How the limbs of vertebrates evolved from the fins of fish

How the limbs of vertebrates evolved from the fins of fish

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A research team led by the researcher from the Institute of Evolutionary Biology (IBE) Borja Esteve Altava, in collaboration with researchers from the Royal Veterinary College (RVC) of London, Harvard University, the University of Auckland, the Institute of Technology of New York and Howard University in Washington DC, has recomposed the anatomy of the fins and limbs of extinct fossil animals by using a new mathematical analysis that uses networks to model animal anatomy.

Models have revealed how the complexity of bony arrangements has decreased during the transition from fins to limbs. This less complexity has been accompanied by an increase in the number of bones and joints.

The team has also found that the variety of connections between bones has decreased since the first four-limbed vertebrates, about 400 million years ago.

Scientists suggest that there must be an evolutionary compromise between the original mechanism of development of the fins and limbs and the new biomechanical demands that were required to walk on the limbs.

"Modeling the fins and limbs as networks of connected bones has allowed us to quantify and compare the anatomy of these two related, but very different, structures in a way that is not accessible to other current measurement methods", comments Borja Esteve-Altava , currently a postdoctoral researcher at the Institute of Evolutionary Biology (IBE), a joint center of the Higher Council for Scientific Research (CSIC) and the Pompeu Fabra University (UPF) and who carried out this research at the RVC.

Greater modularity of the limbs

'One of the most interesting findings of this groundbreaking study has been demonstrate that the limbs have greater modularity than the fins; some parts of the limbs are more associated with each other, forming an exclusive club of interactions. That modularity allowed many later specializations, such as the mobility of our fingers to type on keyboards compared to the stiffness of our toes to walk with them, ”says John Hutchinson, professor of evolutionary biomechanics at RVC.

According Stephanie E. Pierce, Associate Professor of Organismic and Evolutionary Biology and Curator of Vertebrate Paleontology at the Museum of Comparative Zoology at Harvard University, “although the connections between bones were simplified as fins became limbs, the evolution of the hands with the fingers and toes with the toes provided the necessary platform to walk, allowing our first ancestors to leave the aquatic environment to live on land.

The study opens the door to biomechanical analysis of the development and evolution of other parts of the body involved in motor skills, such as the tail of reptiles or the wings of birds, as well as the integration of the skeleton and musculature in macroevolution studies.

Bibliographic reference:

Borja Esteve-Altava et. to the. «Evolutionary parallelisms of pectoral and pelvic network-anatomy from fins to limbs»Science Advances 2019; 5: eaau7459.

Video: Evolution of reduced limbs