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The cranium (skull) is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the facial bones and the brain case, or cranial vault. The facial bones underlie the facial structures, form the nasal cavity, enclose the eyeballs, and support the teeth of the upper and lower jaws.
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The human skull is composed of several bones that come together to protect the brain and support the structures of the face. The junctions where these bones meet are called sutures.
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Scientists record evolutionary history by analyzing fossil, morphological, and genetic data. The fossil record documents the history of life on Earth and provides evidence for evolution. However, both fossil and living organisms offer evidence that outlines Earth’s evolutionary history.
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Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.
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The superior view of the cranium shows the frontal and paired parietal bones.
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Evolutionary origin of the turtle skull.

G S Bever1,2,3, Tyler R Lyson3,4, Daniel J Field5

  • 1Department of Anatomy, New York Institute of Technology, College of Osteopathic Medicine, Old Westbury, New York 11568, USA.

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|September 3, 2015
PubMed
Summary
This summary is machine-generated.

Fossil analysis of Eunotosaurus africanus reveals it as a key transitional reptile, extending the turtle evolutionary stem by 40 million years and suggesting an origin on land. This finding clarifies the diapsid to anapsid skull transformation in early turtle evolution.

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Area of Science:

  • Paleontology
  • Evolutionary Biology
  • Comparative Anatomy

Background:

  • The evolutionary origin of turtles and the transition from diapsid to anapsid skulls remain poorly understood.
  • Genomic data suggest turtles evolved from diapsid reptiles, but fossil evidence for this skull transformation is scarce.
  • Eunotosaurus africanus possesses a postcranial skeleton with turtle-like features, but its cranial evidence for turtle ancestry was previously debated.

Purpose of the Study:

  • To investigate the cranial anatomy of Eunotosaurus africanus using advanced imaging techniques.
  • To determine the phylogenetic position of Eunotosaurus africanus and its implications for turtle evolution.
  • To test hypotheses regarding skull fenestration changes during the early evolution of turtles.

Main Methods:

  • High-resolution computed tomography (CT) scanning of the Eunotosaurus africanus skull.
  • Construction and analysis of a novel character/taxon matrix for phylogenetic reconstruction.
  • Comparative analysis of cranial and postcranial features with extant and fossil reptiles.

Main Results:

  • Phylogenetic analyses provide strong cranial support for Eunotosaurus africanus as an early stem turtle.
  • This placement extends the turtle stem lineage by approximately 40 million years and suggests a terrestrial origin.
  • Eunotosaurus exhibits a secondary anapsid condition, indicating a transitional state from diapsid ancestry.

Conclusions:

  • Eunotosaurus africanus is a critical transitional fossil, offering significant cranial evidence for turtle origins.
  • The study provides a detailed hypothesis for fenestral closure along the turtle stem lineage.
  • These findings contribute to resolving systematic relationships within reptiles and inform broader amniote evolutionary studies.