3D imaging of shark embryos reveals evolution of pelvic fins

Curtin University researchers have revealed how the pelvic fins of fish such as sharks and chimeras have evolved from their sudden appearance in the fossil record over 410 million years ago.

The team used CT scanning and 3D modeling to study the growth of pelvic fins in fish embryos to help understand how the skeleton of these fins changed over evolutionary history.

Published in the Journal of Developmental Biology, the research is titled "The Development of the Chimaeroid pelvic skeleton and the Evolution of Chondrichthyan Pelvic Fins."

Lead author and Ph.D. candidate Jacob Pears from Curtin's School of Molecular and Life Sciences said the research showed what the development of modern animals can tell us about their evolution.

"Our work focused on cartilaginous fish and in particular looked at the pelvic fins of elephant sharks. The fine detail from our imaging revealed the basipterygium (pelvic fin bar), which like the femur and tibia in humans, were formed by the fusion of fin radials during early embryonic development," Mr. Pears said.

"In primitive sharks and cartilaginous fish, pelvic fin radials attach primarily to the pelvis while in more modern fish the radials are almost always found on the pelvic fin bar.

"Our findings suggests that the mechanism responsible for these alterations in the pelvic fin skeleton over millions of years is changes in where and how much the fin radials fuse together during early development."

Shark embryos as small as 65mm were nano-CT scanned in collaboration with researchers at McGill University in Canada, with each part of the pelvic skeleton modeled in 3D at the Curtin HIVE (Hub for Immersive Visualization and eResearch).

Visualization technology specialist at the Curtin HIVE Carley Tillett said the CT scans were used to visualize and model the earliest stages of skeletal development of the elephant shark embryos.

"Our work illustrates how modern imaging technologies can provide insight into the development of modern animals and inform our understanding of the evolution of their anatomy," Ms. Tillett said.