219 Paleontology, Diversity, Extinction, Origination (Posters)

Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

A Juvenile Crocodylian From the Kootenai Formation, Montana

Paper number: 219-9
Program: Technical Sessions
Time: 9:45 AM – 10:00 AM

Authors

Abstract

The Lower Cretaceous Kootenai Formation is located throughout Southwestern Montana. Detrital zircon geochronology analysis estimate the age of the Kootenai to range between approximately 135 – 110 million years old. Despite the rich paleontological Cretaceous record of Montana, the Lower Cretaceous is not as well studied. In 2017, staff from the Sam Noble Museum of Natural History and University of Arkansas recovered a disarticulated vertebrate specimen from Ziegler Gulch, north of Dillon, MT. The specimen, VZ1761, is composed of vertebral elements, rib fragments, and miscellaneous bone fragments. The small size of the neural arch, measuring at 35.14 mm laterally across, and physical characteristics, such as the unfused dorsal vertebrae-neural arch suggest the individual recovered is a young juvenile mesoeucrocodylian. Here we describe the features of VZ1761 and compare elements to juvenile and adult American Alligator (Alligator mississippiensis) and American Crocodile (Crocodylus acutus) specimens using digital calipers. Preliminary analysis indicate the specimen is a crocodilian. For example, the widening of the anterior end of an identified sacral vertebra for connection of the transverse process bears resemblance to C. acutus. The shape and low angle of the recovered ribs appear to resemble that of the gastralia of A. mississippiansis. Further study, such as comparative analysis of near contemporaneous taxa are needed to determine the specific genera, and species, if possible. This specimen serves to improve upon the understudied paleontological record of the Kootenai Formation, and the Lower Cretaceous in general.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413591

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