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New remains of the dryolestoid mammal Leonardus cuspidatus from the Los Alamitos Formation (Late Cretaceous, Argentina)

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Abstract

The great diversity of mammals from the Los Alamitos Formation (Campanian–Maastrichtian) in Río Negro Province, Argentina has provided significant information about the evolution of South American dryolestoids. Among these mammals the alleged dryolestid Leonardus cuspidatus Bonaparte was described based on a fragment of maxilla with four molariforms. A right mandibular fragment with two molariforms from the same site as the maxilla is here assigned to L. cuspidatus. The lower molariforms are compatible in the expected morphology with those from the holotype. Even though referred to Dryolestidae, Leonardus shows unique features: (1) the presence of a huge and dome-like stylocone, disconnected and more centrally placed from the other cusps than in other dryolestoids such as Groebertherium, but contacting the preparacrista in the first preserved molar; (2) the absence of cingulae in both upper and lower molars, the latter being similar in shape to the former; (3) the presence of three roots in at least one of the lower molars, which has only been documented in the mesungulatid Coloniatherium for the m1. These characters confirm the diversity and uniqueness of the South American Mesozoic mammals.

Kurzfassung

Die große Säugetiervielfalt der Los Alamitos-Formation (Campanium–Maastrichtium, Río Negro Provinz, Argentinien) leistet einen erheblichen Beitrag zum Verständnis der Evolution der südamerikanischen Dryolestoiden. Basierend auf einem Oberkieferfragment mit vier Molaren, wurde auch der angebliche Dryolestidae Leonardus cuspidatus Bonaparte aus dieser Lokalität beschrieben. Ein weiteres Kieferfragment mit zwei Zähnen wird ebenfalls L. cuspidatus zu geordnet. Die unteren Molaren zeigen die nach dem Holotypus zu erwartende Morphologie. Obwohl Leonardus den Dryolestidae zugeschrieben wird, weist dieser einige einzigartige Merkmale auf: (1) das Vorhandensein eines prominenten und kuppelförmigen Stylocon, der, verglichen mit dem anderer Dryolestoiden wie beispielsweise Groebertherium, stärker von den anderen Höckern isoliert ist und zentraler liegt, obwohl dennoch beim ersten erhaltenen Molaren ein Kontakt des Stylocon mit der Präparacrista auftritt; (2) das Fehlen der Cingulide sowohl in den oberen als auch in den unteren Molaren, wodurch letztere in der Form den oberen Molaren ähneln; (3) das Vorhandensein von drei Wurzeln bei mindestens einem der unteren Molaren, was bisher nur für den m1 des mesungulatiden Dryolestoiden Coloniatherium beschrieben wurde. Diese besonderen Merkmale untersteichen die Diversität und Einzigartigkeit der mesozoischen Säugetierfauna Südamerikas.

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Acknowledgments

I want to thank Thomas Martin and an anonymous reviewer whose observations helped to improve the manuscript. I am grateful to José F. Bonaparte, who gave me the opportunity to study the Mesozoic mammals from the Los Alamitos Formation and to Francisco J. Goin. J.F. Bonaparte and Alejandro Kramarz gave me access to the mammal collection of the Museo Argentino de Ciencias Naturales. Guillermo Rougier and Javier N. Gelfo helped me with previous versions of this manuscript. Finally, I wish to thank Simone Hoffmann and Julia Schultz for there help with the German version of the abstract, and to Fabian Tricarico for taking the SEM photographs of the specimens described in this paper.

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  1. CONICET. Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Av. Ángel Gallardo 470, C1405DRJ, Buenos Aires, Argentina

    Laura Chornogubsky

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Correspondence to Laura Chornogubsky.

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Chornogubsky, L. New remains of the dryolestoid mammal Leonardus cuspidatus from the Los Alamitos Formation (Late Cretaceous, Argentina). Paläontol Z 85, 343–350 (2011). https://doi.org/10.1007/s12542-010-0095-4

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