Lunge feeding in early marine reptiles and fast evolution of marine tetrapod feeding guilds

Abstract

Traditional wisdom holds that biotic recovery from the end-Permian extinction was slow and gradual, and was not complete until the Middle Triassic. Here, we report that the evolution of marine predator feeding guilds, and their trophic structure, proceeded faster. Marine reptile lineages with unique feeding adaptations emerged during the Early Triassic (about 248 million years ago), including the enigmatic Hupehsuchus that possessed an unusually slender mandible. A new specimen of this genus reveals a well-preserved palate and mandible, which suggest that it was a rare lunge feeder as also occurs in rorqual whales and pelicans. The diversity of feeding strategies among Triassic marine tetrapods reached their peak in the Early Triassic, soon after their first appearance in the fossil record. The diet of these early marine tetrapods most likely included soft-bodied animals that are not preserved as fossils. Early marine tetrapods most likely introduced a new trophic mechanism to redistribute nutrients to the top 10 m of the sea, where the primary productivity is highest. Therefore, a simple recovery to a Permian-like trophic structure does not explain the biotic changes seen after the Early Triassic.

Ecomorphological diversifications of Mesozoic marine reptiles: the roles of ecological opportunity and extinction

“…EB, early burst; BM, Brownian motion. Motani et al 2015a)? Although this study was not designed to test these competing hypotheses, the results can still be used to inform this debate.…”

“…Numerical studies show that marine reptile species diversity first peaked in the Anisian, just 10 Myr into the Triassic (Benson et al 2010;Benson and Butler 2011). In addition, qualitative observations from the fossil record reveal that marine reptiles broadly diversified into a variety of trophic strategies in their first 20 Myr of evolution (Motani et al 2015a). These included largeskulled macropredatory ichthyosaurs , small suction-feeding edentulous ichthyosauromorphs (Motani et al 2015b), shell-crushing placodonts (Neenan et al 2014), long-necked and fanged nothosaurs (Rieppel 2002), bizarre heterodont thalattosaurs , and enigmatic apparent filter-feeders, such as Atopodentatus (Cheng et al 2014).…”

“…The rise of marine reptiles as an adaptive assemblage is considered one of the most significant components of this recovery (Liu et al 2014;Motani et al 2015a). Numerical studies show that marine reptile species diversity first peaked in the Anisian, just 10 Myr into the Triassic (Benson et al 2010;Benson and Butler 2011).…”

“…Recent research has emphasized that a broad-based ecological approach is essential for understanding marine reptile evolution (Motani et al 2015a). Thus far, studies have focused on body-size trends and trophic web establishment in the first 5-10 Myr of the Mesozoic (Liu et al 2014;Scheyer et al 2014), while others have examined the proportions of categorical ecomorphs and guilds through the whole Triassic Kelley et al 2014;Motani et al 2015a).…”

“…Thus far, studies have focused on body-size trends and trophic web establishment in the first 5-10 Myr of the Mesozoic (Liu et al 2014;Scheyer et al 2014), while others have examined the proportions of categorical ecomorphs and guilds through the whole Triassic Kelley et al 2014;Motani et al 2015a). However, no study has examined whether the Triassic was truly a time of unusual trophic proliferation or whether the accumulated diversity of forms was any greater than at other points in the Mesozoic -was the first wave of marine reptile evolution in the aftermath of the PTME really exceptional?…”