YouTube Palaeocast video on the origin of teeth

From the video caption
“Determining the origin of teeth in vertebrates is an incredibly significant but notoriously difficult problem within palaeontology. Teeth didn’t evolve in the mouths of our ancestors, but are first seen as part of the external skeletons of jawless fish as structures called ‘odontodes’. These would later migrate into the mouth with the evolution of jaws, becoming the teeth we have today, but odontodes still remain present in the skin of modern cartilaginous fish, giving them their rough texture. The oldest known odontodes are from the late Cambrian Period and represent the very first evidence for vertebrates in the fossil record. Unfortunately, they are only ever found as part of fragmentary pieces of exoskeleton, however, given that their specific construction is only known in vertebrates, there is little else they could possibly be

Joining us for this episode is Dr Yara Haridy, University of Chicago, who set out to use modern new scanning techniques to better understand the nature of these first teeth and what they tell us about the evolution of vertebrates. What she discovered was unexpected, but also led to better understanding of the purpose of odontodes in the dermal exoskeletons of our ancestors. Her research was recently published in Nature and is free to access.”

The paper focused on
the Ordovician pre-shark, Eriptychius (Fig 1) and involved synchostron scanning that revealed “deep ultrastructural similarities between odontodes and sensory structures also extend to definitive vertebrate tissues.”

Figure 1. Ordovician Eriptychius compared to Early Silurian Shenacanthus demonstrates the origin of jaws in that clade. ” data-image-caption=”

Figure 1. Ordovician Eriptychius compared to Early Silurian Shenacanthus demonstrates the origin of jaws in that clade.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg?w=98″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg?w=335″ class=”size-full wp-image-83952″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg” alt=”Figure 1. Ordovician Eriptychius compared to Early Silurian Shenacanthus demonstrates the origin of jaws in that clade.” width=”584″ height=”1788″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg?w=584&h=1788 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg?w=49&h=150 49w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg?w=98&h=300 98w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/01/eriptychius-arctolepis-shenacanthus588-2.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />

Figure 1. Ordovician Eriptychius compared to Early Silurian Shenacanthus demonstrates the origin of jaws in that clade.

The origin of any structure
must be considered in a phylogenetic context.

In ‘the large reptile tree’ traditional members of the traditional clade ‘Gnathostomata’ do not form a monophyletic clade with a single jawed last common ancestor. Contra the hypothesis presented in the video, teeth did appear in the jaws prior to denticles on the skin – and did so several times by convergence.

1. Jaws developed with Lasanius following conodonts, which have many barbed jaw elements that emerge when feeding from a circular oral cavity. This clade gave rise to Cheirolepis, Engrauls, Tarpon, and ultimately lungfish and tetrapods in which the teeth, when present, separate from the jaw bones.
2. Jaws of a sort also developed to a lesser extent in sturgeon young. Small teeth of a sort appear on sturgeon young, but are lost in adults.
3. Jaws without teeth also appeared in basal placoderms, like Qilinyu. Manta is an extant relative.
4. Jaws are better developed in the placoderm Xiushanosteus, but teeth remain absent. In placoderms early Coccosteus species lacked teeth, but later species developed tooth pads and these gave rise to Clarias, the most primitive catfish.
5. In the Ordovician Eriptychius started to develop a sort of jaw with a diagonal axis of rotation, followed by Silurian Shenacanthus, which had more typical, but toothless jaws. These gave rise to two clades: the shark clade beginning with a late-survivor in the Carboniferous, Gregorius, which had small teeth and to the spiny shark clade (Acanthodii), which were similar at first. The former gave rise to sharks and later chimaera. The spiny shark clade gave rise to sea robins, coelacanths, gars, salmon, swordfish, moray eels and all the other traditional bony fish not in the tetrapod ancestry – and not catfish.

Both of the major bony fish clades gave rise to ‘biters’ and to toothless ‘suckers’ with flexible rostra able to extend to engulf small prey. So, it’s complicated.

To backtrack a little: mineralized piercing elements surrounding an oral cavity go back to Enoplus, a marine nematode with roots back to the Ediacaran, followed by the similar hagfish (Myxine) and lamprey (Pteromyzon), none of which have dentine in their ‘teeth’.

The authors note:
“Cambrian conodonts are the earliest mineralizing vertebrates³, but remain problematic owing to their uncertain phylogenetic position and the uniqueness of the mineralized tissues in their pharyngeal elements. Critically, conodont elements lack true dentine.”

So, apparently dentine evolved more than once in chordates.
Always be ready for the possibility of convergence.
Always begin every ‘origin’ problem with a wide gamut trait-based analysis.

References
Haridy Y et al (10 co-authors) 2025. The origin of vertebrate teeth and evolution of sensory exoskeletons Nature 642:119–124.
https://yaraharidy.com/

Publicity
https://www.npr.org/2025/05/24/nx-s1-5409367/armored-fish-human-teeth-cold-pain-evolution