A CT-based revised description and phylogenetic analysis of the skull of the basal maniraptoran Ornitholestes hermanni Osborn 1903

Ornitholestes hermanni was one of the first small-bodiedtheropods named in the 1900s. It is known from a singlespecimen discovered during the American MuseumExpedition of 1900, at the Jurassic Morrison Formationsite known as Bone Cabin Quarry, in Wyoming. It haslong been a critical taxon in understanding the evolutionof the Coelurosauria, the clade that includestyrannosauroids, living birds, and their commonancestors. The holotype specimen comprises a nearlycomplete skull and most of a postcranial skeleton. Despitethis abundant material, its precise phylogeneticrelationships have been difficult to determine. This is inpart due to the intense mediolateral crushing of the skulland the relatively generalized postcranial anatomy. Herewe present the results of a micro- computed tomographybasedinvestigation of the cranial anatomy and subsequentincorporation of these data into a phylogenetic data matrixdesigned to test coelurosaurian interrelationships. We findrobust evidence across different optimality criteria thatOrnitholestes is the earliest-branching oviraptorosaurianspecies. Using parsimony as an optimality criterion, thisphylogenetic position is supported by 14 unambiguoussynapomorphies, including: a short frontal process of thepostorbital; short, deep, and pendant paroccipitalprocesses; a large mandibular foramen; an anterodorsallyoriented dentary symphysis; a surangular that is longerthan the dentary; short maxillary and dentary tooth rows;and procumbent dentary and premaxillary teeth. UsingBayesian fossilized birth-death models, we find highposterior probabilities (>.99) that Ornitholestes is theearliest-branching oviraptorosaurian species. Weadditionally find strong support in both analyses that thesuperficially bat-like and possibly arborealscansoriopterygids are an early branching lineage withinOviraptorosauria. This new phylogenetic position fills in apersistent ghost lineage in Oviraptorosauria and confirmsthat scansoriopterygids are basally branchingoviraptorosaurians that represent an independent origin ofaerial habits, separate from those of dromaeosaurs andavialans.Fil: Chapelle, Kimberley E.. American Museum of Natural History; Estados UnidosFil: Norell, Mark. American Museum of Natural History; Estados UnidosFil: Ford, David P.. University of the Witwatersrand; SudáfricaFil: Hendrickx, Christophe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico - Tucumán. Unidad Ejecutora Lillo; ArgentinaFil: Radermacher, Viktor J.. University of Minnesota; Estados UnidosFil: Balanoff, Amy. University Johns Hopkins; Estados UnidosFil: Zanno, Lindsay E.. North Carolina Museum of Natural Sciences; Estados UnidosFil: Choiniere, Jonah N.. University of the Witwatersrand; Sudáfrica81st Annual Meeting of the Society of Vertebrate PaleontologyMc LeanEstados UnidosSociety of Vertebrate Paleontolog

BP/1/4779 left endosseous labyrinth

Surface file of the left labyrinth from BP/1/477

Data from: Ontogeny of the Massospondylus labyrinth: implications for locomotory shifts in a basal sauropodomorph dinosaur

Ontogeny is a vital aspect of life history sometimes overlooked in palaeontological studies. However, the changing geometry of anatomical structures during growth can be informative regarding ecological and functional reconstructions. The inner ear, or labyrinth, is an ideal ontogenetic study system because it has a strong functional signal in its morphology that is linked to locomotor mode. Yet almost nothing is known about labyrinth development in dinosaurs. We quantified labyrinth scale and geometry through ontogeny in the Early Jurassic dinosaur Massospondylus carinatus, which has an exceptional fossil record and is hypothesized to have undergone a gait change, from quadrupedal juvenile to bipedal adult. To test whether this putative locomotor shift is reflected in labyrinth morphology, computed microtomography (μCT) and propagation phase‐contrast synchrotron radiation microtomography (PPC‐SRμCT) were used to obtain labyrinths from eight specimens, ranging from near‐hatchling to adult. Labyrinths grow substantially but scale with slight negative allometry compared to skull length throughout ontogeny, the first time this has been documented in dinosaurs. Geometric morphometric analysis of the labyrinth using a sliding semilandmark approach shows some morphological change through ontogeny, but little evidence supporting a locomotor shift. These results have implications for our understanding of sauropodomorph development and provide a better understanding of dinosaur locomotory evolution

BP/1/5231 left endosseous labyrinth

Surface file of the left labyrinth from BP/1/523

BP/1/4998 left endosseous labyrinth

Surface file of the left labyrinth from BP/1/499

Supplementary Figure S2

FIG. S2. Extreme shapes from PC axes overlain to demonstrate geometry change in lateral (left), dorsal (middle) and posterior (right) views. A, PC1. Negative values are in green and positive values in red. B, PC2, the axis that shows ontogenetic shape change. Colour scheme follows figure 3, with negative values in dark blue and positive values in light blue. C, PC3. Colour scheme follows A

Supplementary Figure S1

The landmarking method employed in this study. A, semilandmarks are placed along the exterior and interior margins of each semicircular canal, additionally capturing the geometries of the crus communis as well as the anterior and lateral ampullae. B, semilandmark sequences are resampled in R to 14 equally-spaced points along each margin

BP/1/4934 left endosseous labyrinth

Surface file of the left labyrinth from BP/1/493

BP/1/5241 right endosseous labyrinth

Surface file of the right labyrinth from BP/1/524

BP/1/4930 left endosseous labyrinth

Surface file of the left labyrinth from BP/1/493