Bone histology of Iberosuchus macrodon (Sebecosuchia, Crocodylomorpha)

Abstract

Iberosuchus macrodon is a Cenozoic crocodyliform interpreted as a terrestrial, cursorial form. To assess whether this adaptation was accompanied by a high growth rate and an elevated resting metabolic rate (two features commonly attributed to several terrestrial Triassic Crocodylomorpha based on histology), we studied bone histology in the femora of two specimens attributed to I. macrodon. Beyond this question is the broader problem of the possible survival to the Cretaceous‐Palaeogene extinction event of tachymetabolic sauropsids other than birds. At mid‐diaphysis, bone cortices in Iberosuchus are made of a parallel‐fibred tissue that turns locally to true lamellar bone. Cortical vascularization consists of simple longitudinal canals forming a network of medium density. The spacing pattern of conspicuous lines of arrested growth suggests asymptotic growth for Iberosuchus. This general histological structure prevails also in the metaphyseal region of the bones. It is basically similar to that encountered in certain large lizards adapted to active predation, the Varanidae and the Teidae. In one of the two Iberosuchus femora, however, an intracortical meniscus made of a tissue displaying a global radial architecture occurs in the region of the fourth trochanter. Histologically, the latter can be interpreted either as compacted spongiosa or as a fibro‐lamellar complex with a gross radial orientation, a tissue corresponding to fast periosteal apposition. These observations suggest that Iberosuchus basically had a slow, cyclical growth indicative of an ecto‐poikilothermic, lizard‐like, resting metabolic rate. However, it might also have retained a limited capacity for fast periosteal accretion in relation to local morphogenetic requirements as, for instance, the development of crests or trochanters.

Evidence for heterochrony in the cranial evolution of fossil crocodyliforms

“…Cubo et al . ), which would allow further investigation on the action of peramorphic processes on the evolution of this group. Moreover, the action of a single evolutionary process on morphological structures is expected to be rare (Alberch et al .…”

First dinosaur from the Isle of Eigg (Valtos Sandstone Formation, Middle Jurassic), Scotland

“…The histology of NMS G.2020.10.1 is most similar to that of dinosaurs, which typically have highly vascularised fibrolamellar zonal bone with LAGs (Horner et al 1999; Padian et al 2004; Padian & Lamm 2013). In contrast, crocodylomorphs and pseudosuchians more commonly show lamellar-zonal bone with lower vascularity and less fibrolamellar tissue (de Ricqlès et al 2003; de Andrade & Sayão 2014;Sayão et al 2016;Cubo et al 2017), whereas pterosaurs have extensive medullary cavities with extremely thin cortical walls (de Ricqlès et al 2000;Padian et al 2004).…”

“…NMS G.2020.10.1 differs histologically from crocodylomorphs in the predominance of fibrolamellar bone with abundant osteons and the absence of parallel-fibered bone in the cortex. Whereas fibrolamellar or woven bone is occasionally present in some crocodylomorphs (Woodward et al 2014;Cubo et al 2017), their cortices are usually formed exclusively of parallel-fibered or lamellar bone with simple vascular canals or sparse primary osteons (Hua & De Buffrénil 1996; de Andrade & Sayão 2014;Sayão et al 2016;Cubo et al 2017). For these reasons, we preclude this bone from being identified as that of a crocodylomorph.…”

“…Whereas fibrolamellar or woven bone is occasionally present in some crocodylomorphs(Woodward et al 2014;Cubo et al 2017), their cortices are usually formed exclusively of parallel-fibered or lamellar bone with simple vascular canals or sparse primary osteons(Hua and De Buffrénil 1996;Andrade and Sayão 2014;Sayão et al 2016;Cubo et al 2017).…”

New information on the anatomy and histology of Gracilisuchus stipanicicorum (Archosauria: Pseudosuchia) from the Chañares Formation (early Carnian), Argentina

“…However, in recent years, palaeohistological studies on pseudosuchian archosaurs and non-archosaurian archosauromorphs have increased interest among palaeontologists, and various studies have begun to be carried out revealing interesting findings regarding these highly diverse groups (e.g. Parker et al 2008;Klein et al 2009Klein et al , 2017Hill 2010;Botha-Brink & Smith 2011;Cerda & Desojo 2011;Filippi et al 2013;Legendre et al 2013;Ezcurra et al 2014;Scheyer et al 2014;Cerda et al 2015;Werning & Nesbitt 2016;Company & Pereda-Suberbiloa 2017;Cubo et al 2017;Ponce et al 2017).…”