58 Future Leaders in Paleontology

The Paleontological Society is pleased to offer the “Future Leaders in Paleontology” topical session. This session will showcase the outstanding work of our student and early career members in a high-profile setting.

Sunday, 19 October 2025
1:30 PM - 5:30 PM
HBGCC, 305

Microscale Cartilage Preservation in Exceptional Tully Monster Specimens

Paper number: 58-5
Program: Technical Sessions
Time: 2:35 PM – 2:50 PM

Authors

Abstract

Tullimonstrum gregarium, commonly referred to as the Tully Monster, is a well-known, charismatic animal from the Late Carboniferous Mazon Creek Lagerstätte in Illinois, USA. Tullimonstrum is represented by thousands of well-preserved fossils across multiple museum collections, providing a detailed picture of its strange, soft-bodied gross anatomy. However, only a handful of studies have focused on microscale features in Tullimonstrum. Here we apply scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) to exceptionally well-preserved Tullimonstrum specimens to investigate the microscale preservation of its recalcitrant, three-dimensionally preserved features. SEM imaging revealed structurally preserved cartilage fragments in the eyebar and eye cup of one exceptionally well-preserved Tullimonstrum specimen. EDS analysis revealed that these fragments were composed of calcium and phosphorous, suggesting that the original cartilage material had been replaced by a calcium and phosphorous mineral such as apatite. Similar materials, although less well-preserved, were found in other Tullimonstrum fossils in recalcitrant regions including the eyebar, eye cup, and an area directly posterior of the eyebar interpreted as the braincase. Preserved cartilage in these recalcitrant areas suggests that Tullimonstrum had a cartilaginous endoskeleton, which narrows the possibilities for its affinity. While cartilage is not a chordate-specific tissue, the distribution of cartilaginous tissues in these areas supports a chordate affinity. This aligns with previous work on Tullimonsturm’s chemical preservation and 3D preservation.

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

doi: 10.1130/abs/2025AM-414110

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