ANTARCTIC FOSSIL BRYOZOANS: AN UNEXPECTED ADDITION (ENCRUSTING CHEILOSTOME, EOCENE, USHUAIA AND SEYMOUR ISLAND)

Many living bryozoans from Antarctic waters have been reported over the past half-century by workers from Rogick to Moyano. Fossil bryozoans are much rarer, known from only few specimens from Lower Devonian (Ohio Range), Lower Cretaceous (Alexander Island), and several Cenozoic horizons/localities (scattered around the continent's margins), but from many colonies from the Eocene (Seymour Island) monographed by Hara '01. These last are especially noteworthy for their abundant massive/globular, multilaminar colonies, both cyclostomes and cheilostomes. All these fossils are curated in established taxonomic collections.

Obtaining paleobiological materials from Antarctica poses challenges more severe than collecting elsewhere. One unexpected problem is the existence of potentially significant fossil bryozoans housed in non-standard repositories not normally considered part of the usual systematic resource base.

In sharp contrast to both the dominant massive colonies and the normal repositories is a fossil encrusting bryozoan, probably from the Eocene shallow-marine clastics of Seymour Island, on the Argentine Navy base (Prefectura Naval, Armada Argentina) at the east end of Ushuaia (Tierra del Fuego, southernmost Argentina).

This bryozoan is on the bottom (floor-level) shelf of a glass cabinet in the small (“Darwin's”) room at the south end of the upper floor of the southwest wing (Pabellon 4) of the Presidio (military prison) now made into the Ushuaia Maritime Museum (Museo Marỉtimo de Ushuaia), which houses exhibits on the navy's history, especially its role in polar exploration. The bryozoan is part of a fossil display (large pelecypods, filled crab burrows, flat echinoids) retrieved by Argentine ships some years ago.

The bryozoan in question is a thin, unilaminar sheet, encrusting half of a flat echinoid (sand-dollar). Other echinoids alongside are clean and smooth-surfaced. Zooecia vary from equidimensional to 3 times longer than wide; lateral walls appear thick, and slightly swollen (low spines?) at zooecial corners; frontal/top is open (opesium) with no skeletal shelf (cryptocyst) within it. Because from so far south, this likely represents an endemic taxon (possibly undescribed),but overall resembling Conopeum Gray 1848 or Eokotosokum Taylor & Cuffey 1992, thus a membraniporoid or malacostegan anascan cheilostome.