New data on Mustelidae (Carnivora) from Southeast Asia: Siamogale thailandica, a peculiar otter-like mustelid from the late middle Miocene Mae Moh Basin, northern Thailand

Abstract

We report new dental remains of Mustelidae from the late middle Miocene of Mae Moh Basin, northern Thailand, improving the poor fossil record of the family in Southeast Asia. Siamogale thailandica is a poorly known mustelid, previously recorded from just a single tooth. Here we present over a hundred new specimens attributable to this species. S. thailandica shows a combination of primitive and convergent features of the dentition that makes its original subfamilial assignment to Lutrinae doubtful. Evidence from the dental morphology suggests that it belongs to a bunodont otter-like mustelid that evolved in convergence with "true" otters (Lutrinae) toward a semi-aquatic way of life. Autapomorphic features such as the height and the position of the m1 metaconid and the shape of the P4 lingual shelf make S. thailandica unique among Mustelidae. The morphology of this species is mostly similar to Mionictis species and Lartetictis dubia, reported in the Miocene of North America and Europe, respectively. These similarities could imply immigration events to Thailand in the early or middle Miocene. Alternately, the lineage leading to Siamogale might have deeper origins from an endemic early Miocene Southeast Asian mustelid.

A new otter of giant size,Siamogale melilutrasp. nov. (Lutrinae: Mustelidae: Carnivora), from the latest Miocene Shuitangba site in north-eastern Yunnan, south-western China, and a total-evidence phylogeny of lutrines

“…Overall, our new Shuitangba form most closely resembles Siamogale thailandica (Ginsburg et al 1983;Grohe et al 2010). Strikingly, the P4s of S. melilutra and S. thailandica share a protocone crest, and the M1s share a medially thickened and distinctly distally enlarged lingual cingulum, which forms an expanded talon, and the presence of a cuspule just distal to the metacone.…”

“…Other fossil taxa included in our cladistic analysis are coded mainly based on illustrations and descriptions from the literature: Roman & Viret (1934), Helbing (1936) for Paralutra jaegeri; Willemsen (1983), Villier et al (2011) for Paralutra garganensis; Ginsburg et al (1983), Villalta & Crusafont-Pairo (1945), H€ urzeler (1987 for Tyrrhenolutra helbingi; Morales & Pickford (2005) for Paludolutra (P. lluecai, P. marammena, P. campanii); Berta & Morgan (1985), Lambert (1997) for Enhydritherium terranovae; Zdansky (1924) for 'Lutra' aonychoides). Finally, coding for extant lutrines and Siamogale is mostly based on our own examination of specimens and from Grohe et al (2010) and Grohe (2011). We did not include the African bunodont genus Djourabus (Peigne et al 2008), which is too poorly known to code.…”

“…Old World Mio-Pleistocene lutrines and other otter-like forms in Asia that warrant close examination include: Vishnuonyx from the middle Miocene of the Indian Subcontinent and Thailand, and middle to late Miocene of Kenya; Sivaonyx from the middle Miocene of Thailand, the late Miocene of Yunnan, the Indian Subcontinent and Europe, and the late Miocene to early Pleistocene of Africa; Enhydriodon from the Plio-Pleistocene of the Indian Subcontinent and probably Africa; 'Lutra' aonychoides from the late Miocene of China; and Siamogale thailandica from the late middle Miocene of Thailand (Ginsburg et al 1983;Qi 1983Qi , 1985Qi , 2006Pickford 2007;Grohe 2011;Grohe et al 2010Grohe et al , 2013. Of these, Vishnuonyx, Sivaonyx and Enhydriodon belong to a clade of their own, the Enhydriodontini of Pickford et al (2007).…”

“…modern Aonyx and fossil relatives). More recently, Grohe et al (2010) described additional dental materials, including upper cheek teeth, of Siamogale thailandica from the type locality. However, despite this increased knowledge, almost 30 years after its initial description, Grohe et al (2010) were still hesitant to place Siamogale in a particular clade (Lutrinae, Melinae or Galictinae), settling instead for an ambiguous characterization of 'bunodont otter-like mustelid', and considered it to be closely related to Mionictis and Lartetictis (see additional comments under Remarks above).…”

“…The most prominent dental difference is the configuration of the P4 protocone. In S. thailandica the P4 has a more or less cuspidate protocone with a broad crest emanating from it distally that ends at the level of the carnassial blade (Grohe et al 2010, fig. 2h1-2).…”