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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...
Development of the Sexual Organs in the Embryo and Fetus01:15

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Development of the reproductive organs in an embryo starts from a bipotential state. This means the early embryo can develop either male or female reproductive organs. The formation of these organs begins with the growth of gonadal ridges that arise from the intermediate mesoderm during the fifth week of development.
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Cleavage and Blastulation01:33

Cleavage and Blastulation

After a large-single-celled zygote is produced via fertilization, the process of cleavage occurs while zygotes travel through the uterine tube. Cleavage is a mitotic cell division that does not result in growth. With each round of successive cell division, daughter cells get increasingly smaller.
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...
Changes in the Appendicular Skeleton with Age01:09

Changes in the Appendicular Skeleton with Age

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Bone Formation by Intramembranous Ossification01:29

Bone Formation by Intramembranous Ossification

Intramembranous ossification is one of the two processes involved in the development of bones within an embryo. The flat bones of the face, most of the cranial bones, and the clavicles are formed via this process. During intramembranous ossification, the bones develop directly from sheets of undifferentiated mesenchymal connective tissue.
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Updated: May 21, 2026

Ablation of a Single Cell From Eight-cell Embryos of the Amphipod Crustacean Parhyale hawaiensis
10:55

Ablation of a Single Cell From Eight-cell Embryos of the Amphipod Crustacean Parhyale hawaiensis

Published on: March 16, 2014

Early evolutionary trends in ammonoid embryonic development.

Kenneth De Baets1, Christian Klug, Dieter Korn

  • 1Paläontologisches Institut und Museum, Universität Zürich, Karl Schmid-Strasse 4, CH-8006 Zürich, Switzerland. kenneth.debaets@pim.uzh.ch

Evolution; International Journal of Organic Evolution
|June 8, 2012
PubMed
Summary
This summary is machine-generated.

Ammonoids evolved tighter shells and smaller embryos during the Devonian, with convergent evolution leading to closed umbilici. This reproductive strategy shift influenced their survival and extinction.

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Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Marine Biology

Background:

  • Ammonoids, extinct shelled cephalopods, emerged from bactritoid ancestors with straight shells in the Early Devonian.
  • The Devonian period witnessed the 'Nekton Revolution,' a significant diversification of marine life.

Purpose of the Study:

  • To investigate evolutionary trends in ammonoid shell coiling and embryonic development during the Devonian.
  • To understand the role of reproductive strategies in ammonoid diversification and extinction.

Main Methods:

  • Analysis of fossil ammonoid shells, focusing on coiling patterns and embryonic features.
  • Comparative study of multiple ammonoid lineages to identify convergent evolutionary trends.

Main Results:

  • Ammonoid embryonic shells showed progressive coiling and size reduction during the Devonian.
  • Convergent evolution of a closed umbilicus occurred in at least three ammonoid lineages.
  • Lineages with open umbilici and less coiled embryonic shells were more prone to extinction during Devonian events.

Conclusions:

  • Synchronous evolutionary changes in ammonoid shell morphology suggest common driving factors.
  • A shift towards smaller embryos and potentially higher fecundity may have impacted ammonoid success and eventual demise.
  • The evolution of tighter coiling and closed umbilici was a key adaptation for survival in changing Devonian environments.