What's inside that tiny head? Braincase osteology of ancient mammal relative Cotylorhynchus

Research output: Contribution to conferencePosterpeer-review


Synapsids are a group of amniotes that first appeared approximately 300 million years ago and include ancient mammal relatives and the living mammals present today. Non-mammalian synapsid neurobiology is relatively understudied compared to other amniote fossil groups like dinosaurs because non-mammalian endocasts are not completely accurate estimates for brain shape. Non-mammalian synapsids do not display the complete braincase ossification that is seen in mammals, and the anterior braincase is often not preserved making it difficult to completely reconstruct the entire endocast. However, the posterior braincase including the otic capsule is still possible to reconstruct. Out of the few non-mammalian synapsid endocasts that have been made, very few have been done for the early diverging group of pelycosaurs. Here, we’ll be reconstructing the posterior braincase and a virtual endocast of Cotylorhynchus romeri, an early pelycosaur from approximately 280 million years ago that is well known for its disproportionately small head compared to its large body. 
A complete skull of Cotylorhynchus from the Sam Noble Museum was computed tomography (CT) scanned. Using the CT-scans, we created three-dimensional reconstructions by manually segmenting out the braincase in Avizo Lite. CT-scans and virtual reconstructions allow us to describe the internal structures of the skull without damaging the fossil specimen. As a prelude to reconstructing an endocast, we provide a preliminary anatomical description of the braincase osteology to add new morphological information to previous descriptions written before CT technologies were widely available and establish the relationship of bones to corresponding brain regions. 
The occipital regions for caseids have been described to have a distinctive broad and flat shape that slopes posteriorly, based on previous descriptions of Cotylorhynchus and of a smaller genus, Casea, and this specimen supports that. Another similarity is that the foramen magnum has a triangular shape that flares out ventrally. One difference is that the supraoccipital in this specimen is relatively large and fuses with the lateral exoccipitals while the supraoccipital in Casea is smaller and does not fuse with the exoccipitals. This may be a size and/or maturity-related difference. The floor of the braincase is formed by a short basioccipital that makes up the ventral border of the foramen magnum and by the parabasisphenoid. The basioccipital and parabasisphenoid contact each other via a suture and are unfused. The parabasisphenoid has a long cultriform process that extends anteriorly between the pterygoids and contains teeth, a feature also found for Casea
Through reconstructing the braincase of Cotylorhynchus, we will estimate the morphology of its lost soft tissues to gain insight into aspects of its paleobiology such as balance, audition, social behaviors, and communications. We will clarify aspects of pelycosaur braincase anatomy and add to the little that is known about their endocasts, providing foundational data for investigating the evolution of non-mammalian synapsid and mammalian neuroanatomy.
Original languageAmerican English
StatePublished - 18 Feb 2022
EventOklahoma State University Center for Health Sciences Research Week 2022 : Poster Presentation - Oklahoma State University Center for Health Sciences, Tulsa, United States
Duration: 14 Feb 202218 Feb 2022


ConferenceOklahoma State University Center for Health Sciences Research Week 2022
Country/TerritoryUnited States


  • paleontology
  • endocast
  • synapsid
  • brain
  • skull


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