Embryonic Enantiornithine Bird Fossils From Campanian Cretaceous Mongolia

An embryonic enantiornithine bird and associated eggs from the cretaceous of Mongolia

Authors:

E. N. Kurochkin, S. Chatterjee and K. E. Mikhailov

Abstract:

Enantiornithes is the most speciose clade of Cretaceous birds, but many taxa are known from isolated postcranial skeletons. Two embryonic enantiornithine bird skeletons of Gobipipus reshetovi gen. et sp. nov. from the Upper Cretaceous (Campanian) Barun Goyot Formation of the Gobi Desert in Mongolia provide new insights into the anatomy, radiation, and mode of development of early avialans. In recent times, both enantiornithine and ornithuromorph birds are known from the Barun Goyot Formation as well as from the Djadokhta and Nemegt Formations. The 80-million-year-old Gobipipus skeletons encased within eggshells shows several features characteristic of enantiornithine birds. The wing skeleton and shoulder girdle show morphological features indicating that Gobipipus achieved sophisticated powered flight. Gobipipus reshetovi gen. et sp. nov. is quite distinct from the sympatric enantiornithine species Gobipteryx minuta from the same strata in many anatomical features. Phylogenetic analysis of 26 avialan ingroup taxa based on distribution of 202 characters indicate that Gobipipus is a basal member of enantiornithine birds along with Confuciusornis and shares more characters with ornithuromorphs than previously recognized. The embryonic nature of Gobipipus specimens sheds new light on the developmental history of enantiornithine birds. The well-ossified bones of the fore- and hind limbs, and fusion of many skeletal elements indicate a precocial mode of development in Gobipipus. Apparently Gobipipus hatchlings could walk away from the ground nests as soon as they emerged from their eggs. The asymmetry of egg poles are unique features of Gobipipus eggs (oogenus Gobioolithus) among Cretaceous avialans. The microstructure of the shell in Gobioolithus eggs with the embryos of Gobipipus is typical avian (of ornithoid basic type) and less ratite-like in morphology of the spongy layer than is that in the other possible egg-remains of enantiornitine birds (oofamily Laevisoolithidae).

Archaeopteryx Feather Colors Are Fanciful

The Archaeopteryx, which lived around 150 million years ago and was a mixture of bird traits (notably feathers) and reptile traits (teeth, claws on its wings), was previously thought to have black feathers. But a new analysis of three Archaeopteryx fossils has revealed that the ancient bird's feathers were in fact light in color, with a dark edge and tips.

The distinct black-and-white patterns on the bird's plumage are comparable to the pigmentation of a magpie, said study co-author Roy Wogelius, a geochemist at the University of Manchester.

"This creature was actually doing very well in terms of evolutionary state. It already has a key adaptation that we see in many modern species of bird," said study leader and University of Manchester paleontologist Phil Manning, who is a National Geographic grantee.

Like modern-day birds, the Archaeopteryx would have benefited from the different shadings.

The scan found traces of copper that produced the dark tips of the bird's feather; copper has properties that can keep away bacteria that would otherwise fray wings. The copper also slowed the "microbial breakdown" of the fossil, Manning notes: "It's the reason the feather has been preserved for 150 million years to the point where we still see astounding resolution in the fossil."

A New Reconstruction of the Skull of Archaeopteryx

New observations on the skull of Archaeopteryx

Author:

1. Oliver W. M. Rauhut (a)

Affiliation:

a. Bayerische Staatssammlung fu¨r Pala¨ontologie und Geologie and Department of Earth and Environmental Sciences, LMU Munich, Richard-Wagner-Str. 10, 80333 Munich, Germany

Abstract:

Although skeletal remains of the iconic oldest known avialian Archaeopteryx have been known for almost 150 years, several aspects of the cranial anatomy of this taxon have remained enigmatic, mainly because of the strongly flattened and often fractured and incomplete nature of available skull materials. New investigation of the skulls of the recently described, excellently preserved tenth (Thermopolis) and the seventh (Munich) specimens revealed several previously unrecognized characters and helps to resolve some problematic issues. Thus, the nasal of Archaeopteryx shows a lateral notch for the lacrimal, as is found in many other saurischian dinosaurs, the maxilla clearly participates in the margin of the external nares, and there seems to be a pneumatic foramen in the lacrimal, comparable to the lacrimal fenestra found in many non-avian theropods. In the braincase, Archaeopteryx shows pneumatic features reminiscent of non-avian theropods, including a ventral basisphenoid recess and an anterior tympanic recess that is laterally incised into the basisphenoid/prootic. Most importantly, however, the postorbital process of the jugal shows a facet for the suture with the postorbital, thus resolving the question of whether Archaeopteryx had a closed postorbital bar. A new reconstruction of the skull of Archaeopteryx is presented, making the skull of this taxon even more theropod-like than previously recognized. Furthermore, the closed postorbital bar and the configuration of the bones of the skull roof cast serious doubt on claims that an avian-style cranial kinesis was present in this taxon.