New insights from bone microanatomy of the Late Triassic Hyperodapedon (Archosauromorpha, Rhynchosauria): implications for archosauromorph growth strategy

Abstract

Bone microanatomy of multiple postcranial skeletal elements of several individuals of Hyperodapedon collected from India is reported. This reveals that fibrolamellar bone tissue is predominant in the mid-and inner cortices, whereas the peripheral region of the cortex is composed of either parallel-fibred and/or lamellar bone. The pattern of primary osteons mostly ranges between laminar and subplexiform. Such predominance of fibrolamellar bone tissue in the cortex suggests an overall fast growth, which slowed down considerably later in ontogeny. Four distinct ontogenetic stages are identified based on the bone microstructure. During the juvenile stage, growth was fast and continuous, but it became punctuated during the early and late sub-adult stages. In adult individuals, growth was slow and showed periodic interruption but did not stop completely, suggesting that Hyperodapedon had an indeterminate growth strategy. Interelemental histovariations affecting cortical thickness, organization of the vascular network, incidence of growth rings and extent of secondary reconstruction are noted.

Bone histology and growth in Stenaulorhynchus stockleyi (Archosauromorpha: Rhynchosauria) from the Middle Triassic of the Ruhuhu Basin of Tanzania

“…In H. tikiensis, this region is well vascularized by laminar or plexiform primary osteons. Porosity is much lower in H. huxleyi, but longitudinal primary osteons anastomose in all directions (Mukherjee, 2015). After the first year, zonal width and porosity decrease, parallelfibered bone becomes progressively more common than fibrolamellar bone, and the primary osteons are arranged circumferentially or in radial rows (similar to NHMUK PV R 36618).…”

“…These taxa differ from NHMUK PV R 36618 in the presence of fibrolamellar bone and in the complexity of vascular canal patterns. Mukherjee (2015) described femoral and tibial growth series from two species, H. huxleyi and H. tikiensis, from the Late Triassic Maleri Formation and Tiki Formation (respectively) of India. In both taxa, the inner cortex (internal to the first LAG) is composed entirely of woven-fibered or fibrolamellar bone.…”

“…In those early diverging archosauromorph taxa that have been characterized, the bone tissue structure generally suggests slower growth compared to archosauriforms, with most taxa exhibiting moderately to poorly vascularized parallel-fibered or lamellar bone (Botha-Brink and Smith, 2011;de Ricqlès et al, 2008;Ezcurra et al, 2014;Veiga et al, in press;. However, with two exceptions (Mukherjee, 2015;, no taxon has been sampled in large enough numbers to address ontogenetic variation in growth or histology. Greater sampling among non-archosauriform archosauromorphs is necessary to understand the distribution of and variation in growth-related histological features.…”

“…More recently, a Stenaulorhynchus limb bone was illustrated by Sanchez et al (2012), but was not described histologically. To date, the only studies to focus on rhynchosaur osteohistology are that of Veiga et al (in press), who sectioned long bones and ribs of a Hyperodapedon species and Teyumbaita sulcognathus, both from Brazil, and Mukherjee (2015), who sectioned long bones from the Indian rhynchosaurs H. huxleyi and H. tikiensis, including a femoral growth series. Although the Late Triassic hyperodapedontine rhynchosaurs are now well sampled, little is known about growth in earlier diverging rhynchosaurs, or whether these forms are representative of the entire clade.…”

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

“…Data on archosauromorphs, archosauriforms, and pseudosuchian archosaurs, however, are still rare (and less well understood) but so far show a variety of bone tissues and vascular systems, resulting in a mixture of bone tissue patterns (Botha-Brink and Smith, 2011). The primary bone tissue type of non-ornithodiran archosauromorphs can be characterized (with a few exceptions, see below) as lamellar-zonal bone tissue type/LZB (Ricql es et al, 2003(Ricql es et al, , 2008Botha-Brink and Smith, 2011;Werning and Irmis, 2011;Ezcurra et al, 2014;Mukherjee, 2015;Veiga et al, 2015;Werning and Nesbitt, 2016). Differences with modern reptiles that also grow with LZB are mainly related to vascularity (density and organization) and a higher organization of tissue.…”