Patagorhynchus, Chimento & Agnolín & Manabe & Tsuihiji & Rich & Vickers-Rich & Novas, 2023

Chimento, Nicolás R., Agnolín, Federico L., Manabe, Makoto, Tsuihiji, Takanobu, Rich, Thomas H., Vickers-Rich, Patricia & Novas, Fernando E., 2023, First monotreme from the Late Cretaceous of South America, Communications Biology (146) 6, pp. 1-6 : 2

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.

Type and the only species. Patagorhynchus pascuali sp. nov.

( Figs. 1 , 2a and Supplementary Fig. 3 ).

Figures

Fig. 1 Images of Patagorhynchus pascuali, MPM-PV-23087. Lower molar 2 and part of the right jaw, in a, occlusal view; b, medial/lingual view; c, lateral/labial view; d, posterior view; e, anterior view. Scale bar: length 2 mm. Abbreviations, ac, anterior cingulid; alv, alveolus; ant, anterior; ar, anterior root; hy, hypoconid; hl, hypoconulid; lapcc, labial posterior cingular cusp; liacc, lingual anterior cingular cusp; me, metaconid; mv, mid-valley; NC1, neomorphic cusp 1; pa, paraconid; pc, posterior cingulid; pr, protoconid; prt, posterior root.

Fig. 2 Comparisons of the second lower molar of selected monotremaformes in occlusal view. a, Patagorhynchus pascuali (based in MPM-PV-23087); b, Obdurodon insignis2,19; c, Monotrematum sudamericanum17; d, Teinolophus trusleri20. Not to scale. Abbreviations: NC1, neoformation cusp 1.

Fig. 3 Simplified calibrated cladogram showing the phylogenetic affinities of Patagorhynchus pascuali. Basal Monotremaformes44 are indicated in red and Monotremata in green. The Late Cretaceous (Maastrichtian) palaeogeographical map (based in Scotese35) indicates the fossiliferous sites that yielded fossil toothed monotremes and distribution of the extant platypus Ornithorhynchus anatinus shaded in light brown. [1], occurrence of Patagorhynchus pascuali, La Anita farm, Chorrillo Formation (Maastrichtian, Late Cretaceous); [2], occurrence of Monotrematum sudamericanum, Punta Peligro locality, Salamanca Formation (Danian, lower Paleocene); [3], occurrence of Obdurodon spp., different localities from South Australia, Queensland, and New South Wales Oligocene-Pliocene); [4], Pleistocene occurrences and geographic distribution of extant Ornithorhynchus anatinus.