In a case of convergent evolution, a saber-toothed tiger once roamed South America until it became extinct about three-and-a-half million years ago. It had a pouch like a marsupial, huge saber-like canine teeth, but a bite that was embarrassing, no more powerful than a modern-day kitty.
Convergent evolution is the process whereby unrelated or distantly related organisms independently evolve similar traits. Wings are a classic example of this. For example, both bats and birds have evolved similarly constructed wings that are capable of flight.
Called by the name Thylacosimilus atrox or “pouch saber,” this ancient predator was a deadly and efficient killing machine, despite its weak bite. According to a new study, pouch saber used its strong jaw and forearms to immobilize its prey. It then killed its victim by puncturing the windpipe or major arteries with its over-sized fangs.
Paleontologist and lead author Dr Stephen Wroe of the University of New South Wales (UNSW) suggests that the Thylacosimilus atrox used “a mix of brute force and delicate precision,” in dispatching its victims.
Dr Wroe said in a statement:
Thylacosimilus looked and behaved like nothing alive today. Frankly, the jaw muscles of Thylacosimilus were embarrassing.”
Thylacosimilus resembled a large cat in some respects, but it was more closely related to the marsupials of Australia and America.
Like kangaroos and opossums, it carried its young in a pouch. The pouch saber-tooth also sported the largest canine teeth of any known saber-toothed animal, including Smilodon fatalis, the well-known North American saber-toothed “tiger.”
According to researchers, Thylacosimilus and Smilodon both had enormous canines designed to bring down large prey, but the creatures were separated by more than a million years of evolution. Smilodon was a true feline that wandered the American continent much more recently than the pouched saber-tooth. It became extinct a mere 10,000 years ago.
The fangs of Thylacosimilus, unlike Smilodon’s, continued to grow throughout its lifetime. They had roots reaching back almost as far as its small brain-case.
Using sophisticated three-dimensional computer models, Dr Wroe and his research team were able to shed light on Thylacosimilus and its predatory behavior, and how it and Smilodon delivered their fatal bites.
Through a comparison between the performance of Thylacosimius with Smilodon and the modern, conical-toothed leopard, Panthera pardus, the research team found that the jaw-adductor-driven bite force of Thylacosimius was extremely weak and likely played no major role in the killing bite.
Despite having a bite less powerful than a domestic cat, the team determined that Thylacosimilus possessed extremely powerful neck muscles that outperformed both the leopard and Smilodon.
According to Dr. Wroe:
We found that both saber-tooth species were similar in possessing weak jaw-muscle-driven bites compared to the leopard, but the mechanical performance of the saber-tooth’s skulls showed that they were both well-adapted to resist forces generated by very powerful neck muscles.”
The saber-like teeth of Thylacosimilus were actually quite fragile and powered by the creature’s neck muscles alone. According to the study, it must have dispatched its prey with astonishing precision.
For Thylacosimilus and other saber-tooths, a fast kill was the primary objective, according to Dr Wroe.
Big prey are dangerous–even to super-predators–and the faster the kill the less likely it is that the predator will get hurt–or for that matter attract unwanted attention from other predators.”
Thylacosimilus may not have been the most intelligent super-predator, but it reigned supreme in the area of specialization.
According to the new study, among saber-toothed species, Thylacosimilus and the later Smilodon represent extreme forms of convergent evolution.
Saber-toothed species, according to Wroe and his colleagues, evolved independently among non-mammals at least twice during the Permo-Triassic period, more than 250 million years ago.
They also did the same at least five times during the Cenozoic era, the period from about 66 million years ago to the present. These examples show how the same traits can emerge in widely diverse lineages due to comparable evolutionary pressures and shared distant ancestry.
Thylacosimilus atrox, the pouch saber-tooth tiger, may have had an embarrassing bite, but it was an efficient predator that had no problem dispatching its prey with ease.
Written by: Douglas Cobb