Gondwanax

Gondwanax; Temporal range: Middle–Upper Triassic, Ladinian–early Carnian PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	†Ornithischia (?)
Family:	†Silesauridae
Clade:	†Sulcimentisauria
Genus:	†Gondwanax; Müller, 2024
Species:	†G. paraisensis
Binomial name
	†Gondwanax paraisensis; Müller, 2024
	Gondwanax type locality in Paraíso do Sul municipality, Brazil

Gondwanax (meaning "Gondwana king") is an extinct genus of silesaurid dinosauriforms from the Triassic Pinheiros-Chiniquá Sequence of Brazil. The genus contains a single species, G. paraisensis, known from a partial skeleton. Gondwanax represents one of the oldest known dinosauromorphs, and, alongside the roughly coeval Gamatavus, one of the oldest South American silesaurs. While the possession of two sacral vertebrae characterizes more basal "silesaurid" taxa, Gondwanax has three—the oldest occurrence of this trait in the fossil record.^[1]

Discovery and naming

The Gondwanax fossil material was discovered at the "Linha Várzea 2" ("Becker") site, belonging to the Pinheiros-Chiniquá Sequence of the Santa Maria Supersequence (Formation) in Paraíso do Sul municipality of Rio Grande do Sul, Brazil. These layers are representative of the Dinodontosaurus Assemblage Zone. The holotype specimen, CAPPA/UFSM 0417, is a single right femur. Several other partially disarticulated bones were found in association with this specimen. While no overlapping bones suggest the presence of multiple individuals, this possibility has not been ruled out as the bones were not found in perfect articulation. The additional material comprises two cervical, several dorsal, three sacral, and at least three caudal vertebrae, and a partial pelvic girdle.^[1]

In 2024, Rodrigo Temp Müller described Gondwanax paraisensis as a new genus and species of silesaurids based on these fossil remains. The generic name, Gondwanax, combines Gondwana—the name of an ancient 'supercontinent' containing South America—with the Ancient Greek ἄναξ, meaning "king" or "lord", in reference to the preeminence of dinosauromorphs throughout the Mesozoic Era. The specific name, paraisensis, references the municipality of Paraíso do Sul, where the specimens were found.^[1]

Classification

In his phylogenetic analysis, Müller (2024) recovered Gondwanax as a basal member of the Sulcimentisauria. Similar to a number of recent studies, these taxa, along with other "traditional" silesaurids, are treated as a paraphyletic grade of ornithischians.^[2]^[3] These results are displayed in the cladogram below:^[1]

Dinosauria

Saurischia

Ornithischia

	Saltopus

	Lewisuchus

Gondwanax

Diodorus

	Ignotosaurus

	Silesaurus

Sacisaurus

	Lutungutali

	Kwanasaurus

Eucoelophysis

Pisanosaurus

	Laquintasaura

	Prionodontia

Paleoenvironment

Gondwanax was found in the "Linha Várzea 2" site of the Dinodontosaurus Assemblage Zone (AZ) of the Santa Maria Formation. The gracilisuchid Parvosuchus was also found in this site.^[4] The roughly coeval "Picada do Gama" site has yielded a closely related "silesaurid", Gamatavus. Other localities indicate that these animals likely shared an ecosystem with dicynodonts, cynodonts,^[5] pseudosuchians, aphanosaurs,^[6] rhynchosaurs,^[7] and procolophonoids.^[8]^[9]

The Brazilian Dinodontosaurus Assemblage Zone shares many faunal similarities with the Argentinian Tarjadia Assemblage Zone, the dinosauromorph-bearing units of the Tanzanian Lifua Member, and the Zambian Ntawere Formation, potentially indicating that these units belong to similar temporal ranges.^[9]

References

^ ^a ^b ^c ^d Temp Müller, Rodrigo (2024). "A new "silesaurid" from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs". Gondwana Research (in press). doi:10.1016/j.gr.2024.09.007.
^ Norman DB, Baron MG, Garcia MS, Müller RT (2022). "Taxonomic, palaeobiological and evolutionary implications of a phylogenetic hypothesis for Ornithischia (Archosauria: Dinosauria)". Zoological Journal of the Linnean Society. 196 (4): 1273–1309. doi:10.1093/zoolinnean/zlac062.
^ Fonseca, A. O.; Reid, I. J.; Venner, A.; Duncan, R. J.; Garcia, M. S.; Müller, R. T. (2024). "A comprehensive phylogenetic analysis on early ornithischian evolution". Journal of Systematic Palaeontology. 22 (1). 2346577. Bibcode:2024JSPal..2246577F. doi:10.1080/14772019.2024.2346577.
^ Müller, Rodrigo T. (2024-06-20). "A new small-sized predatory pseudosuchian archosaur from the Middle-Late Triassic of Southern Brazil". Scientific Reports. 14 (1): 12706. doi:10.1038/s41598-024-63313-3. ISSN 2045-2322. PMC 11189902.
^ Schmitt, Maurício Rodrigo; Martinelli, Agustín G.; Melo, Tomaz Panceri; Soares, Marina Bento (2019). "On the occurrence of the traversodontid Massetognathus ochagaviae (Synapsida, Cynodontia) in the early late Triassic Santacruzodon Assemblage Zone (Santa Maria Supersequence, southern Brazil): Taxonomic and biostratigraphic implications". Journal of South American Earth Sciences. 93: 36–50. doi:10.1016/j.jsames.2019.04.011.
^ Nesbitt, Sterling J.; Butler, Richard J.; Ezcurra, Martín D.; Barrett, Paul M.; Stocker, Michelle R.; Angielczyk, Kenneth D.; Smith, Roger M. H.; Sidor, Christian A.; Niedźwiedzki, Grzegorz (April 2017). "The earliest bird-line archosaurs and the assembly of the dinosaur body plan". Nature. 544 (7651): 484–487. Bibcode:2017Natur.544..484N. doi:10.1038/nature22037. ISSN 0028-0836. S2CID 9095072.
^ Cesar Leandro Schultz; Max Cardoso Langer & Felipe Chinaglia Montefeltro (2016). "A new rhynchosaur from south Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle-Late Triassic boundary". Paläontologische Zeitschrift. 90 (3): 593–609. doi:10.1007/s12542-016-0307-7. hdl:11449/161986. S2CID 130644209.
^ Cisneros, Juan C.; Damiani, Ross; Schultz, Cesar; da Rosa, Átila; Schwanke, Cibele; Neto, Leopoldo W.; Aurélio, Pedro L. P. (2004-07-22). "A procolophonoid reptile with temporal fenestration from the Middle Triassic of Brazil". Proceedings of the Royal Society of London. Series B: Biological Sciences. 271 (1547): 1541–1546. doi:10.1098/rspb.2004.2748. ISSN 0962-8452. PMC 1691751. PMID 15306328.
^ ^a ^b Pretto, Flávio Augusto; Müller, Rodrigo Temp; Moro, Debora; Garcia, Maurício Silva; Paes Neto, Voltaire Dutra; da Rosa, Átila Augusto Stock (2022-09-28). "The oldest South American silesaurid: New remains from the Middle Triassic (Pinheiros-Chiniquá Sequence, Dinodontosaurus Assemblage Zone) increase the time range of silesaurid fossil record in southern Brazil". Journal of South American Earth Sciences. 120: 104039. doi:10.1016/j.jsames.2022.104039. ISSN 0895-9811. S2CID 252609210.

[Gondwanax-1] Temp Müller, Rodrigo (2024). "A new "silesaurid" from the oldest dinosauromorph-bearing beds of South America provides insights into the early evolution of bird-line archosaurs". Gondwana Research (in press). doi:10.1016/j.gr.2024.09.007.

[2] Norman DB, Baron MG, Garcia MS, Müller RT (2022). "Taxonomic, palaeobiological and evolutionary implications of a phylogenetic hypothesis for Ornithischia (Archosauria: Dinosauria)". Zoological Journal of the Linnean Society. 196 (4): 1273–1309. doi:10.1093/zoolinnean/zlac062.

[3] Fonseca, A. O.; Reid, I. J.; Venner, A.; Duncan, R. J.; Garcia, M. S.; Müller, R. T. (2024). "A comprehensive phylogenetic analysis on early ornithischian evolution". Journal of Systematic Palaeontology. 22 (1). 2346577. Bibcode:2024JSPal..2246577F. doi:10.1080/14772019.2024.2346577.

[Parvosuchus-4] Müller, Rodrigo T. (2024-06-20). "A new small-sized predatory pseudosuchian archosaur from the Middle-Late Triassic of Southern Brazil". Scientific Reports. 14 (1): 12706. doi:10.1038/s41598-024-63313-3. ISSN 2045-2322. PMC 11189902.

[Schmitt2019-5] Schmitt, Maurício Rodrigo; Martinelli, Agustín G.; Melo, Tomaz Panceri; Soares, Marina Bento (2019). "On the occurrence of the traversodontid Massetognathus ochagaviae (Synapsida, Cynodontia) in the early late Triassic Santacruzodon Assemblage Zone (Santa Maria Supersequence, southern Brazil): Taxonomic and biostratigraphic implications". Journal of South American Earth Sciences. 93: 36–50. doi:10.1016/j.jsames.2019.04.011.

[Nesbitt2017-6] Nesbitt, Sterling J.; Butler, Richard J.; Ezcurra, Martín D.; Barrett, Paul M.; Stocker, Michelle R.; Angielczyk, Kenneth D.; Smith, Roger M. H.; Sidor, Christian A.; Niedźwiedzki, Grzegorz (April 2017). "The earliest bird-line archosaurs and the assembly of the dinosaur body plan". Nature. 544 (7651): 484–487. Bibcode:2017Natur.544..484N. doi:10.1038/nature22037. ISSN 0028-0836. S2CID 9095072.

[Brasinorhynchus-7] Cesar Leandro Schultz; Max Cardoso Langer & Felipe Chinaglia Montefeltro (2016). "A new rhynchosaur from south Brazil (Santa Maria Formation) and rhynchosaur diversity patterns across the Middle-Late Triassic boundary". Paläontologische Zeitschrift. 90 (3): 593–609. doi:10.1007/s12542-016-0307-7. hdl:11449/161986. S2CID 130644209.

[Candelaria-8] Cisneros, Juan C.; Damiani, Ross; Schultz, Cesar; da Rosa, Átila; Schwanke, Cibele; Neto, Leopoldo W.; Aurélio, Pedro L. P. (2004-07-22). "A procolophonoid reptile with temporal fenestration from the Middle Triassic of Brazil". Proceedings of the Royal Society of London. Series B: Biological Sciences. 271 (1547): 1541–1546. doi:10.1098/rspb.2004.2748. ISSN 0962-8452. PMC 1691751. PMID 15306328.

[Gamatavus-9] Pretto, Flávio Augusto; Müller, Rodrigo Temp; Moro, Debora; Garcia, Maurício Silva; Paes Neto, Voltaire Dutra; da Rosa, Átila Augusto Stock (2022-09-28). "The oldest South American silesaurid: New remains from the Middle Triassic (Pinheiros-Chiniquá Sequence, Dinodontosaurus Assemblage Zone) increase the time range of silesaurid fossil record in southern Brazil". Journal of South American Earth Sciences. 120: 104039. doi:10.1016/j.jsames.2022.104039. ISSN 0895-9811. S2CID 252609210.

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]