''Cipactlichthys'' is a

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 extinct marine holostean fish from the

Lower Cretaceous Lower may refer to: * ''Lower'' (album), 2025 album by Benjamin Booker * Lower (surname) * Lower Township, New Jersey *Lower Receiver (firearms) * Lower Wick Gloucestershire, England See also * Nizhny {{Disambiguation ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

, distantly related to modern bowfins. The only known species is ''Cipactlichthys scutatus''.

Discovery and etymology

''Cipactlichthys scutatus'' is known from two fossils discovered in the Tlayua Formation near the town of Tepexi de Rodríguez, in Puebla, Mexico. The Tlayua Formation, is

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

(

Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name) is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 143.1 ...

) in age, interpreted as an epicontinental marine deposit. Due to its high quality preservation and abundance of fish fossils, the formation is considered one of the most important sources of Cretaceous fishes in Mexico. The genus name is a combination of ''

Cipactli Cipactli ( "crocodile" or "caiman") was the first day of the Aztec divinatory count of 13 X 20 days (the '' tonalpohualli'') and ''Cipactonal'' "Sign of Cipactli" was considered to have been the first diviner. In Aztec cosmology, the crocodile sy ...

'', the

Aztec The Aztecs ( ) were a Mesoamerican civilization that flourished in central Mexico in the Post-Classic stage, post-classic period from 1300 to 1521. The Aztec people included different Indigenous peoples of Mexico, ethnic groups of central ...

mythological sea monster said to be part fish and part reptile, and ''ichthys'',

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 ...

for "fish". The specific epithet ''scutatus'' is Latin for shielded, referring to the large dorsal and ventral

scutes A scute () or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterio ...

Description

''Cipactlichthys'' is an elongate fish, approximately 130 mm in

total length Fish measurement is the measuring of individual fish and various parts of their anatomies, for data used in many areas of ichthyology, including taxonomy and fishery biology. Overall length Standard length (SL) is the length of a fish measured f ...

, or 100 mm in

standard length Fish measurement is the measuring of individual fish and various parts of fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...

. Its dermal bones and

scales Scale or scales may refer to: Mathematics * Scale (descriptive set theory), an object defined on a set of points * Scale (ratio), the ratio of a linear dimension of a model to the corresponding dimension of the original * Scale factor, a number ...

are covered in ganoine and decorated with tubercles and ridges. The jaw extends to behind the rear end of the

orbit In celestial mechanics, an orbit (also known as orbital revolution) is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an ...

. The

pectoral fins Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only b ...

are relatively long, with the first ray extending to the anterior edge of the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s. The

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

is forked and homocercal (upper and lower lobes of equal length). The

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

contains at least 8 fin rays. The

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

is larger than the dorsal fin and also bears at least 8 rays. The

vary greatly in size and shape, with a series of large plate-like scutes along the dorsal and ventral midline behind the dorsal and anal fin.

Classification

''Cipactlichthys'' is classified in the

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 ...

Halecomorphi Halecomorphi is a taxon of Actinopterygii, ray-finned bony fish in the clade Neopterygii. The only extant Halecomorph species are the bowfin (''Amia calva'') and eyespot bowfin (''Amia ocellicauda''), but the group contains many extinct species i ...

due to possession of a crescent-shaped

preopercle The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bon ...

and the involvement of the

symplectic bone 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 jaw articulation. However, it has not yet been assigned to an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

, instead considered a halecomorph of uncertain placement (''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

''). The only living halecomorph is the bowfin, ''

Amia calva The ruddy bowfin (''Amia calva'') is a ray-finned fish native to North America. Common names include mudfish, mud pike, dogfish, grindle, grinnel, swamp trout, and choupique. It is regarded as a relict species, relict, being one of only two sur ...

,'' but this group has a diverse fossil record. A phylogenetic analysis placed ''Cipactlichthys ''as

sister A sister is a woman or a girl who shares parents or a parent with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a familial relationship, it is sometimes used endearingly to ref ...

to a clade containing

Amiiformes The Amiiformes order (biology), order of fish has only two extant taxa, extant species, the bowfins: ''Amia calva'' and ''Amia ocellicauda'', the latter recognized as a separate species in 2022. These Amiiformes are found in the freshwater syste ...

and the extinct order Ionoscopiformes. Cipactlichthys scutatus IGM 6606

References

{{Taxonbar, from=Q15716042 Prehistoric ray-finned fish genera Halecomorphi Early Cretaceous fish of North America Early Cretaceous bony fish Fossils of Mexico Albian genera Fossil taxa described in 2013 Taxa named by Alberto Brito