The first non-therian dryolestoid from Antarctica

MARTINELLI, A. G.; CHORNOGUBSKY, L.; ABELLO, M. A.; GOIN, F. J.; REGUERO, M.

Auckland

Congreso; XXXIII Scar Biennial Meetings; 2014

The Scientific Committee on Antarctic Research

The Early Eocene strata (Cucullaea I Allomember) of La Meseta Formation of Seymour Island, Antarctic Peninsula contain a diverse mammalian assemblage including gondwanatherians, marsupials, pilosans, litopterns and astrapotheres. This composition reflects a strong paleogeographical link between Paleogene faunas of Patagonia and West Antarctica. A small isolated tooth, MLP 91-II-4-3, found at IAA 1/90, with zalambdodont morphology was originally interpreted as a possible bat or ?insectivore?, although after subsequent comparisons with therians it was assigned to Mammalia incertae sedis, with possible placental affinities. It was interpreted as a M3 with zalambdocone, mesiostyle (parastyle), stylocone, distostyle (metastyle), and pre- and post-cingulum. Zalambdodont morphology is convergent in several mammalian groups and the evaluation of an isolated tooth could generate conflictive hypotheses. An alternative interpretation for the primary homology of MLP 91-II-4-3 is the base of the present contribution. Based on it, MLP 91-II-4-3 is considered as a right lower molar of a new taxon of non-therian Dryolestoidea, perhaps related to, or member of the clade Meridiolestida. The crown is dominated by three cusps and a distolingual talonid cusp. The protoconid is flanked mesially by the paracristid and distally by the metacristid, which reach the paraconid and metaconid, respectively. Both crests form an acute angle and there is no distinctive notch at mid-way. The labial wall of the protoconid is convex while the lingual face is slightly concave. The paraconid is worn out, and lower than the other cusps. The flexid is notorious and forms a ?v? shaped notch between paraconid and metaconid. The metaconid and protoconid are similar in height. The metaconid connects by means of a crest the talonid. The talonid has a hook-like disto-lingual projection with a large cusp. Its relationships with the distal cingulum are obscured due to preservation. The mesial cingulum starts as a fait line below the paraconid and gets wider ventrolabially. Due to preservation it is unknown if the cingulum continues on the labial slope of the protoconid. Information on root morphology is sparse. There is a portion of root preserved below the paranoid-protoconid, which seems to be transversely wide. This crown morphology resembles the meridiolestidan Barberenia from the Late Cretaceous of Patagonia. Meridiolestidan dryolestoids are a conspicuous component of the Late Cretaceous mammalian association of Patagonia. The group survived the Cretaceous/Paleogene boundary and one taxon (Necrolestes) persisted until the early Miocene of Patagonia. If the taxonomic interpretation we present here is correct, MLP 91-II-4-3 constitutes the second Mesozoic lineage surviving in the Eocene of Antarctica and certainly represents a new component of the taxonomically diverse mammalian assemblage of La Meseta Formation.