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Updated: Jul 6, 2025
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Systematic Assessment of Mammalian Skull Specimens for Dental and Temporomandibular Joint Pathology
Published on: August 22, 2022
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Basicranial evidence suggests picrodontid mammals are not stem primates
Jordan W Crowell1,2, John R Wible3, Stephen G B Chester1,2,4
1Department of Anthropology, The Graduate Center, City University of New York, 365 Fifth Avenue, New York, NY 10016, USA.
Biology Letters
|January 9, 2024
Summary
Picrodontidae mammals are not early primates. New cranial data reveals their basicranial features are distinct from plesiadapiforms, suggesting independent evolution of dental traits.
Area of Science:
- Paleontology
- Vertebrate Paleontology
- Mammalian Evolution
Background:
- Picrodontidae, enigmatic placental mammals from the middle Paleocene of North America, have uncertain phylogenetic affinities.
- Previous classifications allied Picrodontidae with various groups, often based on dental features suggesting links to plesiadapiforms.
- The fossil record of Picrodontidae is predominantly dental and gnathic, with limited cranial material available for study.
Purpose of the Study:
- To investigate the basicranial morphology of the picrodontid mammal *Zanycteris paleocenus* using micro-computed tomography (µCT).
- To compare the basicranial features of *Z. paleocenus* with other mammalian groups to clarify picrodontid phylogenetic placement.
- To integrate new morphological data into cladistic analyses to reassess the evolutionary relationships of Picrodontidae.
Main Methods:
- Micro-computed tomography (µCT) scanning of the partial cranium of *Zanycteris paleocenus* (AMNH 17180) to reveal internal and external morphology.
- Detailed description and comparative analysis of the basicranial anatomy of *Z. paleocenus*.
- Phylogenetic analyses incorporating the new cranial data with existing morphological datasets for early mammals.
Main Results:
- The basicranial morphology of *Zanycteris paleocenus* is significantly distinct from known plesiadapiforms.
- Cranial features of *Z. paleocenus* exhibit similarities to Palaeogene taxa such as Apatemyidae and Nyctitheriidae.
- Cladistic analyses indicate that Picrodontidae are not stem primates or euarchontan mammals, and shared dental traits with plesiadapiforms are likely homoplasies (independent evolution).
Conclusions:
- Picrodontidae are removed from the immediate ancestry of primates and Euarchonta.
- The proposed dental synapomorphies linking Picrodontidae to Plesiadapiforms are reinterpreted as independently evolved.
- This study underscores the importance of scrutinizing proposed synapomorphies in taxa with limited fossil evidence and high degrees of autapomorphy.
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