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On-line version ISSN 1678-2690
An. Acad. Bras. Ciênc. vol.74 no.2 Rio de Janeiro June 2002
ON THE OCCURRENCE OF AN AVIAN VERTEBRA IN CRETACEOUS STRATA OF MOROCCO, AFRICA
DOUGLAS RIFF 1, ALEXANDER W.A. KELLNER 1, BRYN MADER 2 AND DALE RUSSEL 3
1 Setor de Paleovertebrados, Departamento de Geologia e Paleontologia, Museu Nacional / UFRJ, Rio de Janeiro, RJ.
2 Long Island Natural History Museum, New York.
3 Department of Marine, Earth and Atmosph. Science, North Carolina State University, North Carolina.
So far, osteological remains of Mesozoic birds in Gondwana are very limited, with some occurrences in South America (around 10 non-neornithine records), Australia (one), Antarctica (one), and Africa. In the latter, this record is restricted to incomplete limb elements and a partial skeleton from Madagascar, and footprints from Late Cretaceous strata of Morocco. Here we report an isolated dorsal vertebra found in the Albo-Cenomanian sandstones of the Kem Kem region, Southeastern Morocco. The specimen is housed in the Canadian Museum of Nature (NMC 50852) and represents the first avian osteological record from Mesozoic strata of the Continental Africa.
The vertebra is well preserved but incomplete. The length of the centrum is 21.0 mm with a preserved height of 25.6 mm. In some areas the bone surface was broken off revealing the pneumatized internal structure (apparently less developed compared to most recent avian taxa). The centrum in elongated, amphicoelous, cylindrical and slightly constricted medially, with the ventral margins arched upwards; no pleurocoels or foramina are present on the lateral surface. The articular facets have a subcircular outline.
The main avian characteristic of NMC 50852 is the large neural canal, with the ratio between the height of the neural canal and the height of the cranial surface of the centrum of 0.67 (in extant birds, this ratio varies from 0.5 to 2.75 and in theropods it is lesser than 0.4). The neural arch is not very tall, being elongated and showing a cranial and caudal groove. The transverse processes and zygapophyses are not preserved. On the left side, a small prominence possibly represents the base of the parapophysis.
The characteristics of this vertebra differ from the main avian clades (Alvarezsauridae, Confunciornithidae, Enantiornithes, Hesperornithiformes, Icthyornithiformes, Neornithes). The main similarities of the Moroccan specimen are observed in the dorsal vertebrae of Rahona ostromi, a basal bird from the Late Cretaceous of Madagascar. Notwithstanding, some differences such as the neural canal, which is larger in the Moroccan specimen, and the presence of pleurocoels in Rahona ostromi suggest that NMC 50852 belongs to a different taxon of basal birds. ( December 20, 2001 ).