Exceptional preservation of starfishes in a hyperpycnal flow deposit from the Antarctic Eocene

PALÓPOLO, EVANGELINA E.; CASADIO, SILVIO; GRIFFIN, MIGUEL

Madrid

Congreso; The 80th Anniversary of Efremov ́s Taphonomy; 2022

Taphonomy Working Group (TWG)

A single paleosurface within the La Meseta Formation (Eocene), exposed in Seymour Island, Antarctica, yielded exceptionally well-preserved starfishes. The fossils –assigned to Zoroaster marambioensis (Forcipulatida, Zoroasteridae)– were preserved with complete discs, articulated proximal and distal parts of rays, and spines, a preservation considered exceptional. Five burial posture categories were recognized among the starfishes on the paleosurface: 1) resting position; 2) pseudocopulation posture; 3) tracked by currents; 4) escape posture; and 5) oral side up. These postures are similar to those known for living starfishes. The exquisite preservation (i.e., almost all specimens lack signs of disarticulation; with most spines, spinelets, pedicellariae and terminal ossicles in life position) suggests that the starfishes were simultaneously killed and buried. The paleosurface with zoroasterids is at the top of a massive fine sandstone bed, and they were covered by laminated fine sandstones. Individual laminae are millimeter thick and lie intercalated between thin levels with abundant carbonaceous material and even charcoal (Fig.1). This observation is consistent with a facies related to flow lofting of a hyperpycnal current,