Fast biting Cretaceous predators on way out


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Here is the bad news for you - if you were a large, predatory fish with a fast bite at the end of the Cretaceous period (65"70 million years ago): you are going extinct.

A study by Matt Friedman published in a recent issue of the Proceedings of the National Academy of Science examined the body form and jaw architecture of 249 genera of fossil fishes that went extinct during the end of the Cretaceous period and found that large-bodied fishes with biomechanically fast jaws were the hardest hit.

This agrees with existing theory that fishes at the top of food chains with low growth rates and lower fecundity are more vulnerable to extinction.

The author found that elevated extinction intensity among teleosts appearing to occupy higher trophic levels is consistent with the collapse of oceanic food webs, corroborating earlier hypotheses implicating diet as an important determinant of survivorship among fishes.

The most prominent teleostean casualties of the end-Cretaceous extinction include the predatory pachycormids, pachyrhizodontids, ichthyodectiforms, enchodontids, and cimolichthyids, all of which are equipped with high-aspect-ratio caudal fins and fusiform bodies that imply fast swimming and sustained cruising.

Taken together, these fishes appear to be the ecological analogues of modern, large-bodied predatory teleosts such as scombroids (tunas, mackerels, cutlassfishes, and the wahoo), xiphioids (billfishes), sphyraenids (barracudas), and carangoids (jacks and dolphinfishes).

Significantly, all of these extant groups make their first appearance in the early Paleogene, suggesting that they might have radiated to fill the functional roles vacated by extinction victims.

Friedman concludes ironically, the very same groups that seem to have diversified into emptied ecospace at the dawn of the Cenozoic now face the greatest risks of extinction from overexploitation; commercial fisheries disproportionately target large, predatory taxa...The mechanisms driving these 2 biodiversity collapses separated by 65 million years clearly differ, but congruent patterns of risk imply that some aspects of fish ecomorphology might consistently correlate with elevated extinction vulnerability regardless of the ultimate factors causing population decline.

For more information, see the paper: Friedman, M (2009) Ecomorphological selectivity among marine teleost fishes during the end-Cretaceous extinction. Proceedings of the National Academy of Sciences 106, pp. 5218"5223.