Livro de Resumos - Dinossauros do Maranhão

Paleontologia 193
On a spinosaurid manus (Dinosauria, Theropoda) from the Romualdo
Formation (Santana Group), Araripe Basin, Brazil
1 Setor de Paleovertebrados, Departamento de Geologia e Paleontologia, Museu Nacional (MN/UFRJ),
Quinta da Boa Vista, s/n 0 - São Cristóvão - 20940-040, Rio de Janeiro, RJ, Brasil.
2 Bolsista de Mestrado CNPq.
3 Membro Academia Brasileira de Ciências.
4 Bolsista de Produtividade em Pesquisa do CNPq.
5 Bolsista Cientista do Nosso Estado FAPERJ.
Elaine B. Machado 1,2 & Alexander W. A. Kellner 1,3,4,5
The most complete Brazilian material attributed to the Spinosauridae (a basal clade of
tetanurans) is a partial skeleton from the Albian Romualdo Formation (Santana Group).
The specimen (MN 4819-V) is composed of a pelvis, dorsal, sacral and caudal vertebrae,
some hindlimb elements, a possible fragment of the ulna and an almost complete manus.
The latter is the best spinosaurid hand known to date and consists of the distal carpal I,
metacarpals I, II and III, phalanx 1 of digit I, phalanx 1 of digit II and the ungual of digit
I. Metacarpal I is short and has a rectangular shape in dorsal view. Metacarpal II is
incomplete, lacking the distal portion. This bone has a wide proximal articulation and a
comparatively slender shaft. Metacarpal III is well preserved and shows a triangular
proximal articular surface. Digit I is formed by an elongate phalanx with a triangular crosssection
and its corresponding ungual, both found in articulation. The ungual is
comparatively small (shorter than its corresponding pre-ungual phalanx), slightly curved,
and oval in cross-section. Phalanx 1 of digit II lacks the distal portion and has a strong
triangular-shaped proximal articulation. The manus of MN 4819-V differs in several
respects with other theropods, including the basal tetanurans Allosaurus and Megaraptor,
the latter recently regarded as a potential spinosaurid. Metacarpal I of MN 4819-V is
similar to that of Allosaurus, but differs from the more elongated one of Megaraptor.
Metacarpal III is comparable to Megaraptor (albeit being proportionally longer), both
differing from the one of Allosaurus by having a distinctive shape of the proximal
articulation. Regarding digit I, the ungual of the Brazilian specimen is half the size of
Megaraptor, despite both have a similarly elongated phalanx 1. The phalanx 1 of digit II is
sharply triangular in proximal aspect, differing from the mediolaterally compressed
condition found in Megaraptor. Comparisons among the manus of MN 4819-V and other
spinosaurids is limited to one element of Suchomimus. The manus of MN 4819-V helps to
understand better the anatomy of those peculiar theropods. In this regard, the only
metacarpal found in the African taxon Suchomimus, originally thought as a metacarpal III,
is now interpreted as the metacarpal II.
E-mails: machado.eb@gmail.com, kellner@mn.ufrj.br
Paleovertebrados