INJURED TRILOBITE EOREDLICHIA INTERMEDIA FROM THE EARLY CAMBRIAN CHENGJIANG BIOTA
Trilobites are common fossil animals in the Cambrian. The fossil record of their healed exoskeletons can provide important information on the competitive arms-race relationship between trilobite prey and their potential predators in the Cambrian ecosystem. The early Cambrian Chengjiang biota from South China, well known for its exceptional fossil preservation, allows us to study the ancient ecological interactions in marine communities during the Cambrian explosion. However, there is no record of healed trilobites so far known from the Chengjiang biota. The trilobite Eoredlichia intermedia Lu, 1940, an index fossil of the second trilobite biozone in eastern Yunnan of China, is one of the commonest arthropods in the deposits. Of more than 2 000 specimens of E. intermedia in our collection, two adult specimens are revealed with deformities in the lateral margin of cephalon, genal spine, and the pleural region. We suggest that such injuries were most likely caused by unknown predators. The scalloped fractures or cracks on these two adult individuals were marginally thickened and smoothed at the edges, indicating obvious signs of healing. If interpreted exactly, these fossils lend some supports for the view that the victim Eoredlichia intermedia was capable of repairing their fractured exoskeletons from sub-lethal attack by unknown predators. Therefore, this research presents the thus-far oldest fossil record of trilobites with injuries and the first report of the trilobite exoskeleton with healed injuries from the Chengjiang biota, signifying an existing escalating arms race between durophagous predators and prey since Cambrian Stage 3.