Animal phylogeny and the ancestry of bilaterians: inferences from morphology and 18S rDNA gene sequences

  title={Animal phylogeny and the ancestry of bilaterians: inferences from morphology and 18S rDNA gene sequences},
  author={Kevin J. Peterson and D. J. Eernisse},
  journal={Evolution \& Development},
SUMMARY Insight into the origin and early evolution of the animal phyla requires an understanding of how animal groups are related to one another. Thus, we set out to explore animal phylogeny by analyzing with maximum parsimony 138 morphological characters from 40 metazoan groups, and 304 18S rDNA sequences, both separately and together. Both types of data agree that arthropods are not closely related to annelids: the former group with nematodes and other molting animals (Ecdysozoa), and the… 

The New View of Animal Phylogeny

The evidence supporting the current understanding of metazoan phylogeny is discussed on a clade by clade basis, supported by molecular and morphological data.

Improved resolution of recalcitrant nodes in the animal phylogeny through the analysis of genome gene content and morphology

The last common animal ancestor may has been a simple, filter-feeding organism without a nervous system and muscles, while the last common ancestor of Bilateria might have been a small, acoelomate-like worm without a through gut.

Phylogeny of Molting Protostomes (Ecdysozoa) as Inferred from 18S and 28S rRNA Gene Sequences

It is concluded that combined data on the 18S and 28S rRNA gene sequences provide a more reliable basis for phylogenetic inferences.

Molecular phylogeny of Gastrotricha on the basis of a comparison of the 18S rRNA genes: Rejection of the hypothesis of a relationship between Gastrotricha and Nematoda

The analysis confirmed monophyly of the families Chaetonotidae and Xenotrichulidae from the order Chaetonida, as well as the families Turbanellidae and Thaumastodermatidae fromThe order Macrodasyida and species belonging to the orders ChaetonOTida and MacrodASYida form two well-supported clades.

A modern look at the Animal Tree of Life

The phylogenetic interrelationships of animals (Metazoa) have been elucidated by refined systematic methods and by new techniques, notably from molecular biology, but the position of several protostome phyla, especially Bryozoa and Chaetognatha, remains intractable.

Bilaterian phylogeny: a broad sampling of 13 nuclear genes provides a new Lophotrochozoa phylogeny and supports a paraphyletic basal acoelomorpha.

A new phylogeny not only agrees with most classical molecular results but also provides new insights into the relationships between lophotrochozoans and challenges the results obtained using high-throughput strategies, highlighting the problems associated with the current trend to increase gene number rather than taxa.

Phylogeny of Eunicida (Annelida) and exploring data congruence using a partition addition bootstrap alteration (PABA) approach.

The definition of both the labidognath and ctenognath jaw type does not address adequately the variation within Eunicida and thus misleads current evolutionary understanding, and a symmetric maxillary apparatus with a carrier and four to six maxillae is most likely the plesiomorphic condition for EunicIDA.

The phylogenetic position of the comb jellies (Ctenophora) and the importance of taxonomic sampling

The reconstructed topology is considered to represent the current best hypothesis of the interrelationships of these old lineages and morphological features supporting alternative hypotheses are discussed in the light of this result.

Polyzoa is back: The effect of complete gene sets on the placement of Ectoprocta and Entoprocta.

This study favors the evolutionary scenario where Entoprocta, Cycliophora, and Bryozoa constitute one of the earliest branches among Lophotrochozoa and thus supports the Polyzoa hypothesis.



Evaluating multiple alternative hypotheses for the origin of Bilateria: an analysis of 18S rRNA molecular evidence.

  • A. Collins
  • Biology
    Proceedings of the National Academy of Sciences of the United States of America
  • 1998
Six alternative hypotheses for the phylogenetic origin of Bilateria are evaluated by using complete 18S rRNA gene sequences for 52 taxa to suggest that there is little support for three of these hypotheses, but one is most strongly supported.

Early evolution of the bilateria.

Estimations of the divergence times show that the major bilaterian phyla did not originate in an explosive radiation during the Cambrian but rather that the Bilateria have a several hundred million years long Precambrian history.

Annelida and Arthropoda are Not Sister Taxa: A Phylogenetic Analysis of Spiralian Metazoan Morphology

This study presents a new analysis of 141 independently assembled characters, purported to represent the current state of knowledge of metazoan morphology and embryology, and results in robust support of the Eutrochozoa hypothesis.

The position of arthropods in the animal kingdom: Ecdysozoa, islands, trees, and the "Parsimony ratchet".

The goal of this paper was to investigate the position of the Arthropoda within the protostome animals and determine arthropod sister-group relationships, and the phylogenetic conclusions were summarized as monophyletic.

A new perspective on lower metazoan relationships from 18S rDNA sequences.

While sequencing additional lineages to identify slowly evolving taxa, the number of complete or nearly complete 18S rDNA sequences for the major diploblastic lineages was increased and the maximum-likelihood framework was used to choose a model which best explains the data.

The demise of a phylum of protists: phylogeny of Myxozoa and other parasitic cnidaria.

Reassessment of myxozoans as metazoans reveals terminal differentiation, typical metazoan cellular junctions, and collagen production, and it is recommended that the group as a whole be removed from all protistan classifications and placed in a more comprehensive cnidarian system.


Testing specific hypotheses of chaetognath affinities to nematodes, mollusks, acanthocephalans, and deuterostomes supported the monophyly of a chaet Cognatha-nematode clade, and an evolutionary scenario for the origin of the Chaetognatha lineage from a vermiform benthic organism was presented.

First molecular evidence for the existence of a Tardigrada + Arthropoda clade.

The results obtained represent the first molecular evidence for a Tardigrada + Arthropoda clade and indicate the need to review those obtained solely on morphological characters.

The phylogenetic position of the pterobranch hemichordates based on 18S rDNA sequence data.

  • K. Halanych
  • Biology
    Molecular phylogenetics and evolution
  • 1995
It is suggested that ciliated gill slits and the dorsal hollow nerve chord are pleisomorphic features of the Deuterostomia, the last common ancestor of the hemichordates and echinoderms.

Monophyly of brachiopods and phoronids: reconciliation of molecular evidence with Linnaean classification (the subphylum Phoroniformea nov.)

  • B. Cohen
  • Biology, Geography
    Proceedings of the Royal Society of London. Series B: Biological Sciences
  • 2000
Molecular phylogenetic analyses of aligned 18S rDNA gene sequences from articulate and inarticulate brachiopods representing all major extant lineages, an enhanced set of phoronids and several