Livro de Resumos - Dinossauros do Maranhão

Paleontologia 192
First occurrence of a titanosaur (Dinosauria, Sauropoda) osteoderm from
the Lower Cenomanian of the São Luís-Grajaú Basin,
northeastern Brazil
Rafael Matos Lindoso 1 , Rodrigo Miloni Santucci 2 , Ronny A. B. Santos 3 & Manuel Alfredo Medeiros 4
The Alcântara Formation is well represented in the coastal cliffs of Cajual Island, and a
number of fossil specimens have been collected from its conglomeratic deposits. It records
a middle Cretaceous paleocommunity similar to that reported from the coeval deposits in
Northern Africa, including charcharodontosaurids, spinosaurids, and sauropods attributed
to both Titanosauridae and Diplodocoidea. In 2008 a complete osteoderm measuring
140mm (length) by 90mm (width) and 105mm (height) was collected in the locality Praia
do Encantado (2º29'47.17''S; 44º28'48.20''W) in the eastern side of the island. The
osteoderm was isolated and free from the host rock. The specimen UFMA 1.10.1958 is
biconvex and has an elliptical outline in dorsal and ventral views, exhibiting a lateral
deformation on its edge. Both surfaces are extensively pitted and one of them is roughly
texturized; the other exhibits a dome or a well developed tuberosity, indicating that it may
possibly pertain to the external surface. Titanosaurs are the only sauropod possessing
osteoderms, and most of these partially armored forms are recorded in South America.
Significative occurrences have also been reported from Cretaceous rocks in Africa,
Madagascar and Europe. In Brazil, titanosaur osteoderms are rare and limited to isolated
remains from Marília Formation (Upper Cretaceous), located in Minas Gerais State. In
Maranhão State (northeastern Brazil), titanosaur remains are poorly known. Some caudal
centra and isolated teeth have been collected from outcrops of the middle Cretaceous
Alcântara Formation (Albian-lower Cenomanian) and also from more inland Albian deposits
of the Itapecuru Group, São Luís-Grajaú Basin. The morphological features observed in
the specimen here described are compatible with those related to titanosaurs. Thus, if this
interpretation is correct, UFMA 1.10.1958 is not only the oldest dinosaur osteoderm
recorded in Brazil, but one of the oldest ever recorded in the world.
1
Centro de Pesquisa de Historia Natural e Arqueologia do Maranhão, Rua do Giz, 59 - Praia Grande - 65010-
680, Centro Histórico de São Luís, São Luís, MA, Brasil.
2
Departamento Nacional de Produção Mineral (DNPM/DF), Quadra 1, 70041-903, Brasília, DF, Brasil.
3
Bolsista FAPEMA.
4 0
Universidade Federal do Maranhão (UFMA), Avenida dos Portugueses, s/n , Campus Universitário do Bacanga,
65085-580, São Luis, MA, Brasil.
E-mail: alf@ufma.br
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