Ontogenetic studies indicating the sternum formed differently in Enantiornithines and Ornithuromorphs

Oct 15, 2012
Ontogenetic studies indicating the sternum formed differently in enantiornithines and ornithuromorphs
Fig.1: New juvenile specimens assigned to Enantiornithes indet. Credit: Jingmai O'Connor

In an article online October 9 in Nature Communications, researchers reveal, for the first time, the formation of the sternum in the largest group of Cretaceous birds, Enantiornithes, highlighting the importance of ontogenetic studies for understanding homology and the evolution of skeletal features in palaeontology.

The study is based on information from new juvenile specimens from the Shandong Tianyu Museum of Nature; these discoveries reveal rare ontogenetic information, in this case the ossification of the sternum, one of the most important elements in the bird skeleton (the two largest and most powerful flight muscles attach to this bone).

The study uncovers a major difference between the sternum in Enantiornithes and all other known groups of birds. The enantiornithine sternum forms from four to six ossification centers, three of which are recognized for the first time; the sternal body primarily forms from two non-symmetrical unilateral ossifications, the caudal of which ossifies first. In contrast, living birds ossify the sternal body from a mediolaterally symmetrical pair of sternal ossifications as in other , and ossifications proceeds from the front to the back.

Ontogenetic studies indicating the sternum formed differently in enantiornithines and ornithuromorphs
Fig.2: Interpretative drawing of the development of the enantiornithine sternum. Red indicates bone and blue indicates cartilage. Credit: Jingmai O'Connor

A number of similar features (e.g. ventral keel, caudal trabeculae, craniolateral processes) that distinguish the sterna of enantiornithines and ornithuromorphs (the group that includes living ) from other groups are now revealed to have very different developmental origins; this suggests these features are not fully homologous, highlighting the high degree of homoplasy that characterizes the dinosaur bird transition and the importance of development for testing hypotheses of homology.

This study suggests that many of the that unite Enantiornithes and Ornithuromorpha as sister-groups may represent parallelisms and through a better understanding of development, this relationship may no longer be supported.

Explore further: Researchers create methylation maps of Neanderthals and Denisovans, compare them to modern humans

add to favorites email to friend print save as pdf

Related Stories

The skull of extinct birds revealed

Mar 21, 2011

Birds are the most diverse clade on the planet, and the skull of the living bird is one of the most highly modified and morphologically variable regions of their skeleton. The large diversity of enantiornithine ...

Archaeopteryx and the dinosaur-bird family tree

Sep 15, 2011

The magpie-sized Archaeopteryx had bird and dinosaur features and helped show that birds evolved from dinosaurs. However, recent research in the journal Nature questions its position in the dinosaur-bird family ...

Recommended for you

Crowd-sourcing Britain's Bronze Age

Apr 17, 2014

A new joint project by the British Museum and the UCL Institute of Archaeology is seeking online contributions from members of the public to enhance a major British Bronze Age archive and artefact collection.

Roman dig 'transforms understanding' of ancient port

Apr 17, 2014

(Phys.org) —Researchers from the universities of Cambridge and Southampton have discovered a new section of the boundary wall of the ancient Roman port of Ostia, proving the city was much larger than previously ...

User comments : 0

More news stories

Study finds law dramatically curbing need for speed

Almost seven years have passed since Ontario's street-racing legislation hit the books and, according to one Western researcher, it has succeeded in putting the brakes on the number of convictions and, more importantly, injuries ...

Impact glass stores biodata for millions of years

(Phys.org) —Bits of plant life encapsulated in molten glass by asteroid and comet impacts millions of years ago give geologists information about climate and life forms on the ancient Earth. Scientists ...

Researchers successfully clone adult human stem cells

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...