The rapid increase in diversity and abundance of biomineralizing organisms during the Early Cambrian epoch (around 535 million years ago) is often attributed to predation and an evolutionary arms race. A Cambrian arms race is typically discussed on a macroevolutionary scale, particularly in the context of escalation. Despite abundant fossils demonstrating early Cambrian predation, empirical evidence of adaptive responses to predations is lacking. To explore the Cambrian arms race hypothesis, paleontologists from the University of New England, the American Museum of Natural History and Macquarie University assessed a large sample of tiny fossilized shells of the tommotiid species Lapworthella fasciculata from South Australia, over 200 of which show holes made by a perforating predator.
The 517-million-year-old shells of Lapworthella fasciculata. Image credit: Bicknell et al., doi: 10.1016/j.cub.2024.12.007.
“Predator-prey interactions are often touted as a major driver of the Cambrian explosion, especially with regard to the rapid increase in diversity and abundance of biomineralizing organisms at this time,” said Dr. Russell Bicknell, a paleontologist at the American Museum of Natural History.
“Yet, there has been a paucity of empirical evidence showing that prey directly responded to predation, and vice versa.”
An evolutionary arms race is a process where predators and prey continuously adapt and evolve in response to each other.
This dynamic is often described as an arms race because one species’ improved abilities lead to the other species improving its abilities in response.
Dr. Bicknell and colleagues studied a large sample of fossilized shells of an early Cambrian tommotiid species, Lapworthella fasciculata, from South Australia.
More than 200 of these extremely small specimens, ranging in size from slightly larger than a grain of sand to just smaller than an apple seed, have holes that were likely made by a hole-punching predator — most likely a kind of soft-bodied mollusk or worm.
The paleontologists analyzed these specimens in relation to their geologic ages, finding an increase in shell wall thickness that coincides with an increase in the number of perforated shells in a short amount of time.
This suggests that a microevolutionary arms race was in place, with Lapworthella fasciculata finding a way to fortify its shell against predation and the predator, in turn, investing in the ability to puncture its prey despite its ever-bulkier armor.
“This critically important evolutionary record demonstrates, for the first time, that predation played a pivotal role in the proliferation of early animal ecosystems and shows the rapid speed at which such phenotypic modifications arose during the Cambrian Explosion event,” Dr. Bicknell said.
The study was published in the journal Current Biology.
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Russell D.C. Bicknell et al. Adaptive responses in Cambrian predator and prey highlight the arms race during the rise of animals. Current Biology, published online January 3, 2025; doi: 10.1016/j.cub.2024.12.007