Pharyngeal Denticles and the Placoderms – #365papers – 2018 – 58

Johanson and Smith, 2005, Origin and evolution of gnathostome dentitions: a question of teeth and pharyngeal denticles in placoderms: Biological Reviews, v. 80, p. 303-345

What’s it about?

This paper presents a detailed discussion of tooth development in fishes. In particular, the authors review the state of knowledge of tooth development in placoderms, among the first of the jawed fishes and now extinct. They also make observations about denticles, tooth-like bumps, on the gill arches of many fishes, including jawless forms, and how the development of these relate the development of teeth and external scales in early fishes. With these details, the authors propose a hypothesis for the origins and development of teeth in placoderms and in modern fishes.

Why does it matter?

I’ve read a few papers recently about the origin of the jaw, and of teeth, and of the relationships among fossil and modern groups of jawed fishes. This paper shows that placoderm teeth and the teeth in ‘higher’ fishes and tetrapods (including us) likely have the same developmental origin.

Why did I read this?

This is another in a long stream of papers that I’ve read in preparation for my vertebrate paleontology class. I’m kind of glad, at this point, that we’re now moving on to tetrapods.

What did I learn?

Admittedly, I got a little lost in this paper, but I did find it interesting that placoderm teeth wear down to shearing edges and are able to do this by infilling the pulp cavity. At least, I think that’s what I learned. I should re-read this. Later.

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