Systematic and trophic diversity of protodidelphines (Mammalia, Marsupialia, Protodidelphidae): Evidence of a short time diversification during the onset of the Eocene

• Published in: Journal of South American earth sciences 2024-11, Vol.148, p.105104, Article 105104
• Main Authors: Carneiro, L.M., Oliveira, E.V., Silva, R.C., Bampi, H., Arêas, M.R.
• Format: Article
• Language: English
• Subjects: Didelphimorphia; Itaboraian SALMA; Itaboraí basin; Marsupialia; Paleocene-Eocene Thermal Maximum; Paleoecology
• ISSN: 0895-9811
• DOI: 10.1016/j.jsames.2024.105104

The Itaboraí Basin, municipality of Itaboraí, Rio de Janeiro, Brazil, preserved an early Eocene vertebrate assemblage. Among its representatives, Metatheria comprises its most diverse clade, with at least 29 genera and 43 species. Among large- to very large-sized taxa, protodidelphids are represented by Protodidelphis vanzolinii, P. mastodontoides, and Carolocoutoia ferigoloi. Protodidelphis mastodontoides was initially considered a different genus, Robertbutleria; however, the synonymy of Robertbutleria with Protodidelphis has never been tested. A phylogenetic analysis recovered Robertbutleria as the sister taxon of Carolocoutoia and not Protodidelphis. Robertbutleria and Carolocoutoia share the presence of rounded upper molars, evident bunodonty, rounded postmetacrista, U-shaped protocone, asymmetric placement of m4, obliquely oriented p1-3, and absence of diastemata. The analysis recovered that the dental features considered for the synonymy of Robertbutleria with Protodidelphis represented plesiomorphies for Protodidelphidae (e.g., sinuous crest between StB and StD, marked increase in the size of the molars from M/m1 to M/m3). Based on the results, an emended diagnosis of Protodidelphinae (the clade that includes Protodidelphis, Robertbutleria, and Carolocoutoia) is presented. Two principal component analyses (PCAs) recognized protodidelphine taxa in different morphospaces, indicating differential allometric and morphofunctional patterns. Protodidelphis was a generalized frugivore, Robertbutleria was a fibrous frugivore, and Carolocoutoia was a turgent frugivore. Moreover, the similar morphological and morphofunctional indexes of protodidelphines suggest a “short time” evolutionary diversification for this clade, and that trophic specializations do not necessarily require great morphological changes, allowing the sympatric co-existence of morphologically similar ingroup genera. •Robertbutleria Marshall, 1987 is rescued as a valid genus of Protodidelphidae.•Robertbutleria was more closely related to Carolocoutoia than to Protodidelphis.•An emended diagnosis of Protodidelphinae (the clade that included Protodidelphis, Robertbutleria, and Carolocoutoia) is presented.•Itaboraí’s protodidelphines explored differential frugivorous trophic niches.•Robertbutleria displays several features indicative of a potential fibrous frugivorous diet.