New information about Irajatherium hernandezi Martinelli, Bonaparte, Schultz & Rubert 2005 (Eucynodontia, Tritheledontidae) from the upper triassic (Caturrita Formation, Paraná Basin) of Brazil

Abstract

In this contribution, new specimens of the tritheledontid eucynodont Irajatherium hernandezi, from the Late Triassic (Caturrita Formation) of southern Brazil, are analyzed. The new material provides significant information about incisor count, canine size and shape, basicranial morphology, and other previously unknown aspects of skull and dentition. A cladistic analysis with inclusion of the new data supports the assignment of Irajatherium to Tritheledontidae, basal to Chalimininae and Pachygenelinae. Previously unknown characters of Irajatherium revealed by the new material include: the presence of three lower incisors; the first lower incisor is enlarged; the presence of large upper and lower canines with deep paracanine fossa on the maxilla; almost complete upper and lower postcanine tooth row with a pattern similar to that of other tritheledontids (e.g. Pachygenelus and Chaliminia); there is a conspicuous crest on the inner surface of the maxilla for the attachment of the inferred maxillary turbinates; partially confluent jugular foramen and fenestra rotunda within the jugular fossa, separated by a finger-like projection of the posterolateral wall of the opisthotic; and hypoglossal foramina located outside the jugular fossa. Irajatherium is a key taxon for understanding the early evolution of ictidosaurs, a group of cynodonts closely related to mammaliaforms, during the cynodont-mammal transition from the Late Triassic to Early Jurassic.

New information on Riograndia guaibensis Bonaparte, Ferigolo & Ribeiro, 2001 (Eucynodontia, Tritheledontidae) from the Late Triassic of southern Brazil: anatomical and biostratigraphic implications

“…Despite the fact that the canines are small in UFRGS-PV-0596-T, these elements are well developed in the specimens, UNISINOS-4881 and UFRGS-PV-0788-T, showing that these teeth are much more robust than the incisors in the upper dentition. The same was observed by Sidor and Hancox (2006) in Elliotherium, and by Oliveira et al (2010) in Irajatherium, differing from Pachygenelus and Diarthrognathus that are characterized by small upper canines. The cranial size of the cited new specimens is greater than the type specimens (MCN-PV2264, MCN-PV2265) and UFRGS-PV-0596-T.…”

“…Fortunately, the description of the new taxon Elliotherium, a description of a new specimen of Chaliminia (Martinelli and Rougier 2007) and the study of new materials of Irajatherium (Oliveira et al 2010) have increased the knowledge about the Tritheledontidae. Now, the detailed description of several new specimens of Riograndia from this contribution makes this taxon one of the most complete, known for nearly all anatomical regions of the skull and dentition, of tritheledontids.…”

The postcranial anatomy of Brasilodon quadrangularis and the acquisition of mammaliaform traits among non-mammaliaform cynodonts

“…The lesser trochanter is projected medially and remains visible in anterior view. This is a derived condition found in several non-mammaliaform cynodonts (e.g., Prozostrodon , Therioherpeton , Trucidocynodon , Irajatherium , Andescynodon , tritylodontids; [16, 38, 43, 98, 104, 112] and in early mammaliaforms ( Morganucodon , Megazostrodon , Haldanodon ), but the later differs from B . quadrangularis having a trochanter located proximally, reaching the level of the femoral head [32, 36].…”

Two New Cynodonts (Therapsida) from the Middle-Early Late Triassic of Brazil and Comments on South American Probainognathians

“…The former AZ includes the probainognathians Trucidocynodon riograndensis [ 26 ], Therioherpeton cargnini [ 16 , 56 – 57 ], Charruodon tetracuspidatus [ 14 ], and Prozostrodon brasiliensis [ 16 ]. The Riograndia AZ includes the probainognathians Brasilodon quadrangularis , Brasilitherium riograndensis [ 18 , 19 , 58 ], Minicynodon maieri [ 11 , 58 ], Botucaraitherium belarminoi [ 31 ], Riograndia guaibensis [ 17 , 29 ], and Irajatherium hernandezi [ 24 , 28 ] ( Fig 1 ).…”