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. 2025 Mar 17;15(1):9159.
doi: 10.1038/s41598-025-91167-w.

Evolutionary trend of the broad-snouted crocodile from the Eocene, Early Miocene and recent ones from Egypt

Affiliations

Evolutionary trend of the broad-snouted crocodile from the Eocene, Early Miocene and recent ones from Egypt

Eman S El-Degwi et al. Sci Rep. .

Abstract

Skulls are a critical part of the crocodile through which we can distinguish between the different genera and species. Most of the crocodiles which previously studied from the Eocene-Oligocene to the Miocene times in Egypt were concerned with the identification of the genus and sometimes on the species without a detailed focusing on the evolution, comparing between them and trying to determine the ancestor or the closest species of them to the living crocodile in Egypt. The only known living species of Crocodylus in Egypt is Crocodylus niloticus which inhabits Lake Nasser in Aswan, southern of Egypt. From the Cenozoic era, broad snouted crocodiles diversity had been reported in Egypt. About 35 million years ago, through the Eocene epoch, the crocodilian fossils from Fayum provided evidence of the diversity of crocodile species including Crocodylus articeps and Crocodylus megarhinus. In addition to that, throughout the Early Miocene epoch, from about 18 million years ago, in Wadi Moghra Egypt crocodilian fossils demonstrate another diversity, extended to the first appearance of Rimasuchus lloydi which placed inside the Osteolaeminae later. By various measurements and carefully morphological examination of the different species recorded from Egypt, it was found that there are high levels of variation in morphology of the skulls including their dimensions, and the sutures shapes especially between premaxilla and maxilla ventrally and also between maxilla and palatine, as well as the extension of the maxillary ramus of the ectopterygoid. Using cluster analysis, it is proven that Eocene Crocodylus is the ancestor to all known broad snouted species recorded from Egypt since the Eocene time. The closest species to the Eocene specimen is the living Crocodylus niloticus. That in fact make that most of the broad snouted crocodiles in Egypt are endemic.

Keywords: Crocodylus niloticus; Rimasuchus lloydi; Ancestor; Broad snouted crocodiles; Egypt; Evolutionary trend.

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Conflict of interest statement

Declarations. Competing interests: The authors declare no competing interests. Statements: The present specimen of Crocodylus niloticus was collected near Lake Nasser under an ethical reference with approval number CU I F C 38 23 issued by Cairo University’s Institutional Animal Care & Use Committee CU-LACUC. This specimen is a mature female of a total length of 218 cm. The skull is complete with a length measuring 34 cm. CUVP001 is referred to the upper and lower jaw of C. niloticus which is preserved in CUVP.

Figures

Fig. 1
Fig. 1
(A–D) CUVP001, Crocodylus niloticus, skull with a line drawing, (A,B) dorsal, (C,D) ventral. Scale bar equals 5 cm.
Fig. 2
Fig. 2
(A–D) CUVP001, Crocodylus niloticus, lower jaw with a line drawing, (A,B) labial, (C,D) lingual. Scale bar equals 5 cm.
Fig. 3
Fig. 3
(A,B) is lateral view of CUVP001 Crocodylus niloticus, A, referred specimen; B, line drawing. Scale bar equals 5 cm.
Fig. 4
Fig. 4
(A,B) is occipital view of CUVP001 Crocodylus niloticus, A referred specimen; B line drawing. Scale bar equals 5 cm.
Fig. 5
Fig. 5
Dorsal crocodylian skulls exhibit differences in premaxilla shape, notch, external naris and the incisive foramen. (a) NHMUK R 3322, cast of Crocodylus articeps; (b) CUVP001, Crocodylus niloticus; (c) YPM VP-058532, Crocodylus megarhinus; (d) CGM84425, Crocodylus sp.; (e) CGM67110, Rimasuchus lloydi; (f) CUWM90, Crocodylus sp.; (g) NHMUK PVR14154, Rimasuchus lloydi; (h) DPC6610, Rimasuchus lloydi; (i) CGM73664, Rimasuchus lloydi; (j) CGM67155, Rimasuchus lloydi. Scale bar equals 5 cm.
Fig. 6
Fig. 6
Differences in premaxilla-maxilla suture ventrally, notch between premaxilla and maxilla of Crocodylian skulls. (a) CUVP001, Crocodylus niloticus; (b) NHMUKR 3322, cast of Crocodylus articeps; (c) YPM VP-058532, Crocodylus megarhinus; (d) CGM 84425, Crocodylus sp.; (e) CUWM90, Crocodylus sp.; (f) NHMUKR. 3327, Crocodylus megarhinus; (g) NHMUK PVR14154, Rimasuchus lloydi; (h) DPC12548, Crocodylus sp.; (i) DPC6610, Rimasuchus lloydi; (j), CGM73664, Rimasuchus lloydi. (no: refers to the notch). Scale bar equals 5 cm.
Fig. 7
Fig. 7
(a,b) Graphs shows the relationship between width and length of premaxilla and snout.
Fig. 8
Fig. 8
Differences between palatine, maxilla suture, maxillary teeth number, ramus of ectopterygoid and maxilla margins. (a) CUVP001, Crocodylus niloticus; (b) NHMUKR 3322, cast of Crocodylus articeps; (c) YPMVP-058532, Crocodylus megarhinus; (d) CGM 84425, Crocodylus sp.; (e) NHMUKPVR14154, Rimasuchus lloydi. (ma. refers to maxillary alveolus). Scale bar equals 5 cm.
Fig. 9
Fig. 9
Differences in orbit, frontal shape, space between supratemporal fenestrae and quadratojugal spine of Crocodylian skulls. (a) CGM73664, Rimasuchus lloydi; (b) CUVP001, Crocodylus niloticus; (c) YPM VP-058532, Crocodylus megarhinus; (d) NHMUK PVR14154, Rimasuchus lloydi; (e) CGM 84425, Crocodylus sp.; (f) NHMUK R 3322, cast of Crocodylus articeps; (g) DPC6646, Rimasuchus lloydi; (h) CGM67156, Rimasuchus lloydi. (qjs, quadratojugal spine; pe. refers to the pointed end and re. refers to rounded end). Scale bar equals 5 cm.
Fig. 10
Fig. 10
(a) Graph shows the relationship between the width and length of the external naris. (b) Graph shows differences in the breadth of the space between the 2 fenestrae.
Fig. 11
Fig. 11
Cranial measurements of Crocodylus niloticus skull from dorsal view, each letter illustrated in (Table 1). Scale bar equals 5 cm.
Fig. 12
Fig. 12
Cluster analysis of the morphometric measurements of different specimens. CUWM90, Crocodylus sp.; YPM VP-058532, Crocodylus megarhinus; CGM84425, Crocodylus sp.; CUVP001, Crocodylus niloticus; NHMUK PVR14154, Rimasuchus lloydi; NHMUK R. 3322, cast of Crocodylus articeps.

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