A thousand ways to die: exceptional preservation of sea stars on a paleosurface from La Meseta Formation (Eocene, Antarctic Peninsula)

PALOPOLO, E.; BREZINA, SOLEDAD; CASADIO, SILVIO; SANTILLANA, S.; GRIFFIN, MIGUEL

Puerto Madryn

Congreso; RCAPA; 2018

Asociación Paleontologica Argentina

A single paleosurface within the Cucullaea I Allomember (La Meseta Formation, Eocene) exposed in Marambio (Seymour) Island,Antarctica, yielded exceptionally well-preserved starfishes. This allomember was deposited in a sandy to muddy-sandy tidal flatenvironment, associated with lenticular densely packed shell-beds with erosive bases interpreted as the infilling of small tidal channels.Fourty-five specimens were identified and assigned to Zoroaster aff. Z. fulgens Blake and Zinsmeister. Individuals were preserved withcomplete discs, articulated proximal and distal parts of rays, and spines, a preservation considered exceptional for fossils in the ClassAsteroidea. Five posture categories were recognized among the sea stars: 1) resting position, with straight extended arms; 2)pseudocopulation posture, with superimposed discs and alternated arms; 3) trackeby currents, with curved and irregularly arranged arms; 4)escape posture, with one or two leading arms raised and the others curved downward; and 5) oral side up, with arms extended and slightlycurved upward. These postures are similar to those known for living starfishes. The exquisite preservation (i.e., almost all specimens lacksigns of disarticulation; with mosts spines, spinelets, pedicellariae and terminal ossicles in life position) allow to infer that the starfisheswere simultaneously killed and buried by a rapid event. This kind of exceptional preservation of starfishes is the third record in the worldand the first from Antarctica.