Tesserae in shark cartilage: Evidence of developmental patterning?

Tessellated calcified cartilage (TCC) is a hallmark chondrichthyan hard tissue that probably arose after the group diverged from osteichthyans. Tesserae do not typically display an ordered arrangement; nevertheless, the ontogenetically earliest tesserae are formed at specific sites in the cranium and visceral skeleton. Thus, ini- tial patterning of TCC in elasmobranchs can be highly organized, but this transient stage largely disappears secondarily. However, rows of large tesserae are sometimes observed along cartilage edges and around foramina even after TCC is fully formed, defining borders to fields of smaller random tesserae. Such site-specific tesserae often exhibit distinct morphologies related to their position on the cartilage. In addition, tesserae never form in certain areas (e.g., on the retinal surface of scleral cartilage and on articulation surfaces). Collectively, these observations suggest the existence of a regulatory mechanism for tesserae that may be locally inhibited, perhaps compa- rable to inhibitory field and odontode regulation mechanisms in the dermal skeleton. Thus, there is evidence suggesting the existence of underlying developmental pat- terning of TCC, possibly analogous to that proposed elsewhere for the elasmobranch dermal skeleton, and individual tesseral development may be regulated by diffusion gradients of an inhibiting signal, possibly through the perichondrium.

John G. Maisey (1) , John S.S. Denton , C.J. Burrows , Alan Pradel

1 AMNH - American Museum of Natural History [New York, USA] = Musée américain d'histoire naturelle [New York, USA]

Domaines: Biologie animale

John G. Maisey, John S.S. Denton, C.J. Burrows, Alan Pradel. Tesserae in shark cartilage: Evidence of developmental patterning?. Comparative Cartilage Biology, Jun 2019, Banyuls, France. ⟨hal-02997875⟩