Warm-blooded ichthyosaurs

Ichthyosaur from Holzmaden with preserved blubber and skin

Exceedingly well-preserved ichthyosaur specimen MH 432, identified as Stenopterygius sp., from the Lower Jurassic (Toarcian) Posidonia Shale of the Holzmaden area in southwestern Germany. Collection of the Urweltmuseum Hauff in Holzmaden.

December 2018

Yesterday the most important study I ever took part of was published in Nature.

Our paper, entitled "Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur" describes an exceedingly well-preserved ichthyosaur from the Lower Jurassic Posidonia Shale of Holzmaden in southern Germany. The specimen (MH 432), housed in the collections at Urweltmuseum Hauff, was first surveyed by Johan Lindgren and myself during a visit to Holzmaden in September 2015.

At that time, it was far from clear to us how spectacular the results of our study would be. From numerous analyses, we were able to demonstrate that the still flexible skin contains pigments and pigment cells, which indicate countershading; that is, the back side of the animal was dark while the belly was bright, similar to what is seen in modern whales such as orcas.

The skin itself was smooth and did not bear any scales or scutes. Another analogue to modern whales is that the specimen preserved blubber. Until now, blubber has only been found in marine mammals, not reptiles (save perhaps for the leatherback sea turtle). Its presence demonstrates that ichthyosaurs were warm-blooded. Additionally, we also identified remnants of the liver and other tissues.

Citation: Lindgren, J., Sjövall, P., Thiel, V., Zheng, W., Ito, S., Wakamatsu, K., Hauff, R., Kear, B.P., Engdahl, A., Alwmark, C., Eriksson, M.E., Jarenmark, M., Sachs, S., Ahlberg, P.E., Marone, F., Kuriyama, T., Gustafsson, O., Malmberg, P., Thomen, A., Rodríguez-Meizoso, I., Uvdal, P., Ojika, M. & Schweitzer, M.H. (2018) Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur. Nature, published online: 05 December 2018.

Closeup of the liver of the ichthyosaur MH 432

Close-up of the liver of MH 432

Closeup of the integument of the ichthyosaur MH 432

Close-up of the integument of MH 432

Closeup of the blubber of the ichthyosaur MH 432

Johan Lindgren stuyding Holzmaden fossils

Johan Lindgren studying MH 432 and other Posidonia Shale fossils during a visit to Holzmaden in 2015 (photo by Sven Sachs)

Some links to articles featuring our study:

Link to a video where Johan Lindgren explains the results of our study.

Youtube

Many thanks to Johan Lindgren for being such a great lead authors and to all fellow co-authors. It was pleasure to work with you all on that fantastic specimen. Photo courtesy (if not stated otherwise) Johan Lindgren.