Paper No. 162-56
Presentation Time: 9:00 AM-6:30 PM
REANALYSIS OF THE ECOMORPHOLOGY OF TANYRHINICHTYS MCALLISTERI, A LONG ROSTRUMED ACTINOPTERYGIAN FISH, BASED ON NOVEL SPECIMENS FROM KINNEY BRICK QUARRY, NEW MEXICO
The Upper Pennsylvanian (Missourian) sediments of the Kinney Brick Quarry (KBQ) in New Mexico contain a diverse and well preserved fish assemblage from the Atrasado Formation. Actinopterygians and acanthodians are commonly collected from KBQ, with sharks and coelacanth rare but diverse within this assemblage. A unique fish known only from KBQ, Tanyrhinichthys mcallisteri is a small actinopterygian with an lengthened rostrum and elongated body. Previously, T. mcallisteri was known only from a single partially complete specimen. New work has recently revealed six new complete and partial specimens of this fish, enabling a more detailed morphological and ecological analysis which is presented here. The new specimens demonstrate variation in body size and rostrum length. This suggests that Tanyrhinichthys may have exhibited sexual dimorphism with males having longer rostrums and more gracile bodies and with females having proportionately shorter rostrums and more robust bodies. Previous descriptions suggested that Tanyrhinichthys was an ambush predator similar to the modern pike (Esox) and gar (Lepisosteus) based on its slender body and elongate rostrum. However, the new material indicates that it was a bottom feeder morphologically similar to the modern sturgeon (Acipenser). Like sturgeon, T. mcallisteri had a long anal fin set farther forward than the dorsal, a small, shallowly cleft caudal fin, an elongate, pointed rostrum, a small, subterminal mouth, small teeth, large lateral line scales, and an anteriorly deepened and caudally tapering body that would have allowed it to feed and swim in a manner similar to sturgeon. Two other long-rostrumed actinopterygians, an unnamed taxon from Indiana and Phanerorhynchus from the U.K., are known from the similarly-aged, Pennsylvanian coal deposits. Phanerorhynchus is similar to Tanyrhinichthys in fin morphology, mouth placement and size, and overall morphology, differing largely in its spine-like fin rays. The unnamed taxon from Indiana is known only from a skull bearing an elongate rostrum, which is similar in size and shape to the specimens of Tanyrhinichthys that exhibit sexually dimorphic male traits. Further analysis will show whether these represent a short-lived, freshwater Euramerican clade or convergent but widespread morphotype among Paleozoic fishes.