An extinct creature described as an amphibious, otter-like “marine bear” may have shared its bite with a saber-toothed cat, according to a study published this week in the Proceedings of the Royal Society B.
First described in the 1960s after fragments of skulls and teeth belonging to two related species – Kolponomos clallamensis and Kolponomos newportensis – were discovered on the coast of Oregon, the strangely enigmatic creature had previously been thought to resemble sea otters in its feeding strategy. This presumption was based on the fact that superficial analysis of its cheek teeth revealed similarities with those of otters in both form and wear, suggesting that Kolponomos fed on the hard-shelled molluscs that abound in the region, using its teeth to crush them.
However, while conducting a more detailed analysis of the specimens, researchers began to realize that they in fact differed significantly from otters, with a jaw structure that bore remarkable resemblance to that of the saber-toothed cat Smilodon. For instance, both Kolpomonos and Smilodon have a deep jaw bone that tapers off towards the back, and large attachment sites for neck muscles.
In saber-toothed cats, these features are thought to have facilitated a particular type of bite known as the canine shear bite, whereby the mandible – or lower jaw – was used to “anchor” prey down, while powerful neck muscles propelled the head forward, driving the canines into the victim’s flesh.
Based on these findings, the researchers hypothesized that Kolpomonos may have used this same technique in order to dislodge molluscs from rock surfaces, utilizing the mandible as a kind of fulcrum around which its head could pivot and force the teeth between its prey and its point of attachment.
The extinct saber-toothed cat known as Smilodon fatalis used a canine shear bite to kill its prey. Valentyna Chukhlyebova/Shutterstock
In order to test this hypothesis, they used a computer simulation technique called finite element analysis to observe how effectively the mandibles of several different carnivores – including Kolpomonos, Smilodon and sea otters – could perform a range of different bite types. Among the bites simulated were the canine shear bite, or “anchor bite,” of the Smilodon, and the sea otter “crushing bite.”
Results showed that the jaw mechanics of Kolpomonos and Smilodon were more similar to each other than any other animals in the study, and that the extinct "marine bear" – thought to have lived around 20 million years ago – actually differed significantly from the sea otter in its biting capabilities.
For instance, while the otter's mandible was found to do much of the work while crushing prey, Kolpomonos exhibited much greater ‘stiffness’ in the lower jaw, which does less of the work.
As such, the researchers conclude that Kolpomonos probably had a bite that was more similar to that of Smilodon than sea otters, even though the two creatures consumed vastly different diets. It is therefore likely that they used this technique for different purposes, with Smilodon using its bite to kill other animals while Kolpomonos utilized the same method in order to pry molluscs off rocks.
The study authors also note that, despite these striking similarities, Kolpomonos and Smilodon are unlikely to be related via a common ancestor. Instead, they believe this coincidence to represent a case of convergence, whereby two distinct species develop the similar features independently of one another.