The first Paleogene mustelid (mammalia, Carnivora) from southern North America and its paleontologic significance

Author links open overlay panelIsmaelFerrusquía-Villafranca^a

XiaomingWang^b

https://doi.org/10.1016/j.jsames.2021.103236Get rights and content

Abstract

Mustelidae are the largest and most diverse family of carnivores, its record dates back to the Early Oligocene, and its early history occurred in western Europe; therefore, the finding of a basal mustelid in southeastern Mexico (northwestern Oaxaca) is quite important.

The material found is a very small, nearly complete skull collected from the Yolomécatl Formation, a ~650 m thick lacustrine/fluvial succession interbedded by tuff sheets, yielding a⁴⁰Ar-³⁹Ar age of 40.3 ± 1.0 Ma, which places this unit and associated fauna in the latest Uintan-earliest Duchesnean NALMAs. However, a purported early Arikareean age has been proposed on the basis of uncritical/unsupported biochronological and isotopic data. The skull is referred to a new genus and species of Mustelidae on the basis of its unique combinaton of plesiomorphic and derived characters. Cladistically, it falls in an unresolved polytomy that inludes only basal European mustelids. This poses a biogeographic problem unsolvable with the evidence at hand: either the new taxon originated in Europe from as yet unknown ancestors, then migrated to southern (tropical) North America, or it evolved there, independently attained the synapomorphies of basal Mustelidae, and migrated to Europe. Finally, the new taxon fits the weasel-ecomorph, approaching the appearance of the extant Mustela frenata, thus suggesting tunnel-hunting habits.

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Introduction

The Sierra Madre del Sur Morphotectonic Province in southeastern Mexico is very significant for both academic and economic reasons. It contains important mineral resources (iron, coal and many others). Its complex geologic makeup includes Precambrian to Quaternary rock units, and records their development and evolution, as well as the assemblage of the tectonic terranes that now form this region. In the study area, the Paleogene sequence unconformably overlies older formations, and includes two volcanic units, two pyro-epiclastic units, and a small ?dacitic intrusion.

Additionally, from one of the pyro-epiclastic units, the Yolomécatl Formation in northwestern Oaxaca (at ~17° N. Lat., in the tropics), we recovered an ?early Oligocene or less likely late Eocene mammal assemblage, the Yolomécatl local fauna, which has a direct bearing on the constitution, evolution and biogeographic relationships between mammal faunas of North and South America, as well as those of Eurasia. The description and discussion of a new carnivore presented here, is a significant addition to the reports coming out on this fauna (e.g., Jiménez-Hidalgo et al., 2015; 2018; Ferrusquía-Villafranca et al., 2018a; Ortíz-Caballero et al., 2020). Such reports are also a welcome increase to the meager published record of Paleogene terrestrial vertebrates in Mexico which includes the following occurrences:

(a) Las Tetas de Cabra local fauna, Wasatchian of Baja California (Novacek et al., 1991). (b) Marfil local fauna, early Bridgerian of Guanajuato; a lava flow interbedded in the faunal bearing Guanajuato Red Conglomerate was K–Ar dated as 49.3 ± 1.0 Ma by Aranda-Gómez and McDowell (1998); faunal reports are in Fries et al. (1955), Black and Stephens (1973), Ferrusquía-Villafranca (1989, 2005). (c) Yolomécatl (= Iniyoo) local fauna, ?early Arikareean or possibly latest Uintan-earliest Duchesnean of Oaxaca; a glass shards sample from the tuff sheet interbedded in the namesake, fossil-bearing formation was ⁴⁰Ar-³⁹Ar dated as 40.3 ± 1.0 Ma (Ferrusquía-Villafranca et al., 2016); faunal reports are in Jiménez-Hidalgo et al. (2015, 2018) and Ferrusquía-Villafranca et al. (2018a). (d) Rancho Gaitán local fauna, Chadronian of Chihuahua (Ferrusquía-Villafranca, 1969; Ferrusquía-Villafranca et al., 1997).

Section snippets

Geographic and geologic settings

The study area (Fig. 1) includes some 90 sq. km of rugged terrain within the Mixteca Region, northwestern Oaxaca State, Sierra Madre del Sur Morphotectonic Province, southeastern Mexico, between 17°25′–17°30′ N. Lat. N and 97°29′–97°36′ W Long. (Fig. 2). The Cenozoic sequence (Fig. 2, Fig. 3) unconformably overlies carbonate rock units of Late Jurassic to Late Cretaceous ages. The area also includes the Mixteco/Oaxaca Terrane boundary, namely the Tamazulapam fault.

The Paleogene sequence (Fig. 2

Materials and methods

A nearlyomplete cranium, discovered in the Yolomécatl Formation, northwestern Oaxaca State, is the basis of this study. The taxonomic identification was obtained following standard procedures, which in this instance include detailed comparisons of key characters and measurements (expressed in milimeters) with those of contemporaneous or potentially related taxa to Oaxacagale ruizi new gen. and sp. (see Supplementary Material Appendices A and E) in order to assess their congenerity or lack of

Systematic paleontology

Class MAMMALIA Linnaeus, 1758.

Order CARNIVORA Bowdich (1821).

Suborder CANIFORMIA Kretzoi (1943).

Infraorder ARCTOIDEA Flower (1869).

Parvorder MUSTELIDA Tedford (1976).

Family MUSTELIDAE Fischer von Waldheim, 1817

“PALEOMUSTELIDAE” Baskin (1998).

Oaxacagale gen. nov.

Type and only species— Oaxacagale ruizi.

Descriptive diagnosis— Oaxacagale is distinguished from other carnivores as follows:

Small overall size (skull length < 50 mm); dorso-ventrally low cranium, whose antero-posterior length is ~10%

Initial remarks

The overall size (Table 1, Table 2; Supplementary Material Appendix A; Supplementary Material Appendix E, Tabs. E.1–34), cranial morphology (Fig. 4, Fig. 5, Fig. 6), and dentition shows that Oaxacagale, in spite of sharing a few characters with most of the discussed taxa, particularly with basal carnivores, including among others musteloids, mustelids, Mustelavus, Plesictis, canids (like Hesperocyon), and Carnivora inc. sed. Palaeogale, is significantly different from all of them, as shown

Summary and conclusions

1.

The Paleogene sequence in the Yolomécatl area (17°25′–17°30′ N Lat., and 97°29′–97°36′ W Long.), northwestern Oaxaca State, Sierra Madre del Sur Morphotectonic Province of Mexico includes two volcanic andesitic lava-flow units, one dacitic dome, and two pyro-epiclastic units; one of them is the Yolomécatl Formation, a red, vertebrate-fossiliferous, ~650 m thick, lacustrine-fluvial succession forming badlands, interbedded by felsic tuff sheets; one of them yielded a⁴⁰Ar-³⁹Ar age of

Credit author statement

Ismael Ferrusquía-Villafranca: Investigation, Writing – original draft preparation, Writing – review & editing, Data curation, Conceptualization, Resources, Supervision, Project administration, Funding acquisition. Xiaoming Wang: Writing – review & editing, Investigation, Formal analysis, Software.

Declaration of competing interest

The authors have no conflict of interest.

Acknowledgments

The authors are indebted to Dr. Josep A. Moreno-Bedmar, Jefe, Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autóma de México (UNAM), for inviting us to partake in the Volume Commemorating the 35th Anniversary of the Sociedad Mexicana de Paleontología, A. C. Long life to this academic association. The authors are indebted to the authorities of the Instituto de Geología, UNAM for their support and encouragement to work in this project. Financial support to develop it

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