New Mexico Geological Society Annual Spring Meeting — Abstracts

New finds of fossil fish in the Tucumcari basin include articulated postcranial material from an indeterminate redfieldiid and abundant Arganodus tooth-plates (Los Esteros Member, Santa Rosa Formation); two skulls and associated postcranial material from a new paleonisciform and several basisphenoids from a newI coelacanth (Bull Canyon Formation); and articulated complete Semionotus (Redonda Formation). The redfieldiid is a crushed body section displaying numerous vertical scale rows immediately anterior to the origin of the caudal lobes. The Arganodus reported here indicates a more extensive distribution for this taxon than has previously been reported in the Tucumcari basin.

The paleonisciform is different than previously reported actinopterygians from the Upper Triassic of North America which, with the exception of Tanaocrossus and Turseodus, are all subholostean-grade taxa. The new form is characterized by paired, borad frontals and a single median parietal to which the dermopterotics are fused. The orbital series is posterior to the presumed position of the nasals and includes at least three infraorbitals, a postorbital and a suborbital. Four extrascapulars are present in a transverse row, and the operculum is directly dorsal to the suboperculum, the former being about twice as large as the latter. The dimensions of the cleithrum cannot be determined, but the branchiostegal is well preserved, and the branchiostegal series consists of 10 segmented rays. The postcranium is represented by articulated body sections displaying overlapping scales devoid of ornamentation. Cranial fragments of a coelacanth include several partial basisphenoids which are similar to Chinlea. These elements differ from C. sorensoni in possessing a much narrower antotic process, more
rounded sphenoid condyles and a deeper cleft between the sphenoid condyles. These specimens represent a new taxon, probably a new species of Chinlea.

Semionotus has been previously reported from the Kayenta Formation and the owl Rock Member of the Chinle Formation in the Four Corners area and is well known from Norian to Bajocan formations of the Newark Supergroup. The Redonda specimens occur as a mass-mortality assemblage and differ from S. kanabensis and Newark forms in that the origins of the dorsal and anal fins are consistently 2-3 vertical scale rows anterior to those of the Newark forms, and the total number of vertical scale rows is 26-29. While this departure may be a function of ontogeny (the Redonda specimens are juveniles), comparison with a similar size specimen and mature individuals from the Hartford Basin of Connecticut indicates these characters to be consistent in the Newark specimens. Poor skull preservation prevents the
identification of the Redonda Semionotus at the specific level, and recognition of semionotoid species based solely on meristic characters is very tenuous, as these characters vary significantly even within a supposed species or "species group."