Llistrofus

Llistrofus was described by Canadian paleontologists Robert Carroll and Pamela Gaskill in 1978.{{Cite book|url=https://books.google.com/books?id=mjcyaQw78X4C&pg=PA30|title=The order Microsauria|last1=Carroll|first1=Robert L.|last2=Gaskill|first2=Pamela|date=1978|publisher=American Philosophical Society|isbn=0871691264|location=Philadelphia|oclc=4314948}} The genus name is an anagram of Fort Sill, the historic name of the Richards Spur locality from which material of Llistrofus was collected. The species name, L. pricei, is given for the Brazilian paleontologist Llewellyn Price. The holotype of this taxon is currently reposited at the Field Museum of Natural History. The skull of the holotype was reappraised by Bolt & Rieppel in 2009.{{Cite journal|last1=Bolt|first1=John R.|last2=Rieppel|first2=Olivier|date=2009|title=The holotype skull of Llistrofus pricei Carroll and Gaskill, 1978 (Microsauria: Hapsidopareiontidae)|journal=Journal of Paleontology|volume=83|issue=3|pages=471–483|doi=10.1666/08-076.1|bibcode=2009JPal...83..471B |s2cid=128436286|issn=0022-3360}} New material from Richards Spur was described by Gee et al. (2019).{{Cite journal|last1=Gee|first1=Bryan M.|last2=Bevitt|first2=Joseph J.|last3=Garbe|first3=Ulf|last4=Reisz|first4=Robert R.|date=2019-01-25|title=New material of the 'microsaur' Llistrofus from the cave deposits of Richards Spur, Oklahoma and the paleoecology of the Hapsidopareiidae|journal=PeerJ|volume=7|pages=e6327|doi=10.7717/peerj.6327|pmid=30701139|issn=2167-8359|pmc=6348957 |doi-access=free }}

File:Llistrofus.jpg]]

Llistrofus is readily identified by the presence of a large temporal emargination, a feature shared with Hapsidopareion lepton that unites the Hapsidopareiidae. Carroll & Gaskill (1978) differentiated Llistrofus from Hapsidopareion by four features: (1) postorbital contacting the tabular; (2) postparietal contacting the squamosal; (3) frontals entering the orbit; and (4) presence of a quadratojugal. Bolt & Rieppel (2009) revised the diagnosis following additional preparation of the holotype's skull and list three features (only one of which is shared with the previous work): (1) skull length approximately twice that of Hapsidopareion; (2) frontals entering the orbit; and (3) cultriform process of the parasphenoid offset from the basal plate by a narrow base. Gee et al. (2019) further revised the diagnosis based on additional material from Richards Spur and listed 11 features: (1) frontals entering the orbit; (2) prefrontal entering the naris; (3) premaxilla contributing to ventral narial margin; (4) postfrontal excluded from the temporal emargination; (5) postorbital contacting the tabular; (6) denticles on the vomer; (7) teeth on the palatine smaller than the marginal teeth; (8) absence of a pterygoid-premaxilla contact; (9) a splenial that contributes to the symphysis; (10) presence of a Meckelian foramen; and (11) presence of a retroarticular process. Using high-resolution micro-CT scans of three skulls of the coeval Hapsidopareion, Jenkins et al. (2025) identified that the characters used to distinguish Llistrofus from it are actually 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.{{Cite journal |last1=Jenkins |first1=Xavier A. |last2=Sues |first2=Hans‐Dieter |last3=Webb |first3=Savannah |last4=Schepis |first4=Zackary |last5=Peecook |first5=Brandon R. |last6=Mann |first6=Arjan |date=2025-01-07 |title=The recumbirostran Hapsidopareion lepton from the early Permian (Cisuralian: Artinskian) of Oklahoma reassessed using HRμCT , and the placement of Recumbirostra on the amniote stem |journal=Papers in Palaeontology |language=en |volume=11 |issue=1 |doi=10.1002/spp2.1610 |issn=2056-2799}}

Llistrofus is recovered as the sister taxon to Hapsidopareion in phylogenetic analyses, forming the family Hapsidopareiidae within the Recumbirostra.{{Cite journal |last1=Mann |first1=Arjan |last2=Pardo |first2=Jason D |last3=Sues |first3=Hans-Dieter |date=2022-07-19 |title=Osteology and phylogenetic position of the diminutive 'microsaur' Odonterpeton triangulare from the Pennsylvanian of Linton, Ohio, and major features of recumbirostran phylogeny |journal=Zoological Journal of the Linnean Society |volume=197 |issue=3 |language=en |pages=641–655 |doi=10.1093/zoolinnean/zlac043 |issn=0024-4082|doi-access=free }} 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:

{{clade

|{{clade

|1={{clade

|1=Limnoscelis

|2={{clade

|1=Captorhinidae

|2={{clade

|1=Protorothyris

|2=Amniota }} }} }}

|label3=Recumbirostra

|3={{clade

|1=Pantylus

|2={{clade

|1={{clade

|1={{clade

|1=Hapsidopareion {{small|(including Llistrofus)}}

|2=Odonterpetidae }}

|label3=Chthonosauria

|3={{clade

|1=Molgophidae

|2=Brachystelechidae }} }}

|label3=Nastrondormes

|3={{clade

|1={{clade

|1=Huskerpeton

|2=Proxilodon }}

|3={{clade

|1=Gymnarthridae

|2={{clade

|1=Rhynchonkidae

|2=Ostodolepididae

}} }} }} }} }} }} }}

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Category:Microsauria