A New Species of Yunnanozoan with Implications for Deuterostome Evolution

Shu, Degan; Morris, Simon Conway; Zhang, Z. F.; Liu, J. N.; Han, Jian; Chen, Ling; Zhang, X. L.; Yasui, Kohichiroh; Li, Yong

doi:10.1126/science.1079846

Cited by 124 publications

(95 citation statements)

References 14 publications

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“…Seven years later, in 2003, Shu et al, (2003b) however, abandoned their hemichordate hypothesis, claiming that Haikouella and Yunnanozoon had no chordatelike or vertebrate-like structures but were closely related to vetulicolians by having a segmented cuticular exoskeleton and a small number of widely spaced gill pouches. Evidence of muscle fibers in some Haikouella (see Fig.…”

Section: Fig 1 Laterally Compressed Haikouella Lanceolatamentioning

confidence: 99%

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

Chen

2008

Genesis

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Summary: The Cristozoa (also known as crest animals) are established as representing the animals containing neural crest and its derivatives, constituting all known craniates and their immediate precraniate precursors. The precraniate crest animals all are extinct and preserved only in Early Cambrian strata of Yunnan (southwestern China). Fine anatomical details of Haikouella and the slightly more advanced species Yunnanozoon exhibit many characters unique to vertebrates, but they lack a skull and most other elaborated placodal and neural crest derivations, throwing novel light onto the previously missing history at the very beginning of cristozoan evolution. Comparative study with the cephalochordate amphioxus suggests that precraniate evolution is marked by a series of innovations including: muscular ventilation with gill-bearing and jointed brachial arches, paired head sensorial organs including paired eyes and nostrils, relatively large, slightly differentiated brain, protovertebrae, and some derivatives of neural crest cells. But, they lack ears, a clear telencephalon, and a skull. Furthermore, comparison of the brains of amphioxus and craniates suggests that the tripartite brain with telencephalon was not an older structure but a novelty of the craniates. genesis 46:623-639,

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Section: Fig 1 Laterally Compressed Haikouella Lanceolatamentioning

confidence: 99%

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

Chen

2008

Genesis

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“…In particular the perforations along either lateral margin, and associated structures which show their most complex development in Vetulicolia, seem to represent gill openings. The bipartite body may also provide a link with the vetulicystids, as well as to the chordates via the somato-visceral hypothesis of Romer (see Shu et al 2001bShu et al , 2003b for further explanation).…”

Section: The Triploblast Storymentioning

confidence: 99%

“…Chen et al 1995a;Shu et al 1996bShu et al , 1999Shu et al , 2003bMallatt & Chen 2003;Chen 2004) have attracted major controversy in terms of their position and so importance. One possibility is that they are allied to the hemichordates (Shu et al 1996b), but the alternative hypothesis that they are effectively pre-vertebrates (Mallatt & Chen 2003) has also attracted support.…”

Section: The Triploblast Storymentioning

confidence: 99%

Darwin's dilemma: the realities of the Cambrian ‘explosion’

Morris

2006

Phil. Trans. R. Soc. B

152

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The Cambrian 'explosion' is widely regarded as one of the fulcrum points in the history of life, yet its origins and causes remain deeply controversial. New data from the fossil record, especially of Burgess Shale-type Lagerstätten, indicate, however, that the assembly of bodyplans is not only largely a Cambrian phenomenon, but can already be documented in fair detail. This speaks against a much more ancient origin of the metazoans, and current work is doing much to reconcile the apparent discrepancies between the fossil record, including the Ediacaran assemblages of latest Neoproterozoic age and molecular 'clocks'. Hypotheses to explain the Cambrian 'explosion' continue to be generated, but the recurrent confusion of cause and effect suggests that the wrong sort of question is being asked. Here I propose that despite its step-like function this evolutionary event is the inevitable consequence of Earth and biospheric change.

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“…Based on the fossil record and the morphology of living chordates, it has been proposed that the head skeleton of the first vertebrates consisted of thin bars of flexible cellular cartilage (Mallatt and Chen, 2003;Shu et al, 2003). This primitive skeleton provided elastic recoil for pharyngeal pumping, which facilitated gill ventilation and filter feeding (Gans and Northcutt, 1983).…”

Section: Introductionmentioning

confidence: 99%

Roles for FGF in lamprey pharyngeal pouch formation and skeletogenesis highlight ancestral functions in the vertebrate head

et al. 2014

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A defining feature of vertebrates (craniates) is a pronounced head supported and protected by a cellularized endoskeleton. In jawed vertebrates (gnathostomes), the head skeleton is made of rigid threedimensional elements connected by joints. By contrast, the head skeleton of modern jawless vertebrates (agnathans) consists of thin rods of flexible cellular cartilage, a condition thought to reflect the ancestral vertebrate state. To better understand the origin and evolution of the gnathostome head skeleton, we have been analyzing head skeleton development in the agnathan, lamprey. The fibroblast growth factors FGF3 and FGF8 have various roles during head development in jawed vertebrates, including pharyngeal pouch morphogenesis, patterning of the oral skeleton and chondrogenesis. We isolated lamprey homologs of FGF3, FGF8 and FGF receptors and asked whether these functions are ancestral features of vertebrate development or gnathostome novelties. Using gene expression and pharmacological agents, we found that proper formation of the lamprey head skeleton requires two phases of FGF signaling: an early phase during which FGFs drive pharyngeal pouch formation, and a later phase when they directly regulate skeletal differentiation and patterning. In the context of gene expression and functional studies in gnathostomes, our results suggest that these roles for FGFs arose in the first vertebrates and that the evolution of the jaw and gnathostome cellular cartilage was driven by changes developmentally downstream from pharyngeal FGF signaling.

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A New Species of Yunnanozoan with Implications for Deuterostome Evolution

Cited by 124 publications

References 14 publications

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

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

Darwin's dilemma: the realities of the Cambrian ‘explosion’

Roles for FGF in lamprey pharyngeal pouch formation and skeletogenesis highlight ancestral functions in the vertebrate head

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