A taphonomic study of marine reptiles from the Upper Jurassic of Svalbard

Abstract

In this study the taphonomy of a collection of 25 marine reptiles from the Slottsmøya member, (Agardhfjellet Formation) Svalbard was investigated. The marine reptiles which include ichthyosaurs, plesiosaurs and pliosaurs were excavated during seven field seasons (2004- 2011). The specimens are divided into three preservation categories: articulated specimens, partly articulated specimens and disarticulated specimens. The specimens are discussed in relation to possible causes of death, the post mortem drift sink and refloat phase, the landing on the seabed, processes acting on the bones at the seabed, and a general discussion of the sedimentology in the Slottsmøya Member. Specimens from the locality are compared to the preservation of marine reptiles in the Oxford Clay and Posidonia Shale. The possible causes of death were difficult to assess although some of the carcasses possess teeth from other marine reptiles, which could be a possible evidence of scavenging or predation. Most of the specimens were exposed to a prolonged post mortem drift phase. The carcasses landed at the seafloor in different modes; seven of the specimens underwent a dorsal landing, three a lateral landing, four a ventral landing and one an anterior landing. In the rest of the skeletons the landing modes were difficult to interpret. There is low faunal diversity in the sediment, and few of the carcasses possess epifauna. Skeletal element orientation is observed in some of the studied skeletons and could be caused by current activity at the seabed. The exposed surface of certain skeletons is more eroded compared to the buried side, possibly caused by prolonged exposure on the seabed. The depositional environment of the Slottsmøya Member is interpreted as dysoxic shelf with alternation of shales, paper shale and silty beds which could make a firm substrate for the skeletons to rest on and this again could explain the high degree of partly articulated skeletons and few fully articulated skeletons. The TOC level is measured in the sediments and has a distinct peak of 4.2% TOC correlated with a peak in abundance of the marine reptiles.

In this study the taphonomy of a collection of 25 marine reptiles from the Slottsmøya member, (Agardhfjellet Formation) Svalbard was investigated. The marine reptiles which include ichthyosaurs, plesiosaurs and pliosaurs were excavated during seven field seasons (2004- 2011). The specimens are divided into three preservation categories: articulated specimens, partly articulated specimens and disarticulated specimens. The specimens are discussed in relation to possible causes of death, the post mortem drift sink and refloat phase, the landing on the seabed, processes acting on the bones at the seabed, and a general discussion of the sedimentology in the Slottsmøya Member. Specimens from the locality are compared to the preservation of marine reptiles in the Oxford Clay and Posidonia Shale. The possible causes of death were difficult to assess although some of the carcasses possess teeth from other marine reptiles, which could be a possible evidence of scavenging or predation. Most of the specimens were exposed to a prolonged post mortem drift phase. The carcasses landed at the seafloor in different modes; seven of the specimens underwent a dorsal landing, three a lateral landing, four a ventral landing and one an anterior landing. In the rest of the skeletons the landing modes were difficult to interpret. There is low faunal diversity in the sediment, and few of the carcasses possess epifauna. Skeletal element orientation is observed in some of the studied skeletons and could be caused by current activity at the seabed. The exposed surface of certain skeletons is more eroded compared to the buried side, possibly caused by prolonged exposure on the seabed. The depositional environment of the Slottsmøya Member is interpreted as dysoxic shelf with alternation of shales, paper shale and silty beds which could make a firm substrate for the skeletons to rest on and this again could explain the high degree of partly articulated skeletons and few fully articulated skeletons. The TOC level is measured in the sediments and has a distinct peak of 4.2% TOC correlated with a peak in abundance of the marine reptiles.