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Related Concept Videos

Gastrulation01:56

Gastrulation

Gastrulation establishes the three primary tissues of an embryo: the ectoderm, mesoderm, and endoderm. This developmental process relies on a series of intricate cellular movements, which in humans transforms a flat, “bilaminar disc” composed of two cell sheets into a three-tiered structure. In the resulting embryo, the endoderm serves as the bottom layer, and stacked directly above it is the intermediate mesoderm, and then the uppermost ectoderm. Respectively, these tissue strata will form...
Neurulation01:30

Neurulation

Neurulation is the embryological process which forms the precursors of the central nervous system and occurs after gastrulation has established the three primary cell layers of the embryo: ectoderm, mesoderm, and endoderm. In humans, the majority of this system is formed via primary neurulation, in which the central portion of the ectoderm—originally appearing as a flat sheet of cells—folds upwards and inwards, sealing off to form a hollow neural tube. As development proceeds, the anterior...
Lampbrush Chromosomes01:51

Lampbrush Chromosomes

In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, Rückert observed LBCs in shark egg cells and coined the term "lampbrush chromosomes" because they looked like brushes used to clean kerosene lamps.
LBCs are made up of two pairs of conjugating homologous chromatids. Each chromatid consists of alternatively positioned regions of condensed-inactive chromatin and loosely placed-active side loops, which can be contracted and extended. The loops resemble the...
The Colonization of Land02:22

The Colonization of Land

Changes in the environment of the early Earth drove the evolution of organisms. As prokaryotic organisms in the oceans began to photosynthesize, they produced oxygen. Eventually, oxygen saturated the oceans and entered the air, resulting in an increase in atmospheric oxygen concentration, known as the oxygen revolution approximately 2.3 billion years ago. Therefore, organisms that could use oxygen for cellular respiration had an advantage. More than 1.5 years ago, eukaryotic cells and...
Phylogeny01:23

Phylogeny

Phylogeny is concerned with the evolutionary diversification of organisms or groups of organisms. A group of organisms with a name is called a taxon (singular). Taxa (plural) can span different levels of the evolutionary hierarchy. For instance, the group containing all birds is a taxon (comprising the class Aves), and the group of all species of daisies (the genus Bellis) is a taxon. Phylogenies can likewise include just one genus (i.e., depict species relationships) or span an entire...
Convergent Evolution01:54

Convergent Evolution

Evolution shapes the features of organisms over time, ensuring that they are suited for the environments in which they live. Sometimes, selection pressure leads to the rise of similar but unrelated adaptations in organisms with no recent common ancestors, a process known as convergent evolution.The structures that arise from convergent evolution are called analogous structures. They are similar in function even if they are dissimilar in structure. Further, structures can be analogous while also...

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Related Experiment Video

Updated: Jun 28, 2026

Dissection and Flat-mounting of the Threespine Stickleback Branchial Skeleton
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Published on: May 7, 2016

An aboral-dorsalization hypothesis for chordate origin.

Nori Satoh1

  • 1Department of Zoology, Graduate School of Science, Kyoto University, Sakyo-Ku, Kyoto, Japan. satoh@ascidian.zool.kyoto-u.ac.jp

Genesis (New York, N.Y. : 2000)
|October 22, 2008
PubMed
Summary

The chordate tadpole larva evolved from a common ancestor with echinoderms and hemichordates. Dorsalization of the aboral side of the ancestral embryo was key to forming the basic chordate body plan.

Area of Science:

  • Evolutionary developmental biology
  • Comparative embryology
  • Phylogenetics

Background:

  • Chordates share a common ancestor with echinoderms and hemichordates (Ambulacraria).
  • Cephalochordates are evolutionarily basal among chordates, preceding urochordates and vertebrates.
  • The evolution of the chordate tadpole larva is a significant area of study.

Purpose of the Study:

  • To propose a hypothesis for the evolution of the chordate tadpole-like larva.
  • To explain the developmental origins of key chordate features like the notochord and dorsal hollow neural tube.
  • To investigate the evolutionary relationship between chordates and other deuterostomes.

Main Methods:

  • Comparative embryology of cephalochordates and nonchordate deuterostomes.

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Expression of Fluorescent Proteins in Branchiostoma lanceolatum by mRNA Injection into Unfertilized Oocytes
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  • Analysis of molecular phylogeny to establish evolutionary relationships.
  • Hypothesis formulation based on developmental constraints and evolutionary events.

    • Main Results:

    • Echinoderms and hemichordates form the clade Ambulacraria.
    • Cephalochordates are more basal than urochordates and vertebrates.
    • The aboral-dorsalization hypothesis suggests dorsalization of the ancestral embryo's aboral side was crucial.

    Conclusions:

    • The tadpole-like larva with a dorsal hollow neural tube and notochord arose from a common deuterostome ancestor.
    • Limited space on the oral side of the ancestral embryo likely drove morphogenesis to the aboral side.
    • Aboral-dorsalization represents a key developmental event in establishing the fundamental chordate body plan.