Review on the temporal skull region in tetrapods - the big question of temporal fenestrae

Short summary on Abel & Werneburg 2021. Morphology of the temporal skull region in tetrapods: research history, functional explanations, and a new comprehensive classification scheme. Biological Reviews.


Me and Ingmar Werneburg (Senckenberg Centre, University of Tübingen) published a review paper on the morphology and macroevolution of the temporal skull region in Tetrapoda in Biological Reviews. Next to a general overview about the research history of the temporal region, we provide a new morphological classification scheme based on the number and arrangement of temporal openings. This study forms part of my doctoral thesis.

What is it all about?

  • The temporal region traditionally has been an important aspect in tetrapod systematics and evolution. Most notably the presence and arrangement of temporal openings have been considered to be a phylogenetic informative trait. This led to the naming of several taxa based on temporal morphology like Anapsida, Synapsida, Diapsida, or Stegokrotaphia.
  • During the last decades, however, advances in phylogenetics and new fossil finds cast doubt on the validity of most of these taxa and the phylogenetic relevance of temporal morphology.
  • Nevertheless, the morphology of the temporal skull region remains an important field of study with the functional and developmental causes behind temporal openings only barely understood.

Traditional subdivision of ‘reptiles’ based on their temporal fenestrae. Modified from Abel & Werneburg (2021).

What did we do?

  • We reviewed the research history on the evolution and functional causes behind temporal openings in tetrapods.
  • We showed how over the last 200 years authors recognized morphological patterns and introduced different terminologies to describe the various morphotypes.
  • We then documented how the evolutionary interpretations on temporal openings developed over time, how it inspired the coining of new taxa, and how most of these taxa fell out of favor again. We also discussed which controversies regarding the distribution and evolutionary origin of specific temporal morphotypes still remain. In this regard, we discussed especially the ancestral morphotypes in amniotes and turtles.
  • Next to the phylogenetic interpretations, we also summarized the different functional and developmental explanations for the evolution of temporal openings and why such openings are more common in amniotes and lissamphibians than in their stem-groups.
  • Lastly, we introduced a new but purely descriptive classification scheme for the tetrapod temporal region to simplify future discussions of convergent developments and illustrated their distribution within tetrapods and their ancestors.


Summary of the different factors proposed to affect the morphology of the temporal region. From Abel & Werneburg (2021).

Summary of different suggestions for the morphological categorization of the temporal skull region. From Abel & Werneburg (2021). Click to enlarge.

Overview of our new descriptive classification scheme with skull examples. From Abel & Werneburg (2021)

Composed and simplified phylogenetic tree depicting the distribution of temporal morphotypes across tetrapods and their stem-group. From Abel & Werneburg (2021).

Do you have any questions about this study? Feel free to contact me.