A DYROSAURID CROCODYLIFORM BRAINCASE FROM MALI

A well-preserved crocodyliform specimen from the Maastrichtian or Paleocene of Mali preserves the braincase and posterior dermatocranium. It is referred to Dyrosauridae on the basis of several derived features (a prominent anterior process of the postorbital, discrete occipital processes on the exoc...

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Bibliographic Details
Published in:Journal of paleontology 2002-11, Vol.76 (6), p.1060-1071
Main Authors: BROCHU, CHRISTOPHER A, BOUARÉ, MAMADOU L, SISSOKO, FAMORY, ROBERTS, ERIC M, O'LEARY, MAUREEN A
Format: Article
Language:English
Subjects:
affinities
Africa
Archosauria
biologic evolution
Bones
Canals
Cenozoic
Chordata
cladistics
Classification
Cretaceous
Crocodilia
Diapsida
Dyrosauridae
Fossils
Geology
Maestrichtian
Mali
Mesozoic
morphology
Nasopharynx
Orbital bone
Palate
Paleocene
Paleogene
Paleontology
Phylogenetics
Phylogeny
Reptilia
Senonian
Skull
Taxa
taxonomy
Tertiary
Tetrapoda
Upper Cretaceous
Vertebrata
vertebrate
West Africa
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Description
Summary:A well-preserved crocodyliform specimen from the Maastrichtian or Paleocene of Mali preserves the braincase and posterior dermatocranium. It is referred to Dyrosauridae on the basis of several derived features (a prominent anterior process of the postorbital, discrete occipital processes on the exoccipitals, significant quadratojugal contribution to jaw joint) and tentatively referred to Rhabdognathus on the basis of supratemporal fenestra shape. The lacrymal and prefrontal are relatively short compared with those published for other dyrosaurids. The palatines border the internal choanae anteriorly, and the choanae are divided by a midline septum derived from the pterygoids. The prefrontal pillars are mediolaterally broad and contact the palate ventrally. One stapes is preserved in place. The basicranial pneumatic system is very unusual, in that the anterior and posterior branches of the median eustachian canal are both separate at the palatal surface, and the pterygoids form part of the border for the anterior branch. The lateral eustachian openings lie within fossae on the lateral surface of the braincase and face laterally, with a descending process of the exoccipital nearly intersecting the opening. The braincase and surrounding dermal bones are elongate anteroposteriorly, and the postorbital's posterior ramus extends along the posterodorsal margin of the infratemporal fenestra. The quadrate ramus projects ventrally. These observations clarify character optimizations in previous phylogenetic analyses of Crocodyliformes.
ISSN:0022-3360
1937-2337
DOI:10.1666/0022-3360(2002)076<1060:ADCBFM>2.0.CO;2