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''Acherontisuchus'' 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 ...
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
dyrosaurid Dyrosauridae is a family (biology), family of extinct neosuchian crocodyliforms that lived from the Campanian to the Eocene. Dyrosaurid fossils are globally distributed, having been found in Africa, Asia, Europe, North America and South America. ...
neosuchia Neosuchia is a clade within Mesoeucrocodylia that includes all modern extant crocodilians and their closest fossil relatives. It is defined as the most inclusive clade containing all Crocodylomorpha, crocodylomorphs more closely related to ''Croc ...
n from
Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...
to
Late Paleocene The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...
deposits of
Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...
.''Acherontisuchus guajiraensis''
at
Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...
.org
The only known species is ''A. guajiraensis'', whose name means "
Acheron The Acheron ( or ; ''Acheron'' or Ἀχερούσιος ''Acherousios''; ''Acherontas'') is a river in the Epirus (region), Epirus region of northwest Greece. It is long, and has a drainage area of . The river's source is located near the vil ...
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 ...
of the
Guajira Peninsula The Guajira Peninsula (, also spelled ''Goajira'', mainly in colonial period texts, ) is a peninsula in northern Colombia and northwestern Venezuela in the Caribbean. It is the northernmost peninsula in South America and has an area of exte ...
".


Description

''Acherontisuchus'' is known from six specimens UF/
IGM Immunoglobulin M (IgM) is the largest of several isotypes of antibodies (also known as immunoglobulin) that are produced by vertebrates. IgM is the first antibody to appear in the response to initial exposure to an antigen; causing it to also ...
34 through 39 (Hastings et al. 2011 noted these six specimens may represent only a single animal), including three partial lower jawbones, four fragments of the
upper jaw In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxillar ...
, fragments of 21 teeth, two
rib In vertebrate anatomy, ribs () are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the ...
s, one upper backbone segment, one
sacral vertebra The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
(a bone that connects the hips to the rest of the spine), ribs that attach to the sacral vertebrae, a partial
hip In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint on t ...
including the ilium and
ischium The ischium (; : is ...
bones, an upper leg bone, and one
metatarsal The metatarsal bones or metatarsus (: metatarsi) are a group of five long bones in the midfoot, located between the tarsal bones (which form the heel and the ankle) and the phalanges ( toes). Lacking individual names, the metatarsal bones are ...
foot bone. All ''Acherontisuchus'' specimens were collected from the
Cerrejón Formation The Cerrejón Formation is a geologic formation in Colombia dating back to the Middle-Late Paleocene. It is found in the El Cerrejón sub-basin of the Cesar-Ranchería Basin of La Guajira Department, La Guajira and Cesar Department, Cesar. The fo ...
within the
Cerrejón Cerrejón is a large Coal mining, open-pit coal mine in Northern Colombia owned by Glencore. At Cerrejón, low-ash, low-sulphur bituminous coal from the Cerrejón Formation is excavated. At over the mine is one of the largest of its type, the la ...
coal mine Coal mining is the process of resource extraction, extracting coal from the ground or from a mine. Coal is valued for its Energy value of coal, energy content and since the 1880s has been widely used to Electricity generation, generate electr ...
of northeastern
Colombia Colombia, officially the Republic of Colombia, is a country primarily located in South America with Insular region of Colombia, insular regions in North America. The Colombian mainland is bordered by the Caribbean Sea to the north, Venezuel ...
and described in
2011 The year marked the start of a Arab Spring, series of protests and revolutions throughout the Arab world advocating for democracy, reform, and economic recovery, later leading to the depositions of world leaders in Tunisia, Egypt, and Yemen ...
in ''
Palaeontology Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geo ...
'' journal by Alexander K. Hastings, Jonathan Bloch and Carlos A. Jaramillo. It is named after the river Acheron, which in
Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...
was a branch of the river
Styx In Greek mythology, Styx (; ; lit. "Shuddering"), also called the River Styx, is a goddess and one of the rivers of the Greek Underworld. Her parents were the Titans Oceanus and Tethys, and she was the wife of the Titan Pallas and the moth ...
meaning "river of woe" (''Acherontisuchus'' is thought to have lived in a large river that emptied out into the
Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...
during the Paleocene). The
type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''A. guajiraensis'' is named after
Guajira Peninsula The Guajira Peninsula (, also spelled ''Goajira'', mainly in colonial period texts, ) is a peninsula in northern Colombia and northwestern Venezuela in the Caribbean. It is the northernmost peninsula in South America and has an area of exte ...
where Cerrejón is located. ''Acherontisuchus'' is found in multiple layers between coal seams, giving it a wide time distribution throughout the formation. Another dyrosaurid called ''
Cerrejonisuchus ''Cerrejonisuchus'' is an extinct genus of Dyrosauridae, dyrosaurid crocodylomorph. It is known from a complete skull and mandible from the Cerrejón Formation in northeastern Colombia, which is Paleocene in age. Specimens belonging to ''Cerrejo ...
'' was named from Cerrejón in 2010, but is only found in one layer of the formation. Aside from the consistently fractured fossils, no evidence exists of an altered fossil size. ''Acherontisuchus'' is considered a long-snouted, or longirostrine, dyrosaurid. Its snout is shorter than those of ''
Dyrosaurus ''Dyrosaurus'' is a genus of extinct crocodylomorph that lived during the early Eocene. The name ''Dyrosaurus'' comes from () the Greek for lizard or reptile, and Dyr for Djebel Dyr (mountain) close to where the type species was discovered. It ...
'', '' Atlantosuchus'', ''
Rhabdognathus ''Rhabdognathus'' is an extinct genus of dyrosaurid crocodylomorph. It is known from rocks dating to the Paleocene epoch from western Africa, and specimens dating back to the Maastrichtian era were identified in 2008. It was named by Swinton in 1 ...
'', and ''
Congosaurus ''Congosaurus'' is an extinct genus of dyrosaurid mesoeucrocodylian. Fossils have been found from Lândana, in Angola and date back to the Paleocene epoch. In 1952 and 1964 ''Congosaurus'' was proposed to be synonymous with '' Dyrosaurus''. The g ...
''. Some of its teeth have pronounced grooves on both sides. The upper jaw is wide rather than high. Its head is estimated to have been long, about midsize for a dyrosaurid. It grew to a relatively large size compared to most dyrosaurids, between .


Life history

''Acherontisuchus'' lived in a calm, shallow, inland
freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...
habitat in the
tropical rainforest Tropical rainforests are dense and warm rainforests with high rainfall typically found between 10° north and south of the Equator. They are a subset of the tropical forest biome that occurs roughly within the 28° latitudes (in the torrid zo ...
s of northeastern Colombia, where its distant cousin ''
Cerrejonisuchus ''Cerrejonisuchus'' is an extinct genus of Dyrosauridae, dyrosaurid crocodylomorph. It is known from a complete skull and mandible from the Cerrejón Formation in northeastern Colombia, which is Paleocene in age. Specimens belonging to ''Cerrejo ...
'' lived as well. Most dyrosaurids, including the ancestors of ''Acherontisuchus'', were well adapted to a coastal marine lifestyle. Like living crocodilians, these dyrosaurids were able to control their pitch and
buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...
in the water by contracting muscles that run between the abdomen and the hip. A projection of bone in the back of the hip called the ischial shaft serves as an anchor for the muscles that control pitch. ''Acherontisuchus'' has a slender ischial shaft, suggesting that the muscles that controlled its position in water were less developed. Oceanic dyrosaurids evolved an advanced system of pitch correction as an adaptation to rough
ocean current An ocean current is a continuous, directed movement of seawater generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours, sh ...
s. Since ''Acherontisuchus'' lived in a shallow freshwater environment, it had less need to control its position. Based on the shape of its ribs and limb bones, ''Acherontisuchus'' probably had strong muscles along its back and in its legs that enabled movement on land. It probably lived in rivers that were present far from the ocean. In these inland rivers, ''Acherontisuchus'' most likely fed on
lungfish Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, inc ...
es and
eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 20 families, 164 genera, and about 1000 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
s.


Systematics

''Acherontisuchus'' is closely related dyrosaurids from both Africa and the Americas. The phylogenetic analysis conducted with its first description placed ''Acherontisuchus'' in a derived
clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...
of dyrosaurids that included ''
Hyposaurus ''Hyposaurus'' is a genus of extinct marine Dyrosauridae, dyrosaurid crocodyliform. Fossils have been found in Paleocene aged rocks of the Iullemmeden Basin in West Africa, Campanian–Maastrichtian (Late Cretaceous, Late Cretaceous) Shendi Forma ...
'' of North America, ''
Congosaurus ''Congosaurus'' is an extinct genus of dyrosaurid mesoeucrocodylian. Fossils have been found from Lândana, in Angola and date back to the Paleocene epoch. In 1952 and 1964 ''Congosaurus'' was proposed to be synonymous with '' Dyrosaurus''. The g ...
'', '' Atlantosuchus'', and ''
Rhabdognathus ''Rhabdognathus'' is an extinct genus of dyrosaurid crocodylomorph. It is known from rocks dating to the Paleocene epoch from western Africa, and specimens dating back to the Maastrichtian era were identified in 2008. It was named by Swinton in 1 ...
'' of Africa, and '' Guarinisuchus'' of South America. The relationships between these dyrosaurids were not resolved, as ''Acherontisuchus'' was placed in a
polytomy An internal node of a phylogenetic tree is described as a polytomy or multifurcation if (i) it is in a rooted tree and is linked to three or more child subtrees or (ii) it is in an unrooted tree and is attached to four or more branches. A tree ...
with ''Hyposaurus'', ''Congosaurus'', and a group containing the other close relatives. ''Acherontisuchus'' has several primitive features that distance it from other members of the derived dyrosaurid clade, including uniformly-spaced teeth and a wide connection between the two halves of the lower jaw. Below is a
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 ...
showing the phylogenetic relationships of ''Acherontisuchus'' and the distributions of dyrosaurids:


References

{{Taxonbar, from=Q2529117 Paleocene crocodylomorphs Paleocene reptiles of South America Peligran Itaboraian Paleogene Colombia Fossils of Colombia Cerrejón Formation Fossil taxa described in 2011 Prehistoric pseudosuchian genera