DENTAL HOMOLOGY OF THE TERTIARY SOUTH AMERICAN UNGULATES

GELFO J. N.

La Plata

Congreso; IX Congreso de la Sociedad de Ciencias Morfológicas y 6ta Jornadas sobre educación; 2007

The native ungulates of the Cenozoic of South America, are an endemic and completely extinct group form by several orders like the Notoungulata, Litopterna (including or not Notopterna), Astrapotheria, Pyrotheria and Xenungulata. In order to search for their phylogenetic relationships, one of the major difficulties are the correct identification of the primary homologies of teeth. All the specific taxa are defined due to their teeth characters, but since more than a century, several researchers have been using different names for homologous characters, and also the same denomination for non homologous one. This nomenclature proliferation, plus the precarious nature of the fossil record, went against the few intent to test the probably monophily of these ungulates.  With the aim of discuss the fit of the dental nomenclature often used to the homology concept, representative remains of lower molars of these orders were analyzed (collections from MLP and MACN) taken in to account the similitude and conjunction criteria.  The characters here discussed due to they ambivalent use are:  (1) protolophid and protocristid used respectively for the lophid and cristid than join together the protoconid and the metaconid; (2) metalophid often used as synonym of protolophid but also for other structures; (3) paralophid and paracristid, defined for the lophid and crsitid that goes mesio-lingual from the protoconid; (4) hypolophid for the lophid that join together the hypoconid and the entoconid but excluding the hypoconulid; (5) entolophid por the lophid that runs from the entoconid to the cristid obliqua mesial to the hypoconid; and (6) paraconid and neoparaconid for the cusp mesial to the metaconid. Of the present analysis it could be concluded that the homonyms and heteronyms for lophids and cristids should be avoided. First, a topographic criteria should be followed, nominating the teeth accident due to their definition free of contradiction from the Cope and Osborn proposal.  New names (e.g. neoparaconid or entolphid) should be only used after a phylogenetic analysis, always that the topographic similitude belongs to an homoplasic character and no presupposing the direction of the evolutionary change.