Rimasuchus
Encyclopedia
Rimasuchus is an extinct genus
of crocodile
from the Neogene period of Africa
and the Middle East
. Its name comes from the Latin words rima, meaning "crack" (referencing the East African rift valley
where it was discovered) and suchus, which means "crocodile". Rimasuchus is a member of the subfamily Crocodylinae, which includes over 20 species, eight of which are extinct. The type
and only species
, Rimasuchus lloydi, lived alongside other crocodiles such as the Nile crocodile
. It preyed on large mammals, including early humans.
e, as well as a deep mandibular
symphysis connecting the two sides of the upper jaw. The premaxillae do not project as far back on the upper surface of the skull as those of other crocodiles and are noticeably wider than they are long on the palate (unlike those of Crocodylus niloticus and Crocodylus cataphractus). The external nares
are positioned close to the tip of the snout. Like other crocodiles, Rimasuchus has an occlusal groove, or notch, between the premaxilla and maxilla
that receives the fourth mandibular tooth. However, in Rimasuchus the groove is noticeably shorter anteroposteriorly than that of C. niloticus. The preorbital region is flat and there is no nasal promontorium, or raised nasal region, as in C. niloticus.
The teeth of Rimasuchus are robust and blunt, unlike those of other crocodiles. They become more bulbous toward the rear of the jaws. The crowns of the teeth are rarely sharp, although crown sharpness tends to lessen with size in crocodylians. The teeth are uniquely bicarinate, meaning that there are ridges on the front and back.
Remains of Rimasuchus show variations in size and proportions, and it is likely that they represent different ontogenic (growth) stages. There has been very little study so far on ontogenic variation in Rimasuchus and living crocodiles. There are many similarities between specimens of R. lloydi and C. niloticus, and it is likely that some specimens of Rimasuchus actually represent particularly large examples of C. niloticus.
under the name C. lloydi. After cladistic
analysis suggested that it did not belong in Crocodylus, however, the new genus was erected in 2003. Among crocodylines, Rimasuchus is most closely related to the living dwarf crocodile Osteolaemus and is placed within the group Osteolaeminae.
after Brochu C. A., Njau J., Blumenschine R. J., Densmore L. D. (2010).
Common over much of East Africa, Rimasuchus fossils have been found in close association with fossils of Nile crocodile
s. Their fossils have been found in Kenya, Egypt
(including the Sinai), Libya
, Chad
, Ethiopia
, Uganda
, Sudan
, Tanzania
and Tunisia
. From Africa their range stretched east into Saudi Arabia
. While earlier specimens have been recovered from north Africa, how the species evolved and spread is still uncertain.
As large, semiterrestrial predators, Rimasuchus probably competed directly with Nile crocodiles, eventually being out-competed by them as their shared habitat became more arid.
Rimasuchus fossil
s, along with those of Euthecodon brumpti
, are the most common crocodile fossils in the Lake Turkana
basin and Koobi fora
ridge in northeast Kenya, where the two crocodiles likely lived in the lake and surrounding rivers. Their bones have been found in situ
with other vertebrates including several species of fish and birds, mammals such as pigs, elephants, giraffes, cows, rhinoceri, primates, even hominids such as Australopithecus afarensis
. Aside from Euthecodon, other predators included the Slender snouted
and Nile crocodiles, the extinct gavialoid Eogavialis andrewsi
, Dinofelis aronoki and Metailurus
(sabre-toothed cats), Bear dog
s, hyenas, and early members of the genus Canis
.
Rocks from Turkana containing Rimasuchus fossils are usually poorly lithified fluvial or lacustrine sandstone
s or mudstone
s that were deposited in lakes and rivers. These deposits come from the Nawata Formation and the Nachukui Formation of the Tortonian age and Pliocene epoch, respectively. Fossils from these rocks usually dates from 1.88 ± 0.02 to 7.44 ± 0.05 million years old.
have been recovered from sites in association with early human bones. In the Olduvai Gorge
of Tanzania
, predation has been documented in the form of crocodile tooth marks on the bones of several hominid specimens, namely OH 7
, OH 8 and OH 35, all of which belong to Homo habilis
. Bone damage in some H. habilis remains include bisected tooth pits and punctures, which are diagnostic of crocodilian predation. The damaged hominin bones have been found at what were considered hominin "living sites" that also included stone artifacts and butchered bones. In addition, the bone accumulations at Beds I and II of the gorge have been specifically attributed to Rimasuchus. A trench containing bones of early bovines, horses, OH 7, and several stone tools has also yielded Rimasuchus teeth.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of crocodile
Crocodile
A crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
from the Neogene period of Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
and the Middle East
Middle East
The Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
. Its name comes from the Latin words rima, meaning "crack" (referencing the East African rift valley
East African Rift
The East African Rift is an active continental rift zone in eastern Africa that appears to be a developing divergent tectonic plate boundary. It is part of the larger Great Rift Valley. The rift is a narrow zone in which the African Plate is in the process of splitting into two new tectonic plates...
where it was discovered) and suchus, which means "crocodile". Rimasuchus is a member of the subfamily Crocodylinae, which includes over 20 species, eight of which are extinct. The type
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
and only species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, Rimasuchus lloydi, lived alongside other crocodiles such as the Nile crocodile
Nile crocodile
The Nile crocodile or Common crocodile is an African crocodile which is common in Somalia, Ethiopia, Uganda, Kenya, Egypt, Tanzania, Zambia, Zimbabwe, Gabon, South Africa, Malawi, Sudan, Botswana, and Cameroon...
. It preyed on large mammals, including early humans.
Description
Rimasuchus grew to 7 meters or more in length. Unlike most living crocodiles, it is brevirostrine, or broad-snouted. Rimasuchus has characteristically short and broad premaxillaPremaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
e, as well as a deep mandibular
Mandibular
Mandibular may refer to:* Mandible, the lower jaw bone* Mandibular canal* Mandibular nerve...
symphysis connecting the two sides of the upper jaw. The premaxillae do not project as far back on the upper surface of the skull as those of other crocodiles and are noticeably wider than they are long on the palate (unlike those of Crocodylus niloticus and Crocodylus cataphractus). The external nares
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
are positioned close to the tip of the snout. Like other crocodiles, Rimasuchus has an occlusal groove, or notch, between the premaxilla and maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
that receives the fourth mandibular tooth. However, in Rimasuchus the groove is noticeably shorter anteroposteriorly than that of C. niloticus. The preorbital region is flat and there is no nasal promontorium, or raised nasal region, as in C. niloticus.
The teeth of Rimasuchus are robust and blunt, unlike those of other crocodiles. They become more bulbous toward the rear of the jaws. The crowns of the teeth are rarely sharp, although crown sharpness tends to lessen with size in crocodylians. The teeth are uniquely bicarinate, meaning that there are ridges on the front and back.
Remains of Rimasuchus show variations in size and proportions, and it is likely that they represent different ontogenic (growth) stages. There has been very little study so far on ontogenic variation in Rimasuchus and living crocodiles. There are many similarities between specimens of R. lloydi and C. niloticus, and it is likely that some specimens of Rimasuchus actually represent particularly large examples of C. niloticus.
Taxonomy
Rimasuchus lloydi was first described in 1918 and originally placed in the genus CrocodylusCrocodylus
Crocodylus is one of three genera from the Crocodylinae subfamily extending from the Crocodylidae family.Established species include three extinct species:* † Crocodylus acer - probably represents a distinct genus....
under the name C. lloydi. After cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analysis suggested that it did not belong in Crocodylus, however, the new genus was erected in 2003. Among crocodylines, Rimasuchus is most closely related to the living dwarf crocodile Osteolaemus and is placed within the group Osteolaeminae.
Phylogeny
CladogramCladogram
A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...
after Brochu C. A., Njau J., Blumenschine R. J., Densmore L. D. (2010).
Distribution and habitat
Nile crocodile
The Nile crocodile or Common crocodile is an African crocodile which is common in Somalia, Ethiopia, Uganda, Kenya, Egypt, Tanzania, Zambia, Zimbabwe, Gabon, South Africa, Malawi, Sudan, Botswana, and Cameroon...
s. Their fossils have been found in Kenya, Egypt
Egypt
Egypt , officially the Arab Republic of Egypt, Arabic: , is a country mainly in North Africa, with the Sinai Peninsula forming a land bridge in Southwest Asia. Egypt is thus a transcontinental country, and a major power in Africa, the Mediterranean Basin, the Middle East and the Muslim world...
(including the Sinai), Libya
Libya
Libya is an African country in the Maghreb region of North Africa bordered by the Mediterranean Sea to the north, Egypt to the east, Sudan to the southeast, Chad and Niger to the south, and Algeria and Tunisia to the west....
, Chad
Chad
Chad , officially known as the Republic of Chad, is a landlocked country in Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west...
, Ethiopia
Ethiopia
Ethiopia , officially known as the Federal Democratic Republic of Ethiopia, is a country located in the Horn of Africa. It is the second-most populous nation in Africa, with over 82 million inhabitants, and the tenth-largest by area, occupying 1,100,000 km2...
, Uganda
Uganda
Uganda , officially the Republic of Uganda, is a landlocked country in East Africa. Uganda is also known as the "Pearl of Africa". It is bordered on the east by Kenya, on the north by South Sudan, on the west by the Democratic Republic of the Congo, on the southwest by Rwanda, and on the south by...
, Sudan
Sudan
Sudan , officially the Republic of the Sudan , is a country in North Africa, sometimes considered part of the Middle East politically. It is bordered by Egypt to the north, the Red Sea to the northeast, Eritrea and Ethiopia to the east, South Sudan to the south, the Central African Republic to the...
, Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
and Tunisia
Tunisia
Tunisia , officially the Tunisian RepublicThe long name of Tunisia in other languages used in the country is: , is the northernmost country in Africa. It is a Maghreb country and is bordered by Algeria to the west, Libya to the southeast, and the Mediterranean Sea to the north and east. Its area...
. From Africa their range stretched east into Saudi Arabia
Saudi Arabia
The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World...
. While earlier specimens have been recovered from north Africa, how the species evolved and spread is still uncertain.
As large, semiterrestrial predators, Rimasuchus probably competed directly with Nile crocodiles, eventually being out-competed by them as their shared habitat became more arid.
Rimasuchus fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s, along with those of Euthecodon brumpti
Euthecodon
Euthecodon is an extinct genus of longirostrine crocodyline crocodilian. It was common throughout much of Africa during the Neogene, with fossils being especially common in Kenya. It existed from the Early Miocene to the Early Pleistocene.-Description:...
, are the most common crocodile fossils in the Lake Turkana
Lake Turkana
Lake Turkana , formerly known as Lake Rudolf, is a lake in the Great Rift Valley in 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...
basin and Koobi fora
Koobi Fora
Koobi Fora refers primarily to a region around Koobi Fora Ridge, located on the eastern shore of Lake Turkana in the territory of the nomadic Gabbra people. According to the National Museums of Kenya, the name comes from the Gabbra language:...
ridge in northeast Kenya, where the two crocodiles likely lived in the lake and surrounding rivers. Their bones have been found in situ
In situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...
with other vertebrates including several species of fish and birds, mammals such as pigs, elephants, giraffes, cows, rhinoceri, primates, even hominids such as Australopithecus afarensis
Australopithecus afarensis
Australopithecus afarensis is an extinct hominid that lived between 3.9 and 2.9 million years ago. A. afarensis was slenderly built, like the younger Australopithecus africanus. It is thought that A...
. Aside from Euthecodon, other predators included the Slender snouted
Slender-snouted Crocodile
The African Slender-snouted Crocodile is a species of crocodile. Recent studies in DNA and morphology suggest that it may belong in its own genus, Mecistops, but at present most continue to use Crocodylus for this species.African Slender-snouted Crocodile are native to freshwater habitats in...
and Nile crocodiles, the extinct gavialoid Eogavialis andrewsi
Eogavialis
Eogavialis is an extinct gavialoid. It superficially resembles Tomistoma schlegelii, the extant false gharial, and consequently material from the genus was originally referred to Tomistoma...
, Dinofelis aronoki and Metailurus
Metailurus
Metailurus is a genus of false saber-toothed cat of the family Felidae, belonging to the tribe Metailurini endemic to North America, Africa, Europe, and Asia during the Miocene to Pleistocene, living from 9 Ma—11,000 years ago and existed for approximately .Metailurus was named by Zdansky...
(sabre-toothed cats), Bear dog
Bear dog
Amphicyonidae is an extinct family of large terrestrial carnivores belonging to the suborder Caniformia and which inhabited North America, Europe, Asia, and Africa from the Middle Eocene subepoch to the Pleistocene epoch 46.2—1.8 Mya, existing for approximately .-Taxonomy:Amphicyonidae was named...
s, hyenas, and early members of the genus Canis
Canis
Canis is a genus containing 7 to 10 extant species, including dogs, wolves, coyotes, and jackals, and many extinct species.-Wolves, dogs and dingos:Wolves, dogs and dingos are subspecies of Canis lupus...
.
Rocks from Turkana containing Rimasuchus fossils are usually poorly lithified fluvial or lacustrine sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s or mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
s that were deposited in lakes and rivers. These deposits come from the Nawata Formation and the Nachukui Formation of the Tortonian age and Pliocene epoch, respectively. Fossils from these rocks usually dates from 1.88 ± 0.02 to 7.44 ± 0.05 million years old.
Predation on early humans
Crocodiles were known predators of early humans. Remains of Rimasuchus, Nile crocodiles, and the extinct Crocodylus anthropophagusCrocodylus anthropophagus
Crocodylus anthropophagus is an extinct species of crocodile from Plio-Pleistocene from Tanzania. It lived 1.84 million years ago.- Etymology :...
have been recovered from sites in association with early human bones. In the Olduvai Gorge
Olduvai Gorge
The Olduvai Gorge is a steep-sided ravine in the Great Rift Valley that stretches through eastern Africa. It is in the eastern Serengeti Plains in northern Tanzania and is about long. It is located 45 km from the Laetoli archaeological site...
of Tanzania
Tanzania
The United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
, predation has been documented in the form of crocodile tooth marks on the bones of several hominid specimens, namely OH 7
OH 7
OH 7 , also nicknamed "Johnny's Child", is the type specimen of Homo habilis. The fossils were discovered on November 4, 1960 in Olduvai Gorge, Tanzania, by Jonathan and Mary Leakey...
, OH 8 and OH 35, all of which belong to Homo habilis
Homo habilis
Homo habilis is a species of the genus Homo, which lived from approximately at the beginning of the Pleistocene period. The discovery and description of this species is credited to both Mary and Louis Leakey, who found fossils in Tanzania, East Africa, between 1962 and 1964. Homo habilis Homo...
. Bone damage in some H. habilis remains include bisected tooth pits and punctures, which are diagnostic of crocodilian predation. The damaged hominin bones have been found at what were considered hominin "living sites" that also included stone artifacts and butchered bones. In addition, the bone accumulations at Beds I and II of the gorge have been specifically attributed to Rimasuchus. A trench containing bones of early bovines, horses, OH 7, and several stone tools has also yielded Rimasuchus teeth.