Early fish had fingers

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A study by scientists from Estonia and Sweden has found that an early fish had finger like features within their fins.

Until recently, researchers believed that early tetrapods (vertebrates with limbs) may have evolved fingers and toes following their transition to land 380 million years ago, as there appeared to be no evidence of these digits in fossil fish records.

However, recent studies on another extinct fish Tiktaalik together with some genetic findings from paddlefish and lungfish had begun to suggest that this was not the case.

As a consequence of these works, studies were undertaken on a near-complete fossilised skeleton of Panderichthys - a predatory fish alive about 385 million years ago and thought to be transition between fish and tetrapods - and they showed that early digits were in fact present in their fins.

The skeleton was analysed using a hospital CT (Computerised Tomography) scanner. Researchers found that that the right pectoral fin contained four bony extensions.

In contrast to early tetrapods, the limbs did not project out at an angle to the body wall but instead back along the line of the body.

The fin was found to contain an endoskeleton consisting of familiar bones such as the humerus, radius, ulna, and four small, slightly flattened ~distal radials - the precursors to our fingers and toes.

The fan-like array of digits would have meant that Panderichthys fins would have been broader at the ends and may well have been used to lean on rather than for swimming.

Catherine Boisvert is quoted in Live Science as saying: It was probably using its front fins as supports to be able to look up, kind of doing push-ups at the bottom of the river looking outside with its eyes So, if it was stuck in a pool and it was drying out, the fish would have been able to get itself out to the next water body,

Together with work done on the development of fins in sharks, paddlefish and the Australian lungfish, this study is the ~last piece in the puzzle confirming that finger-like precursors were already present in our fish ancestors.

For more information see: Catherine A. Boisvert, Elga Mark-Kurik and Per E. Ahlberg. The pectoral fin of Panderichthys and the origin of digits. Letters to Nature: Nature,doi:10.1038/nature07339; 21 September 2008.