Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks - PubMed (original) (raw)

Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic networks

Nadia B Fröbisch et al. Proc Natl Acad Sci U S A. 2013.

Abstract

The biotic recovery from Earth's most severe extinction event at the Permian-Triassic boundary largely reestablished the preextinction structure of marine trophic networks, with marine reptiles assuming the predator roles. However, the highest trophic level of today's marine ecosystems, i.e., macropredatory tetrapods that forage on prey of similar size to their own, was thus far lacking in the Paleozoic and early Mesozoic. Here we report a top-tier tetrapod predator, a very large (>8.6 m) ichthyosaur from the early Middle Triassic (244 Ma), of Nevada. This ichthyosaur had a massive skull and large labiolingually flattened teeth with two cutting edges indicative of a macropredatory feeding style. Its presence documents the rapid evolution of modern marine ecosystems in the Triassic where the same level of complexity as observed in today's marine ecosystems is reached within 8 My after the Permian-Triassic mass extinction and within 4 My of the time reptiles first invaded the sea. This find also indicates that the biotic recovery in the marine realm may have occurred faster compared with terrestrial ecosystems, where the first apex predators may not have evolved before the Carnian.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

T. saurophagis gen. et sp. nov. FMNH PR 3032 from the middle Anisian (Middle Triassic) part of the Fossil Hill Member of the Favret Formation, Favret Canyon, Augusta Mountains, Nevada. (A) Photograph of the skull in dorsal view. (B) Drawing of same view. (C) Photograph of the skull in left lateral view. Note the flattening of the skull by sediment compaction. Arrow marks the maxillary tooth figured in E–I. (D) Drawing of same view. (E–I) Left maxillary tooth crown in (E) labial view, (F) lingual view, (G) apical view, (H) distal view, and (I) mesial view. Note the lingually recurved shape and the sharp but unserrated cutting edges. [Scale bars: (A_–_D) 100 and (E_–_I) 10 mm.]

Fig. 2.

Fig. 2.

Reconstruction of the skull of T. saurophagis. (A) Left lateral view. (B) Dorsal view. Rostrum length is a conservative estimate. Tooth size is reconstructed as increasing anteriorly beyond the preserved part because the preserved posterior and middle maxillary teeth are unlikely to have been the largest teeth. (Scale bar: 100 mm.)

Fig. 3.

Fig. 3.

Time-calibrated phylogeny of Ichthyosauria based on a Bayesian analysis. See ref. for details of the phylogenetic analysis. Stratigraphic ranges of taxa are based on ref. . Note the very early appearance of Thalattoarchon. (Inset) Relative tooth size in ichthyosaurs. Thalattoarchon has the relatively largest teeth compared with body length in any ichthyosaur together with two smaller forms with crushing dentitions. The solid line represents the ordinary least square regression line, which is flanked by 95% confidence belts (dashed lines). See

Table S1

for data.

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