A large, crocodile-like animal that lived more than 340 million years ago was one of the earliest vertebrates to have a fast-growing phase in its youth.
Whatcheeria was an early tetrapod 鈥� one of the first vertebrates to have arms and legs instead of fins. At 2 metres long, it was one of the biggest carnivores of the era, and its anatomy hints that it snatched prey from the water by ambush, just like modern crocodiles. But how Whatcheeria reached such an impressive size for its time has been unknown.
The bones of Whatcheeria contain a record of the animal鈥檚 growth, just as a tree鈥檚 rings keep a timeline of its life history. at the Field Museum of Natural History in Chicago and his colleagues looked at these microscopic clues in nine Whatcheeria femur bones.
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They found that the animal grew much more rapidly early in life than many of the earliest four-legged vertebrates to dwell at the water鈥檚 edge. 鈥淲hen we came up with evidence of rapid, sustained growth, it was quite a surprise,鈥� says Angielczyk.
Getting big quickly would have given Whatcheeria an edge. The tetrapod鈥檚 growth spurt not only opened up a broader array of menu choices for the carnivore, but also helped Whatcheeria quickly get too big for other predators to eat.
Up until now, early tetrapods were thought to have grown relatively slowly throughout their lives, much the same way that many modern amphibians do. Fast growth was thought to be an evolutionary shift that came later among animals that were more reptile-like and laid their eggs on dry land.
The new study overturns that view. 鈥淚t鈥檚 an elegant study based on one of the best and most completely preserved early tetrapods we have,鈥� says at the University of Cambridge, who wasn鈥檛 involved in the study. Whatcheeria and related animals set the stage for vertebrates to flourish on land, he adds.
Communications Biology
