Temporal Holes in Dinosaurs’ and Humans’ Skulls Formed by Dietary Habits, Study Suggests
Whether human or dinosaur: In the skull of most land vertebrates there is a hole in the temple area, and in the case of most reptiles there are even two. Scientists have been looking for explanations for these skull shapes for 150 years. A research team from the University of Tübingen and the Ruhr University Bochum is now showing in a study: Depending on how and where food is held, bitten and chewed in the mouth, the forces that act on a skull change – and lead to this over the course of millions of years Formation of bone connections or openings. This knowledge makes it possible to better reconstruct the lifestyle of extinct animals.
“The variety of skull and bone shapes has been described in detail by paleontologists and zoologists – but the origin of the temporal brackets and openings and what they say about the biology and relationships of the animals have not yet been convincingly explained,” says PD Dr. Ingmar Werneburg from the Senckenberg Center for Human Evolution and Palaeoenvironment at the University of Tübingen and curator of the university’s paleontological collection.
“Our model is based on the idea that bone mass can only be formed in places where compressive stresses exist,” says Professor Holger Preuschoft, emeritus functional morphologist at the Anatomical Institute of the Ruhr University Bochum and co-author of the study, which is now published in the journal The Anatomical Record has been published. “In addition, there must be mechanical calm at the points of bone formation. There must be no movement that could lead to the formation of a false joint, a nonunion.”
Humans also have a large temple opening above the zygomatic arch. Through them, the jaw muscle pulls down to the lower jaw. When chewing, the movement of this muscle can be felt in the wide temple opening. In many dinosaur species the openings are shaped very differently. The two scientists compared dozens of skulls from land vertebrates spanning several million years of evolutionary history.
“When animals bite hard at the front of the jaw – for example with the help of fangs – scientists believe that great tension spreads above and below the eyes and towards the neck and leads to the formation of bone braces in the temple,” says Werneburg. Reptiles have another effect: they bite primarily at the back of the jaw, where a shorter lever arm from the jaw joint allows for more biting force. “Here, too, there is a compressive stress that creates a bone bridge behind the eye. If this now comes into contact with the upper tension of the front bite, both force streams are partially redirected and a second zygomatic arch can form.” In previous studies, Holger Preuschoft has experimentally demonstrated and tested the effect of these forces on the skulls of animal species that are still alive today , under what load do bones break? The study is now applying these findings to the evolutionary history of vertebrates for the first time.
When the animal shakes its prey or tears leaves from a plant, additional lateral shear forces are created, which lead to further modifications of the temple shape. The acting forces are returned in a force circle to the starting point of the force in the teeth, also with the help of the jaw muscles. “Otherwise the skull would not be stable and would shatter,” says Preuschoft