Elsevier

Cretaceous Research

Volume 127, November 2021, 104947
Cretaceous Research

Short communication
New gondwanatherian (Mammaliaformes) remains from the Chorrillo Formation (Upper Cretaceous) of southern Patagonia, Argentina

https://doi.org/10.1016/j.cretres.2021.104947Get rights and content

Abstract

The fossil record of gondwanatherian mammaliaforms from Patagonia is represented by several species known on the basis of isolated teeth, with the single exception of a partial dentary with two molariforms of the Paleocene species Sudamerica ameghinoi. The aim of the present contribution is to describe both a fragmentary dentary (with the base of the lower incisive) and a partial upper incisor coming from the Campanian–Maastrichtian Chorrillo Formation, at the La Anita Farm, SW Santa Cruz province, Argentina. The specimens are referred to Magallanodon baikashkenke, a species previously known by isolated teeth from the Dorotea (Chile) and Chorrillo (Argentina) beds. The present discovery expands our knowledge of this mammaliaform clade.

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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