Primitive deuterostomes from the Chengjiang Lagerstätte (Lower Cambrian, China)

Abstract

Cambrian fossil-Lagerstätten (sites of exceptional fossil preservation), such as those from Chengjiang (Lower Cambrian) and the Burgess Shale (Middle Cambrian), provide our best window into the Cambrian 'explosion'. Such faunas are known from about 40 localities, and have yielded a widely disparate series of taxa ranging from ctenophores to agnathan fish. Recent excavations of the Chengjiang fossil-Lagerstätte, known from a series of sites near Kunming in Yunnan, south China, have resulted in the discovery of several new forms. In conjunction with material described earlier, these provide evidence for a new group of metazoans, the vetulicolians. Several features, notably a series of gill slits, suggest that this group can throw light on an early stage of deuterostome diversification.

Early crest animals and the insight they provide into the evolutionary origin of craniates

“…2C), however, argue against interpretation of the segments as part of a segmented cuticular exoskeleton . The presence of gilled branchial chambers in vetulicolians had led Shu et al (1999a) to claim vetulicolians as vertebrates in 1999, but they abandoned the vertebrate hypothesis later, claiming vetulicolians as basal deuterostomes in 2001 (Shu et al, 2001b). In spite of a striking resemblance in the gilled branchial chambers between vetulicolians and vertebrates in some aspects, the gilled branchial chambers in vetulicolians are pharynx-independent structures, which are fundamentally different than those in deuterostomes but resemble those in arthropods.…”

The earliest history of the deuterostomes: the importance of the Chengjiang Fossil-Lagerstätte

“…Stach et al 2005), butt heir remarkable simplicityr enders the xenoturbellansm orphologically uninstructive when it comes to envisaging further steps in the evolution of early deuterostome. In fact, we havep roposed (Shu et al 2001b ;S hu 2005)t hat the vetulicolians are currently the best candidates for the earliest deuterostomes, but given the very peculiar nature of these animals, unsurprisingly, this has proved to be controversial. Moreover, even though the geographical range (Butterfield 2005)a nd diversity of this group (e.g.…”

“…In addition, and apparently yetm ore fatal to the arthropod hypothesis, are the five prominent structures along the midline of either side. These structures werei nterpreted as gills with external openings by Shu et al( 2001b )( see figure 1i nt he electronics upplementary material),l eadingt ot heir conclusion that vetulicolians were early deuterostomes.…”

Chordate origins and evolution

“…Chen goes on to remark that although tunicates display important molecular and morphological synapomorphies in their pumping organs, nervous systems, and photoreceptor apparatuses that link them to vertebrates (Jeffery et al, 2007;Schubert et al, 2006;Shimeld et al, 2005;Simões-Costa et al, 2005), they display such derived bodies that few other characters will be useful to reconstruct the proximate ancestor of vertebrates, a task for which the Haikouella and Yunnanozoon fossils are better qualified. These interpretations sum up very well not only the potential that fossils have to influence our thinking about the evolution of chordate development, but also the problems associated with them, since the affinities of both Hai-kouella and Yunnanozoon are still hotly debated (Mallat and Chen, 2003;Mallat et al, 2003;Shu and ConwayMorris, 2003;, with alternative views linking them to possible basal deuterostomes such as vetulicolians, precambrian fossils with divergent and even bizarre bodies that, have, so far, defied attempts to establish a consensual classification (Shu et al, 2001;Lacalli, 2002).…”