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Fossilized Fish Larvae Findings Could Challenge the Long Accepted Theory of Vertebrate Evolution

Lampreys have been in existence for half-a-billion years and have been key in understanding vertebrate evolution. (Image for representation)

Lampreys have been in existence for half-a-billion years and have been key in understanding vertebrate evolution. (Image for representation)

According to Michael Coates, co-author of the study, the ancient hatchlings/larvae were basically miniature adults. This means the evolutionary traits of modern lampreys are wildly different.

A lot of what we understand about evolution is in parts credited to ancient animals that survive even today, like lamprey fish. A recent study conducted on a lamprey fossil from 300 million years ago could shake up our knowledge-bank about vertebrates’ origin and evolution. Scientists with the Canadian Museum of Nature, the University of Chicago and the Albany Museum in South Africa analysed tiny fossils to track the life stages and growth of ancient lampreys, from hatchlings to juveniles to adults.

Lampreys have been in existence for half-a-billion years and have been key in understanding vertebrate evolution. The new research suggests their modern successors’ larvae, ammocoetes, are the survivors from the ancestors of all living vertebrates. The team observed that the modern hatchlings are completely different from their ancient counterparts (based on the fossils).

“We’ve basically removed lampreys from the position of the ancestral condition of vertebrates. So now we need an alternative,” Tetsuto Miyashita, lead author, a paleontologist with the Canadian Museum of Nature was quoted by Science Daily.

The study has been published in the journal Nature.Lampreys are filter feeders. Hatched larvae bury themselves in a riverbed and later metamorphose into blood-sucking adults. The adult and larvae are so different that they were once believed to be different species.

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But in these larvae, scientists sought the origins of vertebrate ancestors. This long-held belief is now challenged by Miyashita’s study.

Four extinct species fossils, discovered in South Africa and the The United States, roughly 310 to 360 million years old were studied. Smallest was the size of 15mm in length (fingernail sized) and still carried a yolk sac (it died just after hatching). It had eyes and tooth suckers, which is only found in adult modern lampreys.

According to Michael Coates, co-author, the ancient hatchlings/larvae were basically miniature adults. This means the evolutionary traits of modern lampreys are wildly different.

The team believes that lampreys can no longer be considered as the primary species for all vertebrate evolution. They suggest ostracoderms, extinct armoured fishes, could be a much better representative for the root of the vertebrate family tree.

“Lampreys are not quite the swimming time capsules that we once thought they were,” said Coates.

Keywords- Lampreys, ostracoderms, vertebrate evolution, lamprey life cycle, ancient lamprey fossil, living fossil, study of vertebrate ancestors