Published on November 1st, 2026 | by David Marshall
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Episode 178: Herugavialis
Gavialoids are a superfamily of crocodilians with distinctive elongated snouts specialised for the capture of fish. Today, the family is represented by just two species: the gharial, Gavialis gangeticus, and the false gharial, Tomistoma schlegelii. Despite their current low diversity and limited geographical range, the fossil record of gavialoids contains significantly more taxa with fossils discovered on nearly every continent.
In this episode, we speak to Dr Paul Burke, Swedish Museum of Natural History, who has been working on the placement of a particularly problematic species from the Eocene of Egypt within the gavialoid tree. ‘Tomistoma‘ cairense was originally described in 1927, so what could modern imaging techniques tell us about its anatomy almost a century on? We look at how redescription of such fossils can allow new family trees to be drawn and what we can learn about the evolution of gavialoids through time.
The gharial (Gavialis gangeticus) is a long-snouted crocodilian from northern India. It possesses a distinctive elongated rostrum (snout) with numerous interlocking teeth for capturing fish. Unfortunately, due to human activity, the species is currently listed as ‘critically endangered’ by the IUCN with their population dropping to fewer than 250 as recently as 2006.The false gharial (Tomistoma schlegelii) gets its common name because of an early belief that it was a crocodile with a superficial resemblance to the gharial. More modern molecular analyses show that the gharial and false gharial are both closely related and together they form the family Gavialidae. Tomistoma is known from Malaysia, Borneo and Sumatra and is listed as ‘threatened’ by the IUCN.A classic cladogram of the relationships within Crocodylia based on comparative anatomy. The alligators and caimans form the family Alligatoridae which, along with the crocodiles, constitute the Brevirostres (short-snouted crocodilians). The gavials (red) are the most distantly related to the rest of the crocodilians. From Rio and Mannion (2021).More modern cladograms can also integrate molecular data (comparing DNA) and produce a different result. Whilst Alligatoridae is still recovered, the crocodiles now group with the gavials (blue) to form the Longirostres (long-snouted crocodilians). Since DNA cannot be recovered from fossils, morphological comparisons will always be required when including extinct species in an analysis. From Rio and Mannion (2021).One problematic species to place within the crocodilian tree is ‘Tomistoma’ cairense. It was described in 1927 and, as the name suggests, was thought to be a false gharial (Tomistoma). It is from the Middle Eocene (Lutetian) Mokattam Formation of Egypt and, at around 45 million years old, represents the oldest known species in the genus. Unfortunately, numerous gavial fossils have been assigned to Tomistoma based on broad/superficial anatomical similarities and the genus had become somewhat of a taxonomic “wastepaper basket”.To address the issue of where in the tree ‘Tomistoma’ cairense fitted, Dr Burke undertook a full redescription of the fossil. The updated anatomical information he obtained would then be placed within a new phylogenetic analysis. Image: Holotype skull (SMNS 10575) in both dorsal (a) and ventral (c) aspects with their interpretive drawings (b and d, respectively). Abbreviations: f, frontal; ic, internal choana; j, jugal; m, maxilla; ma, maxillary alveoli; n, nasals; o, orbit; p, parietal; pa, palatines; pf, prefrontal; po, postorbital; pt, pterygoid; q, quadrate; so, supraoccipital; sof, suborbital fenestra; sq, squamosal; sqp, squamosal prong; stf, supratemporal fenestra. Scale bar, 100 mm.This skull is slightly crushed but is otherwise well preserved with only the tip of the snout missing. Several other fossil specimens were collected from the same area and were included in the original description. These are either skulls or skull fragments and so it’s not entirely certain how many individual animals might have been collected. Image: Left and right sides of holotype skull (SMNS 10575). Abbreviations and scale as above.Using modern techniques such as CT scanning, a lot more information about the morphology of these fossils could be obtained. In this example, details of the frontal bone (red) can be compared between ‘Tomistoma’ cairense (a, e), Tomistoma (b, f) and Gavialis (c, g). In ‘Tomistoma’ cairense, the frontal bone extends a lot further towards the snout than either of the modern examples but does so below the nasal bones (clearest in e). This detail cannot be seen on the surface of the fossil and shows the value of using such imaging techniques.Additionally, CT scanning was able to reveal the shape of the endocast of the skull as well as details about the paratympanic sinus system and the nasal cavity. These interior details of the skull are all incredibly significant and would have been impossible to study otherwise without breaking the skull. Abbreviations: cer, cerebrum; ob, olfactory bulb; ot, olfactory tract. Scale bar, 10 mm.All this new morphological information was coded into a matrix of binary characters (basically an anatomical comparison chart recording the presence and absence of characteristics for each species) and run through phylogenetic software (TNT) to produce a new cladogram showing the most mathematically probable relationships within Gavialoidea. When this cladogram is plotted against time, it becomes a phylogenetic tree and these can be incredible useful for tracing the evolution of groups, traits and a whole range of other attributes through time. This tree shows which continent each species is from and when. Notably, ‘Tomistoma’ cairense didn’t group with the modern false gharial, Tomistoma schlegelii meaning that it can’t be the same genus.The taxon was renamed Herugavialis cairensis in honour of the Egyptian god Heru (Horus). This name was chosen because the fossils were found within the Mokattam Formation, the same rock that was used to create the Great Sphinx of Giza, which is often associated, and possibly inspired by, Heru. Like the Sphinx, Herugavialis is also missing the tip of its nose. Image: Karim Zenaty.Reconstruction of Herugavialis cairensis and its palaeoenvironment during the Eocene. Image: Saioa Gómez.Dr Paul Burke, Swedish Museum of Natural History.
Cover image: Reconstruction of Herugavialis cairensis by Adel Lee.
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