Um novo icnotáxon de tetrápode para a Formação Botucatu, Cretáceo Inferior (Neocomiano) do Brasil: aspectos locomotoriais, preservacionais e paleoecológicos
Abstract
Trace fossils (e.g. tracks and trackways), objects of Paleoichnology studys, represent
behavioral responses of biota. They are vestiges produced by biological activity of past
organisms and can be used for paleobiologicaL, paleoecological and
paleoenvironmental reconstructions. The Botucatu Formation (Neocomian) was an
immense paleoerg and is know worldwide for its ichnofossiliferous record, comprising
traces of vertebrates (dinosaurs and mammal-like tracks) and invertebrates (coleoptera
and arachnids). Among vertebrates, are of great importance tracks and trackways from
the ichnogenus Brasilichnium Leonardi 1981, endemic of aeolian deposits and assign to
mammal-like trackmakers. In the present study is described a new ichnotaxon,
Brasilichnium saltatorium isp. nov., with saltatorial progression in phases, distinct and
rare in fossil record, attempting to understanding locomotorial aspects and the
paleoecology of the geologic unit. The new ichnotaxon show biological variation in
behavioural level, and not in preservatonal level, when compared to brasilichnium
elusivum, reflecting a great difference in autopodial configuration on trackways. In total,
were analyzed 12 trackways, with upward and downard direction relative to the inclined
plane of the paleodune. Neoichnological experiment were conducted with Meriones
unguiculatus. In the experiment and in fossil trackways, autopodial dimensions are
larger in downard direction due to the higher displacement of sediment, and may skew
interpretations of the possible trackmaker for change the length/width ratio. Another
parameter with the same observation among experiment and fossil trackways is the
distance between sets of foot/hand, being greater in the downward direction due to the
4 movement dynamics. Compared to others ichnotaxa presenting the saltatorial
locomotion, Brasilichnium saltatorium isp. nov. differs both in morphology of tracks
and in the autopodium configuration in trackway, reiterating the new description.
Regardless of the direction, the quadruped locomotion appears to be the rule, even when
the marks of the hands are not printed, possibly because of the overlap of autopodia
and/or production of footprints in the subsurface. Heteropody is most evident in the
downward direction, however, it has a higher degree in the upward direction. Based on
the study of current desserts, Brasilichnium trackmakers probably were opportunistic
omnivores consumers, adopting asymmetrical locomotion to get speed. Near the São
Bento Quarry, Araraquara, there must have been ephemeral ponds as a result of pluvial
episodes recorded as impact craters in sandstone and the abundant ichnofauna. Such
environments could support the biota of the region, enhancing the ecological
relationships in these areas and forming locally productive communities.