Updates on sawskates

Onchopristis new skeletal

My reconstruction of Onchopristis numida.

Since my last post about Onchopristis and sclerorhynchoids was written over a year and a half ago, there have been significant updates to this topic. Usually I would write an addendum to the original post, but this time there is enough new information to warrant its own post. First, an excellent description of new cranial and rostral material of Onchopristis was published by Villalobos-Segura et al. (2021). These well-preserved fossils reveal the previously unknown chondrocranium and jaws, as well as the growth and replacement pattern of the rostral denticles. Villalobos-Segura et al. also performed a new phylogenetic analysis which reaffirms the monophyly of Sclerorhynchoidei. This paper allowed me to create my own Onchopristis reconstruction and I highly recommend reading it.

Second, I published some of my own research on sclerorhynchoids last year. In September, I published a short paper in Bionomina that makes corrections to the taxonomy and nomenclature of the group (Greenfield, 2021a). I pointed out that Ganopristidae has priority over Sclerorhynchidae for the family containing Sclerorhynchus, of which Ganopristis is a junior synonym. Building on the results of Villalobos-Segura et al., I revised Sclerorhynchoidei to include five families: Schizorhizidae, Ischyrhizidae, Onchopristidae, Ptychotrygonidae, and Ganopristidae. I also emended the spelling of Onchopristis numidus to numida to fix a grammatical error. The title of this paper is the first formally published usage of the word “sawskate”!

In December, I gave a presentation and abstract at the 3rd Palaeontological Virtual Congress (Greenfield, 2021b). These focused on broader issues with sclerorhynchoids, like using sawskate as a common name and the characteristics that distinguish them from sawfishes. I highlighted the saw as a remarkable case of convergent evolution, with it evolving three times in chondrichthyans. I proposed the term “pristification” for this phenomenon to use in science communication. I briefly discussed the ecology of sclerorhynchoids, noting their similarities to benthic ambush predators like wobbegongs and angelsharks. I also covered possible candidates for pristification like bandringid sharks. Additionally, I presented a preliminary version of my Onchopristis reconstruction.

Sclerorhynchoidei tree

A phylogenetic tree of Sclerorhynchoidei based on the analysis of Villalobos-Segura et al. (2021), with the family-level taxonomy based on Greenfield (2021a). Names in parentheses are junior synonyms.

My reconstruction of Onchopristis numida is mainly based on the most complete rostral/cranial specimen (IPUW 353500; Villalobos-Segura et al., 2021). The missing tip of the rostrum is based on a specimen of O. numida that was destroyed in WWII (BSPG coll.; Stromer, 1925). Missing or distorted elements of the chondrocranium and jaws are based on Libanopristis hiram (MNHN 1973-3-1; Cappetta, 1980). The arrangement of the lateral cephalic denticles is based on Sclerorhynchus atavus (NHMUK PV P 4776 & NHMUK PV OR 88663; Underwood et al., 2016). The postcranial proportions are based on an undescribed and privately-owned specimen of O. numida (Underwood, pers. comm.). The outlines of the fins are based on S. atavus (MNHN 1939-7-204 & MNHN 1946-18-208; Cappetta, 1980).

The bases of the rostral denticles are depicted embedded in skin similar to sawsharks (Welten et al., 2015). The dermal denticles and oral teeth are omitted because their arrangements are currently unknown. The antorbital cartilages are partially transparent to show the nasal capsules underneath. The grey ovals behind the antorbital cartilages represent the eyes. While the spiracles are not shown, they likely would be located right behind the eyes like in skates. The gills are also omitted and there would be five slits on each side between the jaws and the pectoral fins. The dorsal fins are in lateral view, and not dorsal view like the rest of the reconstruction, to clearly show their size and shape. Note that IPUW 353500 is not the largest specimen of Onchopristis; the estimated total length is only 1.44 meters (4.72 feet)1.

Special thanks go to Dr. Charlie Underwood, who gave helpful feedback on my Onchopristis reconstruction and provided photos of the private specimen. If you would like to use my full reconstruction in a publication or presentation, please contact me first at tgreenfield999@gmail.com. The silhouette of my reconstruction is available for use under a Creative Commons 3.0 license on PhyloPic. My publications on sclerorhynchoids can be accessed or requested on ResearchGate.

Notes

1This is significantly smaller than the 2.94-4.25 m (9.65-13.94 ft) estimated by Villalobos-Segura et al. (2021), who used generalized sclerorhynchoid proportions.

References

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