Crock-shock – using CT data to explore extinct crocodyliforms

Posted by a.hay on 11 November 2014 - 10:00am

3D models of the aquatic crocodyliform Pelagosaurus typus. By Felipe Montefeltro, postdoctoral researcher at São Paulo State University, Brazil.

This article is part of our series: a day in the software life, in which we ask researchers from all disciplines to discuss the tools that make their research possible.

The application of computer-based technologies was once largely constrained by the high price of both hardware and software. In the past decade, the price of both has fallen to a much more affordable level. Now, computer-based methods are available for a greater number of palaeontologists.

This is particularly true of X-ray computed tomography (CT) which has profoundly changed how we study fossils. I study the internal structure of fossil crocodile skulls based on CT data and use it to search for clues as to how they lived.

Someone who looks at a crocodile basking on a river-bank might think it is little changed from the time when cold-blooded animals ruled the earth. Yet crocodiles, alligators, caimans and the Indian gharial form only a small and relatively new branch of the group Crocodyliformes. This group also includes a plethora of fossil species, some of them strongly deviating from the general image we have of their extant semi-aquatic relatives.

The groups Thalattosuchia and Baurusuchidae are perhaps the best examples of extremes among fossil crocodyliforms. Thalattosuchia is a distinct group found across the world in marine rocks from the Early Jurassic (180 million years ago) to the Early Cretaceous (132 million years ago). The components of this group have remarkable adaptation for marine life and were, in effect, sea crocodiles.

Baurusuchidae, on the other hand, are fossil crocodyliforms restricted to continental rocks of the Late Cretaceous (80 million years ago). This group’s remains are mostly found in Brazil, encompass forms with adaptation to life on land and competed with and even preyed upon the Dinosaurs. Since the Baurusuchidae and Thalattosuchia both have characteristics not found in any living crocodiliform, these two groups were selected to be the main subject of my study.

The study was made possible via my collaboration with Dr. Richard Butler from the University of Birmingham, Dr. Hans Larsson form McGill University, and Dr. Max Langer from Universidade de São Paulo. They granted me access to fossils, computers and software. The crucial step of the project was the digitalisation of the fossil skulls in medical CT and micro-CT machines. The stored CT images, in this case DICOM or TIFF formats, were visualised using two software packages, the commercial product Avizo and the open-source SPIERS.

Both packages are capable of assembling CT images and highlighting the structures that were of most interest for me. This process allowed access to the morphology and 3D modeling of inner structures of the skulls studied, such as the inner ear and the cranial cavity. My ultimate goal is to use the data to understand how different the fossil species, both aquatic and terrestrial, are in comparison to living species and what it implies for both the evolution and palaeoecology of crocodyliforms.

3D models of the aquatic crocodyliform Pelagosaurus typus.

3D models of the aquatic crocodyliform Pelagosaurus typus.

However, the database gathered along the development of the project intrigues me as much as the results themselves. Fossils skulls are rare, and well-preserved skulls are rarer still. It is very important to keep them safe and intact. It is understandable then that most collections have a policy to not lend holotypes - the specimen in which the species name is attached to.

So digitisation has at last made it possible to have ready access to skull data, from the UK and France to Colombia and Brazil. This allows me to access the morphology and the virtual manipulation of skulls that are more than 9,000 km away! This is of particular interest for more old fashioned palaeontological studies, such as the description, comparison and scoring of new species on the phylogenetic matrix.

The use of CT data in palaeontological studies is growing fast, as anyone who’s recently read a journal or attended a conference will know. However, it is not only in cutting edge science that CT data is making an impression. It also improves more traditional types of work as it reduces the distance between researches and fossils from thousands of kilometres to only a click away.