| Hapsidopareion Temporal range: Permian, Artinskian PreꞒ Ꞓ O S D C P T J K Pg N | |
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Order: | †Microsauria |
| Family: | †Hapsidopareiidae |
| Genus: | †Hapsidopareion Daly, 1973 |
| Species | |
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| Synonyms | |
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Hapsidopareion is an extinct genus of microsaur belonging to the family Hapsidopareiidae. Fossils have been found in the early Permian of Oklahoma.
History of study
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Hapsidopareion was named in 1973 by American paleontologist Eleanor Daly based on material collected from the early Permian South Grandfield locality in southwestern Oklahoma. The genus name is given for the Greek hapsido- ('arch') and -pareion ('cheek'). The species name, H. lepton, is given for the slightness of the animal. The taxon is known from several partial to complete skulls and possibly by some isolated postcranial material.
Anatomy
Hapsidopareion was originally differentiated from other microsaurs by the large temporal emargination, which produced other variable morphology of the circum-emargination bones (e.g., postorbital). It is similar to the more recently described Llistrofus pricei in this regard, but can be differentiated from L. pricei by features such as the absence of a quadratojugal and a frontal excluded from the orbit. Because all specimens of H. lepton are notably smaller than those of L. pricei, and a number of anatomical differences are likely ontogenetically variable (e.g., contact between neural arch and centrum), some researchers considered that the former maybe represent a juvenile of the latter, but recent workers have maintained the separation of these taxa. Using high-resolution micro-CT scans of three skulls of the coeval Hapsidopareion, Jenkins et al. (2025) identified that many of the characters used to distinguish Llistrofus from it are shared by both taxa. Due to its larger size, they identified Llistrofus as representing a more mature ontogenetic stage of Hapsidopareion, and argued that the former should be regarded as a junior synonym of the latter.
Relationships
Hapsidopareion is the sister taxon to Llistrofus forms the family Hapsidopareiidae (traditionally called the 'Hapsidopareiontidae') within the Recumbirostra. The family is recognized by the greatly enlarged temporal emargination. In their 2025 publication, Jenkins et al. discussed the possible synonymy of Hapsidopareion and Llistrofus. The results of their phylogenetic analyses are displayed in the cladogram below, where they found recumbirostrans to be a clade along the amniote stem:
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References
- ^ Daly, Eleanor (1973). "A Lower Permian Vertebrate Fauna from Southern Oklahoma". Journal of Paleontology. 47 (3): 562–589. ISSN 0022-3360. JSTOR 1303204.
- Carroll, Robert L.; Gaskill, Pamela (1978). The order Microsauria. Philadelphia: American Philosophical Society. pp. 1–126. ISBN 978-0871691262. OCLC 4314948.
- ^ Bolt, John R.; Rieppel, Olivier (2009). "The holotype skull of Llistrofus pricei Carroll and Gaskill, 1978 (Microsauria: Hapsidopareiontidae)". Journal of Paleontology. 83 (3): 471–483. Bibcode:2009JPal...83..471B. doi:10.1666/08-076.1. ISSN 0022-3360. S2CID 128436286.
- ^ Gee, Bryan M.; Bevitt, Joseph J.; Garbe, Ulf; Reisz, Robert R. (2019-01-25). "New material of the 'microsaur' Llistrofus from the cave deposits of Richards Spur, Oklahoma and the paleoecology of the Hapsidopareiidae". PeerJ. 7: e6327. doi:10.7717/peerj.6327. ISSN 2167-8359. PMC 6348957. PMID 30701139.
- ^ Jenkins, Xavier A.; Sues, Hans‐Dieter; Webb, Savannah; Schepis, Zackary; Peecook, Brandon R.; Mann, Arjan (2025-01-07). "The recumbirostran Hapsidopareion lepton from the early Permian (Cisuralian: Artinskian) of Oklahoma reassessed using HRμCT , and the placement of Recumbirostra on the amniote stem". Papers in Palaeontology. 11 (1). doi:10.1002/spp2.1610. ISSN 2056-2799.
| Taxon identifiers | |
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| Hapsidopareion | |