Abstract
Present-day ecosystems host a huge variety of organisms that interact and transfer mass and energy via a cascade of trophic levels. When and how this complex machinery was established remains largely unknown. Although exceptionally preserved biotas clearly show that Early Cambrian animals had already acquired functionalities that enabled them to exploit a wide range of food resources, there is scant direct evidence concerning their diet and exact trophic relationships. Here I describe the gut contents of Ottoia prolifica, an abundant priapulid worm from the middle Cambrian (Stage 5) Burgess Shale biota. I identify the undigested exoskeletal remains of a wide range of small invertebrates that lived at or near the water sediment interface such as hyolithids, brachiopods, different types of arthropods, polychaetes and wiwaxiids. This set of direct fossil evidence allows the first detailed reconstruction of the diet of a 505-million-year-old animal. Ottoia was a dietary generalist and had no strict feeding regime. It fed on both living individuals and decaying organic matter present in its habitat. The feeding behavior of Ottoia was remarkably simple, reduced to the transit of food through an eversible pharynx and a tubular gut with limited physical breakdown and no storage. The recognition of generalist feeding strategies, exemplified by Ottoia, reveals key-aspects of modern-style trophic complexity in the immediate aftermath of the Cambrian explosion. It also shows that the middle Cambrian ecosystem was already too complex to be understood in terms of simple linear dynamics and unique pathways.
Highlights
The study of exceptionally preserved Cambrian biotas [e.g., Burgess Shale [1,2], Chengjiang [3,4], Sirius Passet [5,6,7] and Emu Bay Shale [8,9,10] has led to accurate reconstructions of the anatomy, lifestyles [11,12,13], visual properties [10], and even behaviors [14,15] of early animals
The contents from coprolites [29] provide a degree of trophic resolution but cannot be tied to particular predators some coprolites composed entirely of crushed skeletal elements from the Cambrian of California, Utah, Canada (Burgess Shale) and Australia [30] may have been produced by arthropods with robust gnathobasic appendages such as Sidneyia [31]
The interpretations here challenge the notion of strict feeding regimes and linear food chain and provide support for a marine trophic web where energy flow circulated via multiple animal interactions and parallel pathways [41], as it does in present-day ecosystems
Summary
The study of exceptionally preserved Cambrian biotas [e.g., Burgess Shale [1,2], Chengjiang [3,4], Sirius Passet [5,6,7] and Emu Bay Shale [8,9,10] has led to accurate reconstructions of the anatomy, lifestyles [11,12,13], visual properties [10], and even behaviors [14,15] of early animals. The analysis of gut contents presented here and exemplified by the priapulid worm Ottoia prolifica from the middle Cambrian Burgess Shale provides direct and detailed evidence for trophic relationships and new insights both into the actual diet and feeding behavior of Cambrian animals. Conway Morris’ comprehensive work [39] on the priapulid worms from the Burgess Shale in which the gut contents of Ottoia are first described This pioneer work is important in that it led to the concept of Ottoia as an iconic Cambrian predator and formed the basis of my study. The interpretations here challenge the notion of strict feeding regimes and linear food chain and provide support for a marine trophic web where energy flow circulated via multiple animal interactions and parallel pathways [41], as it does in present-day ecosystems
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