizards means that there is now at least some literature on claw curvature and its correlation (or lack of correlation) with behaviour in these animals too (Zani 2000, Tulli et al. 2009).

What we did

We aimed to advance our understanding of this area by analysing an increased number of taxa, by seeing if the inclusion of a distantly related group (namely, lizards) affected the analysis, by looking at different kinds of claw measurement, and by testing claw curvature against phylogenetic control (Birn-Jeffery et al. 2012). A huge amount of data was collected: Aleksandra and Charlotte measured over 830 specimens belonging to 331 species. And several individuals of the sampled species (as many as six) were measured and included in the study.

(A) Feduccia's method of measuring inner claw curvature versus (B) Pike & Maitland's technique for measuring outer claw curvature. Fig. 1 from Birn-Jeffery et al. (2012).

Inner claw curvature (the measurement analysed by Feduccia) and outer claw curvature (the measurement analysed by Pike and Maitland) were both recorded, as was the vertical height of the claw at mid-length. The claw of pedal digit III is preferred for these studies, since it’s longest and is the one that interacts for the longest time with the substrate during locomotion. However, we also took data from the claws on the other digits and compared this with the digit III measurements when appropriate. We also included body mass data because one hypothesis we aimed to test was whether mass had any link with claw curvature (note that Pike & Maitland (2004) tested for the effects of mass on their dataset too). And we also mapped species onto phylogenies in order to see if relatedness had any special control over claw morphology. Animals were placed into four behavioural categories determined by dominant aspects of their lifestyle: we recognised ‘predatory’, ‘climber’, ‘percher’ and ‘ground-dweller’ categories (Birn-Jeffery et al. 2012).

Some basic (and, perhaps, predictable) conclusions were arrived at, by which I mean that we found some of the generalisations made about claw shape to be reliable… approximately. The claws of ‘ground-dwellers’ are less curved than those of animals in other categories, and ‘ground-dweller’ claws are also deeper at mid-length than the claws present in animals belonging to other categories. Animals in the ‘ground-dweller’ category were more variable in both inner and outer curvature measurements and in mid-length claw height than members of other categories (Birn-Jeffery et al. 2012), perhaps showing that animals with phylogenetically distinct backgrounds and histories become ground-adapted via numerous different evolutionary ‘routes’.

There are caveats

Otherwise, things turn out to be more complicated than we might prefer and our results are, to a degree, confusing and even conflicting. The animals we measured did not group into neat sets, there was substantial overlap between sets, there were various outliers and exceptions, and different data sets sometimes gave different conclusions.

Box plots showing inner claw curvature distinguished by behavioural category (Fig. 3 from Birn-Jeffery et al. 2012). On the left we see data from all extant taxa measured for the study, and - on the right - birds only. Note that both sets of plots are approximately similar. The most obvious thing is the massive overlap between the categories. Medians are marked by horizontal lines.

But this isn’t wholly a surprise. As discussed above, we already know that grouping animals into behavioural categories is difficult and relies on making broad (and perhaps unacceptable, even erroneous) generalisations. We also know that animals consist of more than just claws, so conclusions based on claw morphology alone need to be taken as provisional: there’s a lot of other data that needs to be considered if we want to properly develop hypotheses about an organism’s way of life*. And claw morphology may represent a compromise between different aspects of an animal’s lifestyle. We included all of these caveats within the paper (Birn-Jeffery et al. 2012): they might be missed since they’re buried in various sections of text so are worth emphasising.

* For a fuller discussion of many of the anatomical considerations that need to be taken into account here, see Dececchi & Larsson (2011). They mostly concluded that birds and other theropods did not possess the anatomical features expected for a climbing lifestyle. However, they relied heavily on comparison with mammals and we are concerned that this may have confused their analysis.

Conclusions, categories, confidence and contradictions

Nice depiction of the sort of difference in pedal claw curvature seen in a 'typical' ground-dweller (a lyrebird, at top) and a 'typical' percher (a bowerbird). From Morell (1993).

Anyway, what did we find? The inclusion of numerous lizard taxa seemingly did nothing to alter the robustness of the conclusions for birds, allowing us “to be more confident in asserting that trends in claw morphology occur across tetrapods” (Birn-Jeffery et al. 2012, p. 7). In other words, our analysis might help us be more confident in linking claw morphology with behaviour and lifestyle in fossil species where behaviour and lifestyle can’t be observed.

What about the relationship between body mass and claw morphology, and between phylogeny and claw morphology? Because we analysed inner and outer claw curvature as well as claw mid-length height, we recovered numerous different correlations. Firstly, there is a correlation between inner and outer claw curvature and claw mid-length height, which is good. Secondly, the claws of different digits differed significantly in morphology – digit III was always least curved, for example. This at least raises the possibility that different behavioural ‘signals’ might be obtained if different claws from the same taxon (or same individual) were analysed and emphasises the need for standardisation across studies.

Thirdly, both inner and outer claw curvature, and claw mid-length height, are correlated with body mass: claws are both less curved, and deeper, in heavier animals than in lighter ones, though the strength of these relationships was extremely low. These relationships were previously discussed by Pike & Maitland (2004). Fourthly, if we account for the impact of phylogeny – if we use a statistical method that removes the effects of relatedness – we find little relationship (or poor relationships) between claw curvature and behaviour (Birn-Jeffery et al. 2012). This result contradicts the general relationship we recovered between claw curvature and behaviour, and it’s difficult to know how to interpret it.

Female Satin bowerbird displaying typical 'ground-dweller' behaviour. Photo by Tatiana Gerus, licensed under Creative Commons Attribution 2.0 Generic license.

Most living taxa plotted where predicted, but there were a few surprises. The Satin bowerbird Ptilonorhynchus violaceus [adjacent photo by Tatiana Gerus] is part of the ‘ground-dweller’ group according to behavioural data, but it’s a consistent outlier in inner claw curvature, better plotting in the region expected for animals in the ‘climber’ category. I wonder if this is because the literature we used was misleading with respect to how much of a ‘ground-dweller’ the Satin bowerbird really is; then again, it does seem to spend more time on the ground than other bowerbirds.

Among the ‘climber’ group, the Frill-necked lizard Chlamydosaurus kingii had lower outer curvature than expected. Again, this might be because our characterisation of it as a ‘climber’ is too much of a generalisation: Frill-necked lizards walk and run on the ground a fair bit (their remarkable bipedal terrestrial behaviour is well known); they certainly aren’t restricted to a life of climbing. Several bird species we analysed (including stilts, bustards, shore larks and rheas) had especially low outer curvature measurements compared to other members of the ‘ground-dweller’ category.

Climbing, perching and ground-running Mesozoic birds and other theropods

Flexion in the foot of Deinonychus as reconstructed by Fowler et al. (2011). Dinosaurs like this could easily grasp things with their feet. Good for predation, but potentially good for climbing too.

What about fossil taxa? As we saw at the start of this article, much of the interest in claw curvature has been driven by a desire to better understand the lifestyle and biology of Archaeopteryx. While work on lizard claw curvature comes from a desire to better understand lizard anatomy and behaviour, work on claw curvature in modern birds has been instigated by palaeontological interest: yet another case where people interested in fossils – as opposed to people who work on modern animals – were the ones who had to get the ball rolling. Insert comment about lazy biologists and their obsession with genetics (I kid, I kid).

It isn’t just the lifestyle of Archaeopteryx that’s been controversial. A general debate about the lifestyles of all archaic Mesozoic birds has encouraged the study of their claws and other anatomical details, and a number of authors have suggested that dromaeosaurids and other non-bird coelurosaurian theropods might have been climbers too. Study of claw curvature and claw function in dromaeosaurids has also been driven by a desire to better understand the function of the remarkable giant, hyperextendable pedal digit II present in these animals (Manning et al. 2006, Fowler et al. 2011); in turn, this has resulted in some excellent research on claw anatomy and function in raptors and owls (Fowler et al. 2009).

My personal take on these studies is that they indicate a probable prey-immobilisation role in dromaeosaurid (and other deinonychosaur) digit II claws, but they also allow for the possibility that the claws had a role in occasional climbing too. The idea that dromaeosaurids clambered up the bodies of giant prey animals – a scenario promoted by Manning et al. (2006) – still seems absurd to me.

The tree-climbing Mesozoic theropods hypothesised to exist by certain authors: Rozhdestvensky's sloth-like Deinocheirus, Chatterjee's tree-climbing compsognathid (!) and ornithomimid (!!), Palm's scansorial dromaeosaurids.

I have a special interest in suggestions that non-bird theropods might have climbed trees and have published two articles on the history of this idea (Naish 2000a, b). Note that these are reviews of what people have said across history, not functional analyses. I’m wary of this part of the article turning into an opinion-fest, but I have to say that I think that the whole idea of climbing abilities in Archaeopteryx, in other Mesozoic birds, and in non-bird theropods has been afflicted by an undue amount of polarisation. On the one hand, some people want Mesozoic birds to be tree-dwellers because they argue that bird flight, and birds themselves, must have arisen in an arboreal setting. These are often (but not always) the same people who argue that birds cannot be dinosaurs. On the other hand, some people insist that Mesozoic birds and bird-like theropods were ground-dwelling animals without any climbing ability at all, and these are often the people who argue that bird flight and birds themselves evolved within a terrestrial, cursorial context.

Life reconstruction of the small dromaeosaurid Microraptor, shown in arboreal setting and with iridescent plumage, by Jason Brougham.

Based on what I know about living animals, I find it hard to look at Archaeopteryx, at an enantiornithine, or even at Deinonychus and Velociraptor without coming away with the idea that these animals very probably could climb if they wanted to (this contention is based on body size, limb proportions, forelimb orientation, and hand and foot anatomy). That doesn’t mean that they didn’t walk, run or forage on the ground for much or most of their time, in fact animals like Velociraptor- and Deinonychus-sized dromaeosaurids were obviously predominantly terrestrial. But if they needed to climb a tree – if it was a good idea in avoiding predators, or when finding food or shelter – I’m confident that they could do it.  When it comes to Microraptor and some other small deinonychosaurs, their curved claws, insane hindlimb plumage and small body size all render it likely that climbing was a frequent activity. The inference that there’s an incompatability between the dinosaurian origin of birds and a ‘trees-down’ origin for flight is flatly incorrect, though I’m not necessarily saying that maniraptoran flight originated in a strictly arboreal context.

With all of this in mind, we included claw data from various Mesozoic birds and other theropods in our analysis. Most non-avialan maniraptorans plotted within the space shared by ground-dwellers, climbers, perchers and predators, though inner curvature and outer curvature measurements sometimes gave different results. Theropods that I would predict to have little to no climbing ability – ornithomimids, compsognathids and Caudipteryx, for example – grouped in the ‘ground-dweller’ space (Birn-Jeffery et al. 2012). Velociraptor did too, perhaps showing that those ideas about hypothetical climbing abilities are sometimes not supported once you start looking at the details (incidentally, Parsons & Parsons (2009) argued that pedal claw shape in Deinonychus resembles that of climbing modern birds while pedal claw shape in Velociraptor does not). Based on outer curvature, certain other dromaeosaurids (including Deinonychus and Microraptor) and Archaeopteryx bavarica fell into the ‘climber’ cluster, as did some unambiguous Mesozoic birds like Changchengornis (Archaeopteryx is an “ambiguous bird”, since it doesn’t fall on the same branch as modern birds in all phylogenies) (Birn-Jeffery et al. 2012).

Inner claw curvature (Y axis) plotted against claw mid-length height in all extant animals (at left) and just modern birds (at right), with 22 different Mesozoic theropods added. The substantial overlap between the different behavioural categories is, again, obvious. See text (or the paper itself!) for discussion. Apologies about typo ('Alvarezsauroidae' should be Alvarezsauroidea).

Anchiornis – an elaborately feathered Jurassic maniraptoran suggested by some authors to be a troodontid (Hu et al. 2009) – plotted in different places according to the sort of data analysed, and two different specimens plotted in different places anyway. When inner curvature was measured, and when claw mid-length depth was accounted for, one specimen plotted within the ‘ground-dweller’ region, but the other one plotted within the shared ‘climber’-‘predatory’-‘percher’-‘ground-dweller’ space. The Cretaceous troodontid Sinornithoides did likewise (Birn-Jeffery et al. 2012). Finding Anchiornis to fall within an exclusive ‘ground-dweller’ region of the graph might seem in agreement with comments that Anchiornis had a “strong cursorial capability” (Hu et al. 2009, p. 462); however, the long feathers growing off the metatarsus and rest of the hindlimb are problematic for a terrestrial lifestyle.

Intriguingly, the different Archaeopteryx species plotted in different places. A. bavarica was in the area shared by members of the ‘climber’, ‘predatory’, ‘percher’ and ‘ground-dweller’ groups while A. lithographica was in the ‘ground-dweller’ space (Birn-Jeffery et al. 2012). This could highlight the unreliability of claw curvature for inferring lifestyle. Or it could show that different archaeopterygid taxa were ecologically and behaviourally very different – a wholly reasonable possibility.

Another climbing Deinonychus - this time climbing a big prey animal in the manner suggested by Manning et al. (2006). This photo was possibly taken in the Braunschweigisches LandesMuseum, Germany.

These results mostly conform to what I said above. Theropods that appear to be truly cursorial grouped as ‘ground-dwellers’, while those that look like ‘ability generalists’ (like Deinonychus) plot in the overlapping space shared by members of all behavioural groups according to some claw data, but in the ‘climber’ category according to other data (Birn-Jeffery et al. 2012).

We didn’t find any strong or convincing evidence for arboreality in any of the Mesozoic taxa we analysed (Birn-Jeffery et al. 2012), a discovery which is in keeping with the fact that none of them exhibit morphological features suggestive of such a lifestyle. There are no woodpecker or treecreeper analogues among Mesozoic dinosaurs, for example… at least, not yet.

All in all, I would say that our study seems to confirm via statistics what we already suspected: that claw curvature provides only an approximate view of lifestyle, that the behavioural categories used in claw curvature studies are overlapping, overly simplistic and perhaps inaccurate, that claw curvature doesn’t provide a single, simple guide to behaviour but needs to be considered alongside other lines of anatomical information, and that the results of claw curvature analysis are affected by body mass, phylogeny and even on how claw curvature itself is measured.

As always, there’s much more that’s worthy of discussion in the paper itself: it’s open access, so you can obtain it for free should you want to.

For previous Tet Zoo articles relevant to some of the themes discussed here, see…

Refs – -

Birn-Jeffery, A. V., Miller, C. E., Naish, D., Rayfield, E. J., Hone, D. W. E. 2012. Pedal claw curvature in birds, lizards and Mesozoic dinosaurs – complicated categories and compensating for mass-specific and phylogenetic control. PLoS ONE 7(12): e50555. doi:10.1371/journal.pone.0050555

Chiappe, L. M. 1997. Climbing Archaeopteryx? A response to Yalden. Archaeopteryx 15, 109-112.

Dececchi, T. A. & Larsson, H.C. E. 2011. Assessing arboreal adaptations of bird antecedents: testing the ecological setting of the origin of the avian flight stroke. PLoS ONE 6(8): e22292. e22292. doi:10.1371/journal.pone.0022292

Feduccia A. 1993. Evidence from claw geometry indicating arboreal habits of Archaeopteryx. Science 259, 790-793.

Fowler, D. W., Freedman, E. A. & Scannella, J. B. 2009. Predatory functional morphology in raptors: interdigital variation in talon size is related to prey restraint and immobilisation technique. PLoS ONE 4(11): e7999. doi:10.1371/journal.pone.0007999

- ., Freedman, E. A., Scannella, J. B. & Kambic, R. E. 2011. The predatory ecology of Deinonychus and the origin of flapping in birds. PLoS ONE 6(12): e28964. doi:10.1371/journal.pone.0028964

Glen, C. L. & Bennett, M. B. 2007. Foraging modes of Mesozoic birds and non-avian theropods. Current Biology 17, 911-912.

Hone, D. W. E., Sullivan, C. & Bennett, S. C. 2009. Interpreting the autopodia of tetrapods:interphalangeal lines hinge on too many assumptions. Historical Biology 21, 67-77.

Hu, D., Hou, L., Zhang, L. & Xu, X. 2009. A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus. Nature 461, 640-643.

Manning, P. L., Margetts, L., Johnson, M. R., Withers, P. J., Sellers, W. I., Falkingham, P. L., Mummery, P. M., Barrett, P. M., Raymont, D. R. 2009. Biomechanics of dromaeosaurid dinosaur claws: application of x-ray microtomography, nanoindentation, and finite element analysis. The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology 292, 1397-1405.

- ., Payne, D., Pennicott, J., Barrett, P. M., & Ennos, R. A. 2006. Dinosaur killer claws or climbing crampons? Biology Letters 2, 110-112.

Morell, V. 1993. Archaeopteryx: early bird catches a can of worms. Science 259, 764-765.

Naish, D. 2000a. 130 years of tree-climbing dinosaurs: Archaeopteryx, ‘arbrosaurs’ and the origin of avian flight. The Quarterly Journal of the Dinosaur Society 4 (1), 20-23.

- . 2000b. Theropod dinosaurs in the trees: a historical review of arboreal habits amongst nonavian theropods. Archaeopteryx 18, 35-41.

Ostrom, J. H. 1974. Archaeopteryx and the origin of flight. Quarterly Review of Biology 49, 27-47.

Parsons, W. L. & Parsons, K. M. 2009. Further descriptions of the osteology of Deinonychus antirrhopus (Saurischia, Theropoda). Bulletin of the Buffalo Society of Natural Sciences 38, 43

Peters, S. F. & Görgner, E. 1992. A comparative study on the claws of Archaeopteryx. In Campbell, K. E. (ed.) Papers in avian palaeontology Honoring Pierce Brodkorb. Los Angeles: Natural History Museum of Los Angeles County 36, 29-37.

Pike, A. V. L. & Maitland, D. P. 2004. Scaling of bird claws. Journal of Zoology 262, 73-81.

Spielmann, J. A., Heckert, A. B. & Spencer, G. L. 2005. The late Triassic archosauromorph Trilophosaurus as an arboreal climber. Rivista Italiana di Paleontologia e Stratigrafia 111, 395-412.

Tulli, M. J., Cruz, F. B., Herrel, A., Vanhooydonck, B. & Abdala, V. 2009. The interplay between claw morphology and microhabitat use in neotropical iguanian lizards. Zoology 112, 379-392.

Xu, X., Zhou, Z. H., & Wang, X.-L. 2000. The smallest known non-avian theropod dinosaur. Nature 408, 705-708.

Yalden, D. W. 1985. Forelimb function in Archaeopteryx. In Hecht, M. K., Ostrom, J. H., Viohl, G. & Wellnhofer, P. (eds) The Beginnings of Birds – Proceedings of the International Archaeopteryx Conference, Eichstätt 1984, pp. 91-97.

Zani, P. A. 2000. The comparative evolution of lizard claw and toe morphology and clinging performance. Journal of Evolutionary Biology 13, 316-325.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com! Follow on Twitter @TetZoo.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. Charles Hollahan 9:27 pm 12/17/2012

    I for one am glad that crocodiles don’t climb but isn’t the claw on a woodpecker for beating its head against the tree?

    I’d bet that Archaeopteryx would climb if it had to or wanted to.

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  2. 2. TimWil 9:43 pm 12/17/2012

    Great article. I also enjoyed reading the paper. I agree that the debate about the origin of flight has tend to become polarised between “trees-down” and “ground-up” ecological scenarios. This is unhelpful, IMHO.

    Firstly, a scansorial/climbing theropod (including the ancestors of birds) need not necessarily have been arboreal.

    Secondly, as you note, it is unfortunate (and occasionally disingenuous) that the “trees-down” vs “ground-up” scenarios have often been tied to different evolutionary hypotheses: “thecodont” (or whatever) vs theropod origin of birds.

    However

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  3. 3. naishd 9:47 pm 12/17/2012

    … something tells me you planned to say more :)

    Darren

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  4. 4. TimWil 9:48 pm 12/17/2012

    However, when you state: “The idea that dromaeosaurids clambered up the bodies of giant prey animals – a scenario promoted by Manning et al. (2006) – still seems absurd to me.”

    I’m willing to take this idea seriously (though not for the reasons presented in Manning &c). There is the association of _Deinonychus_ teeth with _Tenontosaurus_ bones. In this case, even if the predator didn’t bring down the much larger prey (i.e., by pack-hunting), then _Deinonychus_ may have scavenged on _Tenontosaurus_ (and carcasses of even larger dinosaurs, like sauropods). Here some clambering ability on the part of _Deinonychus_ might have been helpful.

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  5. 5. TimWil 9:49 pm 12/17/2012

    Sorry, bit trigger-happy with the “Submit”. :-)

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  6. 6. John Harshman 9:51 pm 12/17/2012

    When it comes to Microraptor and some other small deinonychosaurs, their curved claws, insane hindlimb plumage and small body size all render it likely that climbing was a frequent activity.

    Given the “insane hindlimb plumage” shared by Archaeopteryx, the inference would be that it was a frequent climber too, right?

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  7. 7. TimWil 9:58 pm 12/17/2012

    [ I’d bet that Archaeopteryx would climb if it had to or wanted to.]

    The question then becomes: *Why* would it want to?

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  8. 8. RaptorX 11:07 pm 12/17/2012

    Great article, I will certainly read the paper sometime in the near-future. I also find myself agreeing with you about Manning’s herbivore-climbing dromeosaurids, and in my opinion, it seems extremely far-fetched. Considering Fowler’s research, I personally agree with him that the claws were used for pinning and holding prey like living predatory birds (well, with the exception of slash-diving peregrines).

    Anyways, keep those papers coming. Not like I’ve got much else to look forward to. :)

    Link to this
  9. 9. Tayo Bethel 12:34 am 12/18/2012

    [ I’d bet that Archaeopteryx would climb if it had to or wanted to.]

    Large theropods, do any of you want an Archaeopteryx snack? Don’t worry, it wont do the obvious thing and climb the nearest tree if possible …

    Link to this
  10. 10. TimWil 12:38 am 12/18/2012

    [ Large theropods, do any of you want an Archaeopteryx snack? Don’t worry, it wont do the obvious thing and climb the nearest tree if possible …]

    If Archaeopteryx climbed the nearest tree, it might put it at just about mouth-level with a large predatory theropod. :-)

    Also… were there any large theropods in Archaeopteryx’s habitat? If it lived on an island (or a group of islands), there might not have been any large terrestrial predators.

    Link to this
  11. 11. Tayo Bethel 12:45 am 12/18/2012

    Incidentaly, how good might Deinonychus and maniraptorans with similar foot morphology have been at grasping?

    Velociraptor being terrestrial makes sense since its assumed habitat was desert.Presumably in a more wooded habitat it would show the specializations that might indicate climbing abilities–it’s certainly not large enough for its own weight to make climbing difficult.

    Link to this
  12. 12. TimWil 1:07 am 12/18/2012

    [ Incidentaly, how good might Deinonychus and maniraptorans with similar foot morphology have been at grasping?]

    Check out (free access):

    Fowler, Freedman and Scanella (2009) Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique. PLoS ONE 6 (12) e28964 doi:10.1371/journal.pone.0007999

    Note that this concerns prey immobilisation using a grasping foot, NOT perching (which, however, the authors do also discuss). One of the figures from the paper is given above, with the caption “Flexion in the foot of Deinonychus as reconstructed by Fowler et al. (2011). Dinosaurs like this could easily grasp things with their feet. Good for predation, but potentially good for climbing too.”

    Though perhaps not much good for perching. :-(

    Link to this
  13. 13. AndreaCau 2:11 am 12/18/2012

    It would be interesting to see where Dalingheornis ends up if included in your analysis.

    Zhang, Z., Hou, L., Hasegawa, Y., O’Connor, J., Martin, L.D. and Chiappe, L.M. (2006). The first Mesozoic heterodactyl bird from China. Acta Geologica Sinica, 80(5): 631-635.

    Link to this
  14. 14. JAHeadden 2:21 am 12/18/2012

    Note that Fowler et al. find better correlation with grasping behavior with the pes when using pedal digit pdIV than with pdIII. PdIII (and its ungual) has been conventionally used since Yalden, and almost exclusively despite some literature on the efficacy being quested. Fowler and Birn-Jeffrey both cite these studies, but Birn-Jeffrey still focused on pdIII. This is not a particular criticism, but it is one which Fowler et al. raised quite extensively. While Fowler et al. do not provide as extensive a database as Birn-Jeffrey, they samples more interdigital variation and claw geometry to digit than other studies, suggesting the extent of sampling is higher and may be better to start with on expanding than simply using pdIII MORE.

    As I raised here — ALLLLL the way at the bottom — I am curious what you might think of apparent predatory adaptations in the pes of therizinosauroids, which are apparently “herbivores” or something.

    Link to this
  15. 15. Elypha 2:59 am 12/18/2012

    “(there’s also a short paper out there on pterosaur claw curvature but, despite having seen it once and allocated its existence to memory, I cannot find it today, nor does anyone I know own it)”

    Hmm… is this one?
    Perkins, Sid. Curved claws hint at pterosaur habits. Science News. Oct. 26, 2002. Vol.162, Iss. 17; pg270

    Link to this
  16. 16. Jerzy v. 3.0. 8:31 am 12/18/2012

    Interesting paper. I wonder about two things:
    - How claws used for digging, eg. chicken and badgers fall in this picture,
    - How claws of climbing and predatory mammals look – say possums, tree porcupines, martens and sun bears. Quadrupedal climbers could be better analogues of non-avian dinosaurs. One may argue, for example, that lack of climbing adaptations in dino hindlimbs was compensated by using forefeet.

    Coming to think about it, cliche Deinonychus is imagined clinging to Teronotosaurs with all four legs. Was any functional analysis made of forelimbs?

    I still didn’t find the right format of your “All Yesterdays” book, but I am already enjoying imagininng what I would draw there – if I had time to draw, of course. One vision was an angry Gorgosaurus trying to knock down a dead tree, with the two Troodon looking out of tree hole, and a third clinging cat-like to the trunk.

    Link to this
  17. 17. Tayo Bethel 9:45 am 12/18/2012

    Dr. Naish:

    Could you explain why you think Deinonychus might have been able to climb trees?

    Link to this
  18. 18. vdinets 9:58 am 12/18/2012

    Charles (#1): crocodiles do climb trees. Juvenile Crocodylus acutus, in particular, are really good at climbing mangroves. A good place to see that is in the coastal lagoons of Santa Rosa National Park in Costa Rica, where many juveniles spend the day up to 3 m above ground. I don’t think it’s ever been published – thanks for the idea!

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  19. 19. David Marjanović 10:49 am 12/18/2012

    “Changchenornis”

    Needs moar g!

    however, the long feathers growing off the metatarsus and rest of the hindlimb are problematic for a terrestrial lifestyle

    Well, yes, but they’re even more problematic for trunk-climbing, aren’t they?

    There are no woodpecker or treecreeper analogues among Mesozoic dinosaurs, for example… at least, not yet.

    Any scansoriopterygids in your dataset?

    A good place to see that is in the coastal lagoons of Santa Rosa National Park in Costa Rica, where many juveniles spend the day up to 3 m above ground.

    Publish!!!

    Link to this
  20. 20. vdinets 11:23 am 12/18/2012

    David: penning a short note for Herp Review at this very moment!

    Link to this
  21. 21. naishd 11:30 am 12/18/2012

    Thanks for great comments so far. Answers are coming.

    Darren

    Link to this
  22. 22. Heteromeles 12:11 pm 12/18/2012

    @TimWil: If Archaeopteryx climbed the nearest tree, it might put it at just about mouth-level with a large predatory theropod. :-)

    Yes yes. Just to be a party pooper, I should point out that many modern conifers have a growth spurt period that takes their leaves out of the mouth ranges of most herbivores. I strongly suspect that Jurassic conifers did the same thing. Even the biggest sauropod could only reach 20 meters or so in the air, and the biggest modern conifers top out around 100 meters.

    This leads to some interesting consequences. In the sauropod-ridden Jurassic, forest trees were probably quite tall and not interconnected by vines or side branches. A modern analogy might be the dipterocarp forests of South East Asia (or, of course, modern redwood forests). In both cases, these forests are a good environment for fliers and gliders, simply because of the climb. Oddly, the redwoods have only one glider, which says that having a suitable environment does not guarantee that any large vertebrates exploit it.

    Still, I would very puzzled if there were no arboreal small dinosaurs. There’s simply too much good stuff up in conifer canopies waiting to be exploited. See the December National Geographic for some modern examples.

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  23. 23. Yodelling Cyclist 2:20 pm 12/18/2012

    It’s a very impressive bit of analysis. With regard to the Deinonychus-climbed-on-its-prey hypothesis, this always seemed to assume that the sickle claw was being used as the climbing claw – the rest were less/not specialised for climbing. Have I misunderstood, or was the sickle claw not analysed in the paper (which was my cursory understanding). Sure, the climbing hypothesis may well be wrong, but surely the relevant claw needs to be studied.

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  24. 24. Yodelling Cyclist 2:23 pm 12/18/2012

    Oh, and that was 23 comments, btw. Why is this significant, now?

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  25. 25. naishd 4:00 pm 12/18/2012

    So many great comments, difficult to know where to start. I’ll do what I can…

    TimWil (comment 4): regarding the idea that Deinonychus climbed onto big prey animals in order to kill them… yes, maybe I should be less mean to this idea. After all, living big cats, falcons and some other predators do sometimes ‘climb’ onto prey, sort of, when reaching for vulnerable regions on the neck and so on (lions sometimes reach hand over hand to pull a hoofed mammal down toward the ground). However, I still think that Manning et al‘s scenario is weird, partly because Tenontosaurus – the prey item they had in mind – is so much bigger than Deinonychus. In those living animals that ‘climb’ on prey, the size discrepancy is less great and the prey is partially restrained or disabled before the predator does its ‘climbing’.. and that ‘climbing’ usually involves one or both feet still being on the ground.

    Also worth saying here is that the ‘prey-climbing’ hypothesis proposed by Manning et al. hinges on the idea that Deinonychus predated adult specimens of Tenontosaurus on a regular basis, and I now think that this is doubtful. As I (and others) have said before, Deinonychus and similar deinonychosaurs probably preyed on small and mid-sized animals; that is, on animals that were smaller than they were.

    More responses to come…

    Darren

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  26. 26. naishd 4:40 pm 12/18/2012

    Responses to John Harshman (comment 6) and David Marjanović (comment 19) on hindlimb feathering and its relation to climbing…

    When I said that “insane hindlimb plumage” (referring to Microraptor) might show that climbing was a frequent activity, I was referring specifically to the incredibly long hindlimb feathers of this taxon (and related forms), not the far shorter hindlimb feathering of Archaeopteryx and some others.

    And… are those feathers “more problematic for trunk-climbing”? There are various in-progress projects on Microraptor that help us better understand how its hindlimb feathers were oriented. Unfortunately I can’t discuss these conclusions yet, but I cannot see that hindlimb feather orientation (which – hint hint – may not have been exactly like the configuration shown in several published reconstructions) poses any major problem for climbing (or sitting on branches).

    The lifestyle of Archaeopteryx

    On tree-climbing in Archaeopteryx (TimWil, comment 7), I suppose you’re thinking that Archaeopteryx/members of Archaeopterygidae were animals of islands where the only vegetation was low scrubby bushes. I’ve always been a fan of this idea. However, like many modern birds and other animals, it may have been beneficial for Archaeopteryx to clamber about in, or perch in, vegetation of this sort.

    Then there’s the assertion from some (Feduccia in particular) that large trees were in fact local to the Solnhofen environment, with woodland-dwelling insects demonstrating the nearby presence of forested regions. Feduccia says that ginkgo fossils from Solnhofen were destroyed during WWII. We probably should think of Archaeopteryx as an animal of scrubby, arid, somewhat barren islands, but remember that it really looks like a generalist – reasonably suited to a bit of everything: some walking, some running, some climbing, some foraging on the shore etc.

    Why climb trees if they are present? To forage for prey, to roost off the ground, to avoid flooding, to find shelter etc. If a hypothetical Archaeopteryx is going to climb a hypothetical tree, I think we can assume that it might ascend to a height beyond the reach of a big predator. To do that, you ‘only’ need to climb beyond 4 m or so.

    More answers later…

    Darren

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  27. 27. Halbred 4:47 pm 12/18/2012

    Two things: On the Microraptor teaser, can we assume these forthcoming studies suggest a hindwing feather orientation different from the “flying squirrel” meme but also the “biplane” configuration? I’ve always liked the latter, because that’s how feathers grow relative to the hand. Second, the main body of the article speaks of multiple species of Archaeopteryx (like A. bavarica). I had thought the multiple genera/species concept has been continuously put down in favor of a single species concept, with differences in size or anatomy being attributed to ontogeny?

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  28. 28. TimWil 5:52 pm 12/18/2012

    “Then there’s the assertion from some (Feduccia in particular) that large trees were in fact local to the Solnhofen environment, with woodland-dwelling insects demonstrating the nearby presence of forested regions.”

    Yes, this was also discussed by Burnham (2007). I’m willing to believe there were true trees in the Solnhofen environment. Although Burnham’s reconstruction of Archaeopteryx as a specialised arboreal bird left me cold.

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  29. 29. TimWil 6:01 pm 12/18/2012

    Jerzy v. 3.0: “One may argue, for example, that lack of climbing adaptations in dino hindlimbs was compensated by using forefeet.”

    I’ve wondered this too. The thing is, dromaeosaurids and “proto-birds” like Arrchaeopteryx typically have forelimbs that were adapted for grasping large objects two-handedly: whether tree trunks or large prey (or both), I don’t know.

    On its own, a single manus had little if any prehensile ability – so grasping narrow branches was out of the question. But the forelimbs might have been useful in trunk-climbing.

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  30. 30. vdinets 7:31 pm 12/18/2012

    Darren: there is only one online reference to tree-climbing behavior in crocodiles, and it is by someone writing to you: http://dml.cmnh.org/1999Feb/msg00060.html
    Do you know who this guy is?

    Link to this
  31. 31. Tayo Bethel 10:17 pm 12/18/2012

    Would the fact that the manus of maniraptorans in general and dromaeosaurids in particular was relatively inflexible have impeded climbing ability?

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  32. 32. Dartian 2:25 am 12/19/2012

    Vladimir:
    there is only one online reference to tree-climbing behavior in crocodiles

    I know of a dead-tree reference. Guggisberg (1972:122-123) writes that baby crocodiles “can climb into bushes, up trees and even hang on reeds like chameleons”.

    Guggisberg, C.A.W. 1972. Crocodiles: Their Natural History, Folklore and Conservation, David & Charles, Newton Abbott.

    Link to this
  33. 33. Jerzy v. 3.0. 4:45 am 12/19/2012

    @Heteromeles
    So how plant communities in Jurassic forests looked like? I mean not single species, but general look of the plant community. I imagine Jurassic landscapes much like today, that is if there is enough moisture, plants push themselves in, and there is dense undergrowth and a layer of lower trees.

    Which brings another fascinating topic – look for adaptations for climbing in smaller ornithischians.
    There was lots of food waiting on treetops, so it seems reasonable that some learned to climb trees.

    Link to this
  34. 34. naishd 4:54 am 12/19/2012

    Still need to respond to many comments upstream… just want to say briefly – with regard to Jurassic flora – that the many cycads and cycadeoids, plus diverse conifers and ginkgos, might mean that the arboreal environment was more ‘climber friendly’ than some modern environments. Some people (e.g., Gary Kaiser) have suggested that the morphology of these plants made climbing up fairly easy while climbing down was less than easy, a situation that perhaps promoted the evolution of leaping and gliding. The Mesozoic was not dominated consistently by super-tall conifers with long, straight trunks.

    While I'm here, a reminder to some of you that there is a fairly lengthy Tet Zoo article on tree kangaroos.

    Darren

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  35. 35. Dartian 6:59 am 12/19/2012

    Darren:
    Some people (e.g., Gary Kaiser) have suggested that the morphology of these plants made climbing up fairly easy while climbing down was less than easy, a situation that perhaps promoted the evolution of leaping and gliding.

    Back in 1979, David Attenborough suggested the same thing in his book Life on Earth (the companion volume to the TV series) as a possible explanation for the evolution of flight in insects in the Carboniferous. Although I suspect that he wasn’t the one who originally came up with that idea.

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  36. 36. vdinets 9:32 am 12/19/2012

    Dartian: thanks!

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  37. 37. David Marjanović 10:39 am 12/19/2012

    Do you know who this guy is?

    Octávio Mateus is a paleontologist from Portugal who has named several Jurassic dinosaurs from there and has, apparently, joined French expeditions to Thailand.

    Link to this
  38. 38. Heteromeles 12:16 pm 12/19/2012

    @Jerzy and Darren: I too doubt that the Jurassic environment was all large trees. The bigger point is that, unlike the Amazon, I don’t know of any evidence of vines linking the conifers that made up Jurassic woodlands, and it’s not clear whether tree canopies interlaced during that period either. Therefore, the environment might favor fliers and gliders moving between trees (as in South East Asia), rather than climbers and leapers, as in the modern Amazon or Africa.

    That said, Darren’s right. Tree height is controlled in large part by how much water is available, and also indirectly by temperature. The biggest redwoods grow in very wet soil, to the point where building Highway 101 in northern California disrupted water flow and caused a groups of trees on the downhill side in Humboldt Redwoods State Park to lose the top 10 meters of their crowns, something that can still be seen today if you know where to look.

    Since wood is basically dead carbon, it tends to accumulate when there’s a surplus of carbon coming in versus carbon needed for cellular respiration. Since trees are ectothermic, respiration rates are related to temperature. As a result, the tallest trees are not in the hot rain forests, they are in the cool rain forests, because the cooler trees have more surplus carbon to turn into wood, while the hot trees respire more. If the Jurassic was hotter (and especially drier) than it is today, the trees would be smaller. Still, small is relative, and we’re talking about the difference between, say, 50 meters and 100 meters very crudely.

    The big issue with Jurassic forests is sauropods, which would open up most forests they could reach. They would almost certainly keep trees from growing away from the shelter of dense rocks or spiny thickets. We don’t have any modern analog for this system. The closest I’m familiar with would be oak savannas or the Serengeti, if you mentally replace the oaks or acacias with Jurassic plants. It wouldn’t look like the modern redwood forest, simply because even loggers aren’t a good analog for what sauropods would do, and also because redwood-style giants need the particular cool, wet conditions they grow in to become truly giant. I’m not at all sure where such conditions would have occurred in the Jurassic.

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  39. 39. naishd 2:41 pm 12/19/2012

    It’s been a busy day, no time for more responses. Here are one or more.. I dunno, I haven’t written them yet, let’s see how it goes.

    Jaime (comment 14) says…

    “Note that Fowler et al. find better correlation with grasping behavior with the pes when using pedal digit pdIV than with pdIII. PdIII (and its ungual) has been conventionally used since Yalden, and almost exclusively despite some literature on the efficacy being quested. Fowler and Birn-Jeffrey both cite these studies, but Birn-Jeffrey still focused on pdIII.”

    However, as I implied when you made similar comments on facebook, you are quoting Fowler et al. out of context. Our study (I mean, Birn-Jeffery et al.) tests the idea that claw curvature can be linked to behaviour/way of life; Fowler et al.’s study is about linking claw anatomy of predatory birds with specific killing styles. There is some overlap between the aims and approaches of these works, of course, but they otherwise are testing very different things. Fowler et al. correctly pointed to issues concerning a focus on the pedal digit III claw, but this is a special issue for them because some raptors so obviously differ in pedal digit claw size and shape. While the pedal claw on digit II is proportionally big in birds other than raptors (some passerines, for example), the digit III claw still serves us well. Besides which, we measured all claws anyway.

    Finally, as goes your mention of the pedal anatomy of therizinosaurs, you make some interesting points BUT – as you yourself note – we don’t yet have any good handle on how flexible the interphalangeal or metatarsophalangeal joints of therizinosaurs were (though I agree with others that they were probably not that flexible, hence not capable of Deinonychus-like grasping). Nor is it clear that the laterally compressed pedal unguals of Erlikosaurus are anywhere near as strongly curved as those of hawks or dromaeosaurids. As always, more work is needed, and I’d love to see where therizinosaurs plot in our analysis…

    On that note, yes, there are many interesting Mesozoic taxa we could have included in our analysis but did not. Without checking the respective literature, remember that it is often difficult to get precise curvature data from published articles or even photos, and we didn’t travel around Asia and elsewhere to look at those interesting taxa. So, sorry, no Dalingheornis (comment 13) or scansoriopterygids (comment 19). Maybe they could be included in a future look at the dataset.

    More later, maybe.

    Darren

    Link to this
  40. 40. vdinets 4:46 pm 12/19/2012

    Darren: thanks! his old email doesn’t work, but I’ll try to find him.

    Link to this
  41. 41. TimWil 6:03 pm 12/19/2012

    Darren Naish: “Some people (e.g., Gary Kaiser) have suggested that the morphology of these plants made climbing up fairly easy while climbing down was less than easy, a situation that perhaps promoted the evolution of leaping and gliding. ”

    Makes perfect sense to me! Furthermore, cycads and cycadeoids had nutritious “fruits” that might have tempted small theropods to climb up (and therefore act as vectors). Incipient wings would then be used to carry the theropod back down to earth. (BTW, no perching or any other specialised arboreal adaptations are required under this scenario. Just the ability to climb trunks, and get back down safely.)

    Jerzey v 3.0: “Which brings another fascinating topic – look for adaptations for climbing in smaller ornithischians. There was lots of food waiting on treetops, so it seems reasonable that some learned to climb trees.”

    There was perhaps not as much food as today in the treetops, because angiosperms really didn’t diversify into fruiting/flowering trees until quite late in the Cretaceous. The first birds evolved in a terrestrial environment that was dominated by various kinds of gymnosperms, especially cycads/cycadeoids in the middle storey.

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  42. 42. TimWil 6:10 pm 12/19/2012

    Tayo Bethel: “Would the fact that the manus of maniraptorans in general and dromaeosaurids in particular was relatively inflexible have impeded climbing ability?”

    I wouldn’t have thought so, but that’s just my interpretation. IMHO trunk-climbing ability would not have been impeded, but branch-grasping ability would have been severely impeded.

    For me, the lack of a prehensile manus is a big obstacle to the hypothesis that non-avialan theropods were arboreal. I wouldn’t be surprised if the first truly arboreal theropods were proto-birds like _Sapeornis_ and confuciusornithids, which show strong evidence of a perching foot. (Although for different reasons, little _Epidendrosaurus_ might have been arboreal… not sure what to make of this critter.)

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  43. 43. JoseD 12:36 am 12/20/2012

    As usual, I’m late to the game. Hopefully, my comment doesn’t go unnoticed or get forgotten.

    Naishd: “We also know that animals consist of more than just claws, so conclusions based on claw morphology alone need to be taken as provisional: there’s a lot of other data that needs to be considered if we want to properly develop hypotheses about an organism’s way of life*.”

    That’s why I really like papers like Holtz 1994 (“Predatory adaptions of the skull and unguals of modern and extinct carnivorous amniotes”) & Maxwell & Ostrom 1995 (More on that later), which this article reminded me of. They combine multiple lines of evidence (including comparisons to living animals) to give an overall idea of what extinct dinos were like when alive (to some extent).

    Naishd: “Velociraptor did too, perhaps showing that those ideas about hypothetical climbing abilities are sometimes not supported once you start looking at the details (incidentally, Parsons & Parsons (2009) argued that pedal claw shape in Deinonychus resembles that of climbing modern birds while pedal claw shape in Velociraptor does not).”

    Does that mean Velociraptor couldn’t have hunted prey RPR-style as hypothesized for Deinonychus, or does using RPR have more to do w/the grasping ability of one’s feet?

    Naishd: “Also worth saying here is that the ‘prey-climbing’ hypothesis proposed by Manning et al. hinges on the idea that Deinonychus predated adult specimens of Tenontosaurus on a regular basis, and I now think that this is doubtful. As I (and others) have said before, Deinonychus and similar deinonychosaurs probably preyed on small and mid-sized animals; that is, on animals that were smaller than they were.”

    To be fair, Maxwell & Ostrom 1995 did show that Tenontosaurus juveniles (to your point) & subadults (which, while only 2/3 adult size, were still larger than Deinonychus) were the preferred prey of Deinonychus individuals & packs (“While Deinonychus fossils are rarely found with other possible prey animals, three or four Deinonychus teeth typically turn up wherever there are Tenontosaurus remains”: go here and here), respectively. It’s been a while since I’ve read said paper, but that’s what I remember 1 of the main points being.

    In reference to Archaeopteryx, I’m curious about why Birn-Jeffery et al. 2012 referred to it as several species for the same reasons as Halbred in Comment 27. I also think it’s worth mentioning that, in “A Jurassic Mystery”, Archaeopteryx is depicted as living on a forested island & using WAIR to escape Juravenator (You can see some pictures in this link here). It’s been a while since I’ve read said book, though, so I don’t remember what evidence was presented.

    In reference to tree-climbing crocs, I think it’s worth mentioning that I 1st read about them in “Mysteries and Marvels of the Reptile World”.

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  44. 44. Dartian 3:14 am 12/20/2012

    Vladimir: No problem. It might also be a good idea to have a glance through Hugh Cott’s crocodile publications, in case he made any similar observations (both Guggisberg and Cott mostly worked with the Nile crocodile).

    Tim: Here, on the Sci Am blogs incarnation of Tet Zoo, the HTML tag for italics is: the less-than sign + the letter ‘i’ + the greater-than sign on the one side of what you want to italicize, and the less-than sign + the slash sign + the letter ‘i’ + the greater-than sign on the other side of it.

    If you want to have bold text you do the same but you replace the letter ‘i’ with the letter ‘b’. You can also use them both at the same time (but keep the tags separate!) and then you get bold italics.

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  45. 45. naishd 10:45 am 12/20/2012

    A few more comments before we all give up and move on to the next thing…

    Some of the comments above refer to the idea of ‘arboreal theropods’ or ‘arboreal Mesozoic birds’, as if that’s what those of us positing a climbing ability in Mesozoic dinosaurs are thinking of. However, arboreal animals don’t just climb – they live in trees. In talking about possible climbing abilities in Mesozoic dinosaurs, we are instead either talking about scansoriality – adaptation to a life of regular climbing – or are merely positing a general ability to climb as and when needed. So – just to be clear – the concept of a climbing Archaeopteryx, say, is not the same as the concept of an arboreal Archaeopteryx.

    On maniraptoran hands and their possible use in climbing (comment 16, 29 and 31): we know that, in theropods like dromaeosaurids, the hands faced inwards and had large, hooked claws. The point has been made in the anti-climbing literature (e.g., Chiappe 1997) that manual claw curvature in dromaeosaurids and oviraptorids was about similar to that seen in Archaeopteryx. This could mean that the claw shape concerned evolved under selection for a role in predation, and perhaps that it was irrelevant to climbing. Or it could mean that all of these animals were capable climbers.. not that they were specialised climbers, or habitually arboreal or anything like that, but that they were opportunistically scansorial. If it isn’t clear by now, this is the opinion I regard as most likely.

    Darren

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  46. 46. naishd 11:04 am 12/20/2012

    Climbing crocs: it may or may not be worth noting that the extinct Australasian mekosuchine Mekosuchus has been suggested to be a climber by croc worker Paul Willis. I know he has mentioned this idea in popular articles, but I would need to check to see whether it’s in any of his technical papers.

    Archaeopteryx taxonomy: my recollection is that the name A. bavarica was retained as a useful label for the Munich specimen – we are well aware of Mayr et al.’s (2007) and Bennett’s (2008) arguments about the proposed sinking of this taxon (into A. siemensii and A. lithographica respectively). Note the caveats in these studies: these things are never a done deal. Indeed, Bennett noted that “if no evidence can be adduced to demonstrate that more than one species is present in a sample of specimens, then it is most parsimonious to consider that sample to consist of a single species” (p. 539). Our results – the plotting of the Munich specimen in a different region of ‘morphospace’ from other archaeopterygids – could be taken as tacit support for the hypothesis that A. bavarica is indeed a distinct taxon.

    Darren

    Refs – -

    Bennett, S. C. 2008. Ontogeny and Archaeopteryx. Journal of Vertebrate Paleontology 28, 535–542.

    Mayr, G., Pohl, B., Hartman, S. & Peters, D. S. 2007. The tenth skeletal specimen of Archaeopteryx. Zoological Journal of the Linnean Society 149, 97-116.

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  47. 47. JAHeadden 4:20 am 12/21/2012

    Darren, thanks for replying to my comment here:
    However, as I implied when you made similar comments on facebook, you are quoting Fowler et al. out of context. Our study (I mean, Birn-Jeffery et al.) tests the idea that claw curvature can be linked to behaviour/way of life; Fowler et al.’s study is about linking claw anatomy of predatory birds with specific killing styles. There is some overlap between the aims and approaches of these works, of course, but they otherwise are testing very different things. Fowler et al. correctly pointed to issues concerning a focus on the pedal digit III claw, but this is a special issue for them because some raptors so obviously differ in pedal digit claw size and shape. While the pedal claw on digit II is proportionally big in birds other than raptors (some passerines, for example), the digit III claw still serves us well. Besides which, we measured all claws anyway.

    Note, however, that as my comment stated you two both address the same topics on selection of digit relative to usefulness to the study, with some equivocation to which toe is more useful. It was to this, and really only this, that I was asking about. Birn-Jeffrey et al. do not dwell on the topic of digit selection as strongly as Fowler et al. do, and so when your study focuses on variation in habitat usage by toe 3, Fowler et al. is focusing on variation among the toes to grasping behavior (including perching), but also to apprehension by the pes of prey items and how. Their useage was based, not on toe 2, but toe 4. My understanding of this is that toe 4 is useful because of its variability in posture among various groups of birds, including scansors, tree-climbers, perchers, raptors, and ground-runners. (Of course, a form of this can be said of toe 2, so distinguishing hetero and zygodactylous pes.)

    Is the use of toe 3 absolutely better than other toes, or is there a form of systematized use that is hard to break? That is the ONLY question where the comparison to these two papers leads me to ask. (I have nothing else but appreciation for the data that this paper provides, and thus nothing else to ask about but about the methodology.)

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  48. 48. naishd 7:23 am 12/21/2012

    Jaime: ok, fair enough. The simplest answer is to quote from the paper: “Following the rationale of previous claw studies, pedal digit III was used for the main analysis since it is longest in birds and is non-avialan Mesozoic theropods. Digit III therefore contacts the substrate first and last during terrestrial locomotion in these taxa” (Birn-Jeffery et al. 2012, p. 2).

    Darren

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  49. 49. David Marjanović 11:51 am 12/21/2012

    in “A Jurassic Mystery”, Archaeopteryx is depicted as

    …having a complete set of tertials like an albatross. *sigh*

    scansoriality – the ability to climb

    That’s not what it means in my experience; it designates animals that do climb regularly, they just don’t spend almost all of their time in trees. I’m not scansorial: I can climb trees of certain shapes just fine, I just almost never do it.

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  50. 50. naishd 12:34 pm 12/21/2012

    David is right – my bad. I will now exhibit some rapid self-correction and go edit comment 45…

    Darren

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  51. 51. David Marjanović 12:01 pm 12/22/2012

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  52. 52. RaptorX 3:47 pm 12/22/2012

    “Also worth saying here is that the ‘prey-climbing’ hypothesis proposed by Manning et al. hinges on the idea that Deinonychus predated adult specimens of Tenontosaurus on a regular basis, and I now think that this is doubtful. As I (and others) have said before, Deinonychus and similar deinonychosaurs probably preyed on small and mid-sized animals; that is, on animals that were smaller than they were.

    Considering this, do you believe that Deinonychus hunted in packs as Bakker and Ostrom have proposed? Or do you think that the assemblages are examples of agonistic behavior as Roach and Brinkman suggested?

    Just curious. :)

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  53. 53. naishd 7:16 pm 12/22/2012

    My personal suspicion is that animals like Deinonychus may well have been somewhat social – hanging out in groups of two or threes, co-operating in Parabuteo-style when it was advantageous etc. I’m not confident about ‘pack hunting’ of the sort often envisioned, nor do I think these animals only interacted agonistically. I personally imagine dromaeosaurid social behaviour to combine what we see in modern raptors, crocs and lizards – lots of complexity and lots of interaction in the social lives of these species, but hardly any long-term ‘pack’ associations of the sort seen in predatory mammals.

    Darren

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  54. 54. Heteromeles 12:36 pm 12/23/2012

    Does it make sense to differentiate between a pack and a mob, a pack being more organized? I’m thinking of, say, wild dog hunts, where they spread out to cut off escape routes, vs., say, herons or vultures flocking to a turtle hatching, but not cooperating to pick off baby turtles.

    I know that crocs practice a size hierarchy in feeding on carcasses, but do we ever see multiple crocs taking down one big animal?

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  55. 55. JoseD 1:32 am 12/24/2012

    RaptorX: “Considering this, do you believe that Deinonychus hunted in packs as Bakker and Ostrom have proposed? Or do you think that the assemblages are examples of agonistic behavior as Roach and Brinkman suggested?”

    You shouldn’t take Roach & Brinkman 2007 too seriously. When you actually look into said paper’s claims, you can see that a lot of them are either very misleading or just plain wrong.

    Heteromeles: “Does it make sense to differentiate between a pack and a mob, a pack being more organized? I’m thinking of, say, wild dog hunts, where they spread out to cut off escape routes, vs., say, herons or vultures flocking to a turtle hatching, but not cooperating to pick off baby turtles.”

    Yes. Ellis et al. 1993 neatly sorts out the various classes of social foraging. If you can’t get past the paywall, the 1st 2 pages of Orellana & Rojas 2005 sums them up. Packs are true cooperative hunters & mobs are either non-cooperative hunters.

    Heteromeles: “I know that crocs practice a size hierarchy in feeding on carcasses, but do we ever see multiple crocs taking down one big animal?”

    Yes, but, based on what I’ve read (E.g. See page 476 of “Animal Life: Secrets of the Animal World Revealed (American Museum of Natural History)”), in a pseudo-cooperative manner.

    [comment from Darren: added here because I can't login to the comments at the moment (!!!). Nile crocs have been seen to co-operate in the dispatching and also carrying and dismembering of large mammalian prey. I think it remains unknown whether this is just opportunism, or if it represents 'planned' co-operation.]

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  56. 56. naishd 9:22 am 12/24/2012

    Ellis et al.’s discussion of co-operative hunting is exactly the sort of thing I have in mind when discussing the possibility of social behaviour in dromaeosaurids. By now, I assume that most people look to crocodylians, lizards and birds when thinking about Mesozoic dinosaur behaviour, not mammals.

    Nile crocs have been seen to co-operate in the dispatching and also carrying and dismembering of large mammalian prey. I think it remains unknown whether this is just opportunism, or if it represents ‘planned’ co-operation. Certainly they ‘co-operate’ frequently enough for it to seem that they are deliberately social. This is seemingly not the case for all extant crocs, however.

    Darren

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  57. 57. Heteromeles 1:47 am 12/25/2012

    Thanks for the link to Elliott et al. On reading those first two pages, I do have an issue with their “pseudo-cooperation” and “true cooperation.” They assume that true cooperation only happens among relatives (on what evidence? Wolf packs that include outsiders seem to violate this category), while pseudo-cooperation has prey sharing being “chaotic.” Again, wolves violate this, but I suspect that crocs do as well, using something as simple as a size and dominance hierarchy. There’s nothing chaotic about that.

    The equation here is simple. If a single predator can neither capture nor eat an entire prey animal, but two (or more) can capture and eat an entire prey animal, then there is a benefit to cooperation, regardless of whether the predators are closely related or not. The question is how complex the cooperation is. I suspect that you could kill almost any large land animal with a sufficient number of Nile crocs, even if they didn’t spend much effort coordinating their attacks.

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  58. 58. Dartian 3:37 am 12/25/2012

    Heteromeles:
    The equation here is simple.

    It’s actually anything but! There are different opposing forces at play when predators (at least seemingly) co-operate. Each individual animal has its own fitness to increase. Optimally, the best course of action for (say) an individual wolf to follow during a moose hunt would be to just tag along with the rest of the pack, let the other wolves do the hard and dangerous work of dispatching the prey, and then just join in when dinner’s ready. Of course, the other wolves might have a problem with such a freeloading pack member and retaliate against it by restricting its access to the food (or something worse); thus, this kind of strategy in its above-described purest form might not pay off – at least not in the long run. However, between the extremes of selfish vs. non-selfish strategies there is a continuum of ways which a pack member can follow in order to increase its own individual gain while decreasing its own individual losses (in the form of minimising energy expenditure and risk of injury during the hunt).

    Or, to put the above in a nutshell: when discussing co-operation in animals, don’t forget your Dawkins! Animal group members are always both co-operating and competing with each other at the same time.

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  59. 59. JoseD 12:04 am 12/26/2012

    Heteromeles: “On reading those first two pages, I do have an issue with their “pseudo-cooperation” and “true cooperation.” They assume that true cooperation only happens among relatives (on what evidence? Wolf packs that include outsiders seem to violate this category), while pseudo-cooperation has prey sharing being “chaotic.” Again, wolves violate this, but I suspect that crocs do as well, using something as simple as a size and dominance hierarchy. There’s nothing chaotic about that.”

    No offense, but I think you might have missed/misunderstood a few things (Dartian covered 1 of them in comment 58): To quote Orellana & Rojas, true cooperative groups are generally “breeding pairs, family groups, or sibling groups” (E.g. “Occasionally an unrelated wolf is adopted into a pack…or a relative of one of the breeders is included…or a dead parent is replaced by an outside wolf…and an offspring of opposite sex from the newcomer may then replace its parent and breed with the stepparent…Nevertheless, these variations are exceptions, and the pack, even in these situations, consists of a pair of breeders and their young offspring”: from here)*; To quote Orellana & Rojas, true cooperative hunters share prey “according to some social order (e.g., dominance, hierarchy)” (E.g. “if the prey is smaller, like a musk ox calf, dominant animals (breeders) may feed first and control when subordinates feed”: from here)**.

    *As for “what evidence”, Orellana & Rojas 2005 cited “Bednarz 1988a, 1988b”.
    **To quote Zachary Miller, “crocodilians will “cooperate” to bring down large game in Africa, but after the carcass is dragged onto the shore, it’s every croc for himself.”

    Naishd: “Ellis et al.’s discussion of co-operative hunting is exactly the sort of thing I have in mind when discussing the possibility of social behaviour in dromaeosaurids.”

    Good to know at least some paleontologists have read it. When discussing social foraging in non-avian dinos, other paleontologists don’t seem to be familiar w/the various classes (I’ll take your advice & refrain from naming anyone in particular).

    Naishd: “By now, I assume that most people look to crocodylians, lizards and birds when thinking about Mesozoic dinosaur behaviour, not mammals.”

    To be fair, based on what I’ve read, bird packs are comparable to mammal packs in terms of social structure & hunting tactics (E.g. See the following quote for ground hornbills & this article for diurnal raptors).

    Quoting Tudge (here): “The sociality that is encouraged by the diet tends to spill over into all aspects of life. So it is that hornbills are fruit eaters and also, as we will see in Chapter 7, are outstandingly social breeders, with various kinds of social arrangements. But also among hornbills we see an interesting twistiwhere the innate sociality has in turn become adapted to a quite different kind of feeding. For among the biggest of all hornbills, and in various ways distinct from the rest, are the two species of ground-hornbills from Africa. Ground-hornbills are not mere fruit eaters: they are formidable predators. The beak is like an icepick. They can hack their way into a tortoise. The Northern species is among the biggest of all avian predators. The ancestors of ground-hornbills were presumably fruit eaters, and that, perhaps, is how they first evolved their sociality. Now, as predators, they hunt in packs. Typically they chase some hapless creature like a hare into a bush and then some act as beaters while others lie in wait and deliver the coup de grace. The packs are usually family groups. They can be seen as strategic predators like wolves or perhaps as problem families, terrorizing the neighborhood.”

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  60. 60. Heteromeles 1:47 am 12/26/2012

    As I like to point out: um, yeah, right. I don’t think animals have a fitness-o-meter. I certainly don’t. They seem to get by pretty well with things like a sense of fairness.

    Here’s the problem with animals calculating fitness: it assumes they can instantaneously calculate the future risk vs. reward from an action, and behave accordingly, and that they’re perfectly rational. Since this kind of behavior has been repeatedly disproved for so-called Homo economicus, it follows that animals with slightly less processing power probably can’t do it either.

    As I demonstrated in a paper on mycorrhizae in New phytologist a few years back, it’s perfectly possible to have a complex symbiotic interaction where neither partner knows what they are getting from the other. They each have a surplus of something the other is deficient in, but they have no idea how much the other partner has of what they so desperately need. So instead of attempting a trade based on instantaneous optimization, they invest and hope to get a return, with no more knowledge than that something they need is available.

    Similarly, you have to trash the math of pure strategies based on any permutation of Homo economicus optimizing trades (it’s BS anyway–see Black Swan for a detailed refutation by a degreed economist), and look at such interactions as investments with limited information, not trades. There’s a whole set of math on this–Wall Street runs on it. Problem is, biology is still mired in outdated economic models, because the math is pretty, you can get stuff published, and a whole bunch of professors have made their careers in it.

    Let me put it this way: if I can cooperate with a shark to catch a school of fish, I’ll give every other fish to the shark. I’m willing to bet the shark will let me have the rest, especially if I do this repeatedly (this has actually been reported in Hawaiian folklore for fisherman that had “guardian” sharks in their families). This is the type of prototypical fairness calculation that is actually quite simple. It doesn’t require a lot of complex math or modeling, and children do it routinely. You get into a problem with the shark if you have one fish, but so long as there’s more than one, it works just fine.

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  61. 61. Dartian 5:22 am 12/26/2012

    Heteromeles:
    I don’t think animals have a fitness-o-meter.

    Let’s put that strawman argument to rest at once. I neither said nor implied that when animals (or, indeed, any organisms) do things that increase their individual fitness they necessarily do so consciously. No, as the Theory of Evolution by Natural Selection predicts, such behaviour patterns (assuming that they have a genetic basis) have evolved. There is a very substantial literature out there dealing with this subject (Dawkins’ The Selfish Gene is still today probably the best general introduction to this topic).

    it assumes they can instantaneously calculate the future risk vs. reward from an action, and behave accordingly, and that they’re perfectly rational

    No, it does not assume any such things.

    biology is still mired in outdated economic models, because the math is pretty, you can get stuff published, and a whole bunch of professors have made their careers in it

    Well, if you think you can refute the theoretical foundations of what is by now a huge and well-established chunk of modern Evolutionary Theory, then by all means go ahead and publish. I’m sure both Nature and Science will be interested.

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  62. 62. Heteromeles 4:04 pm 12/26/2012

    Actually, if you check the math, it does make these assumptions. While I agree that organisms can demonstrate complex math unconsciously (as with wing shape in birds), I think there’s a real issue with any argument that boils down to “they are making decisions in a perfectly rational fashion that requires a super computer to deduce, they’re just doing it with a lot less brainpower than the model requires.” The problem with this model should be obvious: when the decision making process is substantially simpler than the model, then the model is most likely wrong. Yes, models are not reality (they’re supposed to be simpler, not more complex), but what I am seeing is that too much in evolution is about mistaking the model for reality and going forward from there.

    I’d suggest the same thing is going on here, with theories about cooperation. If bacteria and fungi can cooperate without using a complex rational decision-making strategy (see The Evolution of Cooperation), then more complex organisms can do the same thing.

    And as for publishing, I already have. Right now, I’d rather get paid for my writing, than pay to publish and have someone else own the copyright.

    If you want to really revolutionize theory, go over, look at how financiers are dealing with investments with limited information and unpredictable risk, and export that to biology. It’s the same process that’s happened repeatedly through history, when biologists swipe models from economics and sociology. Or better yet, read Taleb’s Black Swan to get the low-math conceptual version, and go from there.

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  63. 63. JoseD 10:59 am 01/1/2013

    @RaptorX

    When I said, “You shouldn’t take Roach & Brinkman 2007 too seriously”, I meant, “other than for the evidence of Deinonychus cannibalism” (the 1 thing said paper has to offer). I just wanted to clear that up.

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