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• ATROX TERRESTRIALS RAR SERIES

Locations of the Cachapoal locality and the similar-aged (likely coeval) Tinguiririca locality in central Chile. In a paper published in the American Museum Novitates on 17 July 2020, Russell Engleman of the Department of Biology at Case Western Reserve University, John Flynn of the Division of Paleontology and Richard Gilder Graduate School at the American Museum of Natural History, André Wyss of the Department of Earth Science at the University of California, Santa Barbara, and Darin Croft of the Department of Anatomy at Case Western Reserve University, describe a new Sparassodont taxon based on a specimen recovered from the upper Cachapoal River drainage in the Andean Main Range of central Chile, approximately 100 km southeast of Santiago. These strata, which postdate the Tinguirirican South American Land Mammal Age and predate the Deseadan South American Land Mammal Age, are informally referred to as the 'Canteran' interval. A third specimen, a left dentary tentatively assigned to the Borhyaenoid Pharsophorus lacerans, has been described from slightly higher early Oligocene levels (La Cantera) at Gran Barranca. Until now only two specimens have been identified from this interval: a fragmentary upper molar of an extremely small ( Pseudonotictis-sized) species, and an isolated premolar of a larger taxon, both from the La Cancha Fauna of Gran Barranca (Chubut, Argentina). Several authors have remarked on the near-absence of Sparassodont remains from the earliest Oligocene Tinguirirican South American Land Mammal Age. Unfortunately, the early Oligocene is among the most poorly sampled intervals in the evolutionary history of Sparassodonts. The early Oligocene record, in particular, is essential for clarifying whether these long ghost lineages result from poor taxonomic sampling or are an artifact of insufficient sampling of morphological characters in character-taxon matrices. Phylogenetic analyses indicate that most major Neogene Sparassodont lineages, including Hathliacynids, Borhyaenids, and Thylacosmilines, diverged from their nearest relatives prior to the late middle Eocene, but representatives of these groups are unknown prior to the late Oligocene. This may reflect the fact that most well-known Thylacosmilines come from geologically young deposits (middle Miocene to early Pliocene) and hence exhibit high numbers of apomorphies not present in non-Thylacosmilines.īoth the early evolutionary history of Thylacosmilines and the origins of their distinctive saber-toothed morphology remain poorly understood. some basicranial features are shared with either Hathliacynids or Borhyaenoids), complicating attempts to phylogenetically place Thylacosmilines within Sparassodonta. Several of these features appear to be related to a 'sabertooth' mode of life, while others occur in various other groups of Sparassodonts (i.e.

ATROX TERRESTRIALS RAR SERIES

Thylacosmilines, as traditionally conceived, are characterized by numerous autapomorphies relative to other Sparassodonts, including hypselodont (ever-growing) upper canines, a highly reduced incisor series that may have been essentially nonfunctional, loss of one premolar locus (thought to be the first upper and lower premolar), retention of the deciduous upper third premolar into adulthood, and a highly distinctive basicranium with a compound squamosal/exoccipital bulla, no alisphenoid tympanic process, no external opening for the primary jugular foramen, and large paratympanic spaces. Perhaps the best-known example of this phenomenon is the Thylacosmilinae (Thylacosmilidae of most previous authors), a group of Sparassodonts whose striking morphological resemblance to Placental sabertooths literally makes them a textbook example of convergent evolution. Sparassodonts occupied many of the niches filled by Placental Carnivorans and 'Creodonts' on other continents and often strongly converged with these groups in morphology.

The Sparassodonta, an extinct group of Metatherians (Marsupials and their extinct relatives), were the dominant group of carnivorous mammals in South America from the early Paleocene (Tiupampan South American Land Mammal Age) to the late early Pliocene (Chapadmalalan South American Land Mammal Age), sharing the ecological role of large terrestrial predator with Phorusrhacid Birds and Sebecid Crocodyliforms during the continent’s long Cenozoic isolation.