doi: 10.7717/peerj.14355. eCollection 2022.
Guttigomphus avilionis gen. et sp. nov., a trirachodontid cynodont from the upperCynognathus Assemblage Zone, Burgersdorp Formation of South Africa
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- PMID:36545384
- PMCID: PMC9762250
- DOI: 10.7717/peerj.14355
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Guttigomphus avilionis gen. et sp. nov., a trirachodontid cynodont from the upperCynognathus Assemblage Zone, Burgersdorp Formation of South Africa
Romy R Rayner et al. PeerJ..
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Abstract
The Burgersdorp Formation of South Africa is a richly fossiliferous rock sequence at the top of the Permian-Triassic Beaufort Group and is known for its abundance of Early-Middle Triassic vertebrate remains, particularly cynodonts. Fossils from the Burgersdorp Formation are referred biostratigraphically to theCynognathus Assemblage Zone (CAZ), which is further divided into three subzones:Langbergia-Garjainia, Trirachodon-Kannemeyeria, andCricodon-Ufudocyclops. Each subzone is characterised by the presence of a distinct species of trirachodontid, a group of gomphodont cynodonts found relatively abundantly throughout the CAZ, with the lower two subzones characterised by the medium-sized trirachodontidsLangbergia andTrirachodon. The uppermost part of the formation, theCricodon-Ufudocyclops subzone, yields trirachodontids of larger size. The majority of these trirachodontid specimens have previously been referred toCricodon metabolus, a taxon also known from the Manda Beds of Tanzania and the Ntawere Formation of Zambia. Here we identify one of the specimens (BP/1/5538) previously referred toCricodon as a new taxon,Guttigomphus avilionis.Guttigomphus can be distinguished from other gomphodont cynodonts by features of the upper postcanine teeth, such as an asymmetric crown in occlusal view (crown narrower along the lingual margin than the labial). Our phylogenetic analysis recoversGuttigomphus as a basal member of Trirachodontidae, outside of the clade includingCricodon,Langbergia andTrirachodon.
Keywords: Anatomy; Anisian; Burgersdorp Formation; Cynodont; Middle Triassic; Phylogenetics; South Africa; Synapsid; Taxonomy; Trirachodontid.
© 2022 Rayner et al.
Conflict of interest statement
The authors declare that they have no competing interests.
Figures
This is a generalized interpretation based on the area around Sterkstroom and modified from the work of Hancox (1998), then updated based on information in Hancox, Neveling & Rubidge (2020). The palaeosol marking the boundary between the upper Katberg and lower Burgersdorp formations is only found across some of the outcrop. Taxa are shown approximately to scale in relation to each other. Silhouettes modified from life reconstructions by Mojca Janezic, Nobu Tamura, and Gabriel Ugueto.
(A) Map of South Africa showing the extent of the Burgersdorp facies and wider Beaufort Group along with the positioning of (B), the southern Burgersdorp facies and (C), the northern Burgersdorp facies. Site 1, Avilion and Thala farms west of the town of Sterkstroom, localities for specimen BP/1/5538 (holotype ofGuttigomphus avilionis gen. et sp. nov.), along with BP/1/5540, a complete skull in occlusion referred toCricodon cf.C.metabolus, and the recently describedImpidens hancoxi. Site 2, Aliwal North, locality of the holotype specimen ofTrirachodon kannemeyeri (Seeley, 1895a). Site 3, Lady Frere, locality of the holotype specimen ofTrirachodon berryi (Seeley, 1895a). Site 4, Langberg, Paul Roux district, locality of the holotype ofLangbergia modisei (Abdala, Hancox & Neveling, 2005). The Burgersdorp outcrop is at its thickest in the area between Lady Frere (Cacadu) and Queenstown (Komani) where it reaches over 600 m. The unit then thins gradually extending from this area to a thickness of just 150–200 m in the area between Aliwal North and Burgersdorp.
(A) Dorsal view. (B) Interpretative drawing. (C) Skull reconstruction showing the part of the skull represented in the specimen in white. The taxaLangbergia modisei andCricodon metabolus were used to make informed reconstruction of missing regions of the skull.
(A) Right lateral view. (B) Interpretative drawing. (C) Skull reconstruction showing the part of the skull represented in the specimen in white. Abbreviations: lc, lacrimal; mxl, maxilla; na, nasal; orb, orbital region; pfr, postfrontal; pft, prefrontal; po, postorbital; pt, palatine. Arrows denote location of lacrimal canals.
Teeth have been assigned as Left A (la), Left B (lb), Left C (lc) and Left D (ld), with the alveolus of (missing) Left E (le) and Right C (rc), Right D (rd) and Right E (re). Numerical positional values have not been provided since the number of postcanines in the row cannot be confidently assessed with the material available. Letters have been assigned with the posterior-most gomphodont postcanine being designated as ‘E’ and working forwards across the tooth row. For the purposes of comparative anatomy, the dentitions of other closely related taxa were also characterized in this way. Since the total number of postcanines are subject to intraspecific variation among trirachodontids, the letters assigned in this study will correspond to different numerical loci in different specimens. Abbreviations: bc, buccal cingulum; bl, buccal ledge; c, cuspule; cc, central cusp; lac, labial cusp; ladc, labial distal cusp; lamc, labial mesial cusp; lic, lingual cusp.
(A)Cricodon metabolus upper postcanine, interpretive drawing of occlusal outline from UMZC T905; (B)Cricodon metabolus, artistic rendition of upper postcanine from UMZC T905; (C)Guttigomphus avilionis gen. et sp. nov., interpretative drawing of occlusal outline from BP/1/5538 (re Fig. 5); (D)Guttigomphus avilionis gen. et sp. nov., artistic rendition of upper postcanine from BP/1/5538 (tooth re, Fig. 5); (E)Langbergia modisei upper postcanine, interpretive drawing of occlusal outline from NMQR 3255; (F)Langbergia modisei, artistic rendition of upper postcanine from NMQR 3255. Abbreviations: c, cuspule; cc, central cusp; lac, labial cusp; lamac, labial mesial accessory cusp; lamc, labial mesial cusp; lic, lingual cusp; lidc, lingual distal cusp; limc, lingual mesial cusp; ob, occlusal basin.
Comparison of the mesial border of the upper postcanines inCricodon metabolus (UMZC T905), two additional specimens ofCricodon cf. metabolus from theCricodon-Ufudocyclops subzone (BP/1/6102 and BP/1/8124) andGuttigomphus avilionis (BP/1/5538), highlighting the difference in position of the labial cusp. lac, labial cusp.
(A) BP/1/5540,Cricodon cf.C. metabolus. Full skull in occlusion, right lateral view. (B) BP/1/5835, large cynognathian, probablyCynognathus, right lateral view of anterior part of skull.
(A1) BP/1/8124,Cricodon cf.C. metabolus,Cricodon-Ufudocyclops subzone, South Africa. Left and right fragments of maxillary cheek teeth row, occlusal view. (A2) Interpretive drawing of BP/1/8124, occlusal view. (B1) UMZC T905,Cricodon metabolus holotype, Manda Beds, Tanzania. (B2) Interpretive drawing of UMZC T905. (C1) BP/1/6102,Cricodon cf.C. metabolus,Cricodon-Ufudocyclops subzone, South Africa. Interpretative drawing in occlusal view. (C2) BP/1/6102, photograph in occlusal view. Abbreviations: c, cuspule; cc, central cusp; lac, labial cusp; lic, lingual cusp; lidc, lingual distal cusp; 1s1, left sectorial one; ls2, left sectorial two; rs1, right sectorial one. Teeth have been assigned as Left A (la), Left B (lb), Left C (lc) and Left D (ld) and Right C (rc), Right D (rd) and Right E (re) to distinguish left from right (see caption to Fig. 5). Numerical values have not been provided since the number of postcanines in the row cannot be confidently assessed with the material available.
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Funding for field work was provided by a Marie Curie Career Integration Grant (630123 to RJB), the NRF African Origins Platform (98800 to JNC), and by Palaeontological Scientific Trust (JNC). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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