Fanged fossil specimens described in a paper published in the journal Royal Society Open Science have revealed the unusual anatomy of “saber-toothed anchovies”, painting a far spikier picture of what modern-day pizza toppings could have been like had the adaptation emerged across the ray-finned fish. The paper reports the discovery of close, predatory cousins of the modern anchovy, which were much bigger and packed an impressive set of teeth. Most bizarrely, the fish sported fangs on the lower jaw with a single upper “sabertooth”, highlighting how dramatically anchovies and their cousins diverged in the wake of the end-Cretaceous extinction.
When mass extinction events occur, the loss of life sees a wealth of ecological niches ripe for the taking, and surviving species will often adapt and change to fill them, driving a sudden surge in anatomical transformations. The end-Cretaceous extinction was no different, and the authors of this paper believe they have stumbled across one such opportunistic group of fish who reinvented themselves at this time. They report on two fossils from the Clupeiform genus, Clupeopsis and Monosmilus found in Belgium and Pakistan respectively, which adapted to be larger in size with lower jaw fangs and a single upper sabertooth. The finding is even more unusual in the context that these specimens are close cousins to the plankton-feeding, tin-can-dwelling anchovies we know today. Far better known for their affinity as a pizza topping than their aggression, the researchers highlight the extraordinary evolutionary changes that took place to enable this genealogically close relative to anatomically transform from its anchovy cousins so dramatically.
The adaptation is an example of remarkable trophic innovation in early Palaeogene Clupeiformes, a group whose modern-day representatives are generally small-bodied plankton feeders. The team discovered specimens of two extinct members of the group, one from the early Eocene and a new genus from the middle Eocene, which have features indicative of predatory animals, including large size, long gapes, and more teeth.
The researchers used micro-computed tomography to reveal the anatomy of the two Clupeiform specimens. Their discovery paints an unexpected picture of how marine Clupeiform looked and behaved in the early Palaeogene. The specimens also represent a previously unrecognized trophic innovation for Clupeiformes, which, for better or worse, has not persisted to modern day. Personally, I think my Pizza Napoli could do without.
