Ancestral echinoderms from the Chengjiang deposits of China

Shu, Degan; Morris, Simon Conway; Han, Jian; Zhang, Z.-F.; Liu, J.-N.

doi:10.1038/nature02648

Cited by 127 publications

(81 citation statements)

References 27 publications

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“…The early fossil record of deuterostomes includes putative chordates and hemichordates with signs of segmentation, (49,50) in the form of segmental gill slits in the head region, often with somites in the trunk, and tail. Echinoderms are found in the earliest Cambrian, (51) and possibly even in the Ediacaran, (52) although this is disputed. All extant echinoderms and most of the basal echinoderms are not segmented in any way.…”

Section: Deuterostomiamentioning

confidence: 98%

Parallel evolution of segmentation by co‐option of ancestral gene regulatory networks

Chipman

2009

BioEssays

116

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Different sources of data on the evolution of segmentation lead to very different conclusions. Molecular similarities in the developmental pathways generating a segmented body plan tend to suggest a segmented common ancestor for all bilaterally symmetrical animals. Data from paleontology and comparative morphology suggest that this is unlikely. A possible solution to this conundrum is that throughout evolution there was a parallel co-option of gene regulatory networks that had conserved ancestral roles in determining body axes and in elongating the anterior-posterior axis. Inherent properties in some of these networks made them easily recruitable for generating repeated patterns and for determining segmental boundaries. Phyla where this process happened are among the most successful in the animal kingdom, as the modular nature of the segmental body organization allowed them to diverge and radiate into a bewildering array of variations on a common theme.

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Section: Deuterostomiamentioning

confidence: 98%

Parallel evolution of segmentation by co‐option of ancestral gene regulatory networks

Chipman

2009

BioEssays

116

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“…Vetulocystids, from the Late Lower Cambrian of China, were described as stem-group echinoderms by Shu et al (2004). Three taxa were erected but two of these were badly preserved and not convincingly different from the better known Vetulocystis.…”

Section: Insights From the Fossil Recordmentioning

confidence: 99%

Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives

Swalla

Smith

2008

Phil. Trans. R. Soc. B

224

219

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Deuterostomes are a monophyletic group of animals that include the vertebrates, invertebrate chordates, ambulacrarians and xenoturbellids. Fossil representatives from most major deuterostome groups, including some phylum-level crown groups, are found in the Lower Cambrian, suggesting that evolutionary divergence occurred in the Late Precambrian, in agreement with some molecular clock estimates. Molecular phylogenies, larval morphology and the adult heart/kidney complex all support echinoderms and hemichordates as a sister grouping (Ambulacraria). Xenoturbellids are a relatively newly discovered phylum of worm-like deuterostomes that lacks a fossil record, but molecular evidence suggests that these animals are a sister group to the Ambulacraria. Within the chordates, cephalochordates share large stretches of chromosomal synteny with the vertebrates, have a complete Hox complex and are sister group to the vertebrates based on ribosomal and mitochondrial gene evidence. In contrast, tunicates have a highly derived adult body plan and are sister group to the vertebrates based on the analyses of concatenated genomic sequences. Cephalochordates and hemichordates share gill slits and an acellular cartilage, suggesting that the ancestral deuterostome also shared these features. Gene network data suggest that the deuterostome ancestor had an anterior-posterior body axis specified by Hox and Wnt genes, a dorsoventral axis specified by a BMP/chordin gradient, and was bilaterally symmetrical with left-right asymmetry determined by expression of nodal.

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“…Primarily based upon Smith (2005Smith ( , 2008 and Bourlat et al (2008) indicate a position higher in a tree are absent because they were never present or merely because they rotted away (Donoghue and Purnell 2009). Thus, various fossil organisms, such as the yunnanozoans (including Haikouella), have been interpreted as primitive deuterostomes (Shu et al 2003b), primitive ambulacrarians (Shu et al 2004), or as primitive chordates (Shu et al 2004) because they seem to possess those few necessary characteristics, such as gill slits. Other features of the fossils, however, are difficult to interpret unequivocally Shu and Morris 2003) and are taken by some to indicate links with hemichordates (Shu et al 1996b) or vertebrates (Donoghue and Purnell 2009;.…”

Section: The Origins Of Other Deuterostome Phyla and The Limitations mentioning

confidence: 99%

The Evolutionary Emergence of Vertebrates From Among Their Spineless Relatives

Donoghue

Purnell

2009

Evo Edu Outreach

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The evolutionary origin of vertebrates has been debated ad nauseam by anatomists, paleontologists, embryologists, and physiologists, but it is only now that molecular phylogenetics is providing a more rigorous framework for the placement of vertebrates among their invertebrate relatives that we can begin to arrive at concrete conclusions concerning the nature of ancient ancestors and the sequence in which characteristic anatomical features were acquired. Vertebrates tunicates and cephalochordates together comprise the chordate phylum, which along with echinoderms and hemichordates constitute the deuterostomes. The origin of vertebrates and of jawed vertebrates is characterized by a doubling of the vertebrate genome, leading to hypotheses that this genomic event drove organismal macroevolution. However, this perspective of evolutionary history, based on living organisms alone, is an artifact. Phylogenetic trees that integrate fossil vertebrates among their living relatives demonstrate the gradual and piecemeal assembly of the gnathostome body plan. Unfortunately, it has not been possible to demonstrate gradual assembly of the vertebrate body plan. This is not because vertebrates are irreducibly complex but because many of the characters that distinguish vertebrates from invertebrates are embryological and cellular and, therefore, inherently unfossilizable. Humans and all other back-boned animals-plus a few others that have no bone at all-comprise the vertebrates. Vertebrates are a clade, meaning that all members of the group have evolved from a common ancestor that they all share. This means that the deeper parts of our evolutionary history are entwined with the origin of the clade, and it should thus come as no surprise to discover, therefore, that the origin of vertebrates has been the subject of intense debate since the earliest days of evolutionary research. In his book Before the backbone, Henry Gee recounts a great number of theories that, over the last century and a half, have invoked almost every other major living animal group as the ancestors of vertebrates (Gee 1996). Mercifully, there is now much less equivocation over the relationships of vertebrates to their living relatives, none of which are thought of as being ancestral. Rather, vertebrates and their nearest kin-the invertebrate chordates, the hemichordates and the echinoderms-are more correctly perceived as living representatives of distinct genealogical lineages that separated one from another deep in geological time. It is the aim of many paleontologists, comparative anatomists, embryologists, and molecular biologists to uncover the genealogical relationships of these animals-their family tree-and to test this tree with evidence that bears on the question of how these distinct organismal designs. Explanations of the emerging evolutionary pattern range from traditional Darwinian gradualistic evolution to those that invoke explosive diversifications (seized upon by creationists and intelligent designers as evidence for irreducible compl...

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Ancestral echinoderms from the Chengjiang deposits of China

Cited by 127 publications

References 27 publications

Parallel evolution of segmentation by co‐option of ancestral gene regulatory networks

Parallel evolution of segmentation by co‐option of ancestral gene regulatory networks

Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives

The Evolutionary Emergence of Vertebrates From Among Their Spineless Relatives

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