''Rimasuchus'' is an
extinct genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
crocodile from the
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
of
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medit ...
and possibly
Libya
Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to the east, Suda ...
. Only one species - ''Rimasuchus lloydi'' - is currently known. It was previously thought to be a species of ''
Crocodylus'', but is now thought to be more closely related to the modern African dwarf crocodiles (''
Osteolaemus
''Osteolaemus'' is a genus of crocodiles. They are small, secretive crocodiles that occur in wetlands of West and Middle Africa. They are commonly known as the African dwarf crocodiles. Unlike other crocodiles, ''Osteolaemus'' are strictly noct ...
'').
History and naming
The first fossil of ''Rimasuchus'' an incomplete skull with associated mandible, was collected by lieutenant colonel Arthur H. Lloyd in the early 20th century in
Wadi Moghara,
Egypt
Egypt ( ar, مصر , ), officially the Arab Republic of Egypt, is a transcontinental country spanning the northeast corner of Africa and southwest corner of Asia via a land bridge formed by the Sinai Peninsula. It is bordered by the Medit ...
. The
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...
specimen, CGM 15597, was given to the
Egyptian Geological Museum
The Egyptian Geological Museum is a museum in Cairo, Egypt. The museum was established in 1901 as part of the Egyptian Geological Survey, which had been started in 1896 under the direction of the Khedive Ismail. The museum was the first of its ki ...
and described by Fourtau in 1920 under the name ''Crocodylus lloydi''. Other material includes an uncatalogued skull housed at the
Natural History Museum, London
The Natural History Museum in London is a museum that exhibits a vast range of specimens from various segments of natural history. It is one of three major museums on Exhibition Road in South Kensington, the others being the Science Museum an ...
(likewise from Wadi Moghara) and fossils found at
Gebel Zelten in
Libya
Libya (; ar, ليبيا, Lībiyā), officially the State of Libya ( ar, دولة ليبيا, Dawlat Lībiyā), is a country in the Maghreb region in North Africa. It is bordered by the Mediterranean Sea to the north, Egypt to the east, Suda ...
.
Eventually other skulls further south in Africa ended up being assigned to ''"Crocodylus" lloydi'' , with the oldest and southern-most material stemming from
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
and the youngest fossils from
Tanzania
Tanzania (; ), officially the United Republic of Tanzania ( sw, Jamhuri ya Muungano wa Tanzania), is a country in East Africa within the African Great Lakes region. It borders Uganda to the north; Kenya to the northeast; Comoro Islands ...
and
Kenya
)
, national_anthem = " Ee Mungu Nguvu Yetu"()
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...
in
East Africa.
This would have given the taxon a massive range both geographically and stratigraphically, spanning large parts of the continent from the Miocene up to the Pleistocene. However revisions of these fossils soon reduced the range of ''"Crocodylus" lloydi'' back to its original state. In 2003 the Namibian material was named ''Crocodylus gariepensis'' by Martin Pickford, who suggested that it was the true ancestor of the Nile crocodile.[ Pickford found his argument strengthened when shortly prior to the release of the publication ''"C." lloydi'' was found to be a distinct genus, named ''Rimasuchus''.][ In 2010 Christopher Brochu and colleagues named '' Crocodylus anthropophagus'' based on remains from Tanzania] and two years later ''Crocodylus thorbjarnarsoni
''Crocodylus thorbjarnarsoni'' is an extinct species of crocodile from the Pliocene and Pleistocene of the Turkana Basin in Kenya. It is closely related to the species ''Crocodylus anthropophagus'', which lived during the same time in Tanzania. ' ...
'' was named from Kenya
)
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, image_map =
, map_caption =
, image_map2 =
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...
. With the Kenyan specimens assigned to their own species, previous size estimates indicating that ''Rimasuchus'' grew to massive sizes and even preyed on humans were rendered out of date. Furthermore, with their description ''Rimasuchus'' was effectively removed from the fossil record of East Africa and the Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...
.
The generic name "''Rimasuchus''" comes from the Latin
Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
words ''rima'', meaning "crack", which is referencing the East African rift valley
The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of a ...
.[Leakey, M. G. and Harris, J. M. (2003). Lothagam: the Dawn of Humanity in Eastern Africa. Columbia University Press, New York. p. 144] However the fact that later studies have shown the absence of ''Rimasuchus'' in the region renders the name somewhat ironic. The species name honors Arthur H. Lloyd, who initially discovered the fossils in Egypt.
Phylogeny
Early studies on ''Rimasuchus'' generally thought it to be a member of the genus ''Crocodylus'' within the Crocodylinae. Given its age it was believed for some time to have been the direct ancestor to the modern 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 throughout sub-Saharan Africa, occurring mostly in the central, eastern, ...
.[ However most later studies came to agree that it was much more closely related to the Osteolaeminae, which includes both species of extant dwarf crocodiles. Given this placement, which was later supported by the animal being considered a distinct genus, the hypothesis that it was ancestral to Nile crocodiles has generally fallen out of favour. Pickford came to consider '']"Crocodylus" gariepensis
''"Crocodylus" gariepensis'' is an extinct species of crocodile that lived in southern Africa during the Early Miocene about 17.5 million years ago (Ma). Fossils have been found along a bank of the Orange River in Namibia, near its border with ...
'' the true ancestor of Nile crocodiles in 2003, however much like Rimasuchus it too was later recovered to likely fall within Osteolaeminae.
A 2018 tip dating Tip dating is a technique used in molecular dating that allows the inference of time-calibrated phylogenetic trees. Its defining feature is that it uses the ages of the samples to provide time information for the analysis, in contrast with traditio ...
study by Lee & Yates simultaneously using morphological, molecular ( DNA sequencing), and stratigraphic
Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks.
Stratigraphy has three related subfields: lithostra ...
(fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
age) data established the inter-relationships within Crocodylidae and in 2021, Hekkala ''et al.'' were able to use paleogenomics Paleogenomics is a field of science based on the reconstruction and analysis of genomic information in extinct species. Improved methods for the extraction of ancient DNA (aDNA) from museum artifacts, ice cores, archeological or paleontological site ...
, extracting DNA from the extinct ''Voay
''Voay'' is an extinct genus of crocodile from Madagascar that lived during the Late Pleistocene to Holocene, containing only one species, ''V. robustus''. Numerous subfossils have been found, including complete skulls, noted for their distinctiv ...
'', to better establish the relationships within Crocodylidae, including the subfamilies Crocodylinae and Osteolaeminae. Their results confirmed ''Rimasuchus status as an osteolaemine. In their phylogenetic tree ''Rimasuchus'' was recovered as the closest relative to the two modern dwarf crocodile species and more derived than '' Brochuchus''.
Restricting the analysis to work based on morphological data alone also finds it to be an osteolaemine, although the internal relationships of the clade differ slightly. Here, it takes a more basal position, neither especially close to the extant forms nor to the long-snouted ''Euthecodon''.
References
External links
Rimasuchus at Paleobiology Database
{{Taxonbar, from=Q3661453
Crocodylidae
Miocene crocodylomorphs
Prehistoric pseudosuchian genera