image: This is a Cambrian trilobite fossil from Utah. view more
Credit: John R. Paterson
A study finds that animal life's "Big Bang" ended much sooner than previously thought. The sudden appearance of numerous diverse animals more than 500 million years ago, known as the Cambrian explosion, is one of the most significant events in the history of life. However, the tempo and duration of this evolutionary milestone remains vigorously debated. John Paterson and colleagues analyzed more than 100 anatomical traits of more than 100 species of trilobites, the most diverse and abundant Cambrian animals, spanning approximately 520-485 million years ago, to estimate the animals' evolutionary rates. Multiple statistical models revealed uniform evolutionary rates throughout the entire time interval. The results suggest that the Cambrian explosion ended much earlier than widely assumed; by around 520 million years ago, the evolutionary rates that presumably characterized the Cambrian explosion had already slowed to levels typical of the ensuing eon. The authors further estimated that all trilobites diverged from a common ancestor less than 540 million years ago, suggesting that trilobites did not have a prolonged history prior to their appearance in the fossil record. The latter finding suggests that modern animal groups first evolved, diversified, and completely reengineered the marine ecosystem, possibly in the brief span of 20 million years, according to the authors
Article #18-19366: "Trilobite evolutionary rates constrain the duration of the Cambrian explosion," by John R. Paterson, Gregory D. Edgecombe, and Michael S. Y. Lee.
MEDIA CONTACT: John R. Paterson, University of New England, Armidale, AUSTRALIA; tel: +61-2-6773-2101, +61-0-407-259-584; e-mail: jpater20@une.edu.au
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