Tafonomia da megafauna pleistocênica brasileira: fluvial transport index (FTI) em análises de representatividade óssea

Abstract

IN BONE REPRESENTATIVITY ANALYSES. In this work FTI is applied in order to obtain more refined conclusions about the transport process involved in taphonomic history of these accumulations. Data of bone representation from Fazenda Nova tank (in Brejo da Madre de Deus Municipality, Pernambuco State), Jirau and João Cativo tanks (both in Itapipoca Municipality, Ceará State) and the fluvial deposits of Araras/Taquara (outcrops of the Rio Madeira Formation, Rondonia State) were used in this analysis. Using the Spearman's nonparametric correlation between bone representation and FTI, we observed the quantitatively homogeneous preservation of skeletal elements less and more transportable in Fazenda Nova and João Cativo tanks, what would be expected for deposits of natural tanks, which were influenced by non-selective depositional processes. In Jirau and Araras/Taquara assemblages the preservation was of less transportable elements. In markedly fluvial deposits, as Araras/Taquara, was as expected sorting of elements due to transport, whereas sorting observed in Jirau tank may have not been related to transport, but to other biostratinomic and diagenetic factors. Simulation with Voorhies Groups (VG) for the same deposits showed conclusions contrary to those observed by use of the FTI, revealing that the taphonomic inferences about transport based in the use of VG for Pleistocene Megafauna assemblages can be misleading.

Diversity and preservation of Pleistocene tetrapods from caves of southwestern Bahia, Brazil

“…The non-parametric correlation between FTI and bone representativity for the associations of Gruna das Três Cobras resulted in a value of −0.05 (p = 0.87). These values are even closer to the neutrality than in Lapa dos Peixes, also indicating homogeneity in relation to the quantity of less and more transportable elements, practically without hydraulic selection (Araújo-Júnior et al, 2012).…”

“…3). Data on representability of skeletal and taxonomic elements were also considered, as well as the Voorhies groups (Behrensmeyer and Hill, 1980;Shipman, 1981;Lyman, 1994;Martin, 1999) and fluvial transport index for large-sized mammals and megamammals (following Araújo-Júnior et al, 2012). Spearman's nonparametric correlation between FTI values and representability of skeletal elements was performed for the analyzed material through the Paleontological Statistics software (PAST; Araújo-Júnior et al, 2012).…”

“…The non-parametric correlation between FTI and bone representativity for the associations of Lapa dos Peixes resulted in a value of −0.13 (p = 0.59). According to Araújo-Júnior et al (2012), these values would be closer to the neutrality, indicating homogeneity in relation to the quantity of less and more transportable elements, practically without hydraulic selection. Some bias in this result is expected due to the current erosive processes involved in the exhumation of the bones, which can cause the loss of fragile elements, and because the analysis is based only on large animals, in this case mainly sloths.…”

“…9A). The minimum number of individuals (MNI) was estimated by observing repetition of the most abundant bones while the number of identified specimens (NISP) was calculated taking into account only taxonomically identified material (Table 1), following Araújo-Júnior et al (2012). Thus, it was verified at least seven individuals of V. bucklandi, three individuals of C. cuvieri, two individuals of N. maquinense and one individual of an undetermined sloth.…”

Observações sobre a repartição espacial dos restos fósseis de preguiça-gigante (gênero Eremotherium) na Lagoa Uri de Cima, Pernambuco, Brasil

“…Restos fósseis pertencentes aos diversos grupos de Voorhies (categorias que representam vários graus de mobilidades; Voorhies, 1969;Behrensmeyer, 1975;Hunt, 1978;Araújo-Júnior et al, 2012) jazem relativamente próximos dos fragmentos de vértebras e costelas. Os restos que se encontram nessa área têm formas, pesos e densidade diferentes.…”