Thread by @tetaneuron

Thrilled to share our new study led by the @FieldMuseum entitled “Subaqueous foraging among carnivorous dinosaurs” published today in @Nature! We found that, while #Spinosaurus and #Baryonyx could swim underwater, #Suchomimus could not. Thread
nature.com/articles/s4158…

Have you ever noticed how some modern semiaquatic animals do not show striking anatomical traits in their skeleton, such as the hippopotamus and tapirs? If these animals weren’t alive today, how easy would have been to correctly guess their ecology from their skeleton?

This is what inspired us to investigate subaqueous behavior in dinosaurs: we wondered if we are underestimating the ecological diversity among non-avian dinosaurs and decided to use bone density to test for aquatic adaptations

High bone density is a striking feature of aquatic animals, because it helps in buoyancy control. On the other hand, terrestrial and flying amniotes (reptiles and mammals) have a large medullary cavity in their long bones, leading to a lighter skeleton. Art by @d_bonadonna

To test for correlations between bone density and ecology, we built a dataset of 380 femora and dorsal ribs representing 291 extinct and extant amniote species, including mammals, modern reptiles and birds, marine reptiles, 39 non-avian dinosaurs, and 7 Mesozoic stem birds

CT scan and thin sectioning were applied to collect cross sections of femoral diaphysis and proximal region of the dorsal ribs. Each cross section was then transformed in a black and white figure to quantify bone density in BoneProfiler (http://134.158.74.46/BoneProfileR/)

Among spinosaurids, we sampled the neotype of #Spinosaurus, the holotype of #Baryonyx, and #Suchomimus

We first tested the validity of bone density for ecological inference among extant amniotes: the best explanatory model shows correlation between high bone density and underwater swimming! Allometry has little to do with increased bone density

We used bone density to infer underwater behavior among extinct taxa: although this is rare among dinosaurs, #Spinosaurus and #Baryonyx are predicted as subaqueous foragers, while #Suchomimus is recovered with a non-diving ecology.

The presence of high bone density in #Spinosaurus and #Baryonyx is not limited to femora and dorsal ribs: this extends to all other appendicular elements and axial skeleton. Additionally, spinosaurids show axial pneumatization only in the cervicals, favoring a denser skeleton

Mapping bone density into an amniote-wide phylogeny, we found that, based on our data, high bone density is ancestral for spinosaurs, indicating that #Suchomimus lost this trait secondarily. Art by @d_bonadonna

High bone density in spinosaurs appeared in concert with crocodile-mimic snouts and conical teeth. Post-cranial modifications, such as paddle-like feet, short legs, and a propulsive tail are known only for #Spinosaurus at the moment

Take away message: we are currently underestimating the ecological diversity in the fossil record. Our method allows to infer underwater swimming in extinct amniotes from bone cross-sections even in fragmentary fossils

All the novel data collected for this study are freely available as Supplementary Material of our study. The CT scans are freely available in @MorphoSource !

A special thanks to my fantastic collaborators: @GNavalon @BensonLabOxford @poldiego @Paleontologista @AnjanBhullar @GBindellini @NizarIbrahimPhD G Erickson M Norell A Orkney M Lamanna S Zouhri J Becker A Emke C Dal Sasso S Maganuco M Auditore

The project was possible thanks to @JurassicFDN @NatGeo @ExplorersClub @ERC_Research. We also want to thank the Moroccan Ministry of Energy, Mines, and the Environment for providing fieldwork permits of the 2015-2019 expedition seasons

Finally, this study is the latest scientific effort resulting from a decade of friendship and collaboration with Samir Zhouri’s Palaeobiology Lab at the Hassan II University of Casablanca, Morocco, which is building and protecting the first public fossil collection of the Country