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About 400 million years ago, vertebrates first began to crawl from the primordial seas onto land. Last week, thanks to a cutting-edge mathematical-analysis technique, a global research team uncovered how a crucial stage in evolution made that advance possible. Published May 8 in Science Advances, the paper deciphers crucial information about how those sea-dwelling creatures' fins became the specialized limbs that made life on dry land feasible.
"All animals that have limbs with hands and feet and fingers and toes [that is, tetrapods] arose from animals that were fish with fins that lived in the water," explained Stephanie E. Pierce, associate professor of organismic and evolutionary biology and curator of vertebrate paleontology at Harvard's Museum of Comparative Zoology (MCZ). "One of the big puzzles is, how did that happen?"
Collaboration - Authors - Borja - Esteve-Altava - John
In collaboration with lead authors Borja Esteve-Altava and John Hutchinson at London's Royal Veterinary College, Pierce and her colleagues present new research that may explain how. Although paleontologists have accumulated plentiful fossil evidence of this particular evolutionary change, it was only when the team examined it via an innovative technique called anatomical network analysis (AnNA) that clear patterns emerged. AnNA, created in 2015 for biological and biomedical research, deals with structures of pairwise relations between objects. Based on graph theory, which essentially compares connections and relations between objects—in this case, the fossilized remains of fins and limb bones—a pattern emerged.
As tetrapods evolved, limb structures became simpler and more modular. In other words, where fin bones tend to be widely interconnected in many directions, the bones in limbs tend to be linked end to end, or "in a string," as Pierce put it. "So one bone is connected to the bone before it and the bone after it. Fingers show this perfectly."
Pierce - Decrease - Complexity - Bone - Contacts
However, Pierce added, "though we have this decrease in complexity in bone contacts,...
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