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A drowned nesting colony of Late Cretaceous birds

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


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Enantiornithine nesting colony, reconstruction by Julio Lacerda.

ResearchBlogging.org

Like modern birds, and like their close relatives among the theropod dinosaurs, the birds of the Mesozoic Era laid eggs and, we reasonably infer, made nests. But what else do we know about reproductive behaviour in Mesozoic birds? Essentially, we know very little, and by “very little” I actually mean “just about nothing”. A new paper just published in Naturwissenschaften by Gareth Dyke, Mátyás Vremir, Gary Kaiser and myself describes an assemblage of bird eggshell and bones that is amazing in its scale, and fascinating in terms of its behavioural implications (Dyke et al. 2012). It shows, for the first time, that some Mesozoic bird species – only distantly related to modern birds – formed enormous breeding colonies.

Enantiornithine embryo, still in its egg, described by Zhou & Zhang (2004). The large wing feathers on this late-stage embryo indicate precocial (or superprecocial) habits for this species.

A few embryos and eggs belonging to the Mesozoic bird group known as Enantiornithines are already known (Elzanowski 1981, Mikhailov 1996, Grellet-Tinner & Norell 2002, Schweitzer et al. 2002, Zhou & Zhang 2004).

The most impressive of these fossils has to be the embryonic, partially feathered Lower Cretaceous Chinese enantiornithine [shown here], discovered within a near-complete egg, and described by Zhou & Zhang (2004). We can infer from the proportions and bone anatomy of this embryo and others that these bird species were precocial or even superprecocial: that is, the hatchlings were able to walk, fly and generally look after themselves within a day, or even within a few hours, of hatching.

But this doesn’t tell us anything about parental behaviour, since parents can still interact substantially with chicks in species where the chicks are precocial (though they don’t in all cases). And most of the other things you might ask about reproductive behaviour in Mesozoic birds remain unknown and often based on inference. Were egg clutches large or small? Where were nests located? What were the nests like? Did adults brood their eggs, or bury them? Did Mesozoic birds nest as lone individuals, in groups, or in colonies?

Given that Mesozoic birds were diverse in terms of body size and shape, and in ecology, they would presumably have been diverse in reproductive biology, just as modern birds are. Indeed, given that the Mesozoic members of Avialae (the bird lineage of Maniraptora) include early forms extremely similar to the little deinonychosaurs that were their close relatives, flightless walkers and runners, flightless, toothed seabirds, finch-, thrush-, crow- and vulture-sized terrestrial species, and early members of the ratite, duck, gamebird and neoavian lineages, it’s plausible that Mesozoic birds possessed a spectrum of reproductive behaviour, extending from ‘dinosaur-like’ at one end to ‘modern bird-like’ at the other.

Romania: fossil treasure trove

Our new research concerns a discovery made in the latest Cretaceous (Maastrichtian) Sebeş* Formation of Transylvania in western Romania. Already the Sebeş Formation (long erroneously considered Oligocene or Miocene in age!) is well known as a source of diverse Late Cretaceous fossils, including pleurodiran turtles, azhdarchid pterosaurs, ornithopods and the amazing dromaeosaurid theropod Balaur bondoc (Csiki et al. 2010, Vremir 2010).

* Pronounced something like “seb-esh”.

The Oarda de Jos sites (Sebeş River, Transylvania) as it looked when I visited it in 2011.

The sediments here were deposited by a large, meandering river system, surrounded by floodplains and forests with large trees. This was a continental environment*, with sedimentological evidence showing that long dry seasons were punctuated by short wet ones when extreme flooding sometimes occurred.

* This doesn’t mean ‘on a continent’, since the region was actually a large island at the time. Rather, it means that the environment was well inland, and without any estuarine or marine influence.

The entire Od accumulation as collected, prior to preparation. Scale bar = 50 mm. From Dyke et al. (2012).

It’s the detailed mapping and exploration of the Sebeş Formation by Mátyás Vremir of the Transylvanian Museum Society that has resulted in so many amazing Sebeş Formation discoveries. And it’s one of these that forms the focus of our new paper. In sediments exposed on the banks of the Sebeş River, Mátyás discovered a large, lens-shaped chunk of calcareous mudstone packed full of thousands of broken eggshell fragments. Unfortunately (but – I hope – understandably), the concretion couldn’t be extracted as a single mass; rather, it broke into lots of separate chunks. When complete it was about 80 cm long, 50 cm wide and 20 cm thick. Its breakage isn’t a bad thing, since this allows the interior of the mass (rather than merely its edges) to be examined in detail. While virtually all of the eggshell within the accumulation is preserved as small, broken fragments, seven near-complete eggshells are included as well, as are more than 60 small bones. We term this mass of sediment, eggshell and bones the ‘Od accumulation’ after the specific outcrop where it was discovered (the Oarda de Jos site).

A whole lot of eggshell

At top: two of the seven complete eggs preserved in the Od accumulation; at bottom, one chunk of the accumulation, showing how densely packed the eggshell fragments are. Scale bars = 10 mm. From Dyke et al. (2012).

The volume of eggshell in the Od accumulation is extraordinary. About 70-80% of the accumulation as a whole is formed by eggshell, meaning that this is an eggshell-supported rock, reminiscent of the Patagonian ‘egg beds’ that incorporate vast quantities of sauropod eggshell. Averaged out, most shell fragments in the Od accumulation are about 36 mm long. They’re so closely packed that, in one 26-cm-sq section of the accumulation, more than 150 eggshell fragments are present. The several complete eggs preserved in the accumulation are 40 mm long and 25 mm wide; based on these measurements, each 100 cubic cm of the accumulation contains eggshell equivalent to about 46 whole eggs (Dyke et al. 2012). As we say in the paper, “The quantity of eggshell fragments in the Od accumulation is astonishing and beyond normal palaeontological experience”.

Adult enantiornithine humerus from the Od accumulation, from Vremir (2010). As preserved, the specimen is c. 50 mm long.

The eggshell looks avialan, and the isolated bones jumbled up within the accumulation are definitely avialan. These bones appear to belong to both adult and juvenile birds: they reveal a number of characters that allow them to be identified as those of enantiornithines, in particular a taxon close to (or congeneric with) the Late Cretaceus Argentinean form Enantiornis (Dyke et al. 2012). SEM analysis of the eggshell fragments reveals two equally thick shell layers formed of calcite crystals, as well as an absence of marked surface ornamentation. This eggshell form is typical of maniraptorans that are closer to crown-birds than to deinonychosaurs but outside of Neornithes, the crown-bird clade (Grellet-Tinner et al. 2006). Several exclusively Mesozoic bird lineages, enantiornithines among them, fit within this phylogenetic bracket. The data on eggshell microstructure is thus consistent with the osteological data from the accumulation (Dyke et al. 2012). Before anyone else says it, I should note that the phylogenetic distribution of certain eggshell characters remains the topic of debate – there are even cases where eggs confidently identified as those of maniraptoran theropods (Buffetaut et al. 2005) have turned out to be from squamates.

A waterside enantiornithine colony

Smaller version of Julio Lacerda's reconstruction.

We therefore hypothesise that the accumulation preserves the remains of an enantiornithine nesting colony, with the numerous eggshell fragments, the several complete eggs, and the various bones all belonging to the same one species.

Given the volume of eggshell, the colony must have been large. Assuming clutches similar in size to those of modern birds, we’re talking about hundreds of nests. The stacked, packed, jumbled nature of the eggshell fragments removes the possibility of this being an in-situ shared ‘mega-nest’ by the way (a bizarre possibility mooted by one reviewer!). There are no fossils of any other sort within the accumulation. It seems that a flood event swept across the colony, carrying eggs and birds (or their remains) before dumping them in a hollow area a short distance from the main channel (Dyke et al. 2012). This transport can only have occurred across a short distance (as in, several metres), since the bones are unabraded and several eggs are intact.

Waterside-nesters like plovers typically deposit their eggs in 'scrapes' - simple nests that don't involve the incorporation of vegetation or feathers. These are Ringed plover (Charadrius hiaticula) eggs. Photo by Arnoldius, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

The form of the eggs is typical of ground-nesters that produce precocial young (Dyke et al. 2012). The absence of vegetation in the accumulation implies that the birds formed scrapes in the sediment for their eggs, as do plovers and some other waterside-nesting modern birds. [Adjacent image of Ringed plover eggs by Arnoldius.]

Given the amount of eggshell, why aren’t there more bones in the accumulation? The inner surfaces of the eggshell fragments are dull and etched, “suggesting that calcium mobilisation was advanced and that the eggs had either hatched or were destroyed late in the second half of incubation” (Dyke et al. 2012). In other words, it’s likely that many or most of the eggs present in the colony at the time of the flooding event were already hatched and lying, empty and discarded, in or close to their nests. This probably wasn’t the case for all nests, since the presence of both juvenile and adult bones implies that these birds perished when the colony flooded. Then again, it’s also conceivable that these bones belong to individuals that were already dead before the colony was swamped – it’s common to see the remains of dead chicks and even dead adults in nesting colonies.

Breeding colonies of marine birds, like these Cape gannets (Morus capensis), can be especially crowded. Photo by Octagon, licensed under Creative Commons Attribution 3.0 Unported license.

Assuming that we’re right in our overall interpretation, what does the discovery mean for enantiornithine nesting and breeding behaviour? A waterside nesting habit for an Enantiornis-like enantiornithine is not all that surprising, since there’s already morphological and stomach-content data showing that some members of this group were aquatic foragers, preying on crustaceans and other such prey (Sanz & Buscalioni 1992, Sanz et al. 1996). The fact that such a large nesting colony of this one enantiornithine species occurred in a waterside habitat strongly suggests reliance on aquatic resources, so the species concerned might have been gull-like or plover-like in ecology. [Adjacent photo of gannet colony by Octagon.]

And, like gulls, waterfowl, flamingos and other waterside, colonial nesters, it seems that these enantiornithines were sometimes unfortunate, and that local flooding events swamped and drowned their nest colonies (Dyke et al. 2012). Flooding occurs quite regularly in some modern bird colonies and is an expected hazard of nesting so close to water. There are even cases where the same colony gets flooded repeatedly during the same one breeding season (e.g., Peresbarbosa & Mellink 2001), and yet still the birds continue to nest there. Why do they nest in such dangerous places? Because they are otherwise highly suitable; more so than adjacent, well-vegetated regions in providing barren, relatively predator-free areas that are suitable for nesting, and are relatively close to the aquatic environment.

Detail of part of Julio Lacerda's reconstruction of the nesting colony. You'll note that Julio's enantiornithines look... like birds, not like the crazy feathered dragon-monsters depicted by some artists elsewhere.

On the one hand, the formation of large, waterside nesting colonies in Mesozoic birds is not all that surprising, since this behaviour is common and widespread in modern birds and has clearly evolved many times independently. On the other hand, enantiornithines are not typically imagined as being all that similar to modern, colony-nesting birds like gulls, terns, gannets, penguins and so on, and I’m not sure that I’d have guessed a colony-nesting habit for any enantiornithine prior to the discovery of the Od accumulation. For Mesozoic seabirds, like hesperornithines and Ichthyornis, sure, but – for enantiornithines – it’s a novel idea.

So we can now say that the latest Cretaceous Transylvanian Basin fauna of Romania was inhabited by peculiar, island-endemic dromaeosaurs, titanosaurian sauropods, both rhabdodontid and hadrosaurid ornithopods, azhdarchid pterosaurs, eusuchian crocodyliforms, pleurodiran turtles, and enantiornithine birds that formed enormous, waterside nesting colonies. More exciting Romanian finds are due to be announced in the near future. Special thanks to the outstanding Julio Lacerda for the excellent artwork he produced for this project. Julio has a DeviantArt page here and blogs at The Casual Paleoartist.

For previous Tet Zoo articles on Mesozoic birds, see…

Refs – -

Buffetaut, E., Grellet-Tinner, G., Suteethorn, V., Cuny, G., Tong, H., Košir, A., Cavin, L., Chitsing, S., Griffiths, P. J., Tabouelle, J. & Le Loeuff, J. 2005. Minute theropod eggs and embryo from the Lower Cretaceous of Thailand and the dinosaur-bird transition. Naturwissenschaften 92, 477-482.

Csiki, Z., Vermir, M., Brusatte, S. L., Norell, M. A. 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. Proceedings of the National Academy of Sciences 107, 15357-15361.

Dyke, G. Vremir, M. Kaiser, G. & Naish, D. 2012. A drowned Mesozoic bird breeding colony from the Late Cretaceous of Transylvania. Naturwissenschaften DOI:10.1007/s00114-012-0917-1

Elzanowski, A. 1981. Embryonic skeletons from the Late Cretaceous of Mongolia. Palaeontologica Polonica 42, 147-179.

Grellet-Tinner, G. & Norell, M. A. 2002. An avian egg from the Campanian of Bayn Dzak, Mongolia. Journal of Vertebrate Paleontology 22, 719-721.

-., Chiappe, L. M., Norell, M., Bottjer, D. 2006. Dinosaur eggs and nesting behaviours: A paleobiological study. Palaeogeography, Palaeoclimatology, Palaeoecology 232, 294-321.

Mikhailov. K. E. 1996. Bird eggs in the Upper Cretaceous of Mongolia. Palaeontology Journal 30, 114-116.

Peresbarbosa, E. & Mellink, E. 2001. Nesting waterbirds of Isla Montague, northern Gulf of California, México: loss of eggs due to predation and flooding, 1993-1994. The International Journal of Waterbird Biology 24, 265-271.

Sanz, J. L. & Buscalioni, A. D. 1992. A new bird from the Early Cretaceousof Las Hoyas, Spain, and the early radiation of birds. Palaeontology 35, 829-845.

- ., Chiappe, L. M., Pérez-Moreno, B., Buscalioni, A. D., Moratalla, J. J.,Ortega, F., Poyata-Ariza, F. J. 1996. An Early Cretaceous bird fromSpain and its implications for the evolution of avian flight. Nature 382, 442-445.

Schweitzer, M. H., Jackson, F. D., Chiappe, L. M., Schmitt, J. G., Calvo, J. O. & Rubilar, D. E. 2002. Late Cretaceous avian eggs with embryos from Argentina. Journal of Vertebrate Paleontology 22, 191-195.

Vremir, M. 2010. New faunal elements from the Late Cretaceous (Maastrichtian) continental deposits of Sebeş area (Transylvania). Acta Musei Sabesiensis 2, 635-684.

Zhou, Z. (2004). A Precocial Avian Embryo from the Lower Cretaceous of China Science, 306 (5696), 653-653 DOI: 10.1126/science.1100000

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. David Marjanović 10:17 am 05/15/2012

    You’ll note that Julio’s enantiornithines look… like birds, not like the crazy feathered dragon-monsters depicted by some artists elsewhere.

    Well, they look exactly like gulls with lengthened legs and… no alulae. They really should have alulae.

    Link to this
  2. 2. naishd 10:38 am 05/15/2012

    Well, there’s a familiar theme here: fossil taxa did not necessarily look as strange and alien as some people have led us to believe. I think this is a pretty plausible life appearance for some enantiornithines.

    As for alulae – based on Eoalulavis and other taxa, you’re right. But how can you be absolutely sure that they don’t have alulae in the reconstruction? Maybe they’re shown with small ones that don’t extend distally beyond the clawed tip of the digit? Some birds do have very short alulae.

    Darren

    Link to this
  3. 3. Heteromeles 11:23 am 05/15/2012

    How big a paleo-island are we talking about? I’m trying to get my head around two things with an inland waterbird colony. One is how such a nesting site stayed safe from predators, and the other is how big a watershed would have been required to produce a big enough flood to produce the fossils. Fascinating find!

    Link to this
  4. 4. Jurassosaurus 11:32 am 05/15/2012

    “…there are even cases where eggs confidently identified as those of maniraptoran theropods (Buffetaut et al. 2005) have turned out to be from squamates.”

    Do you happen to have the reference for this? I didn’t think we had any squamate egg fossils. Given that this was confused with a theropod I’m guessing these were calcite eggs.

    Link to this
  5. 5. naishd 11:47 am 05/15/2012

    Heteromeles (comment 3): the Hateg Island was large, though its exact size is controversial. I’ve seen published figures ranging from 7500 to 100,000 km sq (Weishampel et al. 1991, Le Loeuff 1995). As for protection from predators, it’s possible that the nesting colony was on an island (or peninsula) within an enormous river system. But that wasn’t necessarily so – many modern waterside bird colonies are very much confluent with mainland areas inhabited by predators, it’s just that the predators rarely go to those places. Of course, when they do go to those places, they can cause enormous damage. You’ve probably heard the stories about Polar bears, Spotted hyaenas and other predators single-handedly destroying whole bird colonies… Incidentally, having mentioned predators, I should note that big theropods are as yet unknown from the Hateg Island fauna (though there were dromaeosaurs and big azhdarchids).

    As for the watershed that must have been involved, I have no idea. But the sedimentological evidence in the formation shows clear evidence of large (but local) overbank flood events. Surely these can occur anywhere so long as there’s enough rain.

    Darren

    Le Loeuff, J. 1995. Romanian Late Cretaceous dinosaurs: Big dwarfs or small giants? Historical Biology 17, 15-17.

    Weishampel, D. B, Grigorescu, D. & Norman, D. B. 1991. The dinosaurs of Transylvania: Island biogeography in the Late Cretaceous. National Geographic Research and Exploration 7, 68-87.

    Link to this
  6. 6. naishd 12:01 pm 05/15/2012

    Jurassosaurus (comment 4): check this out. I’ve tried and tried and tried and cannot access this paper.

    These are certainly not the only fossil squamate eggs – there are gekkotan eggs from the Cretaceous of Spain, India, Mongolia and the USA, the Miocene of Kenya, Oligocene of Germany and elsewhere.

    Darren

    Link to this
  7. 7. David Marjanović 12:09 pm 05/15/2012

    Some birds do have very short alulae.

    Oh, OK.

    I’ve tried and tried and tried and cannot access this paper.

    Nobody can access Cambridge journals!

    Link to this
  8. 8. Heteromeles 1:20 pm 05/15/2012

    Thanks Darren. It takes a bit of land to make a watershed with a braided river on it. I’m also used to very small islands (like the California Channel Islands) nonetheless supporting things like dwarf mammoths. That’s a very different case than Hateg Island, which was an order of magnitude larger.

    The other imponderable is one of those questions we don’t ask often enough: how big can an island be and still have an island dwarfism/gigantism effect? Personally, I’m choking on Hatzegopteryx being an example of island gigantism–we’d have to include all albatrosses as island giants if this were true. Still, there seem to have been some dwarf dinosaurs…

    Link to this
  9. 9. Therizinosaurus 1:35 pm 05/15/2012

    Any tarsometatarsi preserved? If so, and if this is so similar to Enantiornis, we might be able to figure out which Lecho foot taxon (Lectavis, Yungavolucris, Soroavisaurus) is a junior synonym of Enantiornis.

    Link to this
  10. 10. Christopher Taylor 9:38 pm 05/15/2012

    Enantiornithine embryo, still in its egg, described by Zhou & Zhang (2004). The large wing feathers on this late-stage embryo indicate precocial (or superprecocial) habits for this species.

    Obviously that’s not an embryo: it’s an adult of an egg-feeding species that has become entombed within the egg of an entirely different animal. Everyone knows that enantiornithines themselves produced live young that were initially born without bones.

    And I won’t bore you all with the tortuous path that Scientific American just made me take for it to allow me to actually sign in effectively and make this brief comment. Fortunately, I only saw a couple of those annoying pop-up ads it’s been throwing at me lately in the process.

    Link to this
  11. 11. alcyonidae 9:55 pm 05/15/2012

    Jurassosaurus, David Marjanović, other folks: I’m at OHSU, which is mostly a medical school, so we have access to just about anything even tangentially related to medicine, but nothing else. Unfortunately, as I study the evolution of birds and their brains, I’m for the most part SOL when I want to read the latest Auk, Emu, or even freakin’ Animal Behavior. Anyway, if you want access to that paper or anything else in Cambridge journals, drop me a line: alcyonidae /\t gmail d0t com

    Link to this
  12. 12. naishd 3:16 am 05/16/2012

    I made a mistake in my comment (# 5) above. Instead of “Incidentally, having mentioned predators, it would be wrong to say that big theropods are as yet unknown from the Hateg Island fauna”, I meant to say “Incidentally, having mentioned predators, it would be wrong not to say that big theropods are as yet unknown from the Hateg Island fauna”. I’m just gonna go change the wording..

    Chris – thanks for registering.

    Darren

    Link to this
  13. 13. naishd 3:18 am 05/16/2012

    Mickey/Therizinosaurs (comment 9): I don’t want to discuss that here (Andrea Cau made similar comments on facebook) – a second, longer paper is in preparation and we’ll cover it then.

    alcyonidae – thanks, you’ll be getting an email :)

    Darren

    Link to this
  14. 14. naishd 3:22 am 05/16/2012

    Ok, I just logged into facebook, and some kind soul has already provided me with the paper. Sorry paywallers, I wasn’t about to find $32 or whatever for it.

    Darren

    Link to this
  15. 15. Therizinosaurus 4:01 am 05/16/2012

    Darren @13- Fair enough. I look forward to the results.

    Link to this
  16. 16. David Marjanović 10:22 am 05/16/2012

    Fortunately, I only saw a couple of those annoying pop-up ads it’s been throwing at me lately in the process.

    Firefox, Adblock Plus.

    Sorry paywallers, I wasn’t about to find $32 or whatever for it.

    $45.

    I suppose the institutional subscription rates are comparably high, and that’s why nobody has access.

    Link to this
  17. 17. calliarcale 2:23 pm 05/16/2012

    Heteromeles:
    “I’m trying to get my head around two things with an inland waterbird colony. One is how such a nesting site stayed safe from predators, and the other is how big a watershed would have been required to produce a big enough flood to produce the fossils.”

    Well, I live in central North America, in Minnesota, and we have tons of waterbirds here. Gulls, pelicans, cormorants, lots of stuff. Even out on the Great Plains there are lots. We had a particularly tragic event when a frustrated farmer destroyed an entire colony of pelicans, because he believed they had destroyed the soil in the adjacent plot of land which he was renting for farming. This particular colony of 3,000 animals was reportedly on an island in Minnesota Lake; you can see the islands in that lake on this Google Maps image.

    For protection from predators, the birds usually seem to nest on islands in lakes or rivers. The islands don’t have to be very big; some of these islands are glorified sandbars (which would of course be rather prone to flooding).

    Link to this
  18. 18. Heteromeles 3:25 pm 05/16/2012

    Thanks Calliarcale. I hadn’t thought about that, but you’re right.

    Of course, one wonders why mesozoic birds would see water as an adequate defense against dinosaur predators, since (evil grin) as one leading researcher recently proposed, dinosaurs were *obviously* aquatic (/evil grin). I guess this leading researcher (ahem) didn’t realize that crocodilians and their relatives did a very good job keeping dinosaurs out of the water for most of the Mesozoic.

    Link to this
  19. 19. Matyas 3:59 am 05/17/2012

    Regarding the size of the Hateg or Transylvanian island, during most of the Maastrichtian and Paleocene, was appreciated as minimum 80.000 sqkm based only on the outcropping area of the continental faciesess, but the allready developed mountain areas including the part of the southern and western Carpathians was probably more extensive. I would say that the E-W elongated island was more than 250 km long and up to 150 km wide with several large intramountain basins and extensive plain areas towards the present day Transylvanian basin. Asubtropical biseasonal monsoonal climate is inferred for the Maastrichtian time, with long dry and short wet seasons. The sedimentological data suggests the presence of mostly extensive brided fluvial systems, occasional meandering rivers with extensive floodplains, and also paludal facieses. In the dry season, probably most of the channels were inactive and the very few freshwater bodies were indeed infested by various crocodyliforms like Allodaposuchus, Theriosuchus, Doratodon…as seen in Oarda de Jos outcrop from where the bird colony was described. Occasional flash floods occured as demonstrated in several other outcrops close to Oarda de Jos, where whole trees (up to 18 m length) were laid down and washed away along with numerous ornithopod and sauropod skeletal parts. Me personally I would say, that the environment was quite similar to what we can see on the foot of the New Zeelander alps, but much more vegetated, with numerous interchannel bodies, sandbars and mudflats where this birds could nest.

    Link to this
  20. 20. Heteromeles 8:56 am 05/17/2012

    Thanks for that description, Matyas. I was thinking that the lowlands sounded a bit like Kakadu in northern Australia. The geology of Kakadu is totally wrong, of course, but the monsoonal climate is more similar than the temperate climate of southern New Zealand. Unless you meant northern New Zealand.

    Link to this
  21. 21. David Marjanović 9:01 am 05/17/2012

    Oops. I seem to have used <blockquote>, which gets removed, instead of <i> in comment 16. Twice.

    Link to this
  22. 22. Jerzy v. 3.0. 8:16 am 05/29/2012

    I wonder if anything is known on food and feeding of those birds?

    As you may know, very few precocial birds nest in large colonies, because chicks will compete for food around the colony (if all food resources were not already eaten by incubating adults). Few examples I can think of are megapodes, which chicks disperse immediately, and some geese which feed on rapidly growing marsh vegetation.

    #18
    Isn’t it thought that all theropod dinosaurs were, due to the air sac system, much lighter than water and likely very good swimmers/floaters?

    Link to this
  23. 23. naishd 2:11 pm 05/30/2012

    Jerzy: nothing is known about the dietary habits and/or ecology of the Romanian birds directly, but (as discussed in the article), we infer from related forms that they perhaps exploited aquatic prey.

    Regarding what you say about precocial birds generally not nesting in large colonies.. you are not quite right. The altricial-precocial spectrum is a spectrum, with numerous shades of grey; colony-nesting gulls, terns and auks are probably best regarded as semi-precocial, but some species are regarded as precocial by some authors. And some plover species with indisputably precocial babies are colonial nesters (lapwings are the classic example), as are crab plovers, some populations of godwits, shanks and so on.

    Megapodes, incidentally, are best thought of as super-precocial.

    Theropods and buoyancy: those animals were not all equally pneumatic, but, among the most pneumatic ones, it has been suggested that their lowered specific gravity would have made them “high in the water”. I don’t think anyone has tested this. Don Henderson did for sauropods and concluded that they were buoyant, but also unstable and prone to tipping when floating. See…

    Henderson D. M. 2003. Tipsy punters: sauropod dinosaur pneumaticity, buoyancy and aquatic habits. Proceedings of the Royal Society of London B 271 (Suppl 4), S180–S183.

    Darren

    Link to this

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