Most fossils preserve the physical remains of organisms and their structure; however, geologists and paleobiologists recently found fossils that show the behaviors of predators preserved as traces in ancient sediments. Thus, fossils from southeast Missouri are helping scientists unlock clues about the behaviors of these predators and their interactions with their prey. Evidence shows that these ancient organisms were behaviorally sophisticated, tailoring their attacks for effectiveness.
Tracks from the site showed that the predators attacked from above, moving alongside to use their many legs for more effective grappling of their prey. Further, predators preferentially selected smaller prey, indicating that they attacked their food rather than randomly bumping into it.
Predation, or the action of attacking one’s prey, is a significant factor in evolution; this discovery is extremely important in the study of how organisms evolved in the Cambrian Period,” Schiffbauer said. “In this study, we provide evidence that these trilobites were likely visual predators, displaying selectivity in seeking and hunting their food.” More.
The trilobite did not have fifty million years to randomly evolve a sophisticated method. Something non-random is at work.
Prediction: We’ll see more of this.
See also: Bateson: Don’t let zoologists hog stage at … at the Royal Society’s November meet on evolution.
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Abstract: Evidence of predatory activity can be observed in the fossil record in the form of drill holes, repair scars, bite marks, and recognizable skeletal fragments in coprolites and preserved gut tracts. It is less common, however, to find fossil snapshots of predators caught in the act of feeding on their prey. Such interactions are preserved in recurring associations of the ichnogenera Rusophycus and Cruziana, most commonly attributed to trilobites, with burrows of likely vermiform (worm-like) organisms. In this study, we examine the Cambrian (Furongian Epoch, Steptoean Stage) Davis Formation, near Leadwood, southeastern Missouri, USA. In the lower to middle Davis Fm., several silty shale beds are extensively burrowed, from which we report a new occurrence and large number of Rusophycus traces associated with burrows of vermiform organisms. Within these beds, Rusophycus traces intersect vermiform burrows more often than expected by random chance and display a positive correlation in size between paired tracemakers. The median diameter of Rusophycus-associated vermiform burrows is significantly smaller than that of the non-intersected burrows. These results suggest that the paired traces record size selective predatory behavior. Moreover, low angle predator–prey trace intersections, though few in number, occurred more frequently than expected by random chance, supporting previous hypotheses that low angle attacks are preferred as they may improve prey handling success rates. (paywall) – Tara Selly, John Warren Huntley, Kevin L. Shelton, James D. Schiffbauer. Ichnofossil record of selective predation by Cambrian trilobites. Palaeogeography, Palaeoclimatology, Palaeoecology, 2016; 444: 28 DOI: 10.1016/j.palaeo.2015.11.033