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| Patagorhynchus pascuali Chimento, Agnolín, Manabe, Tsuihiji, Rich, Vickers-Rich & Novas, 2023 |
Abstract
Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
Mammalia, Linnaeus 1758
Monotremata, Bonaparte, 1837
Patagorhynchus gen. nov. (monotypic genus)
Etymology: Patago, from Patagonia, and rhynchus, nose.
Diagnosis: Patagorhynchus differs from basal monotremaformes (including Steropodon) in having a dilambdodont crown morphology and a labial cingulid;12 dilambdodont disposition of cusps and crests on molar crown is shared with Teinolophos and ornithorhynchids; Patagorhynchus and ornithorhynchids differ from the basal monotremaformes Teinolophos in having notably low and mesiodistally expanded teeth with the anterior lobe (equivalent to trigonid) positioned lower than the posterior one (equivalent to talonid), in having talonid composed of two (rather than one) transverse lophids, and lacking a labial cingulid. The anterior cingulid of Patagorhynchus is wider than that in Teinolophos but narrower than that in Obdurodon. Patagorhynchus shares with the toothed monotremes Obdurodon and Monotrematum both lingual and buccal extremes of the V-shaped lobe (equivalent to trigonid) with one buccal and two lingual cusps, with the first being more elevated than the latter two, and a complete mid-valley. Patagorhynchus bears two roots on m2 (as also probably in Monotrematum) and differs from Obdurodon and Ornithorhynchus, in which more than 5 roots are present. The lobes of Patagorhynchus and Obdurodon show hypsodonty, in contrast with the much more brachyodont molariforms of Monotrematum. Patagorhynchus exhibits the following features that are lacking in other monotremes, and may be considered autapomorphic among monotremes: mid-valley labially diverges (i.e., the length of the labial edge of this valley represents two times its lingual length) and anterior cingulid labially narrow and does not reach the labial margin of the protoconid.
Patagorhynchus pascuali sp. nov.
Etymology: Species name honors the Argentine paleomammalogist Rosendo Pascual (1923–2012), who described the first Cenozoic monotreme remains from Patagonia, thus demonstrating the presence of this clade outside Australia.
Holotype: MPM-PV-23087, Museo Padre Molina (Rio Gallegos, Santa Cruz, Argentina), a right lower m2 attached to a fragment of dentary. Collected by N. R. Chimento during a joint Argentine-Japanese field trip in March 2022.
Type locality and age: La Anita farm, Santa Cruz Province, Patagonia, Argentina. The tooth was collected from the “Puma Cave” fossil site (S 50 30.639 W 72 33.617), Chorrillo Formation, early Maastrichtian7,8. This new discovery expands the list of Late Cretaceous mammaliaforms recorded in the Chorrillo Formation and equivalent Dorotea Formation in southern Chile, previously known to include gondwanatherians (Magallanodon) and dryolestoids (Orretherium).
Nicolás R. Chimento, Federico L. Agnolín, Makoto Manabe, Takanobu Tsuihiji, Thomas H. Rich, Patricia Vickers-Rich and Fernando E. Novas. 2023. First Monotreme from the Late Cretaceous of South America. Communications Biology. 6: 146. DOI: 10.1038/s42003-023-04498-7
