Preliminary observations on the bone histology of the Middle Triassic pseudosuchian archosaurBatrachotomus kupferzellensisreveal fast growth with laminar fibrolamellar bone tissue

Abstract

ABSTRACT-The bone tissue of femur, rib, and gastralia from three different individuals of the Middle Triassic pseudosuchian Batrachotomus kupferzellensis from southern Germany is studied. The femoral bone tissue comprises laminar fibrolamellar bone tissue throughout and is stratified by three annual growth cycles, indicating that the individual died early in its fourth year of life, at which time it had reached 87% of maximum known femur length. Thus, compared with most other Pseudosuchia (e.g., phytosaurs, aetosaurs, and most crocodylomorphs, including marine taxa), Batrachotomus achieved its large body size in a very short time by fast, although interrupted, growth and not by protracted longevity. Such fast growth as well as the organization of the tissue is similar to the condition observed in ornithodirans. The pseudosuchians Effigia and Postosuchus also show fibrolamellar tissue, but vascular density is lower when compared with Batrachotomus and dominated by a longitudinal organization of primary osteons. The rib and gastralium of Batrachotomus both show an inner spongious organization surrounded by a ring of compact, avascular, highly organized parallel-fibered and/or lamellar bone largely covered by short fibers. Maximal growth cycle count in the proximal rib sample suggests an age of at least 11 years for this individual with a reduction of growth rate after the sixth cycle.

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

“…If CRILAR PV 490 and PULR 08 are considered juveniles (see below) and both of them present already low growth rates, it appears likely that the fully grown adult would have not reached very large size. This is also consistent with the consideration that the growth rate decreases though ontogeny as a strategy to shorten the period of vulnerability (Erickson 2005;Klein et al 2017;Sander et al 2011), a slowing down already inferred from the femur section (see above).…”

“…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).…”

“…The capacity to form the fast-growing FLB tissue was already present in basal Archosauriformes (Botha-Brink & Smith 2011;Legendre et al 2013;Klein et al 2017;Cubo & Jalil 2019), and retained within both Pseudosuchia and Avemetatarsalia (Legendre et al 2013;Klein et al 2017). The deposition of fibrolamellar bone tissue (FLB) was retained in Avemetatarsalia, including dinosaurs and pterosaurs, and in most pseudosuchian groups, such as aetosaurs and basal paracrocodylomorphs, but reverted to a slow-growing lamellar zonal bone (LZB) in derived Crocodyliformes, including living representatives (e.g.…”

“…The deposition of fibrolamellar bone tissue (FLB) was retained in Avemetatarsalia, including dinosaurs and pterosaurs, and in most pseudosuchian groups, such as aetosaurs and basal paracrocodylomorphs, but reverted to a slow-growing lamellar zonal bone (LZB) in derived Crocodyliformes, including living representatives (e.g. de Ricqlès et al 2003;Woodward et al 2011;Company & Pereda-Suberbiola 2017;Klein et al 2017). In this scenario, the presence of a slow-growing PFB in the relatively deeply nested suchian Gracilisuchus stipanicicorum may indicate a reversion to a low growth rate, but it also differs from the slow-growing LZB present in lepidosaurs and in the non-archosauriform archosauromorphs Trilophosaurus Case, 1928 andrhynchosaurs (Legendre et al 2013).…”

Response to formal comment on Myhrvold (2016) submitted by Griebeler and Werner (2017)

“…Other independent lines of evidence suggest that high metabolic rates could be ancestral to all archosaurs [ 42 ], and that crocodiles may be secondarily ectothermic [ 43 ]. Middle Triassic archosaurs appear to have had fast growth rates [ 44 ]. Evidence suggests that at least some early therapsids had elevated body temperature [ 45 ].…”