'Fishimal' Was Part Fish, Part Limbed Animal
Image courtesy of Kalliopi Monoyios, University of Chicago
A color illustration of Tiktaalik swimming and walking in water.
April 22, 2011 --
Earth Day isn't just about life on land. It's also an opportunity to explore the organisms that inhabit the oceans. The University of Miami's Rosenstiel of Marine and Atmospheric Science hosts an annual photo contest for the best snapshot of life under the sea. More than 600 images were submitted from an international pool of photographers. This shot of two transparent gobies, taken in MarsaAlam, Egypt, claimed the top prize as the best overall photo of the competition. Explore some of the other photos to claim top prizes in the 2011 underwater photography contest in this slide show.
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This pygmy seahorse, Hippocampus bargibanti, may be difficult to spot, given how well it blends into its environment and the fact that these seahorses don't grow any larger than an inch. But this snapshot earned first prize in the contest's "Marco" category.
This vibrantly colored nudibranch (Cratena peregrina) was seen in Tarragona, Catalonia, Spain.
A nudibranch and a mantis shrimp rest on the sea floor of Bali's Seraya Beach in Indonesia.
Cuttlefish are seen mating off in the Oosterschelde estuary near the town of Zeeland, Netherlands. This photo took the top prize in the "Wide-Angle" category.
A stingray is surround by cardinal fish in this photo taken in Mogan in Gran Canaria, Spain.
This brightly colored jellyfish was spotted in Lake Worth Lagoon in Riviera Beach, Fla. The photo took the top prize in the "Fish or Marine Animal Portrait" category.
This web burrfish (Chilomycterus antillarum was spotted in the same location as the jellyfish in the previous slide. If it looks like it's smiling, that's because this photo took home second prize in the portrait category.
This frog catches its own reflection at the surface of a lake in Belgium just as the photographer snaps a picture.
This snapshot of an orange spotted filefish, Oxymonacanthus longirostris, claimed the top prize in the "Student" category. The fish was spotted in the water of YasawasIslands, Fiji.
This whale shark (Rhincodon typus) and its entourage were spotted cruising the depths of Ningaloo Reef, Western Australia.
Fossils for a creature that looked part fish and part limbed animal were recently found in northern Canada, a paper in the latest issue of Proceedings of the National Academy of Sciences reports.
The beastie, Tiktaalik roseae, represents the best-known transitional species between fish and land-dwelling animals, according to researchers. It lived 375 million years ago.
“Tiktaalik was a combination of primitive and advanced features,” co-author Edward Daeschler, Associate Curator of Vertebrate Zoology at the Academy of Natural Sciences of Drexel University, said in a press release.
While classified as a fish, Tiktaalik looked like a cross between a fish and a crocodile. It could grow to 9 feet in length, and likely spent its days hunting in shallow freshwater environments. It had gills, scales and fins, but also had features associated with terrestrial animals. These included a mobile neck, a robust ribcage and primitive lungs.
Of most interest to the researchers, its large forefins had shoulders, elbows and partial wrists, which allowed it to support itself on ground.
The presence of these limb-like features challenges the theory that such mobile hind appendages developed only after species transitioned to life on land.
“Previous theories, based on the best available data, propose that a shift occurred from ‘front-wheel drive’ locomotion in fish to more of a ‘four-wheel drive’ in tetrapods (four-footed animals),” said co-author Neil Shubin, who is a professor of Anatomy at the University of Chicago. “But it looks like this shift actually began to happen in fish, not in limbed animals.”
Even some modern fish can walk, such as the African lungfish. You can see a bit of that, and learn more about this unusual fish, in this video.
Lungfish often look like they are slithering, more than walking, but if you see them in an aquarium, their little limbs are evident, and they do walk around.
It’s likely that Tiktaalik did the same, with its later relatives walking completely out of water and onto land, where they eventually evolved into animals.
“Regardless of the gait Tiktaalik used, it’s clear that the emphasis on hind appendages and pelvic-propelled locomotion is a trend that began in fish, and was later exaggerated during the origin of tetrapods,” Shubin said.