An old Egyptian skull reveals a lost crocodilian branch

The limestone formation from which the Great Sphinx was carved also preserves evidence of an Egypt where fish-eating crocodilians hunted coastal waters. One skull from that limestone has now acquired a new identity: researchers say an animal described almost a century ago belongs to a previously unrecognized genus. Looking inside the skull helped them see past its familiar outline. Science News reports the reclassification.

The animal lived roughly 45 million years ago. German researchers described its skull in 1927, after it had been collected from hills near Cairo. The October 7 analysis in Royal Society Open Science revisits that old fossil, whose snout is missing its tip.

Its original identification placed it in Tomistoma, a genus represented today by a single species in Southeast Asia. A genus groups species judged to be closely related. The researchers now place the Egyptian animal in a genus of its own, Herugavialis, giving it the name Herugavialis cairensis. This is a new classification for an already described animal.

That change affects the history the fossil tells. Keeping it within Tomistoma would connect it to one particular group of crocodilians. Recognizing a separate genus adds another branch to the picture of ancient diversity. The name refers to Heru, or Horus, the Egyptian god associated with the Sphinx.

Living gavials, the crocodilian group to which this fossil belongs, have long, slender snouts lined with fine teeth. That provides a recognizable outline, but classification asks a more specific question: which relatives does the Egyptian fossil most closely resemble across its anatomy? The answer requires comparisons beyond a silhouette.

More recent evolutionary studies had already suggested that the Egyptian skull’s old classification was a poor fit. In 2023, paleontologist Paul Burke, then working on a doctorate at University College London, travelled to Germany to examine it in detail.

Burke and his colleagues measured the skull and used three-dimensional X-ray methods to investigate its brain and nasal cavities. Those measurements added internal anatomy to the external features available for comparison. A brain cavity is a space enclosed by the skull: measuring it describes internal architecture, rather than preserved brain tissue.

The team compared these measurements with those from living and fossil gavials. That made the hidden anatomy useful for classification: it could be assessed alongside the corresponding structures in other animals. The comparisons supported separating the Egyptian fossil into its own genus, according to Science News’s account.

The museum’s accompanying illustration offers a useful way to separate those kinds of evidence. It shows a reconstruction of the animal beside a skull, with the Sphinx and pyramids behind them. The long, tooth-lined snout is immediately visible. The internal spaces measured with X-rays cannot be judged from that profile. The image is an illustration, not a specimen photograph.

Khalafallah Salih, a paleontologist at Al Neelain University in Sudan, told Science News that the finding supports a more complex history for African gavials and their relatives. He said Herugavialis appears to have branched off early and does not seem closely related to other known gavial-type crocodilians from Africa or the Mediterranean.

Its surroundings were different, too. Today’s two surviving gavial species inhabit freshwater in tropical Asia. Herugavialis appears to have been a coastal predator when the Tethys Ocean covered northern Egypt—a saltwater setting preserved in the limestone that would eventually become the Sphinx.