Have you ever had a bad neighbor? The kind that blasts heavy metal at 3AM, “exercises” their dog on your lawn, and is just an all-around jerk? Well, bad as they were, chances are that you didn’t have to worry about them eating you (unless they were into some REALLY weird stuff). Our ancient, 375 million year old cousin Tiktaalik wasn’t as lucky. In a paper just published in the Journal of Vertebrate Paleontology, Jason Downs and colleagues have named a new species of big, wide-mouthed predatory fish which shared the same habitat as the famous “fishapod.”
The discovery of the imposing fish species is part of a long-running project to mine the fossil depths of the Late Devonian rock found on Ellesmere Island in Nunavut, Canada. Neil Shubin laid out the reason why such a remote location was selected in his excellent evo-devo tale Your Inner Fish – the 375 million year old strata of Ellesmere appeared to be of just the right type and the right age to contain the close relatives of the first, four-legged vertebrates to walk around on land (known as tetrapods). Tiktaalik – named in 2006 – confirmed their hypothesis, but was not the only fish to be found in the rock. The fossils collected from Ellesmere Island between 2000 and 2008 included a variety of fish from the same ecosystem. There were armored bottom-feeders, lungfish, Tiktaalik, and a variety of other lobe-finned fish* – technically called sarcopterygians – which came in a disparate array of shapes, including the newly-described predator.
*(A brief point of historical interest – among the lobe-finned fish found at the site is Eusthenopteron, a fish which looked something like a cross between its living lungfish and coelacanth cousins. Until very recently, Eusthenopteron was often cast as the fish which began the march of tetrapod evolution by crawling across baking Devonian mudflats. The discovery of Tiktaalik – and other genera close to tetrapod ancestry – have drastically altered the story. Limbs and other traits essential to moving on land had their origin in the water and were not direct adaptations to walking over land in search of ephemeral water holes. Perhaps it’s just a gauge of my geekery, but I can’t help but be amused by the fact that the deposed Eusthenopteron is found in the same deposit as the icon which supplanted it in one of the greatest evolutionary tales of all time.)
Downs and co-authors were already familiar with the genus of wide-headed fish found in the Tiktaalik quarry. In 1941 paleontologist Walter Gross used some jaw fragments found in Latvia to name the fish Laccognathus panderi, and since that time additional parts of the head and post-cranial skeleton have been found in both Latvia and Russia. As recently as 2006, paleontologist Emilia Vorobyeva even named a new species – Laccognathus grossi – on the basis of more complete skull specimens found in Latvia (although, as the authors of the new study point out, this name is probably not valid). Despite being known for decades, our understanding of Laccognathus has been relatively incomplete until recently, and the new specimens from Nunavut add a significant amount of information about the genus.
Named Laccognathus embryi, the new fish species is represented by skull elements from over 22 individuals. The occurrence of the fossils in North America significantly expands the range of the genus, and the fossils are identified as a new species based upon several characteristics such as a lack of peculiar teeth on the coronoid bones and the possession of four gill arches instead of the expected five. Though the paper is primarily descriptive, and does not consider the habits of Laccognathus embryi in detail, Downs and collaborators suggest that the wide, flattened head shape of the fish suggests that it was an ambush predator – perhaps waiting on the river bottom to snap up unwary prey in a manner similar to angel sharks.
But the larger significance of Laccognathus embryi isn’t to be found in its capacious maw, but in its association with the other fish of its time. The entire assemblage of fish at the Ellesmere Island site corresponds closely to those found at sites in Latvia and Quebec – the same sorts of fish, and even some of the same genera, are found among all three. Armored fish called placoderms, a variety of lobe-finned fish, creatures close to tetrapod ancestry, and predators allied with Laccognathus are found across the range. This may help identify future sites of interests for paleontologists interested in how early tetrapods evolved. If there is a Late Devonian site with placoderms, lungfish, wide-headed predators, and the rest, then perhaps “fishapods” such as Tiktaalik and Panderichthys might be found in the same place.
There is something strange about the correspondence between sites in Nunavut, Quebec, and Latvia, though. Each assemblage comes from a different kind of environment. As pointed out by Downs and co-authors, the three environments ranged from marine slopes (Latvia) to estuaries (Quebec) to freshwater streams (Nunavut), which suggests that the common fishy components of each of these assemblages may have been able to tolerate a range of salinity levels – from fully marine to freshwater. You might think that the roughly equivalent aggregations of fish types would signal a common environment, but something more complex was going on. Given how little we yet know about life at the water’s edge in the Late Devonian, this and other mysteries will likely crop up as more fossils are found.
Top Image: Laccognathus embryi lies in wait. Restoration by Jason Poole/ANSP.
Downs, J., Daeschler, E., Jenkins, F., & Shubin, N. (2011). A new species of (Sarcopterygii, Porolepiformes) from the Late Devonian of Ellesmere Island, Nunavut, Canada Journal of Vertebrate Paleontology, 31 (5), 981-996 DOI: 10.1080/02724634.2011.599462