Corriebaatar marywaltersae, Rich & Vickers-Rich & Flannery & Kear & Cantrill & Komarower & Kool & Pickering & Trusler & Morton & Klaveren & Fitzgerald, 2009

Rich, Thomas H., Vickers-Rich, Patricia, Flannery, Timothy F., Kear, Benjamin P., Cantrill, David J., Komarower, Patricia, Kool, Lesley, Pickering, David, Trusler, Peter, Morton, Steven, Klaveren, Nicholas Van & Fitzgerald, Erich M. G., 2009, An Australian multituberculate and its palaeobiogeographic implications, Acta Palaeontologica Polonica 54 (1), pp. 1-6 : 2-3

publication ID	https://doi.org/ 10.4202/app.2009.0101
persistent identifier	https://treatment.plazi.org/id/046F87EB-F635-6D7F-FFEF-B65297B6FF78
treatment provided by	Felipe
scientific name	Corriebaatar marywaltersae
status	sp. nov.

Treatment

Corriebaatar marywaltersae sp. nov.

Figs. 1 View Fig , 2 View Fig .

Etymology: In honour of Mrs. Mary Walters who found the holotype in 2004.

Holotype: NMV P216655 About NMV , a fragment of a left dentary bearing a complete plagiaulacoid p4 and the anterior root of m1 ( Figs. 1 View Fig , 2 View Fig ).

Type locality: Flat Rocks fossil site on the marine shore platform in the Bunurong Marine Park near Inverloch, Victoria, Australia (38° 39‘ 40±02“ S, 145° 40‘ 52±03” E, World Geodetic System 1984). Three other mammalian taxa are known from this locality: two possible eutherians/australosphenidians, Ausktribosphenos nyktos ( Rich et al. 1997) and Bishops whitmorei ( Rich et al. 2001a) and a monotreme, Teinolophos trusleri ( Rich et al. 2001b) .

Type horizon: Wonthaggi Formation (Strzelecki Group), Aptian (late Early Cretaceous) in age ( Rich et al. 1997).

Diagnosis.—Distinguished from the non−multituberculate mammals with plagiaulacoid premolars in that the base of the enamel on the labial side of the anterior root extends far ventral to the remaining tooth crown, the exodaenodont condition ( Figs. 1A View Fig , 2B View Fig ). Distinguished from all multituberculates in the Plagiaulacida with the exception of Pinheirodon pygmaeus in lacking either a buccal cusp or cusps or a row of buccal pits on the p4 ( Kielan−Jaworowska and Hurum 2001) ( Figs. 1A View Fig , 2B View Fig ). Although the single known specimen of the p4 of Pinheirodon pygmaeus lacks a distinct buccal cusp, Hahn and Hahn (1999: fig. 26a) indicate an area in the posteroventral buccal region of the crown setting it off from the immediate surrounding region of the tooth, suggestive of the former presence of a cusp that had been abraded. Corriebaatar is distinguished from all other multituberculates by its “double exodaenodont” condition on the p4 (see Description) and an excavation on the lingual side of the posterior root of the p4 ( Figs. 1B View Fig , 2A View Fig ).

Description.—The p4 of Corriebaatar marywaltersae ( Fig. 2 View Fig ) is 3.4 mm in length. It can be uniquely differentiated from all other multituberculates by at least three key features.

(1) Restriction of the crown ridges to two on the labial side and one on the lingual. Typically, the ridges on the p 4 in multituberculates densely cover the entire crown; however, in some taxa their number may be reduced. For example, Cimolomys gracilis has eight or nine serrations on the crest of the tooth but only three or four external ridges and two or three internal ridges ( Clemens 1963).

(2) Presence of both labial and lingual excavations into the roots of the p4. The anterolabial excavation possibly accommodated the p3, as in Cimolodon nitidus ( Clemens 1963: fig. 23a). Note that the anterior edge of the dentary fragment in NMV P216655 is broken posterior to where the p3 alveolus would be expected, thus presence or absence of the p3 cannot be confirmed with certainty. The posterolingual excavation does not conform to the tooth positions in any other known multituberculate, so consequently its function remains unknown. The excavation may have been occupied by an anterior projection of the m1, a remnant of which is preserved as a root fragment well posterior to the p4.

(3) The ventrally directed lobe of enamel on the labial surface of the posterior root. This condition is here termed “double exodaenodont” taking into account the presence of an accompanying enamel lobe on the labial surface of the anterior root. The “double exodaenodont” state has not been noted in any other previously reported multituberculate ( Kielan−Jaworowska et al. 2004: fig. 3).

As Kielan−Jaworowska and Hurum (2001) pointed out, although the p4 of cimolodontans can be for the most part characterised as “arcuate” or “triangular” in profile while those of plagiaulacidans can be contrasted as “rectangular”, this is not a rigid distinction between the two groups. In any case, Corriebataar marywaltersae has a p4 which is as “arcuate” as the unquestioned cimolodontan Microcosmodon conus ( Jepsen 1940: pl. 5: 3).