New observations and reinterpretation on the enigmatic taxon Colombitherium (?Pyrotheria, Mammalia) from Colombia

Abstract

Abstract:The controversial taxon Colombitherium tolimense (Mammalia) (probably Late Eocene in age) from Colombia, although known for nearly 40 years, still bears much mystery. Aside from the problematic ordinal attribution of the holotype and only specimen, its determination as an upper or lower jaw remains a highly debated issue. New observations include the presence of a contact facet on the distal face of the most posterior tooth, which indicates that the fragmentary jaw preserves three premolars and two molars; the M3, unpreserved but present, being most probably reduced. This new interpretation completely fits the morphology of the teeth. Furthermore, the shape of these latter and the deeper wear encompassed by their lingual part relative to the labial one is typical of upper dentition. This is in agreement with the internal curving of the roots of the anterior premolars and with several other arguments that lead interpreting the holotype of C. tolimense as a maxillary bearing P2-M2. This new interpretation deepens the morphological gap between Colombitherium and other pyrotherians (except Proticia) and challenges further its referral to Pyrotheria. The peculiar morphology of Colombitherium relative to other pyrotherians is indeed striking. In fact, Colombitherium has nothing in common with pyrotherians but bilophodont cheek teeth, a feature largely widespread in placental mammals. It is here referred to ?Pyrotheria until additional evidence of its relationships is known. Associated with the putative removal of Proticia from Pyrotheria as argued by some authors, the hypothetical removal of Colombitherium from the order would adjust the widely accepted assumption that the pyrotherian bilophodont cheek teeth originated from bunodont cheek teeth. It would also make an origin from lophodont forms plausible. This in turn would have critical relevance, especially to the hypothesis that pyrotherians are notoungulates.

Identifying tooth position of isolated teeth of sparassodonts (Mammalia: Metatheria) using geometric morphometrics

“…Teeth are the most frequently recovered remains in the mammalian fossil record and, due to their complex morphology, often preserve significant phylogenetic and ecological information (Rose, 2006;Ungar, 2010). Mammalian molars are frequently diagnostic to species, even if recovered as isolated elements, and many taxa have been named based on isolated molars (e.g., Antoine et al, 2012;Beck, 2013;Bond et al, 2015). Character lists in phylogenetic analyses of mammals are dominated by dental characters (Brocklehurst and Benevento, 2020;Sansom et al, 2017), and isolated molars can be used to determine dietary habits and estimate body mass (e.g., Zimicz, 2012).…”

“…The taxonomic, phylogenetic, and paleobiologic utility of a tooth is maximized when it can be assigned to the correct locus, as this allows for direct comparisons among taxa. Assigning a tooth to class (e.g., premolar, molar) is often straightforward, particularly when it is preserved in situ in the cranium or dentary (but see Billet et al, 2010). By contrast, correct locus identification can be challenging when a tooth that could belong to one of several morphologically similar loci is found in isolation, as often happens with screen washing or surface collecting.…”

“…By contrast, correct locus identification can be challenging when a tooth that could belong to one of several morphologically similar loci is found in isolation, as often happens with screen washing or surface collecting. Misidentification of tooth locus can result in incorrect taxonomic or paleobiological interpretations (for examples, see Billet et al, 2010;Borths and Stevens, 2017;Zack, 2012). In such situations the conservative and frequently exercised option is to refer the tooth only to class, such as premolar or molar.…”

Osteologia de Taubatherium paulacoutoi Soria & Alvarenga, 1989 (Notoungulata, Leontiniidae) e de um novo Pyrotheria: dois mamíferos fósseis da Formação Tremembé, Brasil (SALMA Deseadense - Oligoceno Superior)

“…Já as estruturas dentárias foram nomeadas de acordo com as referências relacionadas aos dois diferentes grupos, Leontiniidae (Paula Couto, 1979;van Valen, 1966;Madden, 1990;Villarroel & Danis, 1997) e Pyrotheria (Shockey & Daza, 2004;Salas et al, 2006;Billet, 2010;Billet et al, 2010 Gênero Taubatherium Soria & Alvarenga, 1989 Espécie tipo: Taubatherium paulacoutoi Soria & Alvarenga, 1989 Sinonímia: Taubatherium major Soria & Alvarenga, 1989 Holótipo -fragmento de maxilar direito com P2-4 e alvéolos de P1 e de C (DGM-1087-M).…”

“…23), sendo Pyrotherium romeroi o membro melhor conhecido do grupo (Loomis, 1914), inclusive pelo conhecimento de parte do esqueleto pós-craniano (Sánchez-Villagra et al, 2000;Billet et al, 2010). Os estudos realizados com os outros membros desta família restringem-se praticamente às características dentárias ou craniodentárias, uma vez que a maioria dos táxons é representada unicamente por dentes.…”