Estimating the body mass of the late pleistocene megafauna from the south America intertropical region and a new regression to estimate the body mass of extinct xenarthrans

Abstract

The palaeobiogeographic distribution of the Ludlow‒Přídolí and Devonian Bivalves in the Bolivian Central Andean Basin of Western Gondwana, has been established from the study of twenty-five genera, twenty-two of which are considered cosmopolitan and three endemics. Taking into account the total studied genera, seven correspond to Protobranchia, such as Praectenodonta, Praenucula, Notonucula, Nuculites, Palaeoneilo, Phestia and Solemya. The Autobranchia are diverse; representing the remaining eighteen genera and are represented by the groups Praecardiidae (Praecardium, Cardiola and Dualina), Ambonychiidae (Mytilarca), Pteriomorphia (Leptodesma (Leptodesma), Ptychopteria (Ptychopteria) and Ptychopteria (Actinopteria)), Pectinidae (Pseudaviculopecten), Heteroconchia (Pleurodapis, Cardiomorpha and Paracyclas), Grammysiidae (Grammysia, Andinodesma, Grammysioidea, Sanguinolites and Pholadella) and Modiomorphidae (Modiomorpha and Sphenotomorpha). Three dendrograms based on the Jaccard affinity coefficient, and three palaeogeographic maps were built, in three intervals of time: Ludlow to early Lochkovian, late Lochkovian to Emsian and Eifelian to Frasnian.The greatest affinity found in the Ludlow-early Lochkovian, in Central Andean Basin was with North Gondwana Basins (Florida and North African Basins) with 62% and with Nova Scotia (Canada) with 58%. During late Lochkovian to Emsian, the greatest affinity found was with South Africa and Paraná Basins with 65% and Uruguay with 40%. During Eifelian to Frasnian times, the affinities remained with South Africa with 74% and Paraná Basins with 73%, Laurentia kept 33% and Amazonas Basin with 24%. According to the distribution of Bivalves, the basin shows a strong influence of equatorial and low palaeolatitude fauna, especially during the Ludlow to the early Lochkovian and during the Eifelian to Frasnian. From this part of Gondwana, between the Ludlow‒Přídolí and the early Lochkovian, sixteen genera are studied throughout the basin, which thirteen are considered cosmopolitan and only three endemics (Notonucula, Pleurodapis and Andinodesma). In contrast, from late Lochkovian to Emsian, eleven cosmopolitan genera colonize a contracted basin, three of which are genera from equatorial palaeolatitude arriving to Western Gondwana in this period (Phestia, Solemya and Pholadella). During the interval from Eifelian to Frasnian, eighteen genera are registered, among which sixteen are cosmopolitan and only two endemics. Those endemic genera appear earlier in the basin (Notonucula and Pleurodapis). The Bivalves do not appear to have been dependent on temperatures or palaeolatitudes between Ludlow to Frasnian. Discussions about dispersal versus vicariant distributions were presented, and different palaeoenvironmental strategies developed by Bivalves were analyzed.