What did the Cambrian spike predator eat? A biomechanical study refutes an earlier suggestion that Anomalocaris used its bizarre gripping tools to prey on trilobites. The structures would have been too fragile for these hard-shelled animals to grasp. Anomalocaris was probably more interested in soft prey. The scientists say that other predators of the era were probably specialized in "cracking" the trilobites.
It was the time of the so-called Cambrian explosion: Around 500 million years ago, many new creatures emerged in a very short time, as did the first representatives of the lines of development that led to today's animal groups. At that time, however, evolution also "experimented" with building plans for which there are no direct comparisons today: the so-called radiodonta resembled arthropods, but in addition to their segmented body and highly developed compound eyes they had one feature that seems strange: two were sitting on their heads Appendages, which in the different species probably fulfilled special functions in the ingestion of food.
Trilobites on the menu?
The most famous representatives of the radiodonta were the anomalocarids - and specifically the species Anomalocaris canadensis. Their fossils have been known since the 19th century and they may have been the biggest predators of the Cambrian Seas. Because with a length of probably up to one meter, they were giants in the living environment characterized by small animals. They also had two appendages on their heads, which they apparently used to grab prey and carry them to their mouths. There have been suggestions that Anomalocaris represented an apex predator that snatched whatever it could get its hands on.
Accordingly, he could also have captured representatives of another prominent animal group of the era: the also relatively large, hard-armored trilobites. Certain marks and bruises on some fossil exoskeletons of these crablike-looking animals have been interpreted as an indication of this. However, some paleontologists have already expressed doubts as to whether Anomalocaris' "devices" would have been able to crack the hard shell structures of the trilobites.
Rather soft food
The research team led by Russell Bicknell from the American Museum of Natural History in New York has therefore now investigated the extent to which the frontal processes of Anomalocaris canadensis would have been mechanically capable of grabbing or even processing hard-shelled prey. As a basis for their study, the scientists developed a detailed 3D reconstruction of Anomalocaris canadensis using fossils from Canada. By biomechanically comparing the model with similar structures in certain modern-day scorpion or spider species, the researchers were initially able to show that the appendages of Anomalocaris could be stretched and bent and were therefore suitable for grasping.
How robust the system was was then made clear by a special analysis method that can show tension and stress points when gripping objects. As the team reports, the modeling shows possible stresses and structural resilience: Above all, the sometimes filigree partial structures of the frontal processes would have been damaged if hard prey such as trilobites were grasped. Armored beings were therefore probably not part of the large predator's range of prey. Apparently, Anomalocaris was more specialized in soft marsupials, which could probably be held well with the pointed elements of its prehensile arms.
The researchers also subjected the modeled structures to a fluidic analysis. It turned out that when they were stretched out, they apparently caused particularly little water resistance when moving. The bottom line is that there is now a clearer picture of the hunting behavior of the bizarre primeval predator: Apparently, Anomalocaris pounced on soft prey in the open water zone with its claws pointing forward, the scientists summarize.
But who then caused the possible gnawing marks found on some trilobite fossils? According to the scientists, other representatives of the radiodonta in the Cambrian environment could also have specialized in these prey animals. "It is becoming apparent that the Cambrian food webs were more complex than we previously thought," concludes Bicknell.
Source: American Museum of Natural History, professional article: Proceedings of the Royal Society B Biological Sciences, doi: 10.1098/rspb.2023.0638