A revision of the putative Late Cretaceous triconodonts from South America
Authors:
L.C. Gaetano, C.A. Marsicano and G.W. Rougier
Abstracts:
Austrotriconodon mckennai and Austrotriconodon sepulvedai, from the Campanian Los Alamitos Formation, Patagonia, Argentina were originally described as triconodont mammals and the sole members of the family Austrotriconodontidae. These mammals were represented by isolated cheek teeth originally regarded as molariforms, but their peculiar morphology later raised doubts about their purported triconodont affinities. Nevertheless, the morphological bases supporting the alternative taxonomic views have not been fully documented. We present here detailed comparisons of Austrotriconodon with other Late Cretaceous taxa and conclude that Austrotriconodon specimens should be assigned to Meridiolestida and Mesungulatoidea. These isolated teeth are likely premolars and might represent unknown dental positions of already described species or correspond to taxa that are yet to be formally recognized. According to our interpretation, there is still no record of Cretaceous triconodonts in South America, but we support the triconodont affinities for Jurassic taxa from the Cañadón Asfalto Formation in central Patagonia.
A new phylogeny for basal Trechnotheria and Cladotheria and affinities of South American endemic Late Cretaceous mammals
Authors:
1. Alexander O. Averianov (a,b)
2. Thomas Martin (c)
3. Alexey V. Lopatin (d)
Affiliations:
a. Zoological Institute of the Russian Academy of Sciences, Universitetskaya nab. 1, 199034, Saint Petersburg, Russia
b. Department of Paleontology, Geological Faculty, Saint Petersburg State University, 16 Liniya VO 29, 199178, Saint Petersburg, Russia
c. Steinmann-Institut für Geologie, Mineralogie und Paläontologie, Universität Bonn, Nussallee 8, 53115, Bonn, Germany
d. Borissiak Paleontological Institute of the Russian Academy of Sciences, Profsouznaya str. 123, 117997, Moscow, Russia
Abstract:
The endemic South American mammals Meridiolestida, considered previously as dryolestoid cladotherians, are found to be non-cladotherian trechnotherians related to spalacotheriid symmetrodontans based on a parsimony analysis of 137 morphological characters among 44 taxa. Spalacotheriidae is the sister taxon to Meridiolestida, and the latter clade is derived from a primitive spalacolestine that migrated to South America from North America at the beginning of the Late Cretaceous. Meridiolestida survived until the early Paleocene (Peligrotherium) and early Miocene (Necrolestes) in South America, and their extinction is probably linked to the increasing competition with metatherian and eutherian tribosphenic mammals. The clade Meridiolestida plus Spalacotheriidae is the sister taxon to Cladotheria and forms a new clade Alethinotheria. Alethinotheria and its sister taxon Zhangheotheria, new clade (Zhangheotheriidae plus basal taxa), comprise Trechnotheria. Cladotheria is divided into Zatheria (plus stem taxa, including Amphitherium) and Dryolestida, including Dryolestidae and a paraphyletic array of basal dryolestidans (formerly classified as “Paurodontidae”). The South American Vincelestes and Groebertherium are basal dryolestidans.
