Dental patterning in the earliest sharks: Implications for tooth evolution

Abstract

Doliodus problematicus is the oldest known fossil shark-like fish with an almost intact dentition (Emsian, Lower Devonian, c. 397Ma). We provide a detailed description of the teeth and dentition in D. problematicus, based on tomographic analysis of NBMG 10127 (New Brunswick Museum, Canada). Comparisons with modern shark dentitions suggest that Doliodus was a ram-feeding predator with a dentition adapted to seizing and disabling prey. Doliodus provides several clues about the early evolution of the "shark-like" dentition in chondrichthyans and also raises new questions about the evolution of oral teeth in jawed vertebrates. As in modern sharks, teeth in Doliodus were replaced in a linguo-labial sequence within tooth families at fixed positions along the jaws (12-14 tooth families per jaw quadrant in NBMG 10127). Doliodus teeth were replaced much more slowly than in modern sharks. Nevertheless, its tooth formation was apparently as highly organized as in modern elasmobranchs, in which future tooth positions are indicated by synchronized expression of shh at fixed loci within the dental epithelium. Comparable dental arrays are absent in osteichthyans, placoderms, and many "acanthodians"; a "shark-like" dentition, therefore, may be a synapomorphy of chondrichthyans and gnathostomes such as Ptomacanthus. The upper anterior teeth in Doliodus were not attached to the palatoquadrates, but were instead supported by the ethmoid region of the prechordal basicranium, as in some other Paleozoic taxa (e.g., Triodus, Ptomacanthus). This suggests that the chondrichthyan dental lamina was originally associated with prechordal basicranial cartilage as well as jaw cartilage, and that the modern elasmobranch condition (in which the oral dentition is confined to the jaws) is phylogenetically advanced. Thus, oral tooth development in modern elasmobranchs does not provide a complete developmental model for chondrichthyans or gnathostomes.

Sox2+ progenitors in sharks link taste development with the evolution of regenerative teeth from denticles

“…1 C-G and Movie S2). This conveyor-belt mechanism of successional regeneration appears to be a synapomorphy of oral teeth in crown gnathostomes (15,16). Although both the precocious embryonic caudal tail ( Fig.…”

A critical appraisal of appendage disparity and homology in fishes

“…latispinosus, which also possesses prepectoral and possibly admedian spines (Burrow et al, 2017;Maisey et al, 2017), and W. priscus (Potvin-Leduc, 2017). Notably, it has also been suggested based on the results of a phylogenetic analyses on cranial morphological characters that D. latispinosus may occupy a more stemward position in the chondrichthyan phylogeny, prior to the Euchondrocephali-Elasmobranchii split (Maisey, Turner, Naylor, & Miller, 2014;Pradel, Tafforeau, Maisey, & Janvier, 2011). If acanthodians are added to the total group chondrichthyans as suggested by recent investigations (e.g., Brazeau & de Winter, 2015;Burrow et al, 2016;Chevrinais et al, 2017;Long et al, 2015;Qiao et al, 2016), the presence of prepelvic spines will become a common character of stem chondrichthyans.…”

New data onKarksiodus(Chondrichthyes) from the Main Devonian Field (East European Platform)

“…The latter differs from Karksiodus in having a lingual extension of the base and elements for tooth-to-tooth articulation, including the apical button and labio-basal projection (Ginter et al 2010). On the other hand, Doliodus dentition includes commonly the tooth row with fused bases but the isolated teeth possess labio-basal extensions of the base (Turner 2004;Maisey et al 2014). None of these groups display the same histological characters presented by Karksiodus, namely, the complex vascularization system made up of four distinct canal types, which is so far unique to Karksiodus among either extinct or extant chondrichthyans.…”