A paleontological perspective of vertebrate origin

Shu, Degan

doi:10.1007/bf03187041

Cited by 51 publications

(45 citation statements)

References 29 publications

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“…Some additional evidence for this supposition comes from as pecimen previously illustrated (see Chen et al2 003a , fig. 1 c ;Shu 2003, fig. 3 h ), where the two sides of the trunk are seen to be clearly displaced.…”

Section: Another Cambrian Headache: the Yunnanozoansmentioning

confidence: 99%

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

et al. 2009

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While the broad framework of deuterostome evolution is now clear, the remarkable diversity of extant forms within this group has rendered the nature of the ancestral types problematic: what, for example, does the common ancestor of asea urchin and lamprey actually look like? The answer to such questions can be addressed on the basis of remarkably well-preserved fossils from Cambrian Lagerstätten, not least the celebrated Chengjiang Lagerstätte (Yunnan, China). This deposit is particularly important because of its rich diversity of deuterostomes.T hese include some of the earliest known representatives, among which are the first vertebrates, as well as more enigmatic groups, notably the vetulicolians and yunnanozoans. The latter groups, in particular, haveb een the subject of some radical divergences in opinion as to their exact phylogenetic placements.H ere, we both review the known diversity of Chengjiang deuterostomes and in particular argue that the vetulicolians and yunnanozoans represent very primitive deuterostomes. Moreover, in the latter case we present new data to indicate that the yunnanozoans are unlikely to be any sorto fchordate.

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Section: Another Cambrian Headache: the Yunnanozoansmentioning

confidence: 99%

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

et al. 2009

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“…However, it has been claimed that this interpretation is based on tenuous characters and that both taxa may form a clade (myllokumingids) that is basal to living craniates (49,50). Subsequently, another described genus, Zhongjianichthys, seems to be a myllokumingid (51). In any case, these taxa seem to have had paired nasal capsules, large lateral eyes, and possibly, paired otic capsules, all of which suggest that that they may have possessed brains comparable with living agnathan vertebrates (51).…”

Section: Fossil Recordmentioning

confidence: 99%

“…Subsequently, another described genus, Zhongjianichthys, seems to be a myllokumingid (51). In any case, these taxa seem to have had paired nasal capsules, large lateral eyes, and possibly, paired otic capsules, all of which suggest that that they may have possessed brains comparable with living agnathan vertebrates (51).…”

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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“…3 The interrelationships of living and extinct jawless and jawed vertebrates. Primarily based upon Donoghue et al (2000) and Donoghue and Smith (2001) and Zangerl 1968; Chang et al 2006;Gess et al 2006;Janvier and Lund 1983;Shu 2003;Shu et al 1999Shu et al , 2003aSweet and Donoghue 2001). They sit among the jawless fishes or between them and gnathostomes (they are not shown in Fig.…”

Section: Genetic Drivers Of Vertebrate and Gnathostome Innovationmentioning

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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A paleontological perspective of vertebrate origin

Cited by 51 publications

References 29 publications

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

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

Evolution of centralized nervous systems: Two schools of evolutionary thought

The Evolutionary Emergence of Vertebrates From Among Their Spineless Relatives

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