217 Paleontology, Paleoecology/Taphonomy

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 305

THE LARGEST REPORTED STEGOSAURID FROM THE MORRISON FORMATION

Paper number: 217-10
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

Stegosaurs are an iconic group of ornithischian dinosaurs well known from the Morrison Formation and the Late Jurassic in general. Except for Australia and Antarctica, they have a global distribution. The Morrison Formation was home to the genera Stegosaurus, Hesperosaurus, Alcovasaurus, and the clade Stegosauria has been well studied within the formation since first recognized in the 1800s. Within the Morrison Formation, stegosaurids comprise a significant portion of the ornithischian record in the Morrison Formation; and while most reported specimens appear to be ‘adults’, there are a few ‘juveniles’ represented by particularly small individuals. Here we report a particularly large and robust individual that appears to represent the largest individual stegosaurid in the Morrison Formation in terms of both linear dimensions and estimated body mass (FHPR 1095). 

Based on our measurements, the humeri of this specimen average 4 cm proximodistally longer than those from the second largest stegosaurid specimen and are approximately 38% proximodistally longer than the average for stegosaurid specimens from the Morrison Formation. If our scaling and estimation methods are correct, then FHPR 1095 is approximately double the body mass of typical, ‘average’-sized stegosaurids from the Morrison Formation; suggesting that stegosaurids may have grown to even larger body sizes during the Late Jurassic than previously realized. The estimated mass of over 7 tonnes nearly overlaps with ‘subadult’ Morrison Formation sauropod specimens. 

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

doi: 10.1130/abs/2025AM-414855

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