Younginiformes
| Younginiformes Temporal range:
| |
|---|---|
| Skull of Youngina | |
| Skull of Acerosodontosaurus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Neodiapsida |
| Order: | †Younginiformes Romer, 1945 |
| Subgroups | |
Younginiformes is a potential group of diapsid reptiles known from the Permian–Triassic of Africa. It has been used as a replacement for the more problematically-defined "Eosuchia".[1] Younginiforms were historically suggested to be lepidosauromorphs, but are now regarded as basal non-saurian neodiapsids.[2][3] Some younginiforms like Hovasaurus and Acerosodontosaurus are thought to have had an amphibious lifestyle, while others like Kenyasaurus, Thadeosaurus, and younginids were probably terrestrial.[4][5]
Classification
Eosuchia is generally seen as comprising two families, Tangasauridae and Younginidae. The monophyly of the group—whether tangasaurids and younginids form a clade rather than distinct branches—is disputed. A 2009 study found them to be an unresolved polytomy at the base of Neodiapsida.[4] In their 2011 description of Orovenator, Reisz et al. recovered the group as paraphyletic. These results are displayed in Topology A below.[6] A 2022 study by Simões et al. recovered the Younginiformes as a monophyletic group of basal neodiapsid reptiles, also including Claudiosaurus and Saurosternon as part of the group. These results are displayed in Topology B below.[7]
| Topology B: Results of Reisz et al. (2011)[6]
|
Topology B: Results of Simões et al. (2022)[7]
|
Subsequent research by Jenkins and colleagues (2025) based on synchrotron data and an expansive phylogenetic dataset supported a placement of tangasaurids (Acerosodontosaurus, Hovasaurus, and Thadeosaurus) diverging after younginids (Youngina and the then-unnamed Endothiodon Assemblage Zone taxon, Scyllacerta).[8] In their description of the EAZ taxon in 2026, Jenkins et al. used an updated version of this matrix for their phylogenetic analyses. They recovered conflicting results regarding the relationships of tangasaurids to younginids; an implied weighting parsimony analysis placed them as successive lineages (rendering 'Younginiformes' paraphyletic), while a time-calibrated Bayesian analysis recovered a monophyletic Younginiformes, with Tangasauridae as the sister group to Younginidae (including Saurosternon). Abbreviated versions of these analyses are displayed below. As explained by Buffa et al. (2025),[5] Jenkins et al. noted that this uncertainty may be partly due to a limited knowledge about the anatomy of some members of this clade, and that future detailed studies may provide improved resolution.[9]
| Topology C: Implied weighting analysis
|
Topology D: Bayesian analysis
|
References
- ^ Gauthier, J.; Estes, R.; de Queiroz, K. (1988). "A phylogenetic analysis of Lepidosauromorpha" (PDF). In R. Estes; G. Pregill (eds.). Phylogenetic relationships of the lizard families. Stanford: Stanford University Press. pp. 15–98. Archived (PDF) from the original on 2023-12-09.
- ^ Laurin, Michel (January 1991). "The osteology of a Lower Permian eosuchian from Texas and a review of diapsid phylogeny". Zoological Journal of the Linnean Society. 101 (1): 59–95. doi:10.1111/j.1096-3642.1991.tb00886.x.
- ^ Ezcurra, Martín D.; Scheyer, Torsten M.; Butler, Richard J. (2014-02-27). Ketmaier, Valerio (ed.). "The Origin and Early Evolution of Sauria: Reassessing the Permian Saurian Fossil Record and the Timing of the Crocodile-Lizard Divergence". PLOS ONE. 9 (2) e89165. Bibcode:2014PLoSO...989165E. doi:10.1371/journal.pone.0089165. ISSN 1932-6203. PMC 3937355. PMID 24586565.
- ^ a b Bickelmann; Müller; Reisz (2009). "The enigmatic diapsid Acerosodontosaurus piveteaui (Reptilia: Neodiapsida) from the Upper Permian of Madagascar and the paraphyly of "younginiform" reptiles". Canadian Journal of Earth Sciences. 46 (9): 651–661. Bibcode:2009CaJES..46..651S. doi:10.1139/E09-038.
- ^ a b Buffa, Valentin; Jalil, Nour‐Eddine; Falconnet, Jocelyn; Vincent, Peggy (2025-03-23). "The neodiapsid Thadeosaurus colcanapi from the upper Permian of Madagascar". Papers in Palaeontology. 11 (2). doi:10.1002/spp2.70008. ISSN 2056-2799.
- ^ a b Robert R. Reisz; Sean P. Modesto; Diane M. Scott (2011). "A new Early Permian reptile and its significance in early diapsid evolution". Proceedings of the Royal Society B. 278 (1725): 3731–3737. doi:10.1098/rspb.2011.0439. PMC 3203498. PMID 21525061.
- ^ a b Simões, Tiago R.; Kammerer, Christian F.; Caldwell, Michael W.; Pierce, Stephanie E. (2022-08-19). "Successive climate crises in the deep past drove the early evolution and radiation of reptiles". Science Advances. 8 (33) eabq1898. Bibcode:2022SciA....8.1898S. doi:10.1126/sciadv.abq1898. ISSN 2375-2548. PMC 9390993. PMID 35984885.
- ^ Jenkins, Xavier A; Benson, Roger BJ; Ford, David P; Browning, Claire; Fernandez, Vincent; Dollman, Kathleen; Gomes, Timothy; Griffiths, Elizabeth; Choiniere, Jonah N; Peecook, Brandon R (2025-08-28). "Evolutionary assembly of crown reptile anatomy clarified by late Paleozoic relatives of Neodiapsida". Peer Community Journal. 5. e89. doi:10.24072/pcjournal.620. ISSN 2804-3871.
- ^ Jenkins, Xavier A.; Buffa, Valentin; Marchant, Cy J.; Ford, David P.; Browning, Claire; Fernandez, Vincent; Dollman, Kathleen; Botha, Jennifer; Choiniere, Jonah N.; Benson, Roger B. J.; Peecook, Brandon R. (2026-01-22). "The origin of the tympanic fossa in reptiles revealed by a late Permian neodiapsid". Palaeontology. 69 (1) e70041: 1–15. doi:10.1111/pala.70041. ISSN 0031-0239.