An Atlas of Malformed Trilobites from North American Repositories Part 2. The American Museum of Natural History

Trilobites with malformations present important insight into the paleoecology of the wholly extinct arthropod group. This includes records of failed predation, developmental complications, and parasitic interactions. The documentation of malformed trilobites therefore allows for a more thorough understanding of these animals. Such summaries also permit larger-scale, synthetic works that consider patterns and processes associated with malformations to be developed. To expand the current record of malformed Cambrian through to Devonian trilobites, we report 16 novel specimens across 12 genera from deposits spanning Australia, Bolivia, Canada, the United States, and Wales. These specimens illustrate examples of injuries potentially caused by predation, molting, and accidental injury, teratological malformations, and pathological infestation. Possible predators; explanations for developmental, genetic, and recovery issues; as well as infestations are considered. Comparison of size distributions of malformed and nonmalformed Elrathia kingii indicates that primarily the largest specimens preserve malformations. This implies that either smaller specimens fully recovered from malformations or did not survive once the malformations were incurred. Continued documentation of malformed specimens will allow larger datasets to be compiled and further promote the use of malformations in understanding trilobite paleoecology.