A Multimillion Years Old Reptile Keeps Its Feet Warm

The realization that biomolecules can survive in the fossil record not only for thousands of years but for millions of years is quite new and revolutionary. It has recently been demonstrated that “original” and essentially unaltered biomolecules, in for instance pigment particles and cuticles, can be preserved in deep time (≤200 Myr) by applying state of the art spectroscopic techniques, in particularly IR-microscopy[1-3]. More revolutionary, however, a deeper understanding of fossil animals and plants based on biomolecular properties and structures may now be within reach. If the integrity of the molecular properties in the fossil material is preserved to a degree that reflects the original molecular content it may be possible to utilize molecular data to extract e.g. functionality or molecular phylogenetic[4] information of the fossil species. The studies of fossil species older than ca 1 Myr are with a few exceptions based on the morphology only of fossilized hard parts, such as bones, teeth, and shells, in animals and leafs, spores and pollen in plants. To base evolutionary relationships on morphology (e.g. shape and appearance only of optical and electronic imaging) alone has many pitfalls and shortcomings. The interpretation of the data is often open to a range of alternatives as a result and in the absence of more robust molecular information consensus on one alternative can be hard to reach.
Here we show how molecular data is successfully extracted from a 180 Myr old fossil of an ichthyosaurus [5]. Using IR-microscopy we record for the first time characteristic spectra of blubber and liver. The presence of blubber, below the skin, in a reptile is remarkable, cold-blooded animals have no thermal regulations and no need for thermal isolation. Our results therefore clearly suggests that ichthyosaurus had an elevated body temperature in contrast to modern reptiles. These findings are supported by previous morphological studies indicating a surprisingly high metabolism of ichthyosaurus, inconsistent with cold-blooded animals.

1 J. Lindgren, P. Sjovall, R. M. Carney, P. Uvdal et al., Nature 506, 484 (2014).
2 J. Lindgren, P. Uvdal, P. Sjövall, et al., Nature Com. 3, 824 (2012).
3 V. Vajda, M. Pucetaite, S. McLoughlin, A. Engdahl, J. Heimdal and P. Uvdal ,
Nature Ecol. Evol. 1, 1093 (2017).
4 Phylogenetics is the evolutionary history and relationships between the different species, often expressed as ecological tree.
5 J. Lindgren, P. Sjövall, V. Thiel, W. Zheng, S. Ito, K. Wakamatsu, R Hauff, B.P. Kear, A Engdahl, C. Alwmark, M.E. Eriksson, M. Jarenmark, S. Sachs, P.E. Ahlberg, F. Marone, T. Kuriyama, O. Gustafsson, P. Malmberg, A. Thomen, I. Rodríguez-Meizoso, P. Uvdal and M.H. Schweitzer, Nature 564, 359 (2018).