Figure 9. Squamosal horns of living and extinct crocodylines, left lateral view. A, AMNH 3101, Voay robustus (right lateral view, photo inverted). B, PNCZ unnumbered, Crocodylus rhombifer. C, NHM 94.6.5.53, C. niloticus. Scale = 5 cm. doi:10.1371/journal.pone.0009333.g009 can be readily distinguished from either living species; C. rhombifer, like other Neotropical species, has a prominent dorsal boss on the rostrum not present in C. anthropophagus, and C. anthropophagus lacks the prominent long preorbital crest found in most Indopacific species of Crocodylus (including C. siamensis) and the midline crest on the frontal diagnostic of C. siamensis [23,57,58]. Although not as prominent, dorsally expanded squamosals are sometimes found in very large specimens of most other living species of Crocodylus, including C. niloticus (Fig. 9C). The horns of C. anthropophagus are more prominent and have more acute dorsal tips than these structures, and in lateral view, there is an abrupt transition from the dorsal surface of the postorbital (which is parallel to the coronal plane) and the upturned squamosal horn. This is most apparent on the KNM FLKNI right squamosal (Fig. 4N), though this is case as well for the holotype (Fig. 1H). Although true for Voay (Fig. 9A) and large C. rhombifer (Fig. 9B) and C. siamensis, this is unlike the condition in other species of Crocodylus; when present, the dorsal expansion arises more gradually behind the postorbital bar (Fig. 9C). A few extinct crocodylians also bear squamosal horns similar to those of C. anthropophagus, including the osteolaemine Voay robustus Extinct Horned Crocodile from the Quaternary of Madagascar (Fig. 9A)[59,60,61]. Indeed, squamosal horns of V. robustus and C. anthropophagus are similar enough that isolated elements may not be assignable to either species. Skeletal morphology strongly supports a close relationship between Voay and Osteolaemus, and squamosal horns are best viewed as independently derived features in Voay and C. anthropophagus. Another crocodylid with squamosal horns is Aldabrachampsus dilophus from the Quaternary of Aldabra Atoll [14]. Aldabrachampsus is incompletely known and its phylogenetic relationships are unclear, but its horns differ from those of both Voay and C. anthropophagus; they are broad and oblique in lateral view, with an apex anterodorsal rather than dorsal to the otic aperture. Moreover, known material of Aldabrachampsus suggests a very small animal (,2m) at maturity, and the holotype of C. anthropophagus is from a substantially larger animal. One character might suggest monophyly of extant Crocodylus to the exclusion of C. anthropophagus – a cleft in the maxillary ramus of the ectopterygoid. Preserved ectopterygoids and maxillae of C. anthropophagus suggest an unforked maxillary ramus that tapers anteriorly (Fig. 10A,B), the condition found in all other crocodylians. Cleft maxillary rami (Fig. 10C) are only seen in Crocodylus, and it was coded as present in all species in previous analyses [23]. If these codings are applied to the present analysis, C. anthropophagus is unambiguously outside (albeit close to) crown Crocodylus. But further examination of Crocodylus skulls indicates variability in living species – the cleft is not apparent in some individuals (Fig. 10E), and it lies right on the margin of the suborbital fenestra in others, making the medial tine of the fork difficult to see in ventral view (Fig. 10D). This character (63) was thus recoded as polymorphic in all living species, causing alternative placements of C. anthropophagus to become no less parsimonious. Variability was not observed in C. palaeindicus, and it remains coded as monomorphic for this trait, but fewer specimens are available and a larger sample may eventually reveal polymorphism. Even fewer specimens of C. anthropophagus preserve the relevant parts of the skull, and our confidence that the species uniformly lacked the cleft is less than robust. Moreover, the partial right ectopterygoid of NHM R5893 (Fig. 10A) bears a slight concavity on its anterior tip. We have interpreted this structure as unforked, but one could argue for the forked condition. Recoding C. anthropophagus as polymorphic has no impact on the results of the parsimony analysis. Crocodylus anthropophagus and Crocodylus niloticus We have no complete skulls for C. anthropophagus and, thus, no solid grasp of the shape of the snout, but compared with C. niloticus, the premaxillae and maxillae indicate a comparatively deeper snout with a more highly vaulted palate; a relatively shorter prenarial rostrum (Fig. 1A,E); a naris with more anterior orientation; and more prominent crests along the margins of the orbit and skull table. Crocodylus niloticus lacks the prominent crest along the maxillonasal suture seen in C. anthropophagus. Although squamosal horns sometimes appear in C. niloticus, they are rarely (if ever) as clearly demarcated from the dorsal surface of the skull table as in C. anthropophagus, and they are neither as prominent nor as sharply angled dorsally (Fig. 9C). Moreover, they appear in all observed squamosals of C. anthropophagus, including some from animals probably between 2 and 3 m in length, which suggests regularity in expression absent from C. niloticus, in whom upturned squamosals are only found in some very large individuals (.3 m). Nevertheless, differentiation of isolated fragments of C. anthropophagus and C. niloticus may not always be possible, and this PLoS ONE | www.plosone.org 10 February 2010 | Volume 5 | Issue 2 | e9333