Head and backbone of the Early Cambrian vertebrate Haikouichthys

Shu, Degan; Morris, Simon Conway; Han, Jie; Zhang, Z.-F.; Yasui, Kohichiroh; Janvier, Philippe; Chen, L.; Zhang, X.-L.; Liu, J.-N.; Li, Y.; Liu, H.-Q.

doi:10.1038/nature01264

Cited by 288 publications

(224 citation statements)

References 20 publications

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“…4), and it fits well with Butler's model that predicts eyes are older structures and all the craniate sensory organs were not elaborated simultaneously (Butler, 2000(Butler, , 2006. The eyes in early crest animals, as exemplified by Haikouella, Yunnanozoon and Haikouichthus, are regularly rounded, relatively large, about 0.2-0.4 mm in Haikouella (Chen, 2004;, 0.6 mm in Yunnanozoon (Chen, 2004), and 0.4 mm in Haikouichthus (Shu et al, 1999b(Shu et al, , 2003a.…”

Section: Groundstate In the Head Sensory Organs In Cristozoasupporting

confidence: 79%

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: Groundstate In the Head Sensory Organs In Cristozoasupporting

confidence: 79%

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

Chen

2008

Genesis

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“…The proposed synonymy of the first two taxa (Hou et al 2002) seems unlikely, because although Myllokunmingia is known only from a single specimen, the anterior, and especially the gills, is very different in arrangement from Haikouichthys where there is a striking array of branchial supports (Shu et al 2003a). The interpretation of the supposed gill areas in a single specimen of Haikouichthys (Hou et al 2002) is also not free from difficulties.…”

Section: The Triploblast Storymentioning

confidence: 99%

“…Mallatt & Chen 2003;Chen 2004), and reconstructions accordingly equipped, the illustrated specimens indicate at best vague structures, sometimes only seen on one side of the head. In the Chengjiang Lagerstätte, however, unequivocal eyes are routinely preserved and often prominent, as in the fish Haikouichthys (see Shu et al 2003a). In the many exquisitely preserved specimens of Haikouella jianshanensis , no eyes were identified.…”

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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“…Haikouella has been interpreted as a craniatelike chordate with a well-developed brain, lateral eyes, a pharynx with gills, and a ventral heart (44,45). A subsequent interpretation of the Haikouella material suggests that the head consisted of separate dorsal and ventral movable units connected by external gills (46) and that Yunnanozoon and Haikouella are stem group deuterostomes that are allied to vetulicolians, another problematic group in the Chengjiang biota (46,47). Thus, the yunnanozoans (Yunnanozoon, Cathaymyrus, and Haikouella) may be stem cephalochordates, or they may be closely allied to vetulicolians and may possibly be stem deuterostomes.…”

Section: Fossil Recordmentioning

confidence: 99%

Evolution of centralized nervous systems: Two schools of evolutionary thought

2012

Proc. Natl. Acad. Sci. U.S.A.

112

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Understanding the evolution of centralized nervous systems requires an understanding of metazoan phylogenetic interrelationships, their fossil record, the variation in their cephalic neural characters, and the development of these characters. Each of these topics involves comparative approaches, and both cladistic and phenetic methodologies have been applied. Our understanding of metazoan phylogeny has increased greatly with the cladistic analysis of molecular data, and relaxed molecular clocks generally date the origin of bilaterians at 600-700 Mya (during the Ediacaran). Although the taxonomic affinities of the Ediacaran biota remain uncertain, a conservative interpretation suggests that a number of these taxa form clades that are closely related, if not stem clades of bilaterian crown clades. Analysis of brain-body complexity among extant bilaterians indicates that diffuse nerve nets and possibly, ganglionated cephalic neural systems existed in Ediacaran organisms. An outgroup analysis of cephalic neural characters among extant metazoans also indicates that the last common bilaterian ancestor possessed a diffuse nerve plexus and that brains evolved independently at least four times. In contrast, the hypothesis of a tripartite brain, based primarily on phenetic analysis of developmental genetic data, indicates that the brain arose in the last common bilaterian ancestor. Hopefully, this debate will be resolved by cladistic analysis of the genomes of additional taxa and an increased understanding of character identity genetic networks.The fact that some of these building stones are universal does not, of course, mean that the organs to which they contribute are as old as these molecules or their precursors.von Salvini-Plawen and Mayr (1) A ny consideration of the evolution of centralized nervous systems is inextricably linked to an understanding of the phylogeny of living metazoans, their fossil history, the vast range of complexity in their nervous systems, and the development of these nervous systems. For this reason, any attempt to reconstruct the phylogeny of metazoan CNSs must be based on all lines of evidence available. The molecular phylogenetic studies of the last 20 y are particularly important in understanding metazoan interrelationships as well as the time frame in which these animals arose and radiated, and we now have increased insights into the genetics underlying the development of CNSs.First, I will review the fossil history of the earliest putative metazoans, and then, I will discuss different comparative approaches to analyzing both molecular and morphological data: the molecular clock hypothesis, which has yielded a range of possible dates for the origin and divergence of metazoans; developmental genetics and its contribution to our understanding of the patterning of metazoan bodies, particularly patterning of the CNS; and conclusions based on the first outgroup analysis of metazoan central neural characters. Finally, I will review two hypotheses concerning the morphological complexity of the ...

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Head and backbone of the Early Cambrian vertebrate Haikouichthys

Cited by 288 publications

References 20 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’

Evolution of centralized nervous systems: Two schools of evolutionary thought

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