Another World’s Lijialaowu

In a world where the KT event didn’t happen, all bets truly are off. Even in the placid climate of the Paleocene – just before the Eocene Thermal Maximum and its ensuing turnover, long before the drastic changes of the Cenozoic – entire biotas were collapsing. Laramidia’s fauna entered Appalachia and South America, Europe’s fauna found itself flanked by Appalachia and North Africa and Asia. This was a period of extensive interchange, and few examples were as dramatic as the Late Paleocene of China.

The Wanghudun Formation spans the Late Paleocene and Early Eocene represents a flood plain environment, likely seasonal in nature. Vegetation was similar to older Cretaceous sites, dominated by conifers and angiosperms, but with a few new additions: grass, and cycads. Starting as a more wet forest environment, it became increasingly more arid towards the end of the Paleocene, resembling a savanna by the time the Eocene Thermal Maximum came.

Earlier Asia fossil sites closely mirrowed those of the Late Cretaceous, but not here. Of the iconic non-avian dinosaur groups in the Nemegt and others, few were present: only six species of pachycephalosaur, two troodontids, four alvarezsaurids, one halzkaraptorine, five ornithomimids and a titanosaur. A new dinosaur had nonetheless arrived on the area: Luosaurotherium inexpectatum, a stegosaur. Of the known avifauna, raptorial avisaurid and crow-like gobipterygid enantiornithes co-existed with flightless hollandids, pigeon-like apsaraviids, spoonbill-like presbyornithids, mesite-like neognaths and crane-like palaeognaths.

By contrast, synapsids and terrestrial crocodylomorphs were much more diverse. The former were represented by a rich diversity of djadochtatherioidean, taeniolabidoid and neoplagiaulacid multituberculates, accompanied by herbivorous zhelestids and gondwanatheres, insectivorous zalambdalestids and anagalids and carnivorous deltatheroideans and sparassodonts while the latter were represented by armoured, herbivorous simosuchids, omnivorous gobiosuchids, mid-sized carnivorous araripesuchids and an enormous sebecian, Shenlong imperator, which at 6 meters in length was one of the largest terrestrial carnivores of the continent and likely of the entire world in the younger strata of the formation. Several squamate taxa are known, the largest at 3.5 meters in length, both as predatory varanids and as herbivorous, multicusped polyglyphanodontians. The water ways were populated by alligatoroids, neochoristoderes, small lizard like choristoderes, meiolaniiforme, baenid, trionychid, carettochelyid and pleurodire turtles and an abundant lissamphibian and ichthyofauna. Pterosaurs were present both as azhdarchids, chaoyangopterids, ctenochasmatids and lonchodectids, with possible anurognathid remains.

The reason for this highly atypical fauna, which quickly replaced the older ceratopsian/oviraptor/trodoontid/ornithomimosaur/therizinosaur/titanosaur/ankylosaur/hadrosaur/tyrannosaur/dromaeosaur complex, lies on the collision between India and Asia. India and Asia had interchanged fauna since the Late Cretaceous, allowing some degree of adaptation on the part of the older Indian endemics. When the two landmasses finally collided, the introduced grass and the monsoon climate favoured both the local crocodylomorph, zhelestid and gondwanathere herbivorous guilds as well as the Asian multituberculate, zhelestid and polyglyphanodontid guilds, while most herbivorous dinosaurs were incapable of dealing with these changes. Those that did were cycad specialists (stegosaurs), generalists (titanosaurs, pachycephalosaurs) or also substantially foraged on aquatic plants (ornithomimosaurs). The extinction of many herbivores and the arrival of competing sebecians also killed off local tyrannosaurs and dromaeosaurs, while several established carnivorous mammal groups expanded as their prey grew larger.

This unique fauna, the Lijialaowu Biota, was one of the first great turnovers of the Cenozoic and a harbinger for things to come. Those hadrosaurs and ceratopsians would eventually spread around across the Eocene, retaking their lost territories in Asia, herbivorous mammals, polyglyphanodontians, ornithomimids and pachycephalosaurs got the first of many adaptive radiations. Stegosaurs would continue on the Eocene of Asia and North America, the last species being Wyomingostega latens from the Late Eocene of the USA. And the old maniraptorans would start on a long decline, their niches taken by flying and flightless ornithothorace birds.

Velociraptors on air remix

Deinonychus-ontogenetic-niche-shift-600-px-tiny-June-2015-Darren-Naish-Tetrapod-Zoology.jpgDeinonychus by Darren Naish, showcasing both flying juveniles and clueless adult.

A brief one. Everyone got acquainted with my hyper-controversial flying dromaeosaur post, right? Well, a more recent study on dromaeosaur flight has been posted. I disagree with some of its conclusions, but it did provided an immeasurably useful tool: a proper value for flight strokes in paravians.

According to said study, humerus-femur proportion rates have to be above 70% in order for a proper flight stroke to be provided and for wing-loading to be carried appropriately. To these ends there is a proper table with examples:

https://peerj.com/articles/7247/#table-3

Some are to be expected, but other are VERY surprising. Deinonychus and Unenlagia, for example, rank 76-80 and 72 respectively. These are some big ass theropods, so to see them within this range certainly makes the hypothesis that they could fly as at least juveniles much more credible.

Then there’s Unenlagiinae being a basically cosmopolitan clade, including both european taxa as well as DAKOTARAPTOR and Rahonavis to tie it all together. So basically they were like ratites, with flying ancestors and multiple flight losses and gigantism. Nice.

1104754913_preview_Dakota (4)Flying up the tree baby!

Now the study as a whole prefers a polyphyletic origin of dinosaur flight, with basal paravians being flightless and then several clades becoming volant. Fair enough, but test on Pelecanimus first and then we’ll talk.

Can’t wait for the aneurisms this will cause on haters.

Welcome Back?

Gwawinapterus beardi
O̳̘̰͎͠l̦̖̰͈̜̺̰͞d̫̗̹͘ ̺͍̬͖̥̝b͎̗̠͈̼͙͔͢o̶̙̙n̨e̲̝̖̰ͅs̱̳ ̘͈͙̲̜̲̀c̛̲̹̯̘͔o̩͠m̥̲͎̼̣̼͍ę̫͖ b͓̠̤̪̭̘ͅạ̝̥̘̻c͎͜k̨̜

https://peerj.com/articles/7688/

Learning about Nurhachius’ tooth replacement gave me chills. This tooth replacement pattern is what disqualified Gwawinapterus beardi from being a pterosaur, so….

The Mystery Of The Sky Dragons

coloborhynchus_attack_by_hodarinundu_d4c0qsz-fullviewColoborhynchus Attack” by HodariNundu.

In 2017 an abstract detailing isotope data on ornitocheiroid* pterosaurs was published. To my knowledge the full paper hasn’t been published yet, which is a shame given its base premise: that some ornithocheiroid pterosaurs might have preffered to hunt terrestrial prey.

*”Ornithocheiroid” here is used as it was conceived by Unwin 2003: any pterodactyloid pterosaur closer to Pteranodon longiceps than to Quetzalcoatlus northropi or Pterodactylus antiquus. The term was invented in Kellner 2003 to refer to a clade composed of Anhanguera blittersdorffi, Pteranodon longiceps, Dsungaripterus weii and Quetzalcoatlus northropi and from Andres 2008 onwards it has been redefined as including both Azhdarchoidea and Pteranodontia, the latter encompassing taxa as defined in Unwin 2003 due to the fact that traditional Pteranodontia (Nyctosauridae + Pteranodontidae) has been found paraphyletic in relation to these other taxa. There are a lot of reasons why this is stupid, most notably the fact that a traditional Pteranodontia is consistently being recovered again (Andres 2018, Longrich 2018), so Unwin 2003 definition it is. If you feel uncomfortable try mentally replacing “ornithocheiroid” with “pteranodontian” in your imagination.

Most ornithocheiroid pterosaurs are assumed to have been piscivores. Even with the “pterosaur revolution” of the 2010’s its pretty undeniable most species fit the traditional “seagull pterosaur” image: most are found in marine settings, most were soarers similar to modern pelagic birds like albatrosses and frigatebirds, several either have adaptations for launching out of water or ossified tendons indicating a perpetually aerial lifestyle and, most importantly, several taxa have been found with fish on their innards or pellets or conversely being eaten by marine predators (Witton 2013). However, quite a few taxa have been recovered in terrestrial settings, have lower aspect ratios and show adaptations for other lifestyles: in the case of istiodactylids for scavenging and in the case of boreopterids for trapping small freshwater prey (Witton 2013). If you assume lonchodectids are ornithocheiroids, then their purported azhdarchid-like morphology would make them an unique case of terrestrial foragers akin to modern storks and cranes (Witton 2013).

image descriptionIstiodactylus latidens devouring a dead stegosaur by Mark Witton.

Still, the idea of raptorial ornithocheiroids has not been explored. Taxa usually identified as ornithocheirids and anhanguerids have large, forward facing eyes, large jaw muscles, “intimidating” teeth and distended palates, as opposed to the small eyes, cookie-cutter shark-like teeth (best suited to simply rip meat instead of killing prey) and non-distended palates of the scavenging istiodactylids and the small eyes,  fragile teeth, weak jaw muscles and non-distended palates of the small-prey piscivore boreopterids (Witton 2013); these adaptations are serviceable for hunting aquatic prey, but they can also be translated to a terrestrial prey context, as seen in other groups. Furthermore, at least one taxa, “Anhanguera” robustus, had hindlimbs comparatively more specialised for terrestrial locomotion, indicating that, much like istiodactylids (Witton 2013) some ornithocheirids/anhanguerids could have walked more or less efficiently while still retaining a mostly aerial lifestyle (Naish 2018).

The presence of raptorial ornithocheiroids could explain a few quirks of pterosaur diversity throught time:

  • Giant azhdarchids do not show up in the fossil reccord until the Late Cretaceous, after the extinction of toothed ornithocheiroids (Witton 2013). This could suggest that toothed ornithocheiroids occupied large volant predatory niches both on terrestrial and marine settings and were succeeded by large azhdarchids on the former and pteranodontians in the latter after the Turonian extinction event.
  • The supposed absence of raptorial pterosaurs (which I’ve brought up several times when discussing flight in volaticothere mammals*) is thus addressed: they were there all along!
  • The diversity of ornithocheiroids more or less parallels that of rhamphorhynchids, which similarly produced terrestrial carnivores and aquatic soarers (though rhamphorhynchid ecological diversity is somewhat more limited). As ornithocheiroids do not co-exist temporally with rhamphorhynchids (the only Jurassic putative representative, Archaeoistiodactylus linglongtaensis, has since turned out to be a basal monofenestratan [Wang 2014]), this leads credence to the idea that they evolved in the Early Cretaceous and are thus more closely related to azhdarchoids than ctenochasmatoids and other Jurassic pterodactyloids are.
  • Given that pterosaurs are superprecocial and likely occupied several niches as they grew, this likely also solves the relative rarity of aerial insectivorous pterodactyloids, since the juveniles of these raptorial ornithocheiroids likely occupied such niches.

* Friendly reminder a paper on volaticotheres is coming out soon!

Hopefully more work on this topic is done on the near future.

References

https://gsa.confex.com/gsa/2017AM/webprogram/Paper305496.html

Kellner, A. W. A., (2003): Pterosaur phylogeny and comments on the evolutionary history of the group. pp. 105-137. — in Buffetaut, E. & Mazin, J.-M., (eds.): Evolution and Palaeobiology of Pterosaurs. Geological Society of London, Special Publications 217, London, 1-347

Unwin, D. M., (2003): On the phylogeny and evolutionary history of pterosaurs. pp. 139-190. — in Buffetaut, E. & Mazin, J.-M., (eds.): Evolution and Palaeobiology of Pterosaurs. Geological Society of London, Special Publications 217, London, 1-347

Andres, B.; Clark, J.; Xu, X. (2014). “The Earliest Pterodactyloid and the Origin of the Group”. Current Biology24: 1011–6. doi:10.1016/j.cub.2014.03.030. PMID 24768054.

Nicholas R. Longrich; David M. Martill; Brian Andres (2018). “Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary”. PLOS Biology. 16 (3): e2001663. doi:10.1371/journal.pbio.2001663. PMC 5849296 Freely accessible. PMID 29534059

Witton, Mark (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. ISBN 978-0691150611.

Martin-Silverstone, E., Sykes, D., Naish, D. (2018). “Does Postcranial Palaeoneurology Provide Insight into Pterosaur Behavior and Lifestyle? New Data from the Azhdarchoid Vectidraco and the Ornithocheirids Coloborhynchus and Anhanguera“. Palaeontology. doi:10.1111/pala.12390

Sullivan, C.; Wang, Y.; Hone, D.W.E.; Wang, Y.; Xu, X. & Zhang, F. (2014). “The vertebrates of the Jurassic Daohugou Biota of northeastern China”. Journal of Vertebrate Paleontology. 34 (2): 243–280. doi:10.1080/02724634.2013.787316.

On sea turtles

Inaechelys_pernambucensis_paleoArt-Julio_Lacerda-EarthArchivesInaechelys pernambucensis by Julio Lacerda. Once upon a time, the sea was full of side-necked turtles, sticking to the sea floor while the ancestors of modern sea turtles swam above them.

Sea turtles are best known as the sea reptiles that got away, the only survivors of the Mesozoic assemblages of ichthyosaurs, plesiosaurs and all that. Technically this is not true (dyrosaurids, gavialids, several sea snake taxa and neochoristoderes would like to have a word), but it also trivialises one small detail about modern sea turtles: they are all members of a single lineage, Chelonioidea. As turtles have dominated aquatic niches since the Triassic, surely one would expect more than one group to have become adapted to life in the sea.

And indeed, that is the case.

Several extinct lineages of turtles have conquered the seas. Depending on who you ask, the number may be as little as 4 times and as high as 8, still a bit short depending on your expectations for an aquatic group but nonetheless a much larger menagerie than the modern survivors would imply. Some of these groups were just as cosmopolitan and diverse as modern sea turtles, while others were apparently short-lived explorations of the sea. Regardless, these animals attest to several guilds of marine shelled reptiles comparable to the modern freshwater diversity of niches, and a few even rank as some of the largest turtles of all time.

Their absence in modern times is quite sad, and sadder still is that some did live up until very recently.

The first mariner

HitchingOdontochelys semitestacea by Brian Choo, hitching a ride from giant crinoids floating near the sea surface.

One of the very earliest turtles was already specialised to a life at sea. Odontochelys semitestacea is best known for its decidely basal, un-turtle-like absence of a carapace and presence of a solitary plastron and teeth (its in the name, after all), but a little known fact is that this animal occurs in deep sea marine deposits otherwise dominated by pelagic or abyssal taxa. As noted by Brian Choo, its unlikely that this critter was dragged from freshwater or even coastoal sites.

So one of the very first turtles lived far out in the open ocean.

As Odontochelys semitestacea lacks speciations for a pelagic lifestyle like flippers, a lifestyle proposed is that this animal hitchhiked rides on the giant crinoids that occupied the main filter feeding niche in Triassic seas, sticking close to the sea surface. Given that turtles are among the few amniotes to breathe underwater, however, its not inconceivable that this was a benthic critter unlike any other vertebrate known, spending most of its life in the depths. Either way, the half-shelled toothed turtle spent its days gazing into the abyss, only leaving the darkness of the sea to lay eggs on land.

Sea turtles like this appear to have been extremely rare, as Triassic oceans were instead home to another clade of armoured marine reptiles, the placodonts. It seems it took the extinction of these animals to allow turtles to expand in the Jurassic, though given the presence of an already specialised turtle living far away from shore it is just as likely that these critters co-existed just fine with their distantly related shelled bretheren.

Angolachelonia

CWSDuO2WcAA0SG2Leyvachelys cipadi by Jorge Blanco, enjoying a crab snack as it watches an ammonite die. Note the massive hands.

The seas of the Jurassic, Cretaceous and Palaeocene were home to an unique lineage of turtles, the angolachelonians. This assemblage is composed by Thalassochelydia, a clade composed by several Late Jurassic turtles of Europe and possibly Argentina, and Sandownidae, a clade ranging from the Cretaceous to Palaeocene with a more or less cosmopolitan distribution. The exact classification of these turtles has been controversial with several members having popped up across the turtle phylogenetic tree in previous studies, but the consensus is that they form a monophyletic group just outside the clade leading to crown-group turtles. They however so strongly converged with chelonioidean sea turtles on a variety of traits that the possibility that they’re actually cryptodires and closely related/ancestral to them can’t be fully ruled out yet.

449px-Solnhofia_parsonsi_54545Solnhofia parsonsi by “Ghedoghedo”. Again, notice the massive hands.

Like modern sea turtles, angolachelonians had enlarged anteorbital fenestrae allowing for large salt glands and shell fontanelles to increase the hydrodynamic value of their shells (Anquetin 2017). Unlike modern sea turtles, however, they did not possess flippers, but did they have enlarged digits, meaning that they were still competent swimmers and that in life their limbs probably resembled the mini-bat wings of modern soft-shelled and pig-nosed turtles (Anquetin 2017). Because of this it is assumed that, unlike modern sea turtles, angolachelonians did not swim much in the open sea and were mostly near-shore specialists, a few species even having secondarily returned to brackish water biomes (Billon-Bruyat 2005). Nonetheless, most species were in fact fully marine (Billon-Bruyat 2005, Anquetin 2017) and given the fact that a few are found in deep sea deposits (Mateus 2009) and the aforementioned adaptations for efficient swimming I wonder if a few like Angolachelys mbaxi weren’t in fact fully pelagic.

golaAngolachelys mbaxi by “BoneSharpe”. The artist seems to have agreed with my beliefs and depicted this animal as a deep sea specialist alongside Angolasaurus.

Both groups of angolachelonians have been recovered as monophyletic true clades, though a ghost lineage for sandownids must have existed for 30 million years or so must have existed to explain the temporal discrepancies between the two groups’ ranges. Thalassochelydians occur both in open sea and marginal marine environments including estuary habitats, putting them as more generalised in terms of ecology, while sandownids are known from both shallow and deep sea sites. Sandownids survived the KT mass extinction much like chelonioidean sea turtles; the exact date of extinction is unclear, but they likely disappeared either at the Eocene Thermal Maximum or in the Miocene alongside bothremyids, both climatic events that deeply affected sea life.

Pleurodires

caribeCaribemys oxfordiensis by Dmitri Bogdanov. One of the oldest crown-group turtles known, it seems to suggest that side-necked turtles were originally marine in habits.

Though side-necked turtles are nowadays restricted to the lakes, rivers and swamps of South America, Africa, Madagascar, New Guinea and Australia, in the past they were a cosmopolitan group occuring not only in freshwater bodies in Europe and Asia but also in the seas all over the world. Marine pleurodires are typically treated in literature as multiple different invasions of the sea by various lineages, but given that the earliest known pleurodire, Caribemys oxfordiensis, is a marine animal (Iturralde-Vinent 2001) as well as the fact that extinct pelomedusids do occur in marine settings (Ferreira 2015) it is just as likely that pleurodires were ancestrally marine and later returned to freshwater environments.

Pleurodires are rather distinctive turtles, so unlike angolachelonians they don’t suffer from taxononomical ambiguity in regards to their relations to chelonioids. Marine species don’t seem to differ much from freshwater species, some speciations like enlarged salt glands probably unecessary given how modern pleurodires have efficient cloacal breathing and filtering. Like angolachelonians pleurodires never seem to have developed flippers and seem to be most common in near-shore environments, but even today some modern species have freakishly enlarged hands, attesting to some moderately efficient swimming capacities; one species, Araripemys barretoi, has been compared to modern pig-nosed turtles in terms of forelimb anatomy. Like modern species, most were probably benthic, ambushing prey from the sea bottom or probing crevaces.

Fbot2A fictional marine pleurodire species from The Speculative Dinosaur Project, drawn by Brian Choo. Real marine pleurodires did not have flippers (though enlarged hands come close enough), but the “ass-gills” might be truer to form.

The most successful lineage of marine pleurodires were the bothremydids, which occured in marine environments in all continents from the mid-Cretaceous to the Miocene. Some marine pelomedusids did survive until much recently to the Pleistocene in the Indian Ocean. Global cooling events seem to have mostly done both lineages, but at least Stereogenyina species seem to have overlapped ecologically with modern carettine sea turtles, implying that competition from the latter did them in.

Meiolaniidae

meioMeiolania platyceps defecating in the sea by Joschua Knüppe. I have nothing to say.

Yes, Meiolania platyceps appears to have been a marine turtle.

As it turns out, the supposed terrestrial habits for at least this species are erroneous, ranking closer to aquatic turtle species than land dwelling ones. Several unique adaptations of meiolaniid turtles, such as the enlarged nasal area and supposed tail club, are thus interpreted as having evolved in an aquatic context, the former housing salt glands and the latter being simply a reinforced tail, a more extreme version of the armoured tails of freshwater turtles like snappers. As there were no large freshwater bodies in Lord Howe island, Meiolania platyceps is interpreted as having been a coastoal herbivore akin to the modern marine iguana; its extinction is even connected to the declining sea levels of the Pleistocene, which would have surely favoured a terrestrial species but not a coastoal amphibious one.

Of course, a few mysteries remain. As noted in the paper, the short hand of Meiolania platyceps could suggest an ancestry from a terrestrial ancestor, implying that other meiolaniids could have been in fact terrestrial herbivores and that this particular species adopted unique marine habits based on its deficient island environment much like the marine iguana. Conversely, it could imply that other meiolaniids were in fact aquatic and that the Meiolania species of Melanesia are in fact the world’s youngest non-chelonioid sea turtles, having become extinct with the arrival of human beings a few hundred years ago.

Regardless, meiolaniids are nowadays agreed to be outside the turtle crown-group, making them also unique for being a truly ancient turtle lineage that survived into moern times. Assuming marine habits for all recently extinct meiolaniids, these are some of the most un-sea turtle like sea turtles of all time, being weird water dragons rather than graceful udnerwater flyers.

Conclusion

Fbot3Another speculative pleurodire by Brian Choo.

Fossil turtles are underappreciated enough as it is. Hopefully this little trip through the prehistoric seas has illustrated why the very image of the sea turtle as we know it does not reflect the true diversity of these amazing animals.

 

References

https://onlinelibrary.wiley.com/doi/pdf/10.1111/pala.12384

Anquetin et al 2017. A review of the fossil record of turtles of the clade Thalassochelydia. Bulletin of the Peabody Museum of Natural History, 58, 317–369.

Octávio Mateus; Louis Jacobs; Michael Polcyn; Anne S. Schulp; Diana Vineyard; André Buta Neto; Miguel Telles Antunes (2009). “The oldest African eucryptodiran turtle from the Cretaceous of Angola” (PDF)Acta Palaeontologica Polonica54 (4): 581–588. doi:10.4202/app.2008.0063.

A new pleurodiran turtle from the Jagua Formation‭ (‬Oxfordian‭) ‬of western Cuba.‭ ‬Journal of Paleontology‭ ‬75‭(‬4‭)‬:860-869.‭ ‬-‭ ‬M.‭ ‬S.‭ ‬de la Fuente‭ & ‬M.‭ ‬Iturralde-Vinent‭ ‬-‭ ‬2001.

Ferreira, G.S., Rincón, A.D., Solórzano, A. & Langer, M.C. (2015) The last marine pelomedusoids (Testudines: Pleurodira): a new species of Bairdemys and the paleoecology of Stereogenyina.