''Crocodylus thorbjarnarsoni'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

crocodile Crocodiles (family (biology), family Crocodylidae) or true crocodiles are large, semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term "crocodile" is sometimes used more loosely to include ...

from the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Pleistocene The Pleistocene ( ; referred to colloquially as the ''ice age, Ice Age'') is the geological epoch (geology), epoch that lasted from to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fin ...

of the Turkana Basin in

Kenya Kenya, officially the Republic of Kenya, is a country located in East Africa. With an estimated population of more than 52.4 million as of mid-2024, Kenya is the 27th-most-populous country in the world and the 7th most populous in Africa. ...

. It is closely related to the species '' Crocodylus anthropophagus'', which lived during the same time in

Tanzania Tanzania, officially the United Republic of Tanzania, is a country in East Africa within the African Great Lakes region. It is bordered by Uganda to the northwest; Kenya to the northeast; the Indian Ocean to the east; Mozambique and Malawi to t ...

. ''C. thorbjarnarsoni'' could be the largest known true crocodile, with the largest skull found indicating a possible total length up to . It may have been a predator of early

hominin The Hominini (hominins) form a taxonomic tribe of the subfamily Homininae (hominines). They comprise two extant genera: ''Homo'' (humans) and '' Pan'' (chimpanzees and bonobos), and in standard usage exclude the genus '' Gorilla'' ( gorillas) ...

s. ''Crocodylus thorbjarnarsoni'' was named by Christopher Brochu and Glenn Storrs in 2012 in honor of John Thorbjarnarson, a conservationist who worked to protect endangered crocodilians.

Description

''Crocodylus thorbjarnarsoni'' is distinguished from other crocodiles by its broad snout. It has small raised rims on the prefrontal bones in front of the eyes, a feature also seen in some

Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and ce ...

individuals. The

squamosal bone The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral ...

s form raised rims along the sides of the skull table, similar to the crests in ''C. anthropophagus'' but much smaller. Also like ''C. anthropophagus'', it has nostrils that open slightly forward rather than directly upward. The largest ''C. thorbjarnarsoni'' skull found (KNM-ER 1682) measures from the tip of the snout to the back of the skull table, in comparison, the largest known extant '' Crocodylus'' skull is that of a saltwater crocodile, measuring . Based on regression analysis for ''Crocodylus'', this corresponds to a total length of but such analysis have been shown to underestimate the size of very large individuals by as much as 20%, which means it could have been as long as .

Paleoecology

''Crocodylus thorbjarnarsoni'' likely preyed on ''

hominids The Hominidae (), whose members are known as the great apes or hominids (), are a taxonomic family of primates that includes eight extant species in four genera: '' Pongo'' (the Bornean, Sumatran and Tapanuli orangutan); '' Gorilla'' (the ...

'' like ''

Paranthropus ''Paranthropus'' is a genus of extinct hominin which contains two widely accepted species: ''Paranthropus robustus, P. robustus'' and ''P. boisei''. However, the validity of ''Paranthropus'' is contested, and it is sometimes considered to be sy ...

'' and early members of the genus ''

Homo ''Homo'' () is a genus of great ape (family Hominidae) that emerged from the genus ''Australopithecus'' and encompasses only a single extant species, ''Homo sapiens'' (modern humans), along with a number of extinct species (collectively called ...

'', both of which are known from the Turkana Basin. Direct evidence of crocodilian predation is known from bite marks on hominin bones from the

Olduvai Gorge The Olduvai Gorge or Oldupai Gorge in Tanzania is one of the most important paleoanthropology, paleoanthropological localities in the world; the many sites exposed by the gorge have proven invaluable in furthering understanding of early human evo ...

, and these marks were likely made by the closely related crocodile ''C. anthropophagus'' (''anthropophagus'' means "human eater" in

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

). No hominin bones from the Turkana Basin bear crocodilian bite marks, so there is no direct evidence that ''C. thorbjarnarsoni'' preyed on hominins. However, modern Nile crocodiles are known to consume adult humans, and since ''C. thorbjarnarsoni'' was larger than any Nile crocodile, it easily could have eaten smaller-bodied human ancestors. Brochu and Storrs hypothesized that the lack of bite marks could have been due to hominin's awareness of crocodiles and ability to evade them, explaining that "this conflict—eat and drink, but maybe die—was presumably foremost amongst the concerns our predecessors felt when approaching ancient waterways inhabited by ''Crocodylus thorbjarnarsoni''." Another explanation was that ''C. thorbjarnarsoni'' may have eaten hominins whole with little need for biting, since it was much larger.

Specimens

''Crocodylus thorbjarnarsoni'' is known from nine skulls, all of which are housed in the National Museum of Kenya. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

is a nearly complete

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

and

lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

called KNM-ER 1683 and comes from the approximately 2-million-year-old Koobi Fora Formation on the eastern shore of

Lake Turkana Lake Turkana () is a saline lake in the Kenyan Rift Valley, in northern Kenya, with its far northern end crossing into Ethiopia. It is the world's largest permanent desert lake and the world's largest alkaline lake. By volume it is the world ...

. The skulls KNM-ER 1681 and KNM-ER 1682 have also been found from the formation. Three other skulls are known from the Nachukui Formation, west of the holotype's locality. KNM-WT 38977 is from the 2.5- to 3.4-million-year-old Lower Lomekwi Member, KNM-LT 26305 is from the 3.9-million-year-old Kaiyumung Member, and KNM-LT 421 is from the 4.2- to 5.0-million-year-old Apak Member. Three additional skulls called KNM-KP 18338, KNM-KP 30604, and KNM-KP 30619 are known from the southern Turkana Basin in the Kanapoi Formation, dating between 4.07 and 4.12 million years. KNM-ER 1682, KNM-LT 421, KNM-LT 26305, and KNM-KP 30619 were previously assigned to '' Rimasuchus lloydi'', and their reassignment to ''C. thorbjarnarsoni'' reduces the range of ''R. lloydi'' to Northern Africa.

Phylogeny

The

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below is from a 2021 study based on the finding of a new '' Crocodylus anthropophagus'' partial

cranium The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

in the

of northern

References

{{Taxonbar, from=Q1647824 Crocodylidae Fossil taxa described in 2012 Cenozoic reptiles of Africa Pliocene crocodylomorphs Pleistocene crocodylomorphs