Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario, Canada.
PLoS One. 2012;7(1):e29233. doi: 10.1371/journal.pone.0029233. Epub 2012 Jan 18.
Burgess Shale-type deposits provide invaluable insights into the early evolution of body plans and the ecological structure of Cambrian communities, but a number of species, continue to defy phylogenetic interpretations. Here we extend this list to include a new soft-bodied animal, Siphusauctum gregarium n. gen. and n. sp., from the Tulip Beds (Campsite Cliff Shale Member, Burgess Shale Formation) of Mount Stephen (Yoho National Park, British Columbia). With 1,133 specimens collected, S. gregarium is clearly the most abundant animal from this locality.This stalked animal (reaching at least 20 cm in length), has a large ovoid calyx connected to a narrow bilayered stem and a small flattened or bulb-like holdfast. The calyx is enclosed by a flexible sheath with six small openings at the base, and a central terminal anus near the top encircled by indistinct openings. A prominent organ, represented by six radially symmetrical segments with comb-like elements, surrounds an internal body cavity with a large stomach, conical median gut and straight intestine. Siphusauctum gregarium was probably an active filter-feeder, with water passing through the calyx openings, capturing food particles with its comb-like elements. It often occurs in large assemblages on single bedding planes suggesting a gregarious lifestyle, with the animal living in high tier clusters. These were probably buried en masse more or less in-situ by rapid mud flow events.Siphusauctum gregarium resembles Dinomischus, another Cambrian enigmatic stalked animal. Principal points of comparison include a long stem with a calyx containing a visceral mass and bract-like elements, and a similar lifestyle albeit occupying different tiering levels. The presence in both animals of a digestive tract with a potential stomach and anus suggest a grade of organization within bilaterians, but relationships with extant phyla are not straightforward. Thus, the broader affinities of S. gregarium remain largely unconstrained.
伯吉斯页岩型矿床为身体结构的早期进化和寒武纪群落的生态结构提供了宝贵的见解，但仍有许多物种继续挑战系统发育解释。在这里，我们将这个名单扩展到包括一种新的软体动物，Siphusauctum gregarium n. gen. and n. sp.，来自 Mount Stephen（Yoho 国家公园，不列颠哥伦比亚省）的郁金香床（Campsite Cliff Shale 成员，伯吉斯页岩组）。通过收集的 1133 个标本，S. gregarium 显然是该地点最丰富的动物。这个有柄动物（至少长 20 厘米），有一个大的卵形花萼连接到一个狭窄的双层茎和一个小的扁平或球根状固着器。花萼被一个灵活的鞘包围，底部有六个小开口，顶部附近有一个中央终端肛门，周围有不明显的开口。一个突出的器官，由六个具有梳状元件的放射状对称段组成，围绕着一个内部体腔，其中有一个大胃、圆锥形中肠和直肠。Siphusauctum gregarium 可能是一种活跃的滤食动物，水通过花萼开口流过，用梳状元件捕捉食物颗粒。它经常在单个层面上大量聚集，表明群居生活方式，动物生活在高层集群中。这些动物可能是通过快速的泥流事件被集体埋葬在原位。Siphusauctum gregarium 类似于 Dinomischus，另一种寒武纪神秘的有柄动物。主要的比较点包括一个带有包含内脏团和苞片样元件的花萼的长茎，以及类似的生活方式，尽管占据不同的分层水平。在这两种动物中，消化道具有潜在的胃和肛门，这表明在两侧动物中存在组织层次，但与现存门的关系并不简单。因此，S. gregarium 的更广泛亲缘关系在很大程度上仍然没有得到限制。
