First Evidence of Dinosaurian Secondary Cartilage in the Post-Hatching Skull of Hypacrosaurus stebingeri (Dinosauria, Ornithischia)

Abstract

Bone and calcified cartilage can be fossilized and preserved for hundreds of millions of years. While primary cartilage is fairly well studied in extant and fossilized organisms, nothing is known about secondary cartilage in fossils. In extant birds, secondary cartilage arises after bone formation during embryonic life at articulations, sutures and muscular attachments in order to accommodate mechanical stress. Considering the phylogenetic inclusion of birds within the Dinosauria, we hypothesized a dinosaurian origin for this “avian” tissue. Therefore, histological thin sectioning was used to investigate secondary chondrogenesis in disarticulated craniofacial elements of several post-hatching specimens of the non-avian dinosaur Hypacrosaurus stebingeri (Ornithischia, Lambeosaurinae). Secondary cartilage was found on three membrane bones directly involved with masticatory function: (1) as nodules on the dorso-caudal face of a surangular; and (2) on the bucco-caudal face of a maxilla; and (3) between teeth as islets in the alveolar processes of a dentary. Secondary chondrogenesis at these sites is consistent with the locations of secondary cartilage in extant birds and with the induction of the cartilage by different mechanical factors - stress generated by the articulation of the quadrate, stress of a ligamentous or muscular insertion, and stress of tooth formation. Thus, our study reveals the first evidence of “avian” secondary cartilage in a non-avian dinosaur. It pushes the origin of this “avian” tissue deep into dinosaurian ancestry, suggesting the creation of the more appropriate term “dinosaurian” secondary cartilage.

Taphonomical and palaeoecological investigation of the Late Cretaceous (Maastrichtian) Tuştea vertebrate assemblage (Romania; Haţeg Basin) - insights into a unique dinosaur nesting locality

“…and 84 mm, respectively early hatchlings with femora ranging from 170 to 235 mm in length, and a body size of up to 1.6 m (Horner and Currie, 1994;Bailleul et al, 2012). Nonetheless, the absolute and relative dimensions of the Tuștea eggs and hatchlings are largely similar to those reported in the brachylophosaurin hadrosaur Maiasaura peeblesorum, with egg diameter of 12 cm and volume of 900 cm 3 , corresponding to embryos with 35-40 cm long femora and early hatchlings of about 45 cm estimated body length (Horner, 1999).…”

Chondroid bone in dinosaur embryos and nestlings (Ornithischia: Hadrosauridae): Insights into the growth of the skull and the evolution of skeletal tissues

“…For this study, we re-analyzed the paleohistological thin sections that were made for two previous studies on secondary cartilage (Bailleul et al, 2012 because secondary cartilage and CB are often found in the same areas. About a hundred sections were analyzed, from a total of 21 separate skull bones (see Table 1).…”

“…About a hundred sections were analyzed, from a total of 21 separate skull bones (see Table 1). All elements were found disarticulated and were collected from nesting horizons or isolated nests in the Two Medicine and Judith River formations (Upper Cretaceous), Montana, USA (see Bailleul et al, 2012and Horner and Currie, 1994 for more information about the localities).…”

“…One last issue that we would like to discuss is the relationship between CB and secondary cartilage, an intermediate tissue that arises secondarily on membrane bones and that has previously been reported in some hadrosaur skulls (Bailleul et al, 2012.…”

“…The most well-known intermediate tissues are secondary cartilage and chondroid bone (Beresford, 1981;and see Hall, 2005, Chapter 5). Secondary cartilage was recently reported in hadrosaur embryos and nestlings (Bailleul et al, 2012; and see section 4), therefore, here, we will focus on chondroid bone in the same taxa.…”