Primitive jaw structure in an articulated brachythoracid arthrodire (placoderm fish; early Devonian) from southeastern Australia

Young, Grant M.; Lelièvre, Hélène; Goujet, Daniel

doi:10.1671/0272-4634(2001)021[0670:pjsiaa]2.0.co;2

Cited by 35 publications

(45 citation statements)

References 26 publications

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“…We do not currently know if they are also composed of the same type of dentine, but each is added to only one locus on the gnathal bone. Therefore, contrary to Young et al (2001) we would suggest that the anterior and lateral row in their ' buchanosteid ' and Maideria falipoui must also represent teeth. As in the coccosteomorph tooth row, teeth in the anterior row of the ' buchanosteid ' supragnathals are added to the (medial) end of the row (Young et al, 2001), are larger in this position, and also have an associated bone of attachment (personal observations ZJ and MMS, 2001).…”

Section: Placoderm Dentitions : Contribution Of Teeth and Denticlescontrasting

confidence: 67%

“…7). Similarity between the Incisoscutum ritchiei juvenile infragnathal and the infragnathal of a brachythoracid arthrodire similar to Buchanosteus fascidens has already been noted (Young et al, 2001). Other ' primitive brachythoracids ' (Carr, 1995), as well as certain pachyosteomorph arthrodires, the Phlyctaeniida and the Phyllolepida (Fig.…”

Section: Placoderm Dentitions : Contribution Of Teeth and Denticlesmentioning

confidence: 65%

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Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Johanson¹,

Smith

2005

Biol. Rev.

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The fossil group Placodermi is the most phylogenetically basal of the clade of jawed vertebrates but lacks a marginal dentition comparable to that of the dentate Chondrichthyes, Acanthodii and Osteichthyes (crown-group Gnathostomata). The teeth of crown-group gnathostomes are part of an ordered dentition replaced from, and patterned by, a dental lamina, exemplified by the elasmobranch model. A dentition recognised by these criteria has been previously judged absent in placoderms, based on structural evidence such as absence of tooth whorls and typical vertebrate dentine. However, evidence for regulated tooth addition in a precise spatiotemporal order can be observed in placoderms, but significantly, only within the group Arthrodira. In these fossils, as in other jawed vertebrates with statodont, non-replacing dentitions, new teeth are added at the ends of rows below the bite, but in line with biting edges of the dentition. The pattern is different on each gnathal bone and probably arises from single odontogenic primordia on each, but tooth rows are arranged in a distinctive placoderm pattern. New teeth are made of regular dentine comparable to that of crown-gnathostomes, formed from a pulp cavity. This differs from semidentine previously described for placoderm gnathalia, a type present in the external dermal tubercles. The Arthrodira is a derived taxon within the Placodermi, hence origin of teeth in placoderms occurs late in the phylogeny and teeth are convergently derived, relative to those of other jawed vertebrates. More basal placoderm taxa adopted other strategies for providing biting surfaces and these vary substantially, but include addition of denticles to the growing gnathal plates, at the margins of pre-existing denticle patches. These alternative strategies and apparent absence of regular dentine have led to previous interpretations that teeth were entirely absent from the placoderm dentition. A consensus view emerged that a dentition, as developed within a dental lamina, is a synapomorphy characterising the clade of crown-group gnathostomes. Recent comparisons between sets of denticle whorls in the pharyngeal region of the jawless fish Loganellia scotica (Thelodonti) and those in sharks suggest homology of these denticle sets on gill arches. Although the placoderm pharyngeal region appears to lack denticles (placoderm gill arches are poorly known), the posterior wall of the pharyngeal cavity, formed by a bony flange termed the postbranchial lamina, is covered in rows of patterned denticle arrays. These arrays differ significantly, both in morphology and arrangement, from those of the denticles located externally on the head and trunkshield plates. Denticles in these arrays are homologous to denticles associated with the gill arches in other crown-gnathostomes, with pattern similarities for order and position of pharyngeal denticles. From their location in the pharynx these are inferred to be under the influence of a cell lineage from endoderm, rather than ectoderm. Tooth sets and tooth whorls in crow...

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Section: Placoderm Dentitions : Contribution Of Teeth and Denticlescontrasting

confidence: 67%

Section: Placoderm Dentitions : Contribution Of Teeth and Denticlesmentioning

confidence: 65%

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Johanson¹,

Smith

2005

Biol. Rev.

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“…In Late Devonian marine environments they included probably the largest predators of the Devonian Period. Their origins can be traced back to the Early Devonian, which has yielded a range of basal brachythoracid taxa that have an uncertain position within the major brachythoracid subgroups of the Middle-Late Devonian (e.g., White, 1978;Young, 1981;Lelièvre, 1995;Young et al, 2001;Mark-Kurik and Young, 2003).…”

Section: Introductionmentioning

confidence: 99%

Large brachythoracid arthrodires (placoderm fishes) from the early Devonian of Wee Jasper, New South Wales, Australia, with a discussion of basal brachythoracid characters

Young¹

2004

Journal of Vertebrate Paleontology

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“…The dorsal border is convex while for all other Cleveland Shale arthrodires in which the posterior superognathal is known, the dorsal margin is concave. However, R. barwickorum shows this same orientation (Young et al, 2001, fig. 5).…”

Section: Systematic Paleontologymentioning

confidence: 80%

New information on Titanichthys (Placodermi, Arthrodira) from the Cleveland Shale (Upper Devonian) of Ohio, USA

Boyle¹,

Ryan²

2017

J. Paleontol.

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Abstract.-The placoderm Titanichthys from the Late Devonian (Famennian) is based on incomplete and fragmentary specimens that have hindered understanding of its overall anatomy and phylogenetic relationships. A new, nearly complete, articulated specimen from the Upper Devonian Cleveland Shale provides new information about the previously undescribed rostral, postmarginal, postsuborbital, submarginal, posterior superognathal plates, and the nasal capsule. A revised diagnosis is provided for the genus. Three new diagnostic characters are identified, including a transversely elliptical rostral plate that does not contact adjacent plates, a reduced posterior superognathal, and a median dorsal plate that inserts into the posterior dorsal lateral plate. The first comprehensive phylogenetic analysis of Titanichthys indicates that the genus is a basal aspinothoracid arthrodire closely related to the enigmatic taxa Bungartius and Tafilalichthys.

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Primitive jaw structure in an articulated brachythoracid arthrodire (placoderm fish; early Devonian) from southeastern Australia

Cited by 35 publications

References 26 publications

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms

Large brachythoracid arthrodires (placoderm fishes) from the early Devonian of Wee Jasper, New South Wales, Australia, with a discussion of basal brachythoracid characters

New information on Titanichthys (Placodermi, Arthrodira) from the Cleveland Shale (Upper Devonian) of Ohio, USA

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