New fossils of the giant African crocodyliform Sarcosuchus imperator clarify its skeletal anatomy, growth patterns, size, longevity, and phylogenetic position. The skull has an expansive narial bulla and elongate jaws studded with stout, smooth crowns that do not interlock. The jaw form suggests a generalized diet of large vertebrates, including fish and dinosaurs. S. imperator is estimated to have grown to a maximum body length of at least 11 to 12 meters and body weight of about 8 metric tons over a life-span of 50 to 60 years. Unlike its closest relatives, which lived as specialized piscivores in marginal marine habitats, S. imperator thrived in fluvial environments.

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Sarcosuchus imperator, revised diagnosis (conditions unknown in S. hartti): crocodyliform with premaxillary narial bulla, maxillae that expand about 25% in width anteriorly, anterior maxillary teeth reduced in size. Sarcosuchus, revised diagnosis (S. imperator, S. hartti): crocodyliforms with dentary teeth 3 and 4 enlarged (28); diastema between dentary tooth 4 and 5; dentaries with fan-shaped distal expansion (28) reaching a width 50% greater than the narrowest portion of the rami; dentary symphysis extending posteriorly to about dentary tooth 20.
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The holotypic skull of S. imperator in the collections of the Musée National du Niger (MNN) has a length of 160 cm (2) and is the largest verified skull length on record (the same reference reported a 170-cm skull, but there are no figures of this specimen).
Regressions of body length (y) against head length (x) for G. gangeticus (y = −69.369 + 7.4x, r2 = 0.972) and C. porosus (y = −20.224 + 7.717x, r2 = 0.98) yield total body length estimates of 11.15 m and 12.15 m, respectively, for a skull length of 160 cm. Mean total body length equals 11.65 m (38 feet, 3 inches) (Fig. 4B). Data for G. gangeticus (n = 17) include measurements taken by P. Sereno from captive bred gharials in the Kukrail Picnic Center and Katerniaghat National Reserve in northern India and available measurements for individuals greater than 1.5 m long (11). Data for C. porosus (n = 28) come from wild individuals in northern Australia (A. Britton) and from available measurements for individuals greater than 1.5 m long (11) (excluding one suspicious record with body length of 4.91 m) (for measurement data, see supplementary material) (29).
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Using linear equations for C. porosus (13), we estimated snout-vent length in S. imperator from skull length (160 cm, yielding 572 cm) and from total body length (11.65 m, yielding 570 cm). We used mean snout-vent length (571 cm), in turn, to estimate a body weight (bw) of 7.96 metric tons [log bw= −2.0894 + 3.2613 (log 571 cm)].
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Phylogenetic definitions are provided below for key higher level taxa for stability of taxonomic content (30): Crocodyliformes, Protosuchus richardsoni, Crocodylus niloticus, and all descendants of their common ancestor; Protosuchia, all crocodyliforms more closely related to Protosuchus richardsoni than to Crocodylus niloticus; Mesoeucrocodylia, all crocodyliforms more closely related to Crocodylus niloticus than to Protosuchus richardsoni; Metasuchia, Notosuchus terrestris, Crocodylus niloticus, and all descendants of their common ancestor; Notosuchia, all crocodyliforms more closely related to Notosuchus terrestris than to Crocodylus niloticus; Neosuchia, all crocodyliforms more closely related to Crocodylus niloticus than to Notosuchus terrestris. Crocodylia is defined as Gavialis gangeticus, Crocodylus niloticus, and all descendants of their common ancestor [modified from (31)].
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Supported by the David and Lucile Packard Foundation, the National Geographic Society, and the Pritzker Foundation. We thank C. Abraczinskas for the finished illustrations; A. Beck, A. Britton, C. Brochu, J. Conrad, J. Head, W. Langston Jr., and J. Wilson for comments on the manuscript; B. Barr, B. C. Choudhury, and G. Martin for help in measuring G. gangeticus; A. Britton for measurements of C. porosus; E. Dong, A. Gray, L. Mahler, T. Keillor, R. Masek, and C. Noto for fossil preparation; A. Beck, D. Blackburn, J. Bradshaw, J.-P. Cavigelli, J. Conrad, E. Duneman, D. Dutheil, M. Hettwer, G. Lyon, T. Lyman, J. Marcot, R. Sadleir, G. Wilson, J. Wilson, and D. Varricchio for their contributions during expeditions in 1997 and 2000; and I. Kouada and the government of the Niger Republic for their support of this research.

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Volume 294 | Issue 5546
16 November 2001

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Received: 24 September 2001
Accepted: 16 October 2001
Published in print: 16 November 2001


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Paul C. Sereno*
Department of Organismal Biology and Anatomy, University of Chicago, Chicago, IL 60637, USA.
Hans C. E. Larsson
Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06511, USA.
Christian A. Sidor
Department of Anatomy, New York College of Osteopathic Medicine, Old Westbury, NY 11568, USA.
Boubé Gado
Institut de Recherches en Sciences Humaines, Niamey, Niger Republic.


To whom correspondence should be addressed. E-mail: [email protected]

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