A fossil crocodile skull missing its snout just like the Great Sphinx finally got its own name after a century

A crocodile skull from the rock of the Great Sphinx was misnamed for a century. CT scans show where Herugavialis fits among the gavials.

The Great Sphinx is famous for its missing nose. Dug from the same Egyptian limestone, a fossil crocodile skull is missing the tip of its snout too. For almost a century, it also carried the wrong name.

The skull was long filed as a relative of the false gharial, a narrow-snouted crocodile that lives in Southeast Asia today. A fresh look inside it shows that it belongs somewhere else on the family tree. It now has a name of its own: Herugavialis cairensis.

Nothing new came out of the ground for this study. The team reexamined bones collected near Cairo about 100 years ago. The species is still known from one fairly complete skull and a few partial jaws and snouts. Those pieces may all come from a single animal.

Paul Burke of the Swedish Museum of Natural History led the work with Philip Mannion of University College London. Researchers in Germany and Egypt, including a team from Mansoura University, joined them.

A name borrowed from the Great Sphinx

The skull came from the Mokattam Formation, a limestone laid down in the sea about 45 million years ago. The Great Sphinx was carved from the same rock.

The shared rock and the shared missing nose tip gave the crocodile its name. Heru is the Egyptian god, also known as Horus, that is often linked to the Sphinx. The second half of the genus name points to the Indian gharial, Gavialis gangeticus.

"Given this coincidence with the famously missing nose of the Great Sphinx, we decided to name the new crocodile after the Egyptian god Heru, who was possibly the inspiration for this iconic monument," said Mannion.

An old name stopped fitting

Only two members of this narrow-snouted crocodile group, the gavials, are alive today: the Indian gharial and the false gharial. Both live in fresh water in southern Asia, and the false gharial is listed as endangered.

More than 40 extinct species are known, and many of them lived along coasts and in shallow seas.

When the Egyptian fossils were first described in 1927, the skull looked enough like a false gharial to be placed in the same genus, Tomistoma.

In recent years, though, studies comparing many crocodiles kept finding that the Egyptian species wasn't a close relative of the living one. Three other fossil species that were once filed under Tomistoma have already been moved to new genera.

The bones are kept at the State Museum of Natural History Stuttgart in Germany. Nobody had described their anatomy in detail since that first account.

Scans showed a different animal

The team used CT scans, stacks of X-ray images that can be assembled into a 3D model, to look inside the skull. That let them map the space that the brain once filled.

The cast of that space had a blunt bump on top that no other member of the group shows. The bony rims around the eye sockets were raised well above the rest of the skull. The snout made up about 64 percent of the skull's length.

Next, the researchers placed the animal on a family tree of 152 crocodile species and their relatives, compared across 331 anatomical features.

The Egyptian crocodile didn't group with the other African or Mediterranean species. It landed closer to the Indian gharial than to the false gharial.

Herugavialis also differed in many ways from two other species in the group known from fossils in Egypt, both from somewhat younger rocks.

Crocodiles came and went

Herugavialis had company. The region that's now the Mediterranean held at least six gavial species in the era that produced Herugavialis, and at least six more much later.

"Throughout much of the last 50 million years, the Mediterranean region hosted a high diversity of crocodiles, including gavials," said Burke.

"However, this diversity fluctuated over time, seemingly corresponding to changes in global temperature and sea level, before the loss of all crocodiles in this region as a result of the drying of the Mediterranean approximately 6 million years ago."

Between those two groups, there's a long stretch with no known species of this kind in the region. The authors suggest that global cooling lowered sea temperatures and sea levels, thus shrinking the coastal waters that these crocodiles needed. Warmer seas later may have let them return.

The family tree backs that idea. If the later species had descended from the earlier local ones, they should cluster together on the tree, and they don't.

Many questions remain

The authors say the empty stretch could partly reflect fossils that haven't been found yet. More bones from that time would settle whether the crocodiles truly left.

Several other extinct Mediterranean species still carry the old Tomistoma label, including one from Portugal.

Burke is reexamining that species and another from Austria, work the authors say should clarify how the region's crocodiles were related and why they disappeared.

The full study was published in the journal Royal Society Open Science.

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