Editorial Type:
Article Category: Research Article
 | 
Online Publication Date: 01 May 2006

A New Miniature Horned Crocodile from the Quaternary of Aldabra Atoll, Western Indian Ocean

Page Range: 149 – 158
DOI: 10.1643/0045-8511(2006)6[149:ANMHCF]2.0.CO;2
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Abstract

A new crocodylid is described on the basis of fragmentary, but diagnostic, material from the Quaternary of Aldabra Atoll. It differs from all other known crocodylians, living or extinct, in having a prominent semicircular crest, or “horn,” on the dorsolateral margin of the squamosal. Unlike the horns seen in some living Crocodylus, the apex of each horn was at its midpoint anterior to the external otic aperture and not near its posterior end. It also has a highly vaulted premaxillary palate and an anterodorsally-oriented external naris, and dorsal exposure of the supraoccipital on the skull table was extensive. Phylogenetic relationships of the new form are unclear, making its biogeographic origins difficult to trace, but it was very likely an immigrant from elsewhere and not endemic to Aldabra Atoll, as it occurs in deposits formed shortly after a period of submergence ended 120,000 years ago.

Copyright: The American Society of Ichthyologists and Herpetologists
Figure 1.
Figure 1.

Aldabrachampsus dilophus, new species. BNMH R8769, right premaxilla, (A) ventral, (B) dorsal, and (C) medial view. (D) Crocodylus niloticus (BMNH uncat.), right premaxilla, medial view. Scale  =  1 cm

Figure 4.
Figure 4.

BMNH R8795, Aldabrachampsus dilophus, new species, left squamosal in (A) posterior and (B) lateral view. For comparative purposes, squamosals are shown for (C) AMNH 29889, Osteolaemus osborni, (D) BMNH uncat., Crocodylus niloticus, (E) BMNH 2077, Crocodylus siamensis, and (F) AMNH 3101, “Crocodylus” ← robustus. E and F are inverted right squamosals and otic regions. (G) “Crocodylus” robustus (AMNH 3101), skull, lateral view, with box showing region of skull detailed in above images. Scale  =  1 cm

Figure 2.
Figure 2.

Aldabrachampsus dilophus, new species. (A) BMNH R8784, frontal, dorsal view; (B) BMNH R8786, right prefrontal, dorsal view; (C) BMNH R8795 (holotype), right exoccipital, posterior view; (D) BMNH R8789, right ectopterygoid, ventral view; BMNH R8795 (holotype), right dentary, anterior fragment, (E) dorsal, (F) lateral, and (G) medial view; BMNH R8796, fragment of dentary, (H) lateral and (I) dorsal view; (J) BMNH R8795 (holotype), right articular, medial view; (K) BMNH R8795 (holotype), left surangular, lateral view; BMNH R8790, left articular, (L) dorsal and (M) medial view; (N) BMNH R8795 (holotype), cervical centrum with portions of neural arch, left lateral view. Scale  =  1 cm

Figure 3.
Figure 3.

Skull tables in dorsal view of (A) BMNH R8795, holotype, Aldabrachampsus dilophus, new species; (B) AMNH 3101, “Crocodylus” robustus; (C) TNHC m-6040, Crocodylus acutus; (D) AMNH 10082, Osteolaemus osborni. Scale  =  1 cm

Figure 5.
Figure 5.

Strict consensus of 12,791 most parsimonious trees (length  =  398, CI without uninformative characters  =  0.439, RI  =  0.740). †  =  extinct species

Figure 6.
Figure 6.

Cladograms showing bimodal placement of Aldabrachampsus dilophus, new species, either as an (A) osteolaemine or (B) within Crocodylus. Black circle  =  root of Osteolaeminae; white circle  =  root of crown Crocodylus. Localities in parentheses for Tomistominae indicate clade range including extinct taxa. Geographic abbreviations: AF, Africa; ALD, Aldabra Atoll; AS, Asia (exclusive of India); AU, Australia/Oceania; EU, Europe; IN, Indonesia; ISC, Indian Subcontinent; MD, Madagascar; NG, New Guinea; PH, Philippines; WH, Western Hemisphere

Received: 28 Jan 2005
Accepted: 09 Feb 2006
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