Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria - PubMed
- ️Thu Jan 01 2015
Vertebral Pneumaticity in the Ornithomimosaur Archaeornithomimus (Dinosauria: Theropoda) Revealed by Computed Tomography Imaging and Reappraisal of Axial Pneumaticity in Ornithomimosauria
Akinobu Watanabe et al. PLoS One. 2015.
Abstract
Among extant vertebrates, pneumatization of postcranial bones is unique to birds, with few known exceptions in other groups. Through reduction in bone mass, this feature is thought to benefit flight capacity in modern birds, but its prevalence in non-avian dinosaurs of variable sizes has generated competing hypotheses on the initial adaptive significance of postcranial pneumaticity. To better understand the evolutionary history of postcranial pneumaticity, studies have surveyed its distribution among non-avian dinosaurs. Nevertheless, the degree of pneumaticity in the basal coelurosaurian group Ornithomimosauria remains poorly known, despite their potential to greatly enhance our understanding of the early evolution of pneumatic bones along the lineage leading to birds. Historically, the identification of postcranial pneumaticity in non-avian dinosaurs has been based on examination of external morphology, and few studies thus far have focused on the internal architecture of pneumatic structures inside the bones. Here, we describe the vertebral pneumaticity of the ornithomimosaur Archaeornithomimus with the aid of X-ray computed tomography (CT) imaging. Complementary examination of external and internal osteology reveals (1) highly pneumatized cervical vertebrae with an elaborate configuration of interconnected chambers within the neural arch and the centrum; (2) anterior dorsal vertebrae with pneumatic chambers inside the neural arch; (3) apneumatic sacral vertebrae; and (4) a subset of proximal caudal vertebrae with limited pneumatic invasion into the neural arch. Comparisons with other theropod dinosaurs suggest that ornithomimosaurs primitively exhibited a plesiomorphic theropod condition for axial pneumaticity that was extended among later taxa, such as Archaeornithomimus and large bodied Deinocheirus. This finding corroborates the notion that evolutionary increases in vertebral pneumaticity occurred in parallel among independent lineages of bird-line archosaurs. Beyond providing a comprehensive view of vertebral pneumaticity in a non-avian coelurosaur, this study demonstrates the utility and need of CT imaging for further clarifying the early evolutionary history of postcranial pneumaticity.
Conflict of interest statement
Competing Interests: The authors have declared that no competing interests exist.
Figures

A, ventral; B, ventral oblique view; C, left lateral; D, right lateral; E, dorsal; F, anterior; G, posterior view.

A–D, select transverse sections; E, midsagittal section; F, frontal section. Dashed lines and associated letters indicate location and letter designation of CT image slices.

A, left lateral view; B, right lateral view; C–G, select transverse sections; H, midsagittal section. Dashed lines and associated letters indicate location and letter designation of CT image slices.

A, left lateral view; B, right lateral view; C–E, select transverse sections; F, midsagittal section. Dashed lines and associated letters indicate location and letter designation of CT image slices.

A, left lateral view; B, right lateral view; C, D, select transverse sections; E, midsagittal section. Dashed lines and associated letters indicate location and letter designation of CT image slices.

A, left lateral view; B, right lateral view; C–E, select transverse section; F, midsagittal section. Dashed lines and associated letters indicate location and letter designation of CT image slices.

A, left lateral view; B, dorsal view; C, D, select transverse sections; E, frontal plane section; F, G, select sagittal sections. Dashed lines and associated letters indicate location and letter designation of CT image slices.

A, right lateral view; B, dorsal view of Nqwebasaurus. C, left lateral view; and D, right lateral view of Pelecanimimus. Numbers denote cervical vertebral number.

A, proximal caudal vertebrae of Senzhousaurus (NGMC-97-4-002), oblique right lateral view; B, cervical vertebrae 7, 8 of Gallimimus (ZPAL MgD-I/94), left lateral view; C, D, left and right lateral views of cervical vertebra and dorsal vertebrae 1, 2 of Gallimimus (ZPAL MgD-I/94) respectively; E, apneumatic dorsal vertebrae 7–10 of Gallimimus (ZPAL MgD-I/94), right lateral view; F, sacrum of Gallimimus (ZPAL MgD-I/94), left lateral view; G, articulated sacral vertebrae of Gallimimus (ZPAL MgD-I/29); H, proximal caudal vertebrae of Gallimimus (ZPAL MgD-I/8), left lateral view. Scale bar equals 3 cm.

A, cervical vertebra 6, right lateral view; B, dorsal vertebra 7, right lateral view; C, dorsal vertebra 10, right lateral view.

Bolded taxonomic names indicate taxa inspected in this study. The common theropod pattern and graphical representation of vertebral pneumaticity is derived from [13]. Colored boxes indicate strong evidence of pneumatization corresponding to the vertebra type and region. Half-filled boxes denote variable pneumatization with respect to the common theropod pattern. “A” signifies ambiguous evidence of pneumatization. “?” indicates no specimen available for the vertebra type and region.
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This study was funded by the Richard Gilder Graduate School at the American Museum of Natural History (AW, MELG), Kalbfleisch Fellowship and Gerstner Scholarship (JNC) administered by the Richard Gilder Graduate School at the American Museum of Natural History; NSF Graduate Research Fellowship (SLB, AW), NSF DEB 1110357 (SLB), Columbia University (SLB), Royal Society Research Grant RG130018 (SLB), Marie Curie Career Integration Grant FP7-PEOPLE-2013-CIG 630652 (SLB), Department of Science and Technology and National Research Foundation of South Africa Centre of Excellence in Palaeosciences grants in aid of research (JNC), Friedel Sellschop Award through the University of the Witwatersrand (JNC), Palaeontological Scientific Trust (PAST) and its Scatterlings of Africa Programmes (JNC), National Research Foundation of South Africa Incentive Funding for Rated Researchers (JNC), and the American Museum of Natural History Division of Paleontology (AW, MELG, SLB, JC, AD, MAN).
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