Osteología Craneana Y Taxonomía De Pronothrotherium (Xenarthra, Folivora, Nothrotheriidae) Del Mioceno Tardío–plioceno Temprano De La Provincia De Catamarca (Argentina)

Abstract

Pronothrotherium typicum is a late Miocene-early Pliocene (Huayquerian-Chapadmalalan SALMA) nothrotheriid sloth known from the Catamarca Province of northwestern Argentina. Pronothrotherium is one of four nothrotheriid genera known from relatively complete skeletal material, but unlike the other three, the osteology of Pronothrotherium has not been formally described. The present study provides the first detailed description and illustration of the cranial anatomy of Pronothrotherium, based largely on a nearly complete, subadult skull of P. typicum from the collections of The Field Museum (Chicago, Illinois, USA), as well as a less well-preserved adult skull and isolated mandible from the same collections. A revised cranial diagnosis of P. typicum is provided in the text. The skull of this species shows a number of distinctive features, most notably a peculiar vomerine keel in the nasopharynx, terminating in a swollen knob, that is, as far we know, a unique morphology among mammals. Based on the results of the present study, there appears to be reason to recognize two contemporaneous species of Pronothrotherium, P. typicum and P. mirabilis, although the latter is less well supported. We do not accept the validity of a third described species, P. figueirasi, considering it instead to be synonymous with P. mirabilis. The present study does not resolve the uncertain phylogenetic relationships among the well-preserved nothrotheriine taxa Pronothrotherium, Mionothropus (late Miocene), and the two Pleistocene genera in Nothrotheriini, Nothrotherium and Nothrotheriops. However, we hope that the data provided will facilitate subsequent phylogenetic studies that may resolve these issues.

Recognition of a new nothrotheriid genus (Mammalia, Folivora) from the early late Miocene of Achiri (Bolivia) and the taxonomic status of the genus Xyophorus

“…The post glenoid region is marked by numerous longitudinal ridges. This differs from the condition in basal megatherioids, Pronothrotherium, and megatheriids, where the post-glenoid region is characterized by rugose bone, but is similar to the condition in Mionothropus and Nothrotheriops (Gaudin 1995(Gaudin , 2004De Iuliis et al 2011;Gaudin et al 2020).…”

“…It would appear that the foramen ovale is almost entirely surrounded by the squamosal bone with a small ventral contribution to its rim from the pterygoid (Figure 3C). This is typical for most megatherioid sloths (Gaudin 2004), with the exception of Pronothrotherium, where the aperture lies entirely within the alisphenoid (Gaudin et al 2020).…”

“…The two new specimens are compared to other late Miocene and Pliocene nothrotheriids, in particular Pronothrotherium typicum, a species from the late Miocene-early Pliocene of southern South America (Huayquerian-Chapadmalalan SALMAs), represented by several nearly complete skulls, one with a well-preserved auditory region (Patterson et al 1992;Gaudin et al 2020), as well as a published description of an isolated astragalus (Kraglievich 1928). We will also compare the skull material to Mionothropus cartellei, a species from the late Miocene (Huayquerian SALMA) of Peruvian Amazonia, represented by a single complete skull with a well-preserved auditory region (De Iuliis et al 2011).…”

“…The ventral portion of the ectotympanic is deep in lateral view, especially anteriorly, i.e., it is much broader than either the anterior or posterior crura. In this respect it resembles Pronothrotherium (Patterson et al 1992;Gaudin et al 2020) and differs from Mionothropus, Hapalops, and Analcimorphus (Scott 1904;Patterson et al 1992;, where the ectotympanic ring has more uniform proportions. This ventral segment of the ectotympanic appears to be attached medially to the tympanohyal and the entotympanic, with the opening for the Eustachian tube situated between the ectotympanic and the latter element (Figure 3C-D).…”

“…Mcdonaldocnus also lacks the canals which perforate the paroccipital process in Nothrotheriidae (Gaudin 1995;De Iuliis et al 2011;Gaudin et al 2020), marked by openings on the lateral surface of the skull posterodorsal to the process.…”