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| Life reconstruction of Herugavialis cairensis depicted with The Great Sphinx and pyramids of Giza in the background. Herugavialis gen. nov. Herugavialis cairensis n. comb. (Müller, 1927) in Burke, Spiekman, Salem, Saber, Sallam et Mannion, 2026. Artwork by Karim Zanaty. |
Abstract
Gavialoidea is presently composed of only two extant crocodylian species, the Indian gharial Gavialis gangeticus, and the false gharial Tomistoma schlegelii, both from southeast Asia. However, Gavialoidea displays a rich and near-cosmopolitan diversity in the fossil record, with over 40 species currently recognized. Several of these gavialoids are recovered from Cenozoic deposits in the Mediterranean region, with many assigned historically to the genus Tomistoma. However, recent phylogenetic analyses do not typically recover these species as closely related to the false gharial, with several fossil species in need of taxonomic revision. Here, we present a detailed re-evaluation of one of these species, Tomistoma cairense from the Middle Eocene Mokattam Formation of Egypt, based on the holotype skull and several referred specimens. Supplemented by endocranial anatomy revealed via computed tomography (CT), we identify numerous anatomical differences with T. schlegelii and other gavialoids, including the approximately contemporaneous Egyptian species, Eogavialis africanum and Paratomistoma courti. These differences are reinforced through phylogenetic analysis under maximum parsimony, in which T. cairense is recovered as a gavialoid that does not cluster with T. schlegelii or Mediterranean taxa. We erect a new genus name for T. cairense, with the resultant new combination of Herugavialis cairensis diagnosed by several characteristics, including telescoped orbits. An apparent decline in Mediterranean gavialoid diversity during the Late Eocene–Oligocene is potentially driven by a reduction in habitat, as a result of global cooling and declining eustatic sea level. Warming in the Miocene might have facilitated a subsequent rebound in gavialoid diversity, prior to the extirpation of crocodylians in the Mediterranean region in the Late Miocene, which might have been caused by the Messinian Salinity Crisis. The taxonomic revision of additional Mediterranean gavialoid species should facilitate greater insight into their evolutionary history and demise.
Keywords: Gavialoidea, Mediterranean, Crocodylia, Tomistoma, neuroanatomy, phylogeny
Eusuchia Huxley, 1875
Crocodylia Gmelin, 1788
Gavialoidea Hay, 1930
Herugavialis gen. nov.,
Herugavialis cairensis n. comb. Müller, 1927
Tomistoma cairense (Müller, 1927).
Etymology: Heru, after the Egyptian god (also known as Horus), is often associated with, and possibly the inspiration for, the Great Sphinx of Giza. The latter was sculpted from the Mokattam Formation, from which the type specimen of H. cairensis was recovered, with both sharing the absence of the anterior tip of their nose/snout. The genus suffix, -gavialis, reflects the relationship of H. cairensis to Gavialis gangeticus within Gavialoidea. Accordingly, the original species epithet, cairense, is modified to cairensis to agree with the masculine gender of Herugavialis.
Locality and horizon: The holotype and referred specimens were collected from Gebel Mokattam, east of Cairo, in northeastern Egypt. They were recovered from the Mokattam Formation, which is a nummulitic marine limestone dated to the Lutetian, Middle Eocene.
Diagnosis: Within Gavialoidea, H. cairensis is characterized by a unique combination of characters: (i) lacrimal with an anteroposterior length more than twice that of the prefrontal; (ii) telescoped orbit formed by raised margins of the lacrimal, prefrontal and frontal; (iii) a squamosal wherein the dorsal and ventral margins do not diverge anteriorly; (iv) the distance between the distal tip of the paraoccipital process and the distal end of the quadrate condyle is greater than the maximum mediolateral width of the latter; and (v) a blunt dural peak on the encephalic endocast.
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| Life reconstruction of Herugavialis cairensis in left lateral view. Herugavialis is depicted with The Great Sphinx and pyramids of Giza in the background. Artwork by Karim Zanaty. |
Conclusions:
The redescription of the holotype and referred specimens of the Middle Eocene crocodylian species ‘Tomistoma’ cairense demonstrates numerous morphological differences from extant T. schlegelii. Coupled with the recognition of several autapomorphies, as well as its phylogenetic separation from T. schlegelii, we erect the new genus, Herugavialis cairensis. Herugavialis can be differentiated from approximately contemporaneous Egyptian gavialoids by numerous anatomical features, exemplifying the diversity of gavialoids in the Mediterranean region during this period. Global cooling and a drop in eustatic sea level during the Late Eocene–Oligocene potentially limited suitable habitat for gavialoids in the Mediterranean region, with subsequent increases in eustatic sea level and temperature potentially facilitating the return to high gavialoid diversity observed in the Miocene. The taxonomic classification of some of these European species awaits re-evaluation, which will facilitate greater insight into the evolutionary history of the Mediterranean gavialoids.
Paul M. J. Burke; Stephan N. F. Spiekman; Belal S. Salem; Sara Saber; Hesham M. Sallam and Philip D. Mannion. 2026. Cranial Anatomy of the Middle Eocene Egyptian crocodylian Herugavialis cairensis provides Nnew Insights into gavialoid diversity in the Mediterranean Region. R. Soc. Open Sci 13 (10): 261173. DOI: doi.org/10.1098/rsos.261173 [07 Oct 2026]
