寒武纪早期澄江生物群中受创伤的中间型始莱德利基三叶虫(Eoredlichia intermedia)

三叶虫是寒武纪海洋中的常见动物,其受伤愈合现象的化石记录可以反映生态系统内物种之间竞争关系。中国华南寒武纪早期澄江化石生物群因保存软躯体构造化石而成为研究寒武纪大爆发时期古海洋生态群落的绝佳窗口,然而,澄江生物群中三叶虫受伤愈合现象的化石至今未见报道。中间型始莱德利基虫(Eoredlichia intermedia Lu,1940)是澄江生物群的常见物种,也是我国寒武系第二个三叶虫化石带的标准带化石。在2 000余枚中间型始莱德利基虫标本中,发现两枚成体标本的头甲侧边缘、颊刺和胸甲肋节保存了不同程度的残缺。据此推测,Eoredlichia intermedia在生命活动过程中曾受到碎壳型捕食动物的攻击或其他伤害而形成伤口。伤口部位边缘加厚且光滑,显示了明显的愈合痕迹。这些特征表明始莱德利基虫在受到非致死的伤害后,具备自身修复损伤的能力。这是迄今所知最为古老的,也是在澄江生物群中首次发现的三叶虫受伤并且愈合的标本,反映了寒武纪第二世第三期底栖生态系统中碎壳型捕食者和三叶虫猎物之间的军备竞赛生态关系。

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.