Thorbjarnarson's crocodile

## Crocodylus thorbjarnarsoni

Credit: Smokeybjb on the Wikimedia Commons (rotated).

Thorbjarnarson's crocodile (*Crocodylus thorbjarnarsoni*) is an extinct species of crocodile that lived in Kenya from the Pliocene to the Pleistocene.

## Description

Thorbjarnarson's crocodile was perhaps the largest crocodile, possibly reaching up to 7.6 meters (25 feet), and was named from John Thorbjarnarson, who works to conserve crocodilians. This animal is differentiated due to a broad skull, with raised ridges at the prefrontal bones, which is shared with some Nile crocodiles. Along the skull table, the squamosals form rims, which is also seen in *C. anthropophagus*. Also like the latter, Thorbjarnarson's crocodile has nostrils that open almost forward rather than upward.

The largest Thorbjarnarson's crocodile skull is KNM-ER 1682, which measures 85 centimeters (33 inches) from tip-to-tip, and is larger than the largest modern crocodile skulls. Based on regression studies on *Crocodylus*, estimates place the total length at 6.2-6.5 meters (20-21 feet). However, these seem to miss the largest individuals by up to 20%, which places the new estimate at 7.6 meters (25 feet).

## Paleoecology

Thorbjarnarson's crocodile is a likely predator to early hominins, including *Paranthropus* and early *Homo*, both inhabiting the Turkana Basin, where Thorbjarnarson's crocodile hunted. From the Olduvai Gorge, direct predation is preserved in fossil pathologies such as bite marks, which fit the teeth of *C. anthropophagus* (also the namesake of the species, meaning "human eater"). Though there is no direct evidence, Nile crocodiles often prey on adult humans, and since early hominins dwarfed it, Thorbjarnarson's crocodile could have easily consumed them. Brochu and Storrs hypothesize the lack of fossil predation evidence could have been due to the hominins awareness of the predator, and could have evaded attacks. They explain:

—Brochu and Storrs, 2012
Other hypotheses include the ability for the animal to swallow the smaller hominins whole, rather than biting like it would larger prey. It was also suggested that they evaded crocodilians or that no bones showing bite marks have yet been discovered or identified.

## Notable Specimens

* KNM-ER 1683: A nearly-complete skull and mandible from the 2-million-year-old Koobi Fora Formation.
* KNM-ER 1681 and KNM-ER 1682: Two skulls, also from the Koobi Fora on the eastern shore of Lake Turkana.
* KNM-WT 38977: A skull from the 2.5-3.4 million year Lower Lomekwi Member, Nachukui Formation.
* KNM-LT 26305: A skull from the 3.9 million year Kaiyumung Member, Nachukai Formation.
* KNM-LT 421: A skull from the 4.2-5 million year Apak Member of the Nachukai Formation.
* KNM-KP 18338, KNM-KP 30604 and KNM-KP 30619: Skulls from the southern Turkana Basin of the Kanapoi Formation. From 4.07-4.12 million years years old.
* KNM-ER 1682, KNM-LT 421, KNM-LT 26305 and KNM-KP 30619: All assigned *Rimasuchus lloydi*, restricting the crocodilians range to North America once reassigned to Throbjarnarson's crocodile. KNM-ER 1682 is the largest of all described skulls, reaching 85 centimeters long[*citation needed*].

## References

* https://en.wikipedia.org/wiki/Crocodylus\_thorbjarnarsoni
* https://www.tandfonline.com/doi/abs/10.1080/02724634.2012.652324