Reconstructing South Korea’s Cretaceous with the First Evidence of Crocodilian Tracks Found

First reports of Crocodylopodus from East Asia: implications for the paleoecology of the Lower Cretaceous

By: Martin G. Lockley, Jong Deock Lim, Hong Deock Park, Anthony Romilio Jae Sang Yoo, Ji Won Choi, Kyung Soo Kim, Yeongi Choi, Seung-Hyeop Kang, Dong Hee Kim, Tae Hyeong Kim.

Summarized by: Noel J. Hernandez G., a current geology senior undergraduat et at The University of South Florida. He plans to continue his education in paleontology by going to graduate school. He is hoping to eventually get his PhD in paleontology and become a professor that performs research throughout the world. He is also known as a video game enthusiast and enjoys science more than any person realistically should.

What data were used? The first samples of Crocodylopodus fossil footprints in the Cretaceous-age Jinju formation of South Korea, and previous samples of other kinds of crocodilian prints from the Mesozoic Era.

Methods: This study was conducted and made possible by many different organizations and study groups all working on the same project on the Jinju formation in South Korea. There were a multitude of samples gathered from four different dig sites, but this study focuses on the best-preserved samples. These samples were photographed using specialized 3D cameras and run through different software to create comprehensive elevation maps that could clearly show the indentations of the prints on the shale rock. Then, each visible print was studied and measured to identify possible the tracks that these animals made, this way, their walking patterns could be identified and matched with existing data to find the proper classification for them.

Results: There are many different kinds of prints that animals can leave behind as fossils. This could be due to different movement behaviors, different feeding methods, or even resting positions; we call fossils of these preserved behaviors, like these prints, ichnofossils. Crocodylopodus is one such type of footprint ichnofossil that was left behind by crocodile-like animals millions of years ago, though there are other kinds of common crocodile ichnofossils, such as Batrachopus and Hatcherichnus. In this study, these other common crocodile ichnofossils are used to compare these new samples of Crocodylopodus found with pre-existing data to try and understand what these tracks means for the organisms that produced them. The study finds that these prints are complete enough to reassemble the possible way that these animals walked. From this information, they found sufficient evidence to say that these crocodilians probably walked on land more than previously thought, unlike Hatcherichnus that demonstrate swimming. Crocodylopodus demonstrates walking in all of the samples found at these sites because of the types of sediments that they were imprinted on, representing shallow rivers and floodplains. Swimming tracks usually have small footprints with tail traces along with them, but Crocodylopodus does not show tail traces.

This changes the idea that most crocodilians in Eastern Asia during the Mesozoic were mostly aquatic animals, and this finding suggests that the trait of being aquatic or terrestrial primarily has been dependent on the kind of environments these animals lived in, as similar ichnofossils from different parts of the world show different habits in varying ecosystems.


Why is this study important? This study is part of a bigger ongoing study of a brand-new region of the world that has not been thoroughly studied for paleontology; specifically, the Jinju Formation is an area of South Korea that has not been heavily studied in the past. Many new species and recurrences of previously known species are coming up as more and more ichnofossils are uncovered. The more studies that are done on these samples, the closer we get to understanding how the paleoecology (i.e., how ancient animals interacted with each other and their environment) functioned there.

Slab with Crocodylopodus and other small mammal ichnofossil. A. Draw representation showing where each trace is located and the direction of the tracks. B. Low exposure picture of the actual fossil assemblage. C. Elevation imaging of the slab to show impression.

The big picture: These assemblages of trace fossils (ichnofossils) had not only the traces of crocodile-like animals, but they also had other kinds of trace fossils made by other organisms. There were many small animal prints and other kinds of reptile and amphibian prints as well, Crocodylopodus was only a part of the active biological community that existed in this area during the Cretaceous. Seeing how these crocodilians moved and lived among all of these other animals helps us understand the region better.

Citation: Martin G. Lockley, Jong Deock Lim, Hong Deock Park, Anthony Romilio, Jae Sang Yoo, Ji Won Choi, Kyung Soo Kim, Yeongi Choi, Seung-Hyeop Kang, Dong Hee Kim, Tae Hyeong Kim, 2020, First reports of Crocodylopodus from East Asia: implications for the paleoecology of the Lower Cretaceous, Cretaceous Research, Volume 111, 104441, ISSN 0195-6671, https://doi.org/10.1016/j.cretres.2020.104441