Estudo bioestratinômico de Itapeuasaurus cajapioensis (Dinosauria, Diplodocoidea) da Formação Alcântara, Cenomaniano da Bacia de São Luís

Abstract

A fossil deposit located in Brazil, on the northern part of the state of Maranhão, at Itapeua beach, on the municipality of Cajapió, Alcântara Formation (Cenomanian), brought a significant record of skeletal remains belonging to Itapeuasaurus cajapioensis (Dinosauria, Diplodocoidea). A study of macroscopic features was carried out, predominantly biostratinomic signatures. The material includes twenty-two specimens, from which the following taphonomic features were analyzed: i) transport; ii) disarticulation; iii) position of the in situ fossils; iv) hydraulic equivalence; v) bioerosion; vi) corrosion vii) predation and/or scavenging marks; viii) trampling marks; ix) physical integrity; x) degrees of abrasion; xi) stages of weathering; xii) breakage; xiii) deformation; and xiv) coloring. The specimen was found 100% disarticulated and no marks of teeth or trampling were identified. According to the analysis of the hydraulic equivalence and the in situ position, there was some transport, but the possibility the animals as carriers is ruled out. Corrosion and bioerosion, occur predominantly in 18 of the fossils. In terms of bioerosion, there was probably a relevant time of exposure before burial that was long enough for organisms colonization to occur. All specimens present signals of abrasion where 7 are in stage 1, 13 are in stage 2, and 2 in stage 3. The abrasive features suggest energy and transport. Relating to weathering, 7 are in stage 2, 14 are in stage 3, and 1 are in stage 4. Stages 0-1 of weathering were not observed, which indicates significant exposure before burial. According to the breakage pattern analyzed in long bones, most of the specimens present pre-burial characteristics. Regarding physical integrity, about 10 are fragments, 6 are partially preserved and 6 are complete. According to the color pattern it is possible to infer evidence of the potential presence of iron oxide, manganese, organic matter, and humidity in the soil. Lithostatic compression was identified in 5 of the specimens. Evidence of taphonomic feedback was also identified, all suggests to its recentness, in 1 fossil, so this specimen was in the intertidal zone or submerged long enough for sessile organisms to colonize. As the fossil remains of this locality were transported, reworked, exhumed and redeposited, so it may not be accurate to infer time to the taphonomic traits. In conclusion, according to the taphonomic analysis of the Itapeua beach samples, the skeletal remains may not belong to only one individual.