| Gallornis Fossil range: Early Cretaceous (Berriasian-Hauterivian?) | |
|---|---|
| Scientific classification
| |
|
Class |
|
|
Subclass |
|
|
Infraclass |
|
|
Superorder |
Galloanserae? |
|
Order |
No information |
|
Suborder |
No information |
|
Genus |
Gallornis |
| |
Gallornis is a genus of prehistoric bird from the Cretaceous. It is of fairly indeterminate age and extremely fragmentary.
Overview[]
Yet it provides a tantalizing glimpse at an apparently crucial point in avian evolution. The single known species Gallornis straeleni lived near today's Auxerre in Yonne département (France); it has been dated very tentatively to the Berriasian-Hauterivian stages, that is about 140-130 million years ago.[1]. The material consists of
"a very worn proximal end of a femur and a humerus fragment"[2]
This is a highly significant taxon for theories about the evolution of birds, less well-known but certainly equal in importance to the famous Archaeopteryx. Unfortunately, it is not known from much or well-preserved material. What can be said is that the remains show features only known from the Neornithes - the group of birds that exists today. Thus, Gallornis demonstrates that as early as about 130 million years ago or more the ancestors of all living birds might already have been an evolutionary lineage distinct from the closely-related Hesperornithes and Ichthyornithes (essentially modern birds retaining some more ancient features like teeth) and the more distantly related Enantiornithes (a group of "dino-birds" which were the most successful avians in the Mesozoic).
Ecology[]
During the time of Gallornis, its range was located around 30°N, north of the Tropic of Cancer aridity belt. However, the Cretaceous was a hot and humid age in general, so the habitat might have more resembled West Africa around the Gulf of Guinea. Higher sealevels had large parts of Europe submerged for much of the time, and Southeast Europe and Asia Minor had not even attached to that continent yet (see also Haţeg Island, Haţeg Basin). The Alpide orogeny (the uplift of the Eurasian latitudinal mountain belt) had not even gotten underway.
Gallornis was a contemporary of many (non-avian) dinosaurs living around the (Second) Tethys Sea. In the archipelago that was then Europe, huge sauropods appear to have been the dominant herbivores.[3] Apart from some early birds, pterosaurs roamed the skies of the European microcontinents[4] (more abundant and diverse than the few birds[5]), while semi-aquatic[6] and finned marine crocodilians[7] were common. Herds of Iguanodon must have been a common sight. Stegosaurs were apparently rare and might have been Huayangosauridae.[8] Heterodontosauridae like Echinodon were contemporaries of this early bird, and part of the lineage which much later gave rise to Triceratops, while the ancestry of the famous Tyrannosaurus rex was still mid-sized long-armed animals like Eotyrannus lengi, which almost certainly lived when Gallornis was already extinct.
Systematics[]
As it is so close to the common origin of all living birds, Gallornis of course cannot be assigned to any living family and probably not even to any extant order.[2] It was allied with the Paleocene Scaniornis, a probable waterbird that is sometimes allied with flamingos (which may or may not be correct and altogether is not too unlikely) to form the supposed "proto-flamingo" family Scaniornithidae.[9] However, the difference in age alone virtually rules out a close relationship between these two, and the early age of the Gallornis fossils makes it highly unlikely that this taxon was allied to the flamingos. A more probable hypothesis, echoing the initial description of 1931, is that Gallornis was an early member of the Galloanserae, the clade that eventually brought forth the Galliformes (landfowl) and Anseriformes (waterfowl) of our time. With the remains at hand, however, it cannot even be reliably determined whether Gallornis was a paleognath or a neognath,[2] and it may actually be among the taxa closest to the LCA of all living birds from ostriches to sparrows. From all these considerations, it is obvious that more complete remains of this enigmatic taxon would be a find of invaluable significance for ornithology.
Though the material is almost beyond recognition, a few features of the femur are still recognizable. In general shape it resembles the Neornithes. Notably, the lateral trochanteric crest is elevated over a large antitrochanteric facet, and somewhat recurved over it. The elevated lateral trochanteric crest is an autapomorphic feature of and plesiomorphic among Neornithes, as far as is known. It is widespread in the most ancient lineages of these, such as tinamous, Galloanserae, shorebirds and seabirds, and changed fundamentally again especially in later landbird lineages.[2]
The material of G. straeleni is highly unsuited for cladistic analysis. However, what uncertain results there are support the view that this is one of the most ancient birds in the modern sense known to date.[1] Nonetheless, given that Gansus yumenensis, an ornithuran close to modern birds but probably not part of their lineage lived some dozen million years later, comparison of the Gallornis material with fossils of such more primitive birds seems warranted.
Footnotes[]
- ^ a b Mortimer (2004)
- ^ a b c d Hope (2002)
- ^ E.g. the camarasaurid Aragosaurus ischiaticus, the diplodocoid Histriasaurus boscarollii, the huge plesiomorphic Turiasauria, or the very peculiar and smallish (for a sauropod - some 15 meters or more) Xenoposeidon proneneukos
- ^ E.g. the plesiomorphic Lonchodectes or the "spoon-billed" Plataleorhynchus streptorophorodon
- ^ E.g. the early enantiornithine Iberomesornis romerali
- ^ E.g. Goniopholis, Pholidosaurus and Vectisuchus
- ^ Metriorhynchidae such as Dakosaurus, Neustosaurus and Enaliosuchus
- ^ See the disputed Craterosaurus pottonensis and Regnosaurus northamptoni
- ^ Or "Torotigidae" sensu Brodkorb (1963: p.269)
References[]
- Brodkorb, Pierce (1963): Catalogue of fossil birds. Part 1 (Archaeopterygiformes through Ardeiformes). Bulletin of the Florida State Museum, Biological Sciences 7(4): 179-293. PDF fulltext
- Hope, Sylvia (2002): The Mesozoic radiation of Neornithes. In: Chiappe, Luis M. & Witmer, Lawrence M. (eds.): Mesozoic Birds: Above the Heads of Dinosaurs: 339-388. ISBN 0520200942
- Mortimer, Michael (2004): The Theropod Database: Phylogeny of taxa. Retrieved 2008-AUG-14.