In the Devonian period , between 415 and 360 million years ago, the seas were spaces full of life. Corals and sponges proliferated creating large reefs where trilobites, nautiluses and bivalves lived. The fish acquired an enormous variability of forms; the ostracoderms , armored-skinned, jawless fish that consumed particles floating in the water; the acanthodians , with large spiny fins; the placoderms , with armored heads; the sarcopterygians , of which the coelacanths are still alive; the early actinopterygians , ancestors of most modern fish; and the sharks. These primitive sharks acquired forms that today would seem alien, as is the case of Stethacanthus, with an anvil-shaped dorsal fin covered with teeth.
But, while the first amphibians began to conquer the land , in the seas an apex predator imposed its dominance. In a world where the largest marine animals barely reached two meters, a fish three times longer, with an armored head and huge jaws, became the largest predator that the earth had known up to that time. We are talking about Dunkleosteus, the ‘tank’ that dominated the seas at the end of the Devonian, between 380 and 360 million years ago.
A shallow apex predator
The various species of Dunkleosteus , fish from the placoderm group, behaved as apex predators. They hunted fish, molluscs, crustaceans and, in general, any animal that came within range; the only rival to a Dunkleosteus was another, larger Dunkleosteus . In fact, they had cannibalistic tendencies.
However, there were differences in behavior compared to those we find today. At that time the geography was very different, and, therefore, so were the currents. There were large expanses of sea whose deep waters remained stagnant, which added to the absence of sunlight due to the depth and absence of photosynthesis, turned the seabed into anoxic places —without oxygen— . Virtually all marine animals of that period breathed dissolved oxygen in the water , so unlike today, animals did not go to the depths during the Devonian, and Dunkleosteus was no exception.
It lived near the surface, where the sunlight reached, and extended through the seas to the southwest of the continent of Euroamerica, up to the coasts of Gondwana. It is believed that it could live and hunt in the open sea, although fossilization is very rare in those places, which makes it very difficult to confirm.
jaws of terror
It is estimated that an adult specimen of Dunkleosteus could weigh a ton. However, both its weight and length are estimates based on anatomy compared to other placoderms, but with no supporting fossils: there are no remains of this animal other than its armor. This completely covered its skull and the front part of its back, and was made up of huge bony plates up to 5 cm thick. Between the plate that covered the skull and the back was a joint that allowed him to move his head up. But the most terrifying thing about this animal was in its mouth.
He had no teeth. I didn’t need them either. Its bony plates covered its jaws, forming a structure similar to a bear trap in a giant and deadly version. In 2007, researchers Philip Anderson, from the University of Chicago, and Mark Westneat, from the Field Museum of Natural History, based on data obtained from several skulls, developed a computer simulation in which they calculated the bite force of Dunkleosteus.
The results were overwhelming: it had one of the most powerful bites in the history of evolution, exceeding a force of 5,000 newtons. No other fish or mammal has ever had such a bite force; only some species of dinosaurs and crocodiles have surpassed it.
But not only strength is relevant. Given the shape of the blade, narrow and sharp , this force was concentrated in a very small area. Thus, the localized bite force could reach 10,700 newtons per square centimeter in the flat blade area, and almost 15,000 in the peaks. For comparison, an adult human barely reaches 800 newtons per square centimeter.
But this deadly bear trap is not only characterized by its enormous strength, but also by its incredible speed. The most generous estimates indicate that an individual could open its jaws and close them again in just 60 milliseconds. The most conservative indicate a delay of 130 milliseconds to open and close the trap. Times that are approximately equivalent to between 20% and 40% of the time it takes to blink.
Anderson, PSL, & Westneat, MW 2007. Feeding mechanics and bite force modeling of the skull of Dunkleosteus terrelli , an ancient apex predator. Biology Letters , 3(1), 77-80. DOI: 10.1098/rsbl.2006.0569
Yeager, KM nd Fossil Fishes (Arthrodira and Acanthodida) from the Upper Devonian Chadakoin Formation of Erie County, Pennsylvania. 96, 5.