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Theropod edentulous beak evolution (free pdf)



From: Ben Creisler
bcreisler@gmail.com

A new advance online paper in open access:


Stephan Lautenschlager, Lawrence M. Witmer, Perle Altangerel, and
Emily J. Rayfield (2013)
Edentulism, beaks, and biomechanical innovations in the evolution of
theropod dinosaurs.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1310711110
http://www.pnas.org/content/early/2013/11/27/1310711110.abstract?sid=eed5bdee-5d5f-464e-8d75-de68dc3e8ee9
pdf:
http://www.pnas.org/content/early/2013/11/27/1310711110.full.pdf+html



Significance

Edentulism and beaks (rhamphothecae) are distinguishing features among
extant birds and are traditionally regarded as a response to
weight-saving demands for the evolution of flight. However,
keratin-covered beaks paralleled by edentulism appeared in non-avian
theropod dinosaurs and as early as the Early Cretaceous. Here,
high-resolution, digital biomechanical models of the skull of the
Cretaceous therizinosaur Erlikosaurus andrewsi are used to investigate
the functional significance of these morphological specialisations and
adaptations occurring in non-avian, maniraptoriform dinosaurs. Results
of finite-element analyses provide evidence that keratinous beaks play
an important role in enhancing cranial stability by mitigation stress
and strain during feeding and represent an evolutionary innovation
developed early in derived theropod dinosaurs.

Abstract

Maniraptoriformes, the speciose group of derived theropod dinosaurs
that ultimately gave rise to modern birds, display a diverse and
remarkable suite of skeletal adaptations. Apart from the evolution of
flight, a large-scale change in dietary behavior appears to have been
one of the main triggers for specializations in the bauplan of these
derived theropods. Among the different skeletal specializations,
partial or even complete edentulism and the development of keratinous
beaks form a recurring and persistent trend in from the evolution of
derived nonavian dinosaurs. Therizinosauria is an enigmatic
maniraptoriform clade, whose members display these and other
osteological characters thought to be correlated with the shift from
carnivory to herbivory. This makes therizinosaurians prime candidates
to assess the functional significance of these morphological
characters. Based on a highly detailed biomechanical model of
Erlikosaurus andrewsi, a therizinosaurid from the Upper Cretaceous of
Mongolia, different morphological configurations incorporating
soft-tissue structures, such as a keratinous rhamphotheca, are
evaluated for their biomechanical performance. Our results indicate
that the development of beaks and the presence of a keratinous
rhamphotheca would have helped to dissipate stress and strain, making
the rostral part of the skull less susceptible to bending and
displacement, and this benefit may extend to other vertebrate clades
that possess rhamphothecae. Keratinous beaks, paralleled by
edentulism, thus represent an evolutionary innovation developed early
in derived theropods to enhance cranial stability, distinct to
postulated mass-saving benefits associated with the origin of flight.


==

Press release from Bristol University



http://www.bris.ac.uk/news/2013/9987.html