Pachycormiformes from the Upper Jurassic of the Neuquen Basin, southern South America-Present state of knowledge

GOUIRIC CAVALLI, SOLEDAD

Viena

Congreso; 6th International Meeting on Mesozoic Fishes. Diversification and Diversity Patterns; 2013

Universitätt Wien and Naturhistorisches museum Wien

PACHYCORMIFORMES FROM THE UPPER JURASSIC OF THE NEUQUEN BASIN, SOUTHERN SOUTH AMERICA. PRESENT STATE OF KNOWLEDGE Soledad Gouiric Cavalli1 1 CONICET, División Paleontología Vertebrados, Museo de La Plata, Facultad de Ciencias Naturales y Museo. UNLP, Paseo del Bosque s/n B1900FWA, La Plata, Argentina; e-mail: sgouiric@fcnym.unlp.edu.ar The Mesozoic Pachycormiformes comprise a single marine family, Pachycormidae, ranging in age from the Early Jurassic to Late Cetaceous. The monophyly of the group is widely accepted. Pachycormiformes includes middle-sized fishes (e.g., Orthocormus, Hypsocormus) as well as large fishes (e.g., Asthencormus, Leedsichthys). The group is mainly known in Europe; the better-preserved and mostly studied specimens come from the Upper Jurassic lithographic limestones of Solnhofen (Germany) and Cerin (France). Pachycormiformes are relatively poorly known in North America and Asia and its knowledge in southern South America is really scarce, only few fragmentary materials from several localities in Chile and Argentina were reported. The pachycormids are easily recognized because they possess a big and furcated caudal fin with many rays which have long bases; rostrodermethmoid forming the anterior part of the mouth (with the exception of Martillichthys); absence of supraorbitals; demosphenotic closing the dorsal margin of the orbit; several infraorbitals; two big suborbitals; supramaxilla posterodorsally to maxilla; vertebral column formed by a persistent notochord; most of the members have pectoral fins with a characteristic shape (scythe-like) which rays distally segmented and with a particular bifurcation pattern (y-type); most of pachycormids have a temporal boss and intermuscular bones (supraneurals) and hypural plate in the caudal skeleton. If they have scales are tiny and with reduced (or even absent) ganoine. The phylogenetic position of the group is still in debate, this is particularly due to differences in the interpretation of some structures and due to incomplete knowledge of several specimes (e.g., large pachycormids are poorly known). Several new and informative materials were recently recovered from different localities at the Neuquen Basin of Argentina. The goal of this contribution is to extend the knowledge of southern South America pachycormids, analyzing the morphological characters of Argentinian specimens.