Abstract

A growth series is described for a new species of Ceratocara Ramskold, 1991, C. argentina, from the Upper Ordovician (Caradoc) part of the Las Aguaditas Formation, near Jachal in San Juan Province, Argentine Precordillera. Another new species of Ceratocara. C. shawi, is described from the Middle Ordovician (lower Chazy) Crown Point Formation of New York. A phylogenetic analysis is presented for these species, other well-known Ordovician species of Ceratocara, and some Ordovician species of Ceratocephala, with Ceratocephalina tridens Whittington, 1956, as outgroup. The analysis presented supports the monophyly of both Ceratocara and Ceratocephala Warder, 1838, their divergence having occurred by the middle Arenig. The ontogenies of the Ceratocara species from Argentina and New York, complete from protaspid to holaspid growth stages, are some of the best preserved odontopleurid ontogenies described to date. Material of Ceratocephala triacantheis Whittington and Evitt, 1954, from the Crown Point Formation of the Chazy Group of New York, is discriminated from that of Ceratocara shawi.