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Tetrapod Zoology

Tetrapod Zoology


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Because giraffes are heartless creatures, and other musings

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


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Those of you who read the recent Tet Zoo article on The Second International Workshop on Sauropod Biology and Gigantism may have been wondering about the odd picture I showed in one of the slides of my talk. It was some sort of ‘survival of the fittest’ cartoon posed as a multi-choice exam question: it shows long-necked giraffes surviving in times of hardship while their short-necked brethren starve to death and decompose. Standard high-school textbook stuff. What makes the diagram funny – the reason it was included in my talk – is that some student genius sought to modify it. And hence we have…

This has become one of those internet meme things (among science nerds, at least) and is easy to find online. If you’re already familiar with it, pat yourself on the back for being wickedly trendy and down with the kids. And while we’re here, here’s another, err, interesting illustration I used in my talk…

What the hell kind of point was I trying to make here? It’s a response to Senter’s proposal that the sauropod neck might have evolved primarily for use in sexual selection (Senter 2007). There are lots of reasons for disputing this proposal – as you’ll know if you’ve read the Tet Zoo article on the subject, or the response I and colleagues published (Taylor et al. 2011) – but it’s a specific reference to our argument that suggesting that sexual selection operated on the same part of the body across the entirety of Sauropoda throughout its long history looks extraordinarily unlikely in view of what we know about other tetrapods. It would be similar to seeing, for example, Megaloceros-like antlers distributed across the whole of Artiodactyla. And there we have it.

Refs – -

Senter, P. 2007. Necks for sex: sexual selection as an explanation for sauropod dinosaur neck elongation. Journal of Zoology 271, 45-53.

Taylor, M., Hone, D., Wedel, M. & Naish, D. 2011. The long necks of sauropods did not evolve primarily through sexual selection. Journal of Zoology 285, 150-161 [free pdf]

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. farandfew 7:16 am 01/16/2012

    “I will eat all the leaves on this tree. I will eat more leaves than I should and then other giraffes…may die!”

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  2. 2. Heteromeles 12:08 pm 01/16/2012

    Oh come on, it takes so much less brainpower to talk about traits in isolation than as part of living animals. Are you trying to make us think or something?

    Actually, on a similar but unrelated subject, I was thinking about feathers on dinosaurs, and wondering how a tyrannosaur would preen its tail feathers. Or its head feathers, for that matter Given how much time and effort birds spend on their feathers (especially when molting), one would expect similar contortions and efforts from all feathered species. If they couldn’t do it, then perhaps they didn’t have feathers in the areas they couldn’t reach…

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  3. 3. vdinets 12:31 pm 01/16/2012

    Heteromeles: I would be surprised if at the time when dinosaur fauna was so diverse and abundant there were no professional cleaners, like modern oxpeckers and cleaner fishes.

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  4. 4. naishd 12:45 pm 01/16/2012

    Heteromeles…

    – point number 1 (on “traits in isolation”): say what? I was talking about ‘primary selective processes’, not the idea that structures can only have a single function.
    – point 2: I suppose tail feathers could be groomed/preened with the teeth (in fact, there’s a Tet Zoo ver 1 article – included as a chapter within Tetrapod Zoology Book One – on unusual premaxillary teeth in theropods and on what they might mean for grooming/preening). Could these animals also use their hand claws on their tail tips? I don’t know but I’m sure some theropods could do this.

    Darren

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  5. 5. hendric 12:51 pm 01/16/2012

    Darren,
    Has anyone actually tried the giraffe experiment to see if that would really happen? Ie, would giraffes let another with a shorter neck starve who wasn’t an offspring?

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  6. 6. Heteromeles 3:00 pm 01/16/2012

    @darren: Sorry, it was not meant seriously.

    As for the feathers, I’m sure theropods could groom in a number of different ways too. Perhaps even those hyper-extended sickle claws were used on occasion.

    Still, that hasn’t stopped, say, the artists on the annoying Terra Nova TV show from sticking some feathers on the arms of a Carnotaurus. Even though I’ve had pet birds, it never really dawned on me til today that preening feathers is *important,* and if a theropod caouldn’t preen a spot on its body, there might not have been feathers there.

    As for allopreening by pterosaurs or similar, I’d believe it when I see the teeth on the cleaner. AFAIK, the only animals that birds let onto their feathers are ants, and feathers are definitely more structurally complicated than the hide of an African ungulate.

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  7. 7. naishd 4:39 pm 01/16/2012

    Heteromeles: oh, ok, sorry :) I hope SIX years of blogging haven’t made me quick to take offence at innocuous comments.

    Grooming/preening: when you have time, check out The war on parasites: the oviraptorosaur’s eye view. The idea that feathered Mesozoic theropods must have groomed/preened has been mentioned a few times in the literature; it would be nice to demonstrate occurrences of this behaviour somehow, but – as usual – that’s asking too much of a crappy fossil record. You’re right that birds use ants for allopreening, but while we’re here, note that there are a few records of cross-species allopreening (e.g., Black vultures have been seen preening Crested caracara: Ng & Jasperson 1984, Souto et al. 2009).

    Refs – -

    Ng, D. & Jasperson, B.D. 1984. Interspecifc allopreening between crested caracara and black vultures. The Condor 86, 214-215.

    Souto, H. N., Franchin, A. G. & Júnior, O. M. 2009. New record of allopreening between Black vultures (Coragyps atratus) and Crested caracara (Caracara plancus). Sociobiology 53, 125-129.

    Darren

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  8. 8. vdinets 4:41 pm 01/16/2012

    Darren: what teeth? For preening feathers, the best tool is a toothless beak. What if early birds have lost their teeth precisely because they were dinosaur cleaners? Perhaps they have evolved the flying ability to glide from one dinosaur to another, or to jump up and reach dinosaur bodies without having to climb up the legs.

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  9. 9. naishd 5:16 pm 01/16/2012

    Vlad: maybe you forget that birds had teeth for something like two-thirds the whole of bird history. As I say in my old (2006) article, what’s interesting is that at least some of these lineages lacked teeth lining the jaws, but retained a small number of distinctive teeth at the jaw tips.

    And how do you know that (with respect to preening feathers) “the best tool is a toothless beak”? Extant birds possess special ‘maxillary overhangs’ that seem to serve almost exclusively in ectoparasite removal – how do you know these aren’t a compromise, and that teeth are actually superior? You might think that birds need to pull the feather vane through a toothless region of the jaws, lined with keratin. But such regions of the jaws were present in toothed birds (and other maniraptorans). I think teeth >and< toothless, rhamphotheca-lined zones together represent the 'best' set-up for effective preening.

    Darren

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  10. 10. vdinets 7:10 pm 01/16/2012

    Darren: Agreed. So, birds had teeth during 2/3 of their history because they needed them for preening dinosaurs. Later some of them developed independent lifestyles and lost their teeth ;-)

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  11. 11. Heteromeles 8:22 pm 01/16/2012

    @Darren: de nada.

    As for preening, perhaps those silly little arms on things like Carnotaurus were there for doing things like picking lice out of ears? Surely the fossil record is good enough that someone can figure out whether they could stick a claw in an earhole or pull out a booger from a nostril…

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  12. 12. HowardRichards 9:25 pm 01/16/2012

    I think it’s a bit unfair to compare sauropods with artiodactyls; the latter are just much too varied in shape, size, and lifestyle. Maybe a better comparison would be with primates and red butts.

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  13. 13. Dartian 2:16 am 01/17/2012

    Heteromeles:
    AFAIK, the only animals that birds let onto their feathers are ants

    Interspecific bird-on-bird cleaning is rare, but it has been recorded; on the Galápagos Islands, both mockingbirds and a couple of species of ground finches sometimes pick parasites from large sea birds. (Of course, both the mockingbirds and the finches occasionally go beyond mere parasite removal and start drinking their ‘client’s’ blood. But that’s another story.)

    As for birds letting other birds onto their feathers, there is also the carmine bee-eater of Africa, which frequently sits on the backs of larger birds (especially kori bustards) and uses them as vantage points. True, the bee-eaters don’t pick ectoparasites from their hosts (at least not AFAIK), but this kind of behaviour might show how such cleaning associations could originate.

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  14. 14. Hai~Ren 2:40 am 01/17/2012

    farandfew: Love the Eddie Izzard reference!

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  15. 15. David Marjanović 6:25 am 01/17/2012

    Actually, on a similar but unrelated subject, I was thinking about feathers on dinosaurs, and wondering how a tyrannosaur would preen its tail feathers. Or its head feathers, for that matter Given how much time and effort birds spend on their feathers (especially when molting), one would expect similar contortions and efforts from all feathered species. If they couldn’t do it, then perhaps they didn’t have feathers in the areas they couldn’t reach…

    Most birds do have feathers on their heads.

    perhaps those silly little arms on things like Carnotaurus were there for doing things like picking lice out of ears?

    Definitely not out of the animal’s own ears.

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  16. 16. vdinets 12:30 pm 01/17/2012

    Has anyone considered the possibility that those tiny arms were for egg turning? Bird eggs need to be turned regularly (although crocodile eggs die if turned… I don’t know about megapode eggs).

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  17. 17. Halbred 3:17 pm 01/17/2012

    I think birds probably use their legs and head to turn eggs (I’ve seen it!). I think it’s more likely that the “tiny little arms” of big guys like Carnotaurus were truly vestigal structures, well on their way out. Although I haven’t read that new paper about Majugasaurus’ complete, articulated arm, so maybe new information has cropped up on their possible usage.

    How do they use their arms on “Terra Nova?” Surely the artists and animators used the most up-to-date scientific knowledge in reconstructing the animal’s behavior OH WAIT

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  18. 18. Heteromeles 6:32 pm 01/17/2012

    They don’t use their arms in Terra Nova, aside from decoration. Admittedly, the idea of a theropod bending its head backwards to pick its nose or scratch its head is a bit goofy. Still, it makes somewhat more sense than, say, using a hind foot for the same function.

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  19. 19. vdinets 7:16 pm 01/17/2012

    Halbred: indeed, birds use their feet and beaks to turn their eggs. But for a Tyrannosaurus balancing on one foot or using its massive head that would be much more difficult. My understanding is that the eggs of large dinosaurs were much smaller relative to body size than bird eggs.

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  20. 20. TZBirder 4:08 am 01/18/2012

    As David has already pointed out, birds have feathers on their heads that they can’t preen themselves (but google “allopreening” to see how widespread mutual grooming is in birds). What’s more, those early feathers weren’t used for flight, so the animals didn’t depend on them so much for critical purposes. And flightless and obviously dinosaur-like birds like ostriches preen their (loose and fluffy, rather dinosaur-like) feathers rather rarely compared to those needing them for flight – they even lack a uropygial gland. They do care about them, of course, but preening isn’t a major passtime.

    Safari Ecology Blog

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  21. 21. David Marjanović 4:54 am 01/18/2012

    Has anyone considered the possibility that those tiny arms were for egg turning?

    Weren’t they too tiny and much too immobile for that?

    Oh, wait. You include tyrannosaurs in this? Tyrannosauroid arms were not tiny; they were extremely powerful and were probably used to hold prey between bites.

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  22. 22. Heteromeles 12:24 pm 01/18/2012

    @TZBirder: I guess the question is where the assumption that feathers are primarily for flight came from. I’m currently reading Thor Hanson’s Feathers, and while I’m not an ornithologist, I can readily see that feathers probably got used for non-trivial things like thermoregulation (especially on small-bodied individuals, perhaps including juvenile theropods), brooding, and signaling. I’d hazard a guess that ostriches get away with less preening because they are big and tend to live in warmer climates. I’d be more interested in finding out what Rheas do in Patagonia. Do they seldom preen as well?

    This actually leads to a more interesting question: presumably fully feathered dinosaurs brooded their eggs bird-style. What about the big girls, like T. Rex? Were they more like megapodes or crocodiles? I can’t see them incubating effectively, small arms or no.

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  23. 23. naishd 12:45 pm 01/18/2012

    Thanks for all these comments. Egg-turning: the literature says that non-bird theropods (even those as birdy as troodontids and oviraptorosaurs) did NOT turn their eggs. After all, their eggs seem to have been variously placed vertically in the substrate, laid in overlapping rings, or buried within vegetation mounds. So, no need to wonder how tyrannosaurids and abelisaurs turned their eggs – they didn’t. Even among crown-birds, egg turning is not ubiquitous. Megapodes don’t do it – remember that some of them deposit the eggs in burrows and don’t exhibit any parental care at all.

    Some more random comments…

    – Preening head feathers: most/all birds can reach their heads with their feet, and often scratch their heads this way. Some non-bird theropods could surely do this. If we’re talking about short-armed theropods that couldn’t reach their heads with their arms, and are unlikely to have balanced on one foot all that often, then it’s plausible that they used trees and rocks and such as scratching posts.

    – Nesting behaviour in theropods like tyrannosaurs: there’s good evidence that maniraptorans sat on their nests, but some/all other theropods likely built nest mounds of vegetation. They may or may not have guarded these mounds, but perhaps they didn’t sit on them.

    – Heteromeles: I’m reading Thor Hanson’s book as well, I mostly like it (will be reviewing it here at some stage).

    Darren

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  24. 24. vdinets 6:07 pm 01/18/2012

    Darren: thank you. I still hope to someday come up with a theory that would not get shot down in the first five seconds.

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  25. 25. William Miller 10:24 pm 01/18/2012

    David Marjanovic @21: “Tyrannosauroid arms were not tiny; they were extremely powerful and were probably used to hold prey between bites.”

    Even for the late, derived ones like Tyrannosaurus? I agree they weren’t small in any absolute sense; but compared to the size of the entire animal…

    Is the idea that Tyrannosaurus charged/bit/backed off while the big wound weakened the prey no longer considered likely?

    (Also… how did hadrosaurs living in Tyrannosaurus‘ age – or around any big theropod – defend themselves? Are they likely to have been faster than tyrannosaurs? Or did they just breed fast/grow fast/herd in huge numbers so *enough* survived? All the continents’ largest herbivores today are much bigger than their potential predators (except maybe tapir – they’re bigger than jaguars, sure, but not by as huge a proportion as elephants, hippopotamuses, and rhinoceroses vs. lions and tigers or bison, moose/elk (Alces alces) vs. wolves) – but the hadrosaurs in Tyrannosaurus’ environment were of comparable size to it, many smaller.)

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  26. 26. Heteromeles 12:18 am 01/19/2012

    @William Miller: I’ll have to dig out Karen Chin’s paper on rotten wood and fungal spores in (hadrosaur) coprolites, but here’s a (imaginative, if not totally facetious) theory:
    –hadrosaurs apparently ate rotten wood (with all that fungi in there, it’s fairly nutritious) *Dr. Chin found evidence of this).
    –According to the mycologists, Amanitas evolved in the Cretaceous. While I don’t think any vertebrate is normally immune to their nastier toxins, I suspect that they weren’t the only toxic fungi in the wood. Let’s assume there were a plethora of toxins in the rotten wood, from fungi struggling to hold on to their biomass.
    –Hypothesis: hadrosaurs secreted mycotoxins from their skin as a result of eating rotten wood, and that made them unpalatable to tyrannosaurs at least some of the time. They spread the fungal spores in their dung, completing the cycle.

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  27. 27. Dartian 1:52 am 01/19/2012

    Darren:
    If we’re talking about short-armed theropods that couldn’t reach their heads with their arms, and are unlikely to have balanced on one foot all that often, then it’s plausible that they used trees and rocks and such as scratching posts.

    Or maybe they scratched their heads with their hind feet when they were lying down – like this.

    William:
    All the continents’ largest herbivores today are much bigger than their potential predators (except maybe tapir – they’re bigger than jaguars, sure, but not by as huge a proportion as elephants, hippopotamuses, and rhinoceroses vs. lions and tigers or bison, moose/elk (Alces alces) vs. wolves)

    That’s true today, but keep in mind that as recently as during the latest Pleistocene, South American jaguars used to coexist with (among other things) mastodons and giant ground sloths.

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  28. 28. David Marjanović 6:29 am 01/19/2012

    Even for the late, derived ones like Tyrannosaurus?

    Particularly for Tyrannosaurus! It was able to lift 200 kg with it biceps alone, and a specimen that shows some healing after tendon avulsion shows that T. engaged in activities that required even more power. I’ll dig up the citation later.

    Is the idea that Tyrannosaurus charged/bit/backed off while the big wound weakened the prey no longer considered likely?

    No, but this requires a halfway well-placed bite, which may not in every case have been the bite used to catch the prey in the first place.

    how did hadrosaurs living in Tyrannosaurus‘ age – or around any big theropod – defend themselves?

    By staying away, walking/running fast and with high endurance, and living in herds, I suppose.

    –Hypothesis: hadrosaurs secreted mycotoxins from their skin as a result of eating rotten wood, and that made them unpalatable to tyrannosaurs at least some of the time. They spread the fungal spores in their dung, completing the cycle.

    Interesting idea.

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  29. 29. Heteromeles 11:32 am 01/19/2012

    Thanks Dave. Too bad I don’t know of a single case of a vertebrate sequestering fungal toxins. Otherwise it’s…plausible.

    Personally, I suspect that burst speed and herd maneuvers were probably more useful for getting away from tyrannosaurs.

    I’m rather more interested in whether the death of herbivorous dinosaurs provided the opening for the evolution of ectomycorrhizal plants (oldest fossil from the Paleocene), or at least their spread across the planet (they didn’t become widespread until the Tertiary). The basic idea is that in the Mesozoic, dinosaurs ate rotten wood and processed it into dung, from where arbuscular mycorrhizal fungi took the nutrients into plants. Ectomycorrhizae take nutrients straight out of rotting litter (or other fungi sometimes) and cycle them into plants. This process sequesters a lot of nutrients away from dead-trunk eaters, and I wonder if that’s one reason why few Cenozoic herbivores got to the size of hadrosaurs.

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  30. 30. Halbred 6:06 pm 01/19/2012

    Well, nobody has to “sweat” toxins. In the summer salmon rush, brown bears eat nothing but salmon, and bears shot and butchered during the salmon season are basically uneatable. Their meat tastes like rotten fish (seriously) and it more…chewy…than during the times of year that bears subsist mainly on large vertebrate prey (like moose) and plants.

    Could’ve been a similar situation with hadrosaurs. Maybe they didn’t bleed toxins, but maybe they were simply unpalatable given their diet.

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  31. 31. Heteromeles 8:38 pm 01/19/2012

    @Halbred: I supposed calling this the “Oscar Wilde Hypothesis” (the unspeakable chasing the uneatable) would tick off too many paleontologists, wouldn’t it? Thought so. Good point though, about the meat. I’m having fun trying to imagine what a T. rex would consider inedible.

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  32. 32. David Marjanović 7:24 am 01/20/2012

    I’m rather more interested in whether the death of herbivorous dinosaurs provided the opening for the evolution of ectomycorrhizal plants (oldest fossil from the Paleocene), or at least their spread across the planet (they didn’t become widespread until the Tertiary). The basic idea is that in the Mesozoic, dinosaurs ate rotten wood and processed it into dung, from where arbuscular mycorrhizal fungi took the nutrients into plants. Ectomycorrhizae take nutrients straight out of rotting litter (or other fungi sometimes) and cycle them into plants. This process sequesters a lot of nutrients away from dead-trunk eaters, and I wonder if that’s one reason why few Cenozoic herbivores got to the size of hadrosaurs.

    That’s fascinating. However, are you sure it’s not just the fossil record giving us the finger? Fungi don’t preserve well at all.

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  33. 33. Jerzy New 9:31 am 01/20/2012

    This theory also neatly solves the T-rex predator vs. scavenger problem.

    To get sufficent nutrition from the rotting wood, hardosaurs would have to eat enough biomass that they were unable to stand up and walk. Tyrannosaurus had no trouble to pick them up.

    Of course, if hardosaurs swallowed bigger tree trunks whole and lived in a hilly area, they might roll downhill on their sides at some speed.

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  34. 34. Heteromeles 9:54 am 01/20/2012

    @David: No, I’m not sure. The things I’m pretty sure about are as follows:
    –ectomycorrhizae didn’t appear in the Paleozoic, because none of the EM plants and only one clade of EM fungi had evolved by the Triassic.
    –Pines showed up…late Jurassic/early Cretaceous(?). They’re one major EM group.
    –The majority of fungal clades with EM members showed up in the middle Mesozoic (according to the molecular clocks).
    –Many EM angiosperms (especially the Fagales) showed up in the fossil record in the late Cretaceous, and expanded through the Paleocene, particularly in highlands. So did pines. Fortunately, their pollen is well preserved.

    The problem with ectomycorrhizal evolution is that it’s a massive example of convergence. EM plants evolved probably a dozen times, EM fungi evolved at least 5 separate times. The best model I’ve come up with is that both EM plants and fungi have some preadaptation(s) to the symbiosis. When such a symbiotic relationship starts, it spreads laterally among all susceptible species in the area, transforming the nutrient cycling in the ecosystem as it goes. My guess is that the preadaptation in plants has to do with a specific root anatomy and possibly the use of tannins as the primary chemical defenses (as opposed to alkaloids), but there’s nowhere near enough data to say for sure.

    My hypothesis is that ectomycorrhizal symbioses started, probably in high mountain pine and early fagalean forests, during the Cretaceous, and that they spread radically during the Paleogene. The impetus for their spread was the above-mentioned demise of large herbivorous dinosaurs, which provided a large new nutrient pool for the fungi to tap into. This gave a big advantage to those plants that could tap the fungi directly, rather than getting nutrients out of the soil after the wood and litter decomposers had finished.

    Long answer short: it’s guesswork. I tried publishing a paper, and found out that mycologists aren’t terribly receptive to evolutionary speculation.

    The fossil evidence might be out there, but there’s a chicken/egg problem. If no one’s looking for the fossils, who’s going to find them, or recognize them when they turn up by accident? The other problem is that fagalean evolution appears to have started in south-east Asia, and (AFAIK), that isn’t a great area for fossil hunting at the present time.

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  35. 35. Heteromeles 10:53 am 01/20/2012

    @Jerzy: And montane hadrosaurs also had one leg shorter than the other, so they could stand upright when walking across steep slopes?

    Link to this
  36. 36. David Marjanović 6:19 pm 01/22/2012

    if hardosaurs swallowed bigger tree trunks whole

    …that would have made them hard, so they’d finally deserve their name change.

    They’re hadrosaurs, from the Greek for “heavy”. See also: the Large Hadron Collider, which smashes comparatively heavy particles together.

    The other problem is that fagalean evolution appears to have started in south-east Asia, and (AFAIK), that isn’t a great area for fossil hunting at the present time.

    There’s wonderful Cretaceous amber in Burma.

    Link to this
  37. 37. Heteromeles 12:15 am 01/23/2012

    There’s wonderful Cretaceous amber in Burma.

    Great news! Now if the politics will just dry up and blow away, we can all go.

    Link to this
  38. 38. Dartian 3:22 am 01/23/2012

    Heteromeles:
    Now if the politics will just dry up and blow away, we can all go.

    Actually, it is already possible for foreign – including American – scientists to do biological and palaeontological field work there. (You’d better play ball with the local authorities by referring to the country as “Myanmar” rather than as “Burma” though.)

    Link to this

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