One of the most important of these fossils came to the world’s attention in 2006. Digging in the Arctic, a team of scientists found a 370-million-year-old creature they dubbed TiktaalikAs I wrote at the time on the Loom,Tiktaalik belonged to a lineage of aquatic vertebrates called lobefins–a group that today includes lungfish and coelacanths. A number of anatomical features set lobefins apart from other fish, and show them to be more closely related to us and other tetrapods. They generally have stout fins that contain bones corresponding to the upper bones of our arms and legs. Some fossils of lobe fins don’t just have a bone corresponding to the humerus–the long bone attached to the shoulder–but the radius and ulna, too.

But even among lobefins,Tiktaalik was remarkably tetrapod-like. It had a distinct neck, for example, and its fins had additional limb-like bones. Along with bones corresponding to a humerus, radius, and ulna, it even had wrist-like bones that functioned as a joint, as they do in our hands. Without digits, Tiktaalik couldn’t grasp a branch with its fins. But it could do a decent push-up in the muddy shallows that it called home in the Devonian Period. (Neil Shubin, one of the discoverers of Tiktaalik, told the creature’s story in his 2009 book Your Inner Fish.)

The bones that Shubin and his colleagues described in 2006 came from the front half of TiktaalikOnly now, eight years later, have Shubin and his colleagues unveiled the other half of this remarkable beast. And they’ve now stretched out the transition from fish to tetrapod even more.