Tiktaalik roseae fossil. Photo used from Wikimedia Commons, uploaded by Eduard Solà.

How is Tiktaalik adapted to its environment?

Tiktaalik fossil. Photo used from Wikimedia Commons, uploaded by Ghedoghedo.Tiktaalik looks like a cross between a prehistoric fish and a tetrapod. Tiktaalik retained both fish and tetrapod characteristics in its body structure. Its retained fish characteristics include scales, fins, and gills (The University of Chicago, 2006). Its tetrapod characteristics include a neck, ribs, a flat head, which has dorsally positioned eyes, a fin skeleton, and ear notches (The University of Chicago, 2006). Tiktaalik began the transition of organisms living only in the water to terrestrial living, and its tetrapod synapomorphies were well adapted for the shallow water environment that it is believed to have lived in.

An example of ribs. Photo used from Wikimedia Commons, Creative Commons License, uploaded by Sunshineconnelly.Tiktaalik had a very strong internal skeleton that was able to support its heavy trunk upon a solid substrate (Ahlberg and Clack, 2006, Downs et al., 2008). Tiktaalik also had larger ribs than the fish it lived among, which also contributed to it being able to support itself out of the water and its changes in respiration (Ahlberg and Clack, 2006). Tiktaalik underwent many cranial endoskeleton changes which point to its decreased reliance on water pumping for respiration (Downs et al., 2008). Another adaptation that resulted in a change of the way Tiktaalik breathed was the loss of an operculum, which changed how Tiktaalik respired (Ahlberg and Clack, 2006). The changes in Tiktaalik's morphology indicates that it very likely breathed like lungfish. Lungfish still retain gills, but are also capable of breathing via modified swim bladders acting as lungs (Owen, 2006).

Tiktaalik roseae. Photo used from Flickr, Creative Commons License, photo credit to Jamie Bernstein, no changes made. Tiktaalik roseae also possessed a head and neck that were very different from other fishes. The head of Tiktaalik was capable of independent motion, which gave it a lot more head mobility than other tetrapodmorph fish (Downs et al., 2008). Because Tiktaalik had a head with independent motion, a neck, a snout with the ability to snap, and dorsally located eyes, it is inferred that it hunted very much like a modern day crocodile (Downs et al., 2008, Ahlberg and Clack, 2006, Shubin et al., 2006). Crocodiles today hunt by sitting camouflaged and motionless in the water with their body hidden beneath the surface (Vancouver Aquarium, 2013). When prey gets close enough, the crocodile will snap its jaws and drag the animal under the water to be drowned and then consumed (Vancouver Aquarium, 2013). It is likely that Tiktaalik possessed a lateral line full of sensory receptors along the upper skin layer, which allowed them to sense movement in the water around them, much like crocodiles today have (Britton, 2012) . While Tiktaalik may not have hunted as large of animals as some modern crocodiles do, it is likely that Tiktaalik hunted small fishes and invertebrates along the shorelines and shallows where they lived (Owen, 2006).

 Crocodile. Photo used from Wikimedia Commons, uploaded by Tomás Castelazo.

Tiktaalik also possessed pectoral fins  that were composed of fin rays and able to support the weight of it (Downs et al., 2008, Ahlberg and Clack, 2006). These fins were not quite forelimbs however.  The limbs and shoulders of Tiktaalik allowed it to swim, as well as prop itself up on a solid substrate (The University of Chicago, 2006). Tiktaalik could prop itself up by flexing the shoulder and elbow, while simultaneously extending the inter-radial joints (Shubin et al., 2006). Not only were the fins of Tiktaalik well adapted to living in the shallows, but also the distal part of the body to the head was able to flex slightly upward (Ahlberg and Clack, 2006). The fins of Tiktaalik allowed it to live in a variety of different substrates (Shubin et al., 2006).                        

Tetrapod limb transition. Tiktaalik roseae's fin is #1. Photo used from Wikimedia Commons, Creative Commons License, uploaded by Conty.


<Habitat                        Reproduction>