A survey of osteoderm histology and ornamentation among Crocodylomorpha: A new proxy to infer lifestyle?

Abstract

Osteoderms of eight extant and extinct species of crocodylomorphs are studied histologically and morphologically. Most osteoderms display the typical “crocodilian” structure with a woven‐fibered matrix surrounded by an upper and a lower parallel fibered matrix. The dorsal ornamentation of those specimens consists of a pit‐and‐ridge structure, with corresponding remodeling mechanisms. However, an osteoderm of Iberosuchus, studied here for the first time, differs in being nearly devoid of ornamentation; moreover, it shows strong bundles of straight Sharpey's fibers perpendicular to the surface in its lateral and dorsal walls, along with a rough plywood‐like structure in its basal plate. This suggests that this osteoderm was more deeply anchored within the dermis than the other osteoderms studied hitherto. This peculiar structure might have been linked to a terrestrial ecology and a specific thermoregulation strategy. Some other notosuchians in our sample do not exhibit ornamentation on their osteoderms, as opposed to neosuchians. Considering current interpretations of osteoderm function(s) in crocodilians, our observations are discussed in reference to possible ecophysiological peculiarities of Notosuchia in general, and Iberosuchus in particular.

Description and phylogenetic relationships of a new species of Torvoneustes (Crocodylomorpha, Thalattosuchia) from the Kimmeridgian of Switzerland

“… Clarac et al (2017) presented evidence that the evolution of ornamentation in pseudosuchians is influenced by both natural selection and Brownian motion. The study shows that heavy ornamentation is present in pseudosuchians with semi-pelagic lifestyle and linked to basking for animals with low mobility, these results are backed by findings from Pochat-Cottilloux et al (2022) . Therefore, the loss of ornamentation in Thalattosuchia may rather be linked to an increasingly pelagic lifestyle than directly to hydrodynamic efficiency.…”

The neuroanatomy and pneumaticity of Hamadasuchus (Crocodylomorpha, Peirosauridae) from the Cretaceous of Morocco and its paleoecological significance for altirostral forms

“…This would be linked with the hypotheses mentioned above, such as improved resonance and better aerial sound pickup or the impact on the buoyancy of such structures. As a result, Hamadasuchus displaying average values of sinus volume would be associated with a terrestrial lifestyle (but with some semi‐aquatic affinities), which was also recently highlighted using an independent histological approach (Pochat‐Cottilloux, Martin, et al, 2023 ). However, these results come only by taking into account the sinus structure and volume which is still poorly understood and will have to be compared with other proxies to reach a more robust answer.…”

A peirosaurid mandible from the Albian–Cenomanian (Lower Cretaceous) of Algeria and the taxonomic content of Hamadasuchus (Crocodylomorpha, Peirosauridae)

“…(2014) and Geroto & Bertini (2019) (and references therein; Appendices S1, S2; Pochat‐Cottilloux et al . 2023 b ) in order to sample as many notosuchian taxa as possible. Dibothrosuchus elaphros Simmons, 1965 was used as the operational outgroup and Hamadasuchus rebouli was separated into two different operational taxonomic units (OTUs) because of the differences observed between the specimens assigned to it (see Discussion and Appendix S1).…”

“…The 3D surface model is available in Dryad (Pochat‐Cottilloux et al . 2023 a ; the video was made and rendered using Blender v.2.91).…”