DRYOLESTIDA (MAMMALIA, CLADOTHERIA): PHYLOGENY AND CONSIDERATIONS ON SOUTH AMERICAN DRYOLESTID RELATIONSHIPS

CHORNOGUBSKY, L.

Teruel, España

Simposio; 10th Mesozoic Terrestrial Ecosystems Symposium; 2009

Universidad Autónoma de Madrid

Dryolestids are cladotherian mammals well recorded in the Jurassic of North America and Europe. They are also documented for the Cretaceous of Africa and South America. In South America, the chief findings are from the late Cretaceous of Patagonia and are represented mainly by isolated teeth, even though giving significant information about the evolution of this group in southern latitudes. The cusp homologies, particularly in the upper molars, of Dryolestida have been difficult to assert, but here a new interpretation is presented: the medio-labial cusp (median cusp of previous authors), present in several gondwanan Dryolestida (including Leonardus), is here interpreted as the stylocone, united to the paracone by a diversely developed median ridge, and isolated from the preparacista. The cusp at the end of the preparacrista in these genera (e.g., Mesungulatum, Donodon) is not the stylocone, but the parastyle. This interpretation is supported by the fact that in some holarctic dryolestids the stylocone is placed in a medial position, and still connected with the preparacrista. In light of this new homology hypothesis, a phylogenetic analysis including the Cretaceous South American and African genera of Dryolestida was carried out, showing a closer relationship among gondwanan dryolestids between them than with holarctic ones (this presented as a possibility by some authors): the African Donodon groups with the Patagonian Brandonia, Quirogatherium, and Mesungulatum, because of the presence of anterior cingulid and subequal para- and metaconid. Leonardus and Grobertherium are the sister group of the latter. The sister taxon of all the gondwanan dryolestids is Laolestes, a Dryolestidae from the late Jurassic of North America. The synapomorphies uniting them includes the presence of a well defined, complete median ridge, and the stylocone isolated from the preparacista. The holarctic Dryolestes and Portopinheirodon form a monophyletic group, sister to the former. These results allow concluding that the radiation of Dryolestida in southern landmasses is gondwanic rather than only South American, and that these gondwanan dryolestis are nested in a major group that includes genera traditionally included in Dryolestidae.