Tiktaalik

Tiktaalik is an ancient, extinct genus of lobe-finned fish. The sole discovered species, Tiktaalik roseae, lived approximately 375 million years ago during the Late Devonian Period. It featured a distinctive flat, triangular-shaped head and sturdy fin bones that allowed it to prop itself up out of the water. Due to its mix of aquatic and terrestrial traits, scientists see Tiktaalik as an evolutionary link between fish and four-legged vertebrates. 

Description & Size

According to fossil records, Tiktaalik measured between 4.1 and 9 feet long. It possessed a flat, triangle-shaped skull like the head of a crocodile. The back of the skull featured notches that likely contained spiracles for breathing air. These notches indicate that Tiktaalik had both lungs and gills. Unlike other fish, Tiktaalik lacked bony plates in the gill area. This meant it had a neck that allowed it to move its head freely and hunt effectively on land or in shallow water. While the original fossil found in 2004 lacked rear fins and a tail, these features were found in later fossils. 

Additionally, unlike other transitional fossils, Tiktaalik possessed fins with features reminiscent of terrestrial vertebrates. It had basic wrist bones and hard rays in its fins similar to “fingers.” The fins could likely bear the Tiktaalik’s weight, thereby allowing it to push its body out of the water and walk on land. Tiktaalik also possessed a strong ribcage, which further supports the theory of it having both lungs and gills. 

In terms of modern equivalents, Tiktaalik somewhat resembles gars in the family Lepisosteidae. These include an elongated, tube-like body, double rows of teeth, broad and flat skull, and both internal and external nostrils.  

Evolution and History

Presently, Tiktaalik roseae represents the only species in the genus Tiktaalik. Its mixture of fish and tetrapod characteristics situate it as a possible transitional species between marine and terrestrial vertebrates. In fact, paleontologist Neil Shubin – a member of the team that discovered the first Tiktaalik fossils – dubbed the Tiktaalik a “fishopod.” Like a fish, Tiktaalik possessed gills, scales, and fins. However, like a tetrapod, it also had rib bones, a mobile neck, and lungs. Additionally, it possessed unique “fishapod” features, such as fins with working wrist joints and half-fish, half-tetrapod ears.  

In terms of its taxonomy, Tiktaalik was originally described as a sister taxon to Elpistostege, another finned tetrapod from the Late Devonian. It resided directly below Acanthostega and Ichthyostega, both of which were limbed vertebrates from the Late Devonian Period. Contrary to what some people claim, Tiktaalik’s discoverers never claimed it was a “missing link” in the evolutionary timeline connecting fish and tetrapods. Rather, it serves as a model to illustrate the evolutionary trends that led to the development of tetrapods. 

Diet – What Did Tiktaalik Eat?

The diet of Tiktaalik remains unknown due to a lack of stomach contents found in fossils. Most likely, Tiktaalik ate an omnivorous diet consisting of both plants and animals. Given its size, Tiktaalik probably preyed on smaller aquatic organisms such as fish. Also, it could have preyed on small semi-terrestrial tetrapods that lived in shallow water or on land. This theory is supplemented by the fact that Tiktaalik possessed weight-bearing limbs and a maneuverable neck. 

Habitat – When and Where it Lived

Tiktaalik lived during the Late Devonian Period around 375 million years ago. Specifically, it lived during the Frasnian Stage, the first stage of the Late Devonian Period that lasted approximately from 382.7 to 372.2 million years ago. 

The first Tiktaalik fossils were discovered in the Fram Formation on Ellesmere Island in the territory of Nunavut, Canada. However, during the Late Devonian Period, Ellesmere Island belonged to the continent Laurentia, which consisted of modern-day Greenland and the eastern part of North America. At that time, Laurentia resided near the equator and possessed a much warmer climate. 

Thanks to the presence of lungs and gills, as well as fins designed for swimming and bearing weight, Tiktaalik could navigate both on land and in the water. Most experts believe that Tiktaalik spent much of its time on the floors of shallow streams and other waterways but also spent brief periods of time on land. It likely lived in mudflats, ponds, or swamps, as its anatomy made it well-suited to thrive in these environments. 

Threats and Predators

Just as we don’t know much about Tiktaalik’s diet, we also know very little about its potential predators. Due to its size, Tiktaalik was most likely situated somewhere near the middle or top of the food chain. At the time it lived, Tiktaalik had to compete with other predators, such as sharks. Larger sharks could have posed a threat to Tiktaalik, both as competitors for food and as predators. However, further discoveries are needed to uncover potential threats to Tiktaalik. 

Discoveries and Fossils – Where It was Found

A team of paleontologists discovered the first Tiktaalik fossils in 2004. The team included Edward “Ted” Daeschler of the Academy of Sciences of Drexel University, Professor Farish Jenkins Jr. of Harvard University, and Neil Shubin of the University of Chicago. Daeschler et al. discovered the first Tiktaalik fossils in the Fram Formation on Ellesmere Island, Nunavut, Canada. The team spent 5 years digging on the island before discovering several well-preserved Tiktaalik fossils.

In 2006, the team published their discovery in the April 6, 2006, issue of the British weekly scientific journal Nature. The discovery set the scientific community on fire, as experts immediately recognized Tiktaalik as a possible transitional fossil linking marine fish to terrestrial vertebrates. Its common and genus name derives from an Inuktitut word meaning “large freshwater fish.” Meanwhile, its specific name roseae refers to the name of an anonymous donor who funded the Tiktaalik project. 

Extinction – When Did It Die Out?

To date, experts don’t know for sure when Tiktaalik went extinct. That said, it most likely died out sometime near the end of the Late Devonian Period, around 360 million years ago. Around that time, a mass extinction occurred known as the Hangenberg event. Also known as the end-Devonian extinction, this event occurred at the end of the Famennian stage of the Late Devonian Period and signaled the start of the Carboniferous Period. 

The Hangenberg event officially ranks as the second-largest extinction event to occur during the Devonian Period. The event lasted anywhere from 100,000 to several hundred thousand years, during which time the planet went through intense changes. Climate, sea levels, and animal life all changed drastically during this period. According to estimates, anywhere from 20% to 50% of all marine genera on Earth went extinct during this period, including Tiktaalik. 

Similar Animals to Tiktaalik

• Acanthostega. Acanthostega appeared during the Famennian stage of the Late Devonian Period around 365 million years ago. Although it lacked wrists, making it poorly adapted to walking on land, it possessed noticeable limbs and eight webbed digits on each hand.     
• Ichthyostega. Ichthyostega is an extinct tetropodomorph that lived 365 to 360 million years ago during the Late Devonian Period. Like Tiktaalik, it possessed four weight-bearing limbs and lungs that helped it to move through shallow swamps.   
• Elginerpeton. Elginerpeton is an extinct genus of stegocephalian. It lived during the Late Devonian Period around 375 million years ago. Based on fossil records, it measured around 5 feet long, and possessed thin, powerful jaws suited to catching small, fast prey. 

1. University of Chicago, Available here: https://shubinlab.uchicago.edu/research-2-2/
2. The Guardian, Available here: https://www.theguardian.com/science/2014/jan/13/tiktaalik-fossil-fish-four-legged-land-animal
3. National Geographic, Available here: https://www.nationalgeographic.com/animals/article/140113-tiktaalik-pelvis-fossil-discovery-science
4. Nature.com, Available here: https://www.nature.com/articles/nature04639