Journal of Vertebrate Paleontology reveals an astonishing discovery in southwestern Montana: a 95-million-year-old miniature crocodyliform, nicknamed Elton, which defies all expectations about these prehistoric reptiles. This exceptional fossil, measuring only 60 centimeters (about 2 feet) long, belonged to a terrestrial species with specialized teeth, quite different from modern crocodiles.
The discovery of Elton dates back to 2021, during excavations in the Blackleaf geological formation, which dates to the middle Cretaceous. Harrison Allen, then a student at Montana State University, spotted a 5-centimeter (about 2 inches) fossilized skull embedded in rock. This small skull, perfectly articulated and preserved, immediately captivated David Varricchio, a professor of paleobiology, with its detailed anatomy.
Artist's depiction of Elton (Thikarisuchus xenodentes), an extinct crocodyliform from the Cretaceous in North America.
Credit: Illustration by Dane Johnson/Museum of the Rockies Allen then spent hours sieving sediments to reconstruct the skeleton piece by piece, collaborating with Dane Johnson from the Museum of the Rockies, all while listening to Elton John's "Crocodile Rock," hence the affectionate nickname.
Elton belongs to a previously unknown family, the Wannchampsidae, within the Neosuchia group, which includes modern crocodilians. Unlike the latter, which are semi-aquatic and carnivorous, Elton and its relatives of the species Thikarisuchus xenodentes measured about 90 centimeters (nearly 3 feet) as adults and lived on land. Their teeth, of varied shapes and sometimes sheathed, indicate a mixed diet of plants and insects. Analysis of their densely packed bones suggests they dug burrows, a rare adaptation among crocodilians.
To refine the study, Allen used computed tomography (CT scanning), a medical imaging technique applied to fossils, allowing bones to be distinguished from rock fragments. This approach revealed precise anatomy, highlighting similarities with the Atopasauridae, a Eurasian family of small crocodyliforms with comparable teeth. These resemblances point to convergent evolution, where distant groups develop similar traits in response to analogous environmental conditions.
This research enriches our understanding of prehistoric crocodilian diversity, showing they occupied varied ecological niches, far beyond aquatic ecosystems.
Neosuchia: Underappreciated Diversity
Neosuchia is a group of crocodilians that includes all modern species, such as crocodiles and alligators, as well as many extinct relatives. Traditionally, they are imagined as aquatic predators with simple conical teeth, but Elton reveals an unsuspected diversity, with terrestrial and omnivorous members.
This diversity is explained by their long evolutionary history, dating back to the Jurassic, which allowed the emergence of forms adapted to various environments. For example, some ancient Neosuchia were marine, while others, like Elton, preferred dry land, exploiting different food resources.
The discovery of the Wannchampsidae, a new family within Neosuchia, expands our view of their adaptive radiation. It reminds us that extinct lineages can offer unique models for studying evolution, showing how traits like reduced size or elaborate dentition may have provided advantages in specific environments.
Convergent Evolution in Crocodilians
Convergent evolution occurs when unrelated species develop similar characteristics in response to identical environmental pressures. In Elton and the Eurasian Atopasauridae, small size and specialized teeth are striking examples, likely resulting from comparable diets and terrestrial habitats.
This phenomenon is common in nature, as seen in marsupials and placental mammals, which evolved separately but exhibit analogous body forms. For crocodilians, it indicates that ecological constraints, such as prey availability or competition, shaped their morphology independently on different continents.
The study of Elton shows that convergent evolution can occur even in ancient groups, offering clues about Cretaceous ecosystems. By understanding these processes, scientists can better predict how species adapt to changes, a relevant issue in the face of current climate upheavals.