Phylogenetic Relationships and Divergence Timing of Crocodylus Based on Morphology and the Fossil Record
Maximum parsimony analysis of 164 morphological characters supports the monophyly of crown-genus Crocodylus relative to other extant lineages. Crocodylus cataphractus is the basalmost living species, and monophyletic New World and Indopacific assemblages are supported. The Indian Mugger (Crocodylus palustris) is closely related to the Indopacific assemblage. Most fossils assigned to Crocodylus do not belong to the crown genus. Only one extinct fossil included in the analysis, Crocodylus palaeindicus (= C. sivalensis), falls within the crown-group Crocodylus and is of uncertain affinities within the group; Adams consensus trees draw C. palaeindicus toward the root of non–cataphractus Crocodylus, and the Nile crocodile (C. niloticus) is the sister taxon to the New World assemblage. The oldest fossil diagnostically belonging to the clade is from the Late Miocene, which is congruent with previous protein distance estimates of a Late Tertiary divergence among living species. Fossils and molecules never actually clashed regarding divergence timing, because very different meanings were applied to the name Crocodylus by paleontologists and neontologists.Abstract
Previous hypotheses of relationships within Crocodylus. (A) Albumin antigenic distance, Densmore, 1983; (B) Nei's D, serum proteins, Densmore, 1983; (C) allozyme phenotypes, Densmore and Owen, 1989; (D) nuclear and mitochondrial restriction site fragment comparison, Densmore and White, 1991; (E) combined molecular and morphological data, Poe, 1996; (F) ND6, tRNAglu, cyt b sequence data, White and Densmore, in press; (G) morphology, Brochu, 1997a
Strict consensus of 4311 equally optimal trees [length = 472, CI (excluding autapomorphies) = 0.430]. Numbers at nodes are bootstrap replicate percentages. Crown-group Crocodylus is indicated with heavy lines; groups outside Crocodyloidea are collapsed and indicated in gray. Large dots indicate node-based group names; names along lines denote stem-based groups. Extinct taxa indicated with †
Characters diagnostic of Crocodylus. (A) The right ilium of Alligator mississippiensis (UF 128131) bears a modestly notched posterior blade, whereas the right ilium (B) of Crocodylus acutus (USNM 211278) is wasp-waisted. (C) The right maxilla (medial view) of A. mississippiensis (TNHC m-7363) is smooth, but that of (D) C. acutus (UCMP 140795) bears numerous caviconchal recesses. (E) The anterior process of the right ectopterygoid in A. mississippiensis (TNHC m-67) is not as deeply notched as that of (F) Crocodylus niloticus (TNHC m-1786). For E and F, arrow indicates anterior tip. (G) Posterior end of right jaw, lateral view, of Gavialis gangeticus (TNHC m-5485), with little lateral exposure of the articular; (H) posterior end of right jaw, lateral view, of Crocodylus intermedius (FMNH 75659), with extensive articular exposure laterally. Abbreviations: an = angular, ar = articular, ect = ectopterygoid, mx = maxilla, sa = surangular. Scale = 1 cm
Basicranium in right ventrolateral view in (A) Crocodylus moreletii (TNHC m-4980) and (B) Crocodylus cataphractus (TNHC m-3529). Abbreviations: leu = lateral eustachian opening; meu = median eustachian opening
Crocodylus skulls in dorsal view, illustrating variation in cranial ornamentation. (A) Crocodylus niloticus (TNHC m-1786) has a broad, unornamented rostrum. (B) Crocodylus moreletii (TNHC m-4980) bears the midline boss characteristic of New World Crocodylus. (C) Crocodylus novaeguineae (FMNH 14043) has slender preorbital ridges. Mature C. johnstoni (AMNH 86540, D) lack these, but they are present in immature specimens (TNHC m-6807, E). Scale = 1 cm
Stratigraphic distribution of ingroup taxa within Crocodyloidea. Taxa in gray were not considered in the parsimony analysis. Thick solid lines indicate lineages included in this analysis; thin solid lines indicate taxon range extensions by published fossils not specifically scored. See Brochu (1997a) for taxon calibrations