在湖北三峡地区纽芬兰统岩家河组小壳化石Ⅰ、Ⅱ组合之间发现了大量锥管状宏体化石,化石体呈平面压扁的平滑圆锥管状,锥体长4—21mm,始端尖细向口端逐渐扩散,扩散角为13°—25°.锥体口端直径宽1—7mm,锥体始端平直或略有弯曲.锥体表面光滑,无或有微弱横纹,没有保存内部构造.与埃迪卡拉纪庙河生物群中的Protoconites minor Chen et al.1994无论从锥体长度、口端直径宽度、扩散角,还是化石的形态特征等方面均一致,因此理应归属Protoconites.通过Protoconites与好运阶(Fortunian)澄江化石库中的Cambrorhytium(或Archotuba conoidalis)和中寒武世Cambrorhytium major对比研究,发现无论从大小、形态,还是生活方式三者之间存在着极大的相似性,可能反映了它们具有较近的亲缘关系,这对揭示早期锥管状生物的归属和演化提供了重要的化石证据.
The bivalved arthropod Branchiocaris? yunnanensis Hou, 1987 is redescribed on the basis of new fossil material from the early Cambrian Chengjiang biota, South China. In total, 81 specimens have been examined. The carapace comprises two identical valves, each valve are sub-circular in outline, ranging from 24 mm to 58 mm in length, and from 15 mm to 46 mm in height. The dorsal margin is straight and bears two short cardinal spines. The valve surface is either smooth or ornamented with polygonal reticular structures, which may result from different preservation conditions. Two morphotypes have been recognized based on the presence or absence of a subdorsal swelling of the valve, which is convex dorsolaterally and extends beyond the dorsal margin when it appears. Statistic and ontogenetic analyses show both morphotypes grow isometrically and have the same growth trajectory. Therefore, the two morphotypes are interpreted as dimorphism within the same species. Our results are helpful for investigating the taxonomy and ontogeny of arthropod fossils and suggest that dimorphism might be fairly common in these early arthropods.
WU YuFU DongjingZHANG XingliangAllison C. DALEYSHU Degan
A number of recently evolved animals possess poison glands for feeding and/or defense.However,examples of such animals are rare in the fossil record.We report a fossil arthropod Isoxys curvirostratus from the Early Cambrian Chengjiang biota of China.This species is regarded as the oldest known venomous arthropod based on the presence of venomous glands in its head region.The adult animal is 2-5 cm long and the body is covered entirely with a carapace.The presence of large stalk eyes and a pair of stout grasping appendages with a terminal spine suggest it was raptorial.Interestingly,the two pear-shaped,three-dimensionally preserved objects that are present in the head region and at the base of the grasping appendages closely resemble the venom glands of some living arthropods in size,shape,and position.These features indicate that the presence of venomous predators could date back 520 million years.Furthermore,our observations suggest that the feeding strategies and organs adapted for this purpose had already reached a high level of diversity and anatomical sophistication in the Early Cambrian ecosystems.
