Short communicationNew gondwanatherian (Mammaliaformes) remains from the Chorrillo Formation (Upper Cretaceous) of southern Patagonia, Argentina
Introduction
Gondwanatheria is a clade of Gondwanan mammaliforms documented in Cretaceous and Paleogene rocks of Argentina (Scillato-Yané and Pascual, 1985; Bonaparte, 1986, 1990, 1994; Goin et al., 2012; Chimento et al., 2015), India (Krause et al., 1997; Prasad et al., 2007; Wilson et al., 2007; Verma et al., 2012), Tanzania (O'Connor et al., 2019), Madagascar (Krause et al., 1997; 2014; 2020; Krause, 2013), and Antarctica (Goin et al., 2006). Gondwanatherians were animals of the size of a beaver and characterized by chisel-like incisors and prismatic molariforms. They are split into two subgroups; the Ferugliotheridae and the Sudamericidae. Phylogenetic relationships of gondwanatherians are debated, having been considered either as paratherians (Scillato Yané and Pascual, 1985; Bonaparte, 1986), multituberculates (Krause et al., 1992; Krause and Bonaparte, 1993; Kielan-Jaworowska and Bonaparte, 1996; Gurovich and Beck, 2009), allotherians or haramiyidans (Pascual and Ortiz Jaureguizar, 2007). Current information on cranial, dental and postcranial anatomy (O'Connor et al., 2019; Krause et al., 2014, 2020) supports the hypothesis that gondwanatherians are members of Allotheria, particularly related with haramiyiids, as originally proposed by Pascual and Ortiz-Jaureguizar (2007).
As far as Mesozoic gondwanatherians from South America are concerned, they are mainly represented by isolated teeth coming from three Maastrichtian-age localities in Patagonia: Los Alamitos and Bajo Trapalcó (Río Negro Province, Argentina), and La Colonia (Chubut Province, Central Patagonia). These fossil sites have yielded a taxonomically diverse sample of South American gondwanatherians.
The fossil record of Patagonian gondwanatherians has been geographically extended with the discovery of several isolated cheek teeth and incisors corresponding to the new taxon Magallanodon baikashkenke (Goin et al., 2020) from the Campanian–Maastrichtian Dorotea Formation, outcropping at Magallanes Region, southern Chile. Chimento et al. (2020) described an isolated molariform coming from stratigraphically equivalent beds of southern Argentina (known as the Chorrillo Formation, in Santa Cruz province; Nullo et al., 2006; Novas et al., 2019), which these authors also referred to Magallanodon baikashkenke.
Here, we report on additional remains of Magallanodon baikashkenke from the Chorrillo Formation, consisting of a fragmentary dentary bearing the base of one of its lower incisors, which was found in close association with an incomplete upper incisor. The new material constitutes an important addition to this still poorly known species and also adds to features that may become diagnostic for gondwanatherians.
Abbreviations - MPM (Museo Padre Molina, Vertebrate Paleontology Collection, Río Gallegos, Santa Cruz Province, Argentina).
The specimen was collected from the upper levels of the Upper Campanian to Lower Maastrichtian Chorrillo Formation, close to the transition with the overlying Calafate Formation (Nullo et al., 2006). The specimens were discovered in a locality named the “Puma Cave”, (S50 30.639 W72 33.617, Fig. 1; Novas et al., 2019). The fossil site belongs to La Anita farm, approximately 30 km SW from El Calafate City, Santa Cruz Province, Argentina. The gondwanatherian specimens here described were found in close proximity to bones of ankylosaurian and hadrosaurian dinosaurs, as well as remains of the elasmarian ornithopod Isasicursor (Novas et al., 2019). This fossil assemblage comes from a level 20 m above the site from which an isolated molariform of Magallanodon baikashkenke (Chimento et al., 2020) was found.
Section snippets
Systematic paleontology
Mammaliaformes Rowe, 1988
Gondwanatheria Mones, 1987
Magallanodon baikashkenke Goin, Martinelli, Soto-Acuña, Vieytes, Manríquez, Fernández, Pino, Trevisan, Kaluza, Reguero, Leppe, Ortiz, Rubilar Rogers, and Vargas, 2020
Referred material. MPM-22512, associated anterior end of a left dentary, bearing part of its gliriform incisor, and upper mesial incisor from the right side, lacking the apex. The specimen is referred to Magallanodon baikashkenke based on congruence in size as well as on the
Taxonomic position of MPM-22512
Specimen MPM-22512 herein described is placed among gondwanatherian sudamericids on the basis of hypertrophied gliriform upper and lower incisors, lower incisor with a characteristic, roughly kidney-shaped cross-section (i.e. slightly concave medial surface, convex lateral surface, ventromedially angled and rounded dorsally; Krause et al., 1992; Koenigswald et al., 1999; Goin et al., 2006), edentulous diastema separating the incisors from the cheek teeth (Krause et al., 1992; Pascual et al.,
Conclusions
The finding of new remains of Magallanodon indicates that this taxon was very common in the Dorotea/Chorrillo beds, from which several elements of this species have already been recovered (Goin et al., 2020; Chimento et al., 2020). From the Chorillo Formation, incomplete caudal vertebrae of a long-tailed, non-gondwanatherian mammal have been described (Novas et al., 2019). Such long-tailed condition is in all probability different from the short-tailed one observed in gondwanatherians (see
Funding
This work was supported generously by Mr. Coleman Burke (New York), and a special internal grant from the National Museum of Nature and Science, Japan.
Acknowledgements
The material here described was collected in the context of a joint Argentine-Japanese exploration, carried out from 9 through 24 of March 2020. We thank other members of the crew, including M. Isasi, F. Brissón-Egli, A. Moreno, G. Lio, M. Aranciaga Rolando, S. Rozadilla, J. D'Angelo, M. Motta, S. Miner, G. Muñoz, J. De Pasqua, C. Thompson, M. Coronel, D. Moyano Paz, E. Vera, D. Piazza, G. Lo Coco, M. A. Novas, F.N. Novas Lo Coco, A. Misantone, S. Rozadilla, G. Stoll, C. Sakata, C. Miyamae, and
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Maastrichtian palynological assemblages from the Chorrillo Formation, Patagonia, Argentina
2023, Review of Palaeobotany and PalynologyPaleobotany of the uppermost Cretaceous Chorrillo Formation, Santa Cruz Province, Argentina: insights in a freshwater floral community
2022, Cretaceous ResearchCitation Excerpt :In this context, the Chorrillo Formation (Feruglio, 1945) provides an important source of information for analyzing a Maastrichtian terrestrial community. Recent studies have revealed a highly diverse fossil assemblage preserved in this formation, containing snails, fish, anurans, turtles, snakes, sauropods, theropods, ornithischians, and mammals, as well as palynomorphs, woods and leaf impressions (e.g., Novas et al., 2019; Moyano-Paz et al., 2022a; Rozadilla et al., 2021; Chimento et al., 2020, 2021; Aranciaga Rolando et al., 2022). The diversity of clades in the Chorrillo Formation not only provides a unique opportunity for analyzing a Maastrichtian paleoflora, but also enables comparison of patterns in changes between floral and zoological diversity in the unit.
Early Late Cretaceous mammals from southern Patagonia (Santa Cruz province, Argentina)
2022, Cretaceous ResearchCitation Excerpt :These specimens are mostly jaw fragments and isolated teeth of gondwanatherians, meridiolestidans, the dryolestid Groebertherium, and a possible multituberculate (Bonaparte 1986, 1990; Rougier et al., 2009a, b; Chornogubsky 2011; Gaetano et al., 2013). The southernmost known Mesozoic mammals are represented by Orretherium tzen and Magallanodon baikashkenke, of which the latter was also discovered at El Chorrillo Formation (Maastrichtian) 30 km SW from El Calafate City, in Santa Cruz province (Chimento et al., 2020, 2021). We present here new remains of fossil mammals from southwestern Santa Cruz province, which not only show a more complete picture of the diversity of southern mammals during the early Late Cretaceous, but generate new paleobiogeographic scenarios, such as the possibility that the Docodonta were not exclusively of Laurasian distribution but were also present in Gondwana, a hypothesis already considered by Pascual et al. (2000).