Again, more recycled text from the Mesozoic bird section of the fieldguide…
Alexornis antecedens from the Upper Cretaceous (?Campanian) La Bocana Roja Formation of Mexico was first described in 1976; its remains were discovered in 1971 by H. J. Garbani and J. Loewe. The bones they found – various elements from the shoulder, wing and leg – were tiny, and evidently from a bird similar in size to a modern finch [adjacent life restoration by Ken Kirkland, from Hilton (2003)]
This discovery pre-dated the 1981 recognition of enantiornithines as a distinct group of Mesozoic birds (see the article on Cyril Walker for more on this subject). Pierce Brodkorb – the fossil’s describer – assumed that Alexornis was a modern-style, neornithine bird (Brodkorb 1976). He even suggested that it might be close to the ancestry of two modern bird groups: the Coraciiformes (rollers and relatives) and the Piciformes (woodpeckers and relatives). The species name – ‘antecedens‘ – reflects this, as it refers to a possible ancestral position for this bird. Larry Martin was later able to show that Alexornis is an enantiornithine (Martin 1983). Like other members of this group, the articular surfaces on its scapula and coracoid are ‘reversed’ relative to those of neornithines*: this had fooled Brodkorb, who had interpreted the scapula as the coracoid and vice versa [Alexornis holotype remains shown below; from Brodkorb (1976)].
* A groove on the ventral surface of the scapula forms the more important part of the triosseal canal, whereas in neornithines it is the dorsal end of the coracoid (specifically, the procoracoid process) that serves this role.
As with so many Mesozoic birds, Alexornis was initially given its own taxonomic ‘family’ (Alexornithidae), and later authors also gave it its own eponymous ‘order’ (Alexornithiformes). Some authors have recently used these names for more inclusive subgroups of Enantiornithes and one expert, Eugevny Kurochkin, has argued that Alexornis should be united with two very poorly known enantiornithines from Uzbekistan, Sazavis prisca and Kizylkumavis cretacea, in the Alexornithidae (Kurochkin 1996). This is difficult to be confident about, however, and most workers regard all three of these forms as of uncertain affinities within the large enantiornithine clade Euenantiornithes. Alexornis‘s generic name honours the palaeornithologist Alexander Wetmore. What little is known of Alexornis shows that it was small (roughly the same size as a sparrow) and capable of flight. Its skull is unknown.
For previous articles on enantiornithines and other Mesozoic birds see…
- Tet Zoo picture of the day # 24 [on archaeopterygids]
- The new Crato Formation enantiornithine
- A stunning new Mesozoic bird… well, new-ish
- Epidexipteryx: bizarre little strap-feathered maniraptoran
- Long and Schouten’s Feathered Dinosaurs, a review
- Cyril Walker
- The Mesozoic birds with weird, plastic-strip-style tail structures
Refs – -
Brodkorb, P. 1976. Discovery of a Cretaceous bird, apparently ancestral to the orders Coraciiformes and Piciformes (Aves: Carinatae). Smithsonian Contributions to Paleobiology 27, 67-73.
Hilton, R. P. 2003. Dinosaurs and Other Mesozoic Reptiles of California. University of California Press, Berkeley.
Kurochkin, E. N. 1996. A new enantiornithid of the Mongolian Late Cretaceous, and a general appraisal of the infraclass Enantiornithes (Aves). Russian Academy of Sciences, Special Issue, pp. 60.
Martin, L. 1983. The origin and early radiation of birds. In Perspectives in Ornithology, Essays Presented for the Centennial of the American Ornithologists’ Union, pp. 291-338.