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Dinosaur ontogeny: Adult dinosaurs + Majungasaurus craniomandibular skeleton (free pdfs)

Ben Creisler

Two new papers in open access:

David W. E. Hone, Andrew A. Farke & Mathew J. Wedel (2016)
Ontogeny and the fossil record: what, if anything, is an adult dinosaur?
Biology Letters 12: 20150947
DOI: 10.1098/rsbl.2015.0947
http: // rsbl.royalsocietypublishing.org/content/12/2/20150947
http: // 

Identification of the ontogenetic status of an extinct organism is
complex, and yet this underpins major areas of research, from taxonomy
and systematics to ecology and evolution. In the case of the
non-avialan dinosaurs, at least some were reproductively mature before
they were skeletally mature, and a lack of consensus on how to define
an ‘adult’ animal causes problems for even basic scientific
investigations. Here we review the current methods available to
determine the age of non-avialan dinosaurs, discuss the definitions of
different ontogenetic stages, and summarize the implications of these
disparate definitions for dinosaur palaeontology. Most critically, a
growing body of evidence suggests that many dinosaurs that would be
considered ‘adults’ in a modern-day field study are considered
‘juveniles’ or ‘subadults’ in palaeontological contexts.


Nirina O. Ratsimbaholison, Ryan N. Felice, and Patrick M. O’Connor (2016)
Ontogenetic changes in the craniomandibular skeleton of the
abelisaurid dinosaur Majungasaurus crenatissimus from the Late
Cretaceous of Madagascar.
Acta Palaeontologica Polonica (in press)
doi:http: // dx.doi.org/10.4202/app.00132.2014
http: // app.pan.pl/article/item/app001322014.html

Abelisaurid theropods were one of the most diverse groups of predatory
dinosaurs in Gondwana during the Cretaceous Period. The group is
characterized by a tall, wide skull and robust cervical region. This
morphology is thought to have facilitated specialized feeding
behaviors such as prolonged contact with prey. The Late Cretaceous
abelisaurid Majungasaurus crenatissimus typifies this abelisaurid
cranial morphotype. Recent fossil discoveries of this species include
a partial growth series that allows for the first time an
investigation of ontogenetic variation in cranial morphology in a
representative abelisaurid. Herein we examine growth trajectories in
the shape of individual cranial bones and articulated skulls of
Majungasaurus using geometric morphometrics. Several major changes in
skull shape were observed through ontogeny, including an increase in
the height of the jugal, postorbital, and quadratojugal, an increase
in the extent of the contacts between bones, and a decrease in the
circumference of the orbit. The skull transitions from relatively
short in the smallest individual to tall and robust in large adults,
as is seen in other theropods. Such morphological change during
ontogeny would likely have resulted in different biomechanical
properties and feeding behaviors between small and large individuals.
These findings provide a post-hatching developmental framework for
understanding the evolution of the distinctive tall skull morphology
seen in abelisaurids and other large-sized theropod dinosaurs.