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Tessellatia
Taxonomy
Tessellatia was named by Gaetano et al. (2022). Its type is Tessellatia bonapartei. It is the type genus of Probainognathia.
It was assigned to Probainognathia by Gaetano et al. (2022).
It was assigned to Probainognathia by Gaetano et al. (2022).
Species
T. bonapartei (type species)
Synonymy list
| Year | Name and author |
|---|---|
| 2022 | Tessellatia Gaetano et al. |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| L. C. Gaetano et al. 2022 | d PDF
Download PDF Article Open Access Published: 25 April 2022 A new cynodont from the Upper Triassic Los Colorados Formation (Argentina, South America) reveals a novel paleobiogeographic context for mammalian ancestors L. C. Gaetano, F. Abdala, F. D. Seoane, A. Tartaglione, M. Schulz, A. Otero, J. M. Leardi, C. Apaldetti, V. Krapovickas & E. Steimbach Show fewer authors Scientific Reports volume 12, Article number: 6451 (2022) Cite this article 2856 Accesses 3 Citations 248 Altmetric Metricsdetails Abstract Probainognathia is a derived lineage of cynodonts which encompass Mammalia as their crown-group. The rich record of probainognathians from the Carnian of Argentina contrasts with their Norian representation, with only one named species. Here we describe a new probainognathian, Tessellatia bonapartei gen. et sp. nov., from the Norian Los Colorados Formation of the Ischigualasto-Villa Unión Basin of Argentina. The new taxon, represented by a partial cranium with associated lower jaws, was analyzed through neutron and X-rays micro-tomography (μCT). The high-resolution neutron μCT data allowed the identification of a unique character combination, including features inaccessible through traditional techniques. We constructed the largest phylogenetic data matrix of non-mammalian cynodonts. The new species and its sister taxon, the Brazilian Therioherpeton cargnini, are recovered as probainognathians, closely related to Mammaliamorpha. We conducted the first quantitative paleobiogeographic analysis of non-mammalian cynodonts, focusing in probainognathians. The results indicate that Probainognathia and Mammaliamorpha originated in southwestern Gondwana (in the Brazilian Paraná Basin), which was an important center of diversification during the Triassic. Finally, the Chinese Lufeng Basin is identified as the ancestral area of Mammaliaformes. These new findings, besides adding to the knowledge of the poorly represented Norian cynodonts from the Los Colorados Formation, are significant to improve our understanding of probainognathian diversity, evolution, and paleobiogeographic history. Introduction Probainognathia (Synapsida: Cynodontia) is one of the two main clades of derived cynodonts (Eucynodontia), represented today by extant Mammalia1,2. With the exception of the highly-specialized, herbivorous tritylodontids, non-mammaliaform probainognathians are mostly small- to medium-sized faunivorous forms. The oldest probainognathian remains are known from Middle Triassic deposits from Gondwana. After an initial diversification during the early Late Triassic (Carnian), basal (non-mammaliaform) probainognathians are also found in Norian, Rhaetian, and Jurassic-to-Cretaceous deposits3. The abundant Carnian record of the lineage in Argentina is in strong contrast with their poor Norian representation. Among the six Norian probainognathian species previously recognized from Gondwana, four were reported from Brazil, one from Argentina, and one from southern Africa (but see Supplementary Information); most of them only represented by a single or a few fragmentary specimens. This is in concordance with the general scarcity of cynodonts from Norian strata globally3,4 (see Supplementary Information). The Norian Los Colorados Formation of the Ischigualasto-Villa Unión Basin of Argentina is renowned for its vertebrate fossil record5,6. One of the youngest dicynodonts of Gondwana, Jachaleria colorata, is represented in the lower levels of the unit7,8,9. The upper levels of the Los Colorados Formation represent a different faunal assemblage 10 that has provided one of the oldest turtles11,12; basal and derived representatives of the crocodylian lineage5,13,14,15,16; and a number of relatively well-represented dinosaurs5,17,18,19,20,21,22. The latter is key to the understanding of the rise of this group as it is the earliest assemblage where dinosaurs are dominant components of the ecosystem23. Non-mammaliaform cynodonts (NMC) are scarcely represented in this unit14,24,25. Only two partial skulls of Chaliminia musteloides24,25 and a few fragmentary postcranial elements of an unnamed taxon5,14,26 have been reported. They are among the oldest tritheledontids, a lineage of mainly Gondwanan cynodonts that have been proposed to be closely related to basal mammals25,27,28,29. Since 2014, renewed exploration efforts in the Los Colorados Formation led to new findings at the Parque Nacional Talampaya (La Rioja Province, north-western Argentina), including five cynodont specimens whose preliminary study suggests that at least three of them might represent previously unrecognized taxa30. Recent geochronological studies of the unit suggest that the richest and most renowned faunal assemblage (‘La Esquina local fauna’), found in the upper levels of Los Colorados Formation, might be mid-Norian (~ 220–211 Ma) in age31,32. Herein we describe a new species of derived NMC found in the upper levels of the Los Colorados Formation (Fig. 1) represented by a partial cranium with associated lower jaws. The specimen was analyzed through neutron and X-rays micro-tomography (μCT). Although only rarely used to analyze fossil specimens, it has become clear that neutron μCT complements X-ray μCT, including circumventing some problems that might arise from the latter methodology depending on the characteristics of the fossil sample studied33,34. In addition, we constructed the most comprehensive data-matrix for non-mammalian cynodonts published to date, allowing us to analyze the phylogenetic relationships of the new species and the main hypotheses regarding the ancestry of mammaliaforms and their close relatives. We also present the first quantitative paleobiogeographic analysis of non-mammalian cynodonts, focusing in probainognathians. Our results provide new insights regarding the evolutionary and paleobiogeographic history of Probainognathia. In particular, the new finding improves our knowledge on the diversity of the poorly represented Norian forms in the rich fauna of the Los Colorados Formation, northwestern Argentina. Figure 1 figure 1 Geographic location of the ‘La Esquina’ locality where Tessellatia bonapartei holotype (PULR-V121) was found. (a) Southern South America; (b) satellite image of north-western Argentina depicting the study area (green, dotted-line rectangle) within the Talampaya National Park, La Rioja Province; (c) satellite image showing the main outcrops of the Los Colorados Formation where the rich faunal assemblage of the ‘La Esquina’ locality was found (yellow, dotted-line rectangle); (d) photograph of the outcrops at the ‘La Esquina’ locality portraying the levels from where Tessellatia bonapartei holotype (PULR-V121) was recovered. Map drawn with Adobe Illustrator CC 18 (https://www.adobe.com/products/illustrator.html). Satellite images from Google Earth, accessed December 2021. Full size image Results SYSTEMATIC PALEONTOLOGY THERAPSIDA35 CYNODONTIA36 EUCYNODONTIA37 PROBAINOGNATHIA38 Tessellatia gen. nov. Type species. Tessellatia bonapartei. Etymology. From the Latin tessella (each one of the tiles composing a mosaic), in reference to the combination of basal and derived features recognized in this taxon. Diagnosis. Same as for species. Tessellatia bonapartei sp. nov. (Fig. 2). Figure 2 figure 2 The holotype of Tessellatia bonapartei, gen. et sp. nov. (PULR-V121). (a) Cranium as preserved in right lateral view; (b) 3D model of the cranium in right lateral view; (c) interpretation line drawing of the skull and right lower jaw (restored to its natural position) in right lateral view; (d) digital render of the skull showing the roots of the anterior upper postcanines, not visible externally; (e) 3D model of the osseous secondary palate and upper teeth in ventral view; (f) interpretation line drawing of the osseous secondary palate and upper teeth in ventral view; (g) right lower jaw in dorsal view; (h) right lower jaw in medial view; (i) 3D model of the pc4 in labial, occlusal and lingual views (from left to right); (j) 3D model of PC9 and PC10 in labial, occlusal and lingual views (from left to right). aac anterior accessory cusp, an angular process, C/c upper/lower canines, cin cingulum, co coronoid, d dentary, fr frontal, I/i upper/lower incisors, iof infraorbital foramen, l lacrimal, mc main cusp, mf masseteric fossa, mx maxilla, n nasal, pac posterior accessory cusp, pal palatine, PC/pc upper/lower postcanines, pmx premaxilla, pt pterygoid. Scale bars a-h: 5 mm; i-j: 2.5 mm. Full size image Etymology. In honor to the late Dr. José F. Bonaparte, who worked unrelentingly to broaden our knowledge of Mesozoic ecosystems and described the first cynodont remains from the Los Colorados Formation. Holotype. PULR-V121, partial cranium, represented by the snout and orbital region, with associated lower jaws. Locality and horizon. Upper third of the Los Colorados Formation, Talampaya National Park, La Rioja Province, Argentina. The specimen was found in a massive- to parallel-laminated sandy mudstone interval locally interbedded with parallel- to rippled- laminated sandstone, representing deposition in a floodplain setting sporadically affected by sandy splays from the fluvial channels. See Supplementary Information online for further details on the geological framework. Diagnosis. Small probainognathian with the antorbital region notably longer than the height of the skull at the level of the anterior margin of the orbit. Autapomorphies of Tessellatia bonapartei are: masseteric fossa and low coronoid process posterior to the lower tooth row; angular process ventrally projected, well-developed, and semicircular in outline; broad groove between the lateral wall of the dentary and the postcanine alveoli; and upper postcanine count larger (14) than the lower postcanines (7), with the last six upper postcanines lacking an opposing lower tooth. Differs from other non-mammaliaform cynodonts except Riograndia guaibensis and the early mammaliaform Morganucodon in the presence of a large upper canine and a small lower canine. Differs from other non-mammaliaform probainognathians (except Aleodon cromptoni, Prozostrodon brasiliensis, Pseudotherium argentinus, and Tritylodon longaevus) in the subequal contribution to the secondary bony palate of the maxilla and palatine. Shares with many derived non-tritylodontid probainognathians and the mammaliaform Morganucodon an anteriorly elevated alveolar margin of the dentary. Shares with some derived probainognathians traditionally grouped in Tritheledontidae (Chaliminia musteloides, Elliotherium kersteni, Irajatherium hernandezi, and Pachygenelus monus), the presence of a ventrally bowed bony secondary palate with deep, narrow, lateral groove for the lower postcanines; posterior upper postcanines with convex labial and concave lingual surfaces, and bearing a centrally placed, symmetrical main cusp with convex mesial and distal margins flanked by smaller, lingually placed accessory cusps; and lower postcanines, comparatively larger than uppers, with a large, asymmetrical, mesial main cusp followed by smaller distal accessory cusps. Differs from Chaliminia musteloides, the only other named cynodont known from the Los Colorados Formation, in having the alveolar margin of the maxilla sigmoidal, with its dorsal-most point at the level of the canine; the horizontal ramus of the dentary comparatively low and lacking a well-developed platform lateral to the posterior postcanines; and the posteriormost lower incisor smaller than the canines and postcanines. |
Measurements
No measurements are available
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| Source: c = class, subp = subphylum, uc = unranked clade | |||||
| References: Hendy et al. 2009, Kiessling 2004, Carroll 1988 | |||||