I've told you before about conodonts, Palaeozoic microcarnivores with impressive tooth arrays. In the earlier post, I referred mostly to ozarkodinids, later conodonts that had grasping teeth in the front of their mouths and crushing plates towards the back. In this post, I'll be referring to panderodontids, an earlier group that lacked the crushing plates of ozarkodinids and had a tooth apparatus made up of simpler fang-like elements, similar to the reconstruction above. Apparatus of panderodontids have been found preserved in association, but we don't yet have preserved examples as good as available for the ozarkodinids.
With such different apparatus, panderodontids were obviously capturing and processing prey differently to ozarkodinids, and a paper just out by Szaniawski (2009) suggests one of those differences. Panderodontids and many other conodonts with coniform teeth had long grooves on the inner surface of some of their teeth (as seen in the photo of a Dapsilodus mutatus element above from Szaniawski, 2009) and Szaniawski points out that these grooves are extremely similar to those seen in the fangs of many venomous fish, lizards and snakes. He therefore infers that panderodontids were similarly venomous. As well as making conodont apparatus even more impressive than they already were, this would make panderodontids the earliest known venomous chordates*.
*Szaniawski refers to them as the "oldest known venomous animals". However, cnidarians had already been around for some time, and while the cnidarian venom delivery system doesn't fossilise, the fact that these were crown-group cnidarians makes it a pretty sure bet that they had it by then.
Earlier suggestions that the groove provided an anchoring point for muscles were couched in the belief that conodont elements were permanently internal, a view that is no longer standard*. Other forms of conodont lacked the venom groove, further evidence of the conodonts' ecological diversity.
*Conodont elements grew as new layers were put down over the outer surface, which is admittedly a little difficult to reconcile with their current interpretation as grasping teeth (which would require the absence of tissue cover). It seems likely that conodont teeth were only exposed when being actively used; at other times they would have been retracted into a covering pocket, in the same manner as the grasping spines of modern chaetognaths.
Dzik, J. 1991. Evolution of oral apparatuses in the conodont chordates. Acta Palaeontologica Polonica 36 (3): 265-323.
Szaniawski, H. 2009. The earliest known venomous animals recognized among conodonts. Acta Palaeontologica Polonica 54 (4): 669-676.