page_title: Tiktaalik
section_title: Paleobiology
hierarchical_section_title: Tiktaalik / Paleobiology
caption_attribution_description: Limb of Tiktaalik (cast of the fossilised limb of a Tiktaalik, looking from fin towards shoulder), photographed at Science Museum, London, 2006
context_page_description: Tiktaalik is a monospecific genus of extinct sarcopterygian from the Late Devonian Period, about 375 Mya, having many features akin to those of tetrapods.
  Unearthed in Arctic Canada, Tiktaalik is technically a fish, complete with scales and gills - but it has the flattened head of a crocodile and unusual fins. Its fins have thin ray bones for paddling like most fish, but they also have sturdy interior bones that would have allowed Tiktaalik to prop itself up in shallow water and use its limbs for support as most four-legged animals do. Those fins and a suite of other characteristics set Tiktaalik apart as something special; it has a combination of features that show the evolutionary transition between swimming fish and their descendants, the four-legged vertebrates - a clade which includes amphibians, reptiles, birds and mammals.
  It and similar animals may possibly be the common ancestors of the broad swath of all vertebrate terrestrial fauna: amphibians, reptiles, birds, and mammals.
  The first well-preserved Tiktaalik fossils were found in 2004 on Ellesmere Island in Nunavut, Canada.
context_section_description: Tiktaalik generally had the characteristics of a lobe-finned fish, but with front fins featuring arm-like skeletal structures more akin to those of a crocodile, including a shoulder, elbow, and wrist. The fossil discovered in 2004 did not include the rear fins and tail. It had rows of sharp teeth indicative of a predator fish, and its neck could move independently of its body, which is not common in other fish (Tarrasius, Mandageria, placoderms, and extant seahorses being some exceptions; see also Lepidogalaxias and Channallabes apus). The animal had a flat skull resembling a crocodile's; eyes on top of its head; a neck and ribs similar to those of tetrapods, with the ribs being used to support its body and aid in breathing via lungs; well developed jaws suitable for catching prey; and a small gill slit called a spiracle that, in more derived animals, became an ear.
  The fossils were found in the "Fram Formation", deposits of meandering stream systems near the Devonian equator, suggesting a benthic animal that lived on the bottom of shallow waters and perhaps even out of the water for short periods, with a skeleton indicating that it could support its body under the force of gravity whether in very shallow water or on land. At that period, for the first time, deciduous plants were flourishing and annually shedding leaves into the water, attracting small prey into warm oxygen-poor shallows that were difficult for larger fish to swim in. The discoverers said that in all likelihood, Tiktaalik flexed its proto-limbs primarily on the floor of streams and may have pulled itself onto the shore for brief periods. In 2014, the discovery of the animal's pelvic girdle was announced; it was strongly built, indicating the animal could have used them for moving in shallow water and across mudflats. Neil Shubin and Ted Daeschler, the leaders of the team, have been searching Ellesmere Island for fossils since 2000
  We're making the hypothesis that this animal was specialized for living in shallow stream systems, perhaps swampy habitats, perhaps even to some of the ponds. And maybe occasionally, using its very specialized fins, for moving up overland. And that's what is particularly important here. The animal is developing features which will eventually allow animals to exploit land.
caption: Limb shoulder to fin
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