Microbiotheria Ameghino, 1889

Beck, Robin M. D., Voss, Robert S. & Jansa, Sharon A., 2022, Craniodental Morphology And Phylogeny Of Marsupials, Bulletin of the American Museum of Natural History 2022 (457), pp. 1-353 : 224

publication ID

https://doi.org/10.1206/0003-0090.457.1.1

DOI

https://doi.org/10.5281/zenodo.7036159

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scientific name

Microbiotheria Ameghino, 1889
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Microbiotheria Ameghino, 1889 View in CoL

CONTENTS: Dromiciops (fig. 43) and † Microbiotherium .

STEM AGE: 45.6 Mya (95% HPD: 41.4–48.8 Mya).

CROWN AGE: 17.3 Mya (95% HPD: 14.0–21.8 Mya).

UNAMBIGUOUS CRANIODENTAL SYNAPOMORPHIES: Basisphenoid with a distinct sagittal keel (char. 48: 0→1; ci = 1.000); auditory bulla large, contacting rostral process of petrosal (char. 55: 1→2; ci = 0.300); caudal and rostral tympanic processes of petrosal seamlessly fused, forming a petrosal plate (char. 68: 0→2; ci = 0.154); and five upper incisors present (char. 103: 2→0; ci = 0.333).

COMMENTS: Of the four unambiguous morphological synapomorphies supporting monophyly of Microbiotheria (equivalent to Microbiotheriidae in our analyses), two occur homoplastically in other marsupial groups and one appears questionable because it is a reversal in the number of upper incisors from three back to the ancestral metatherian complement of five. However, presence of a basiphenoid with a distinct sagittal keel is a distinctive cranial apomorphy that is apparently unique to microbiotherians ( Hershkovitz, 1992a; 1999; Giannini et al., 2004; Wible et al., 2018). Although several genera of fossil microbiotherians are known from South America ( Marshall, 1982; Goin and Abello, 2013; Goin et al., 2016), all except † Microbiotherium (for which cranial material, including a specimen [MACN A 8505] preserving the part of the basisphenoid sagittal keel, is known; Segall, 1969b; Marshall, 1982) are known from dental remains only.

As already discussed (see Australidelphia above), the oldest definitive member of the order described to date is probably the woodburnodontid † Woodburnodon casei from the Cucullaea I Allomember of the La Meseta Formation, Seymour Island, off the Antarctic Penninsula. Based on current evidence, the age of † W. casei appears to be ~40 Mya ( Douglas et al., 2014; Amenábar et al., 2019; Mörs et al., 2020). Most recent studies have concluded that the early or middle Palaeocene † Khasia cordillerensis is not a member of Microbiotheria ( Oliveira and Goin, 2006; Goin et al., 2016; Carneiro et al., 2018; but see Muizon et al., 2018), and putative microbiotherian specimens reported from the early Eocene Las Flores Fauna ( Goin, 2003; Zimicz, 2012; Woodburne et al., 2014a; Goin et al., 2016) have yet to be formally described (see Australidelphia above).

Amenabar, C. R., M. Montes, F. Nozal, and S. Santillana. 2019. Dinoflagellate cysts of the La Meseta Formation (middle to late Eocene), Antarctic Peninsula: implications for biostratigraphy, palaeoceanography and palaeoenvironment. Geological Magazine 157 (3): 351 - 366.

Carneiro, L. M., E. V. Oliveira, and F. J. Goin. 2018. Austropediomys marshalli gen. et sp. nov., a new Pediomyoidea (Mammalia, Metatheria) from the Paleogene of Brazil: paleobiogeographic implications. Revista Brasileira de Paleontologia 21 (2): 120 - 131.

Douglas, P. M., et al. 2014. Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures. Proceedings of the National Academy of Sciences of the United States of America 111 (18): 6582 - 6587.

Giannini, N. P., F. Abdala, and D. A. Flores. 2004. Comparative postnatal ontogeny of the skull in Dromiciops gliroides (Marsupialia: Microbiotheriidae). American Museum Novitates 3460: 1 - 17.

Goin, F. J. 2003. Early marsupial radiations in South America. In M. Jones, C. Dickman, and M. Archer (editors), Predators with pouches: the biology of carnivorous marsupials: 30 - 42. Collingwood, Australia: CSIRO (Commonwealth Scientific and Industrial Research Organization).

Goin, F. J., and M. A. Abello. 2013. Los Metatheria sudamericanos de comienzos del Neogeno (Mioceno temprano, edad mamifero Colhuehuapense). Parte 2: Microbiotheria y Polydolopimorphia. Ameghiniana 50 (1): 51 - 78.

Goin, F. J., M. O. Woodburne, A. N. Zimicz, G. M. Martin, and L. Chornogubsky. 2016. A brief history of South American metatherians: Evolutionary contexts and intercontinental dispersals. Dordrecht: Springer.

Hershkovitz, P. 1992 a. Ankle bones: the Chilean opossum Dromiciops gliroides Thomas, and marsupial phylogeny. Bonner Zoologische Beitrage 43: 181 - 213.

Hershkovitz, P. 1999. Dromiciops gliroides Thomas, 1894, last of the Microbiotheria (Marsupialia), with a review of the family Microbiotheriidae. Fieldiana Zoology 93: 1 - 60.

Marshall, L. G. 1982. Systematics of the South American marsupial family Microbiotheriidae. Fieldiana Geology 10: 1 - 75.

Mors, T., M. Reguero, and D. Vasilyan. 2020. First fossil frog from Antarctica: implications for Eocene high latitude climate conditions and Gondwanan cosmopolitanism of Australobatrachia. Scientific Reports 10: 5051.

Muizon, C. de, S. Ladeveze, C. Selva, R. Vignaud, and F. Goussard. 2018. Allqokirus australis (Sparassodonta, Metatheria) from the early Palaeocene of Tiupampa (Bolivia) and the rise of the metatherian carnivorous radiation in South America. Geodiversitas 40 (16): 363 - 459.

Oliveira, E. V., and F. J. Goin. 2006. Marsupiais do inicio do Terciario do Brasil: origem, irradiacao e historia biogeografica. In N. C. Caceres and E. L. A. Monteiro Filho (editors), Os Marsupiais do Brasil: biologia, ecologia e evolucao: 299 - 320. Campo Grande: UFMS.

Segall, W. 1969 b. The middle ear region of Dromiciops. Acta Anatomica 73: 489 - 501.

Wible, J. R., S. L. Shelley, and G. W. Rougier. 2018. The mammalian parasphenoid: Its occurrence in marsupials. Annals of Carnegie Museum 85 (2): 113 - 164.

Woodburne, M. O., et al. 2014 a. Revised timing of the South American early Paleogene land mammal ages. Journal of South American Earth Sciences 54: 109 - 119.

Zimicz, A. N. 2012. Ecomorfologia de los marsupiales paleogenos de America del Sur. Ph. D. dissertation, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, La Plata.