Shaking Up The Fish Family Tree: ‘Living Fossil’ Not As Old As We Thought

2017-09-05T17:33:33+00:00 September 5, 2017|
The skull of a 250 million year old fossil fish and a virtual model of its internal skeleton, along with a life reconstruction. (Credit: Andrey Atuchin)

(Click to enlarge) The skull of a 250 million year old fossil fish and a virtual model of its internal skeleton, along with a life reconstruction. (Credit: Andrey Atuchin)

Polypterids are weird and puzzling African fish that have perplexed biologists since they were discovered during Napoleon’s expedition to Egypt in the late 1700s.Often called living fossils, these eel-like misfits have lungs and fleshy pectoral fins, bony plates and thick scales reminiscent of ancient fossil fish, and flag-like fins along their back that are unique.

(From Science Daily) — For several decades, scientists have placed polypterids down near the base of the family tree of ray-finned fish, a large group believed to have originated around 385 million years ago.

But a new study that used CT scans to probe three-dimensionally preserved fossil fish skulls shakes up the fish family tree by concluding that the emergence of polypterids occurred much later than researchers had thought. The findings also suggest that the origin of all modern ray-finned fish may have occurred tens of millions of years later than is generally believed.

The international research team was led by Sam Giles of the University of Oxford and includes University of Michigan paleontologist Matt Friedman. A paper summarizing the findings is scheduled for publication Aug. 30 in Nature.

“This causes a shakeup in the fish family tree, which indicates that the ancestor shared by all ray-finned fishes lived tens of millions of years after previously thought, maybe in the aftermath of a mass extinction event around 360 million years ago that decimated many other groups,” said Friedman, an associate curator at the U-M Museum of Paleontology and an associate professor in the Department of Earth and Environmental Sciences.

Ray-finned fish represent about half of all backboned animals on Earth. For every species of mammal, bird, reptile and amphibian on land, there is a species of bony fish in the ocean.

Polypterids include about a dozen species of African fish called bichirs and a single species of ropefish. They have long defied classification but are generally accepted to be the most primitive living ray-finned fish, separated from the other modern groups by a host of long-extinct fossil fish.

But the new CT study repositions polypterids on the fish evolutionary tree so they are “nestled neatly back more closely with other living ray-finned fishes, kicking a range of fossil ray-fins to a more distant branch of the evolutionary tree,” said Oxford’s Giles, first author of the Nature paper.

Read the full story here: https://www.sciencedaily.com/releases/2017/08/170830132232.htm