Head and backbone of the Early Cambrian vertebrate Haikouichthys

  title={Head and backbone of the Early Cambrian vertebrate Haikouichthys},
  author={De-gan Shu and Simon Conway Morris and J. Han and Z.-F. Zhang and Kinya Yasui and Philippe Janvier and L. Chen and X-L. Zhang and J.-N. Liu and Y. Li and H.-Q. Liu},
Agnathan fish hold a key position in vertebrate evolution, especially regarding the origin of the head and neural-crest-derived tissue. In contrast to amphioxus, lampreys and other vertebrates possess a complex brain and placodes that contribute to well-developed eyes, as well as auditory and olfactory systems. These sensory sytems were arguably a trigger to subsequent vertebrate diversifications. However, although they are known from skeletal impressions in younger Palaeozoic agnathans… 
A paleontological perspective of vertebrate origin
A five-step hypothesis for vertebrate origin is proposed, intended to bridge the longstanding gap between protostomes and vertebrates, and four of the five steps accord with established ideas current in modern evolutionary zoology.
Early Jawless Vertebrates and Cyclostome Origins
  • P. Janvier
  • Geography, Environmental Science
    Zoological science
  • 2008
The anatomy and physiology of lampreys and hagfishes are so different that it is difficult to reconstruct an ancestral morphotype of the cyclostomes, assuming that they are a clade, and there is no clear evidence of any fossil taxon that is neither a fossil hagfish nor a fossil lamprey, but would be more closely related to the Cyclostomes than to the gnathostomes.
A lamprey from the Devonian period of South Africa
A marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa is reported, the identity of which is established easily because many of the key specializations of modern forms are already in place, evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period.
A primitive fish from the Cambrian of North America
Phylogenetic analysis places Metaspriggina as a basal vertebrate, apparently close to the Chengjiang taxa Haikouichthys and Myllokunmingia, demonstrating also that this primitive group of fish was cosmopolitan during Lower–Middle Cambrian times.
A rare lobopod with well-preserved eyes from Chengjiang Lagerstätte and its implications for origin of arthropods
The discovery of the rare transitional form may throw new light on the origin of arthropod and suggests that the most primitive arthropods began with paired uniramous legs and the biramous ones evolved later.
Fossils, histology, and phylogeny: Why conodonts are not vertebrates
It is considered that conodont hard tissues and several other anatomical structures in Conodonts are not homologous with those of vertebrates, and the phylogenetic relationships of conodons and chordates should be extended to include non-chordate taxa.
Palaeospondylus as a primitive hagfish
The first comparative morphological analysis of hagfish embryos and Palaeospondylus is reported, and a hitherto overlooked resemblance in the chondrocranial elements of these animals is reported; i.e., congruence in the arrangement of the nasal capsule, neurocranium and mandibular arch-derived velar bar.
Decay of vertebrate characters in hagfish and lamprey (Cyclostomata) and the implications for the vertebrate fossil record
An experimental analysis of decay of vertebrate characters based on the extant jawless vertebrates (Lampetra and Myxine) provides a framework for the interpretation of the anatomy of soft-bodied fossil vertebrates and putative cyclostomes, and a context for reading the fossil record of non-biomineralized vertebrates.
Early crest animals and the insight they provide into the evolutionary origin of craniates
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, and some derivatives of neural crest cells.


A Pikaia-like chordate from the Lower Cambrian of China
A single specimen of a Lower Cambrian chordate, Cathaymyrus diadexus, new genus and species, that is similar to Pikaia but predates it by about 10 million years (Myr).
Embryology of the lamprey and evolution of the vertebrate jaw: insights from molecular and developmental perspectives.
The gnathostome jaw may have arisen through a process of ontogenetic repatterning, in which a heterotopic shift of mesenchyme-epithelial relationships would have been involved.
Lower Cambrian vertebrates from south China
The discovery of two distinct types of agnathan from the Lower Cambrian Chengjiang fossil-Lagerstätte imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, ∼555 Myr BP), if not earlier.
New perspectives on the evolution of protochordate sensory and locomotory systems, and the origin of brains and heads.
  • T. Lacalli
  • Biology
    Philosophical transactions of the Royal Society of London. Series B, Biological sciences
  • 2001
The sense organs of both amphioxus and tunicate larvae serve essentially as navigational aids and, despite some uncertainty as to homologies, current molecular and ultrastructural data imply a close relationship between them.
Origin and early evolution of the vertebrates: New insights from advances in molecular biology, anatomy, and palaeontology
  • N. Holland, J. Chen
  • Biology, Geography
    BioEssays : news and reviews in molecular, cellular and developmental biology
  • 2001
The earliest vertebrates had an unequivocally marine origin, probably evolved mineralised pharyngeal denticles before the dermal skeleton, and evidently utilised elastic recoil of the visceral arch skeleton for suction feeding, and the advent of definitive neural crest was supremely important for the evolutionary origin of the vertebrates.
28S and 18S rDNA sequences support the monophyly of lampreys and hagfishes.
Moderate to very strong support is provided for the monophyly of the cyclostomes in lampreys plus hagfishes and the currently accepted hypothesis of a lamprey-gnathostome clade is moderately rejected by the Kishino-Hasegawa test and resoundingly rejected by parametric bootstrap tests.
Evolution of neural crest and placodes: amphioxus as a model for the ancestral vertebrate?
Comparisons of developmental gene expression data suggest that the anterior ectoderm in amphioxus may be homologous to the vertebrate olfactory placode, the only vertebrate placode with primary, not secondary, neurons.
Morphology of the pineal complex of the anadromous sea lamprey, Petromyzon marinus L.
It is concluded that the pineal organ of P. marinus is a structurally well-developed photosensory and photoneuroendocrine organ that is probably capable of transducing photic stimuli into nervous and endocrine messages to the brain and other organs.
Evolutionary biology: Lamprey Hox genes and the origin of jaws
It is shown that in the lamprey, a primitively jawless (agnathan) fish that is a sister group to the gnathostomes, a Hox gene is expressed in the mandibular arch of developing embryos, which suggests that loss of Hox expression from the mandibia arch of gnathOSTomes may have facilitated the evolution of jaws.
Monophyly of Lampreys and Hagfishes Supported by Nuclear DNA–Coded Genes
Cl cloning and sequencing of the four nuclear DNA–coded single-copy genes encoding the triose phosphate isomerase, calreticulin, and the largest subunit of RNA polymerase II and III were conducted, and it was shown that all the five proteins prefer the monophyletic tree of cyclostomes, which significantly supports the cyclostome monophyly at the level of ±1 SE.