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Blind fish that crawls on land holds clues to evolution

One small fish in Thailand could hold insights into the evolution of life on earth and how primitive ocean-dwellers developed into animals that could walk on land.

Researchers from the New Jersey Institute of Technology have identified the walking cavefish, a fish that can walk on land and even climb waterfalls using its salamander-like limbs in the same way as a tetrapod, or a four-footed mammal or amphibian. So far, no other fish has been found with these anatomical features.

Research on discovery of the cavefish, Cryptotora thamicola,was published Thursday in the journal Nature Scientific Reports.

The unusual, blind, two-inch-long fish was found in caves located in the Tham Maelana and the Tham Susa karst cave formation in northern Thailand. It has not been seen anywhere else on Earth.

The researchers say the fish has been observed climbing rocks and waterfalls and walking on both rough and smooth wet surfaces while out of the water.

Their study analyzes how the fish manages this unusual feat. "The pelvis and vertebral column of this fish allow it to support its weight against gravity and provide large sites for muscle attachment for walking," Brooke Flammang, one of the study's authors, said in a press release.

Segmented reconstruction of computed microtomography scan of the pelvic girdle of the blind cavefish,Cryptotora thamicola. Color format: dark purple, sacral rib and iliac process; tan,puboischiadic plate; blue, pelvic fin. Flammang et. al./Nature Scientific Reports

"This research gives us insight into the plasticity of the fish body plan and the convergent morphological features that were seen in the evolution of tetrapods," Flammang added.

The discovery is significant in that scientists have long believed that the ancestors of modern-day land animals literally pulled themselves out of the ocean and onto land in a similar manner more than 400 million years ago. This fish could provide insights into how creatures made the transition.

"While there have been multiple cases of secondarily aquatic vertebrates, we only have fossil evidence of one period of time in which vertebrates emerged from an aquatic lifestyle and evolved terrestrial walking behavior," the study reads. "These findings are significant because they represent the first example of behavioural and morphological adaptation in an extant fish that converges on the tetrapodal walking behaviour and morphology."

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