PALEOBIOLOGY OF HUAYQUERIANA, A LATE MIOCENE LITOPTERN FROM WESTERN ARGENTINA: INTERPRETING CONFLICTING SIGNALS FROM MORPHOLOGICAL ATTRIBUTES

FORASIEPI, ANALÍA M.; SCHMIDT, GABRIELA I.; HERNANDEZ DEL PINO, S.; GROHÉ, C.; MACPHEE, R.D.E.; AMSON, E.

Salt Lake City, Utah

Otro; SVP 76TH ANNUAL MEETING; 2016

IANIGLA-PV 29, a well preserved skull of the macraucheniine litoptern Huayqueriana from the Huayquerías Formation (L. Miocene), presents several morphological and paleobiological puzzles.Nasal apparatus: The highly derived dorsal positioning of the macraucheniine external nares has provoked discussion for more than a century. MicroCT scanning of IANIGLA-PV 29 reveals simplified turbinate architecture and an air passageway oriented perpendicular to, rather than aligned with, the palate as inmost mammals (including elephants). The primitive nasal vestibule is present, but only as a blind diverticulum within the rostrum. To a degree these innovations recall conditions in cetaceans and some other aquatically adapted taxa, but macraucheniine limb skeletons lack obvious adaptations for aquaticlife. Orientation of the lateral semicircular canal relative to the skull base is ~ 26°, indicating that in life the head was habitually oriented much as in modern horses. If there was a proboscis, it would have been positioned frontally, not dorsally as in many reconstructions.Endocast: Although the identity of the pathways of certain cranial nerves in litopterns have been disputed, conditions in Huayqueriana conform to those in other placentals. The orbitotemporal canal runs well below the rhinal fissure, along the lateroventral aspect of the piriform lobe instead of more dorsally. Nofunctional consequences for this rearrangement are evident.Body mass: Making size estimates for fossil taxa, especially those having no close living relatives, presents many difficulties. For IANIGLA-PV 29, conventional estimators, especially those employing dental measurements, yielded highly conflicting results (mean, 400 kg; range 154-721 kg, prediction error>25%). Our preferred estimate of ~250 kg (prediction error ~6%) is based on an alternative approach utilizing centroid size of 36 3D cranial landmarks.Longevity and diet: Advanced tooth wear implies that IANIGLA-PV 29 was senile at death. However, cementum line counts on a sectioned M2 are consistent with a 10-11 year lifespan, much shorter than its body mass would suggest. The L. Miocene flora of western Argentina was dominated by xerophytic plants with thick foliar cuticles and hard-shelled fruits to combat desiccation, and perhaps excessive wear reflects a very abrasive diet. Oddly, unlike the vast majority of Neogene SANU lineages, litopterns did not develop euhypsodonty. There is no decisive evidence for the proposition that Huayqueriana (or any other litoptern) was a foregut fermenter.