Vertebral microanatomy in squamates: structure, growth and ecological correlates

Abstract

The histological study of vertebrae in extant squamates shows that the internal vertebral structure in this group differs from that of other tetrapods. Squamate vertebrae are lightly built and basically composed of two roughly concentric osseous tubes -one surrounding the neural canal and the other constituting the peripheral cortex of the vertebra -connected by few thin trabeculae. This structure, which characteristically evokes that of a tubular bone, results from a peculiar remodelling process characterised by an imbalance between local bone resorption and redeposition; in both periosteal and endosteo-endochondral territories, bone is extensively resorbed but not reconstructed in the same proportion by secondary deposits. This process is particularly intense in the deep region of the centrum, where originally compact cortices are made cancellous, and where the endochondral spongiosa is very loose. This remodelling process starts at an early stage of development and remains active throughout subsequent growth. The growth of squamate centra is also strongly asymmetrical, with the posterior (condylar) part growing much faster than the anterior (cotylar) part. Preliminary analyses testing for associations between vertebral structure and habitat use suggest that vertebrae of fossorial taxa are denser than those of terrestrial taxa, those in aquatic taxa being of intermediate density. However, phylogenetically informed analyses do not corroborate these findings, thus suggesting a strong phylogenetic signal in the data. As our analyses demonstrate that vertebrae in snakes are generally denser than those of lizards sensu stricto, this may drive the presence of a phylogenetic signal in the data. More comprehensive sampling of fossorial and aquatic lizards is clearly needed to more rigorously evaluate these patterns.

Microanatomical and Histological Features in the Long Bones of Mosasaurine Mosasaurs (Reptilia, Squamata) – Implications for Aquatic Adaptation and Growth Rates

“…However, some differences are observed in the tightness of the spongiosa; it is tighter (i.e., more numerous trabeculae but smaller intertrabecular spaces) in UCMP 152554 than in UCMP 152664 (UCMP: University of California Museum of Paleontology, University of California, Berkeley, California, USA). This difference is consistent with the increase in number but decrease in the size of cavities with increased size of the individual, a condition also observed in extant squamates and hydropelvic mosasauroid vertebrae [12], [30].…”

Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia, Afrotheria)

“…It cannot be determined if this feature is a result of ontogeny (as has been observed in squamate vertebrae; cf. [52]) or a characteristic of this taxon.…”

Amniote vertebral microanatomy - what are the major trends?

“…Both conventional and synchrotron X-ray microtomography were used: (1) highresolution computed tomography (Gephoenix|X-ray v|tome|xs 180 and 240; reconstructions performed using datox/res software) at the Steinmann-Institut, University of Bonn (Germany) and (2) third-generation synchrotron microtomography (Tafforeau et al, 2006) at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) at the ID17 and ID19 beam lines (reconstruction performed using filtered backprojection algorithm with the ESRF PyHST software). Some additional sections, either histological thin sections or virtual thin sections, come from previous studies (Houssaye et al, 2010Hayashi et al, 2013). observ.…”

“…Germain & Laurin, 2005;Kriloff et al, 2008;Quemeneur, de Buffrénil & Laurin, 2013) but also, more recently, in vertebrae of mammals to analyse differences linked with the secondary adaptation to an aquatic life (Dumont et al, 2013), and in squamates (Houssaye et al, 2010;2013). These signals have previously been investigated to some degree in amniote long bones (e.g.…”