Pachycormiformes is an extinct order of marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

known from the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic� ...

to the end of the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

. It only includes a single family, Pachycormidae. They were characterized by having serrated

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s (though more recent studies demonstrated that fin shape diversity in this group was high), reduced pelvic fins and a bony

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit ** podium * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ...

. Pachycormiformes are morphologically diverse, containing both

tuna A tuna (: tunas or tuna) is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae ( mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bul ...

and

swordfish The swordfish (''Xiphias gladius''), also known as the broadbill in some countries, are large, highly migratory predatory fish characterized by a long, flat, pointed bill. They are the sole member of the Family (biology), family Xiphiidae. They ...

-like carnivorous forms, as well as

edentulous Toothlessness or edentulism is the condition of having no teeth. In organisms that naturally have teeth, it is the result of tooth loss. Organisms that never possessed teeth can also be described as edentulous. Examples are the members of the fo ...

suspension-feeding forms.

Description

Pachycormiformes are united by "a compound bone (rostrodermethmoid) forming the anterodorsal border of the mouth; a reduced

coronoid process of the mandible In human anatomy, the mandible's coronoid process () is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. Its anterior border is convex and is continuous below with the anterior border of the ramus. ...

; absence of supraorbitals associated with a dermosphenotic defining the dorsal margin 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 ...

; two large, plate-like suborbital bones posterior to the infraorbitals; long, slender

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 ...

; asymmetrical branching of pectoral fin

lepidotrichia In a zoological context, spines are hard, needle-like anatomical structures found in both vertebrate and invertebrate species. The spines of most spiny mammals are modified hairs, with a spongy center covered in a thick, hard layer of keratin and ...

; considerable overlap of the hypurals by caudal fin rays (hypurostegy); and the presence of distinctive uroneural-like ossifications of 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 ...

endoskeleton". Pachycormiformes varied substantially in size, from medium-sized fishes around in length like the macropredator '' Pachycormus'', to the largest known ray-finned fish, the

suspension feeding Filter feeders are aquatic animals that acquire nutrients by feeding on organic matters, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specia ...

Leedsichthys ''Leedsichthys'' is an extinct genus of pachycormid fish that lived in the oceans of the Middle to Late Jurassic.Liston, JJ (2004). An overview of the pachycormiform ''Leedsichthys''. In: Arratia G and Tintori A (eds) Mesozoic Fishes 3 - Systema ...

'', which is estimated to have reached a maximum length of around .

Relationships

Pachycormiformes are generally interpreted as basal members of

Teleosteomorpha Teleosteomorpha is an infraclass of ray-finned fishes containing all teleost fish and their closest extinct relatives. Also in this group are two diverse Mesozoic fish orders, the Aspidorhynchiformes and the Pachycormiformes. Several other non- ...

, the group that includes all fish more closely related to modern

teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

s than to

Holostei Holostei is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by the single living genus, '' Amia'' with two species, the bowfins (''Amia calva'' and '' Amia ocellicauda''), as well as the Gin ...

(the group containing

bowfin 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, being one of only two surviving species ...

and

gar Gars are an ancient group of ray-finned fish in the family Lepisosteidae. They comprise seven living species of fish in two genera that inhabit fresh, brackish, and occasionally marine waters of eastern North America, Central America and Cuba ...

s), often they have been considered to be the

sister group In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of the

Aspidorhynchiformes Aspidorhynchidae (from Neo-Latin "shield-snouts") is an extinct Family (biology), family of Actinopterygii, ray-finned fish from the Mesozoic, Mesozoic Era. It is the only member of the Monotypic taxon, monotypic Order (biology), order Aspidorhync ...

Gallery

Taxonomy

Taxonomy according to Cooper ''et al.'' (2022): * ?'' Eugnathides'' Gregory, 1923 * '' Euthynotus'' Wagner, 1860 * '' Haasichthys'' Delsate, 1999 * '' Notodectes'' Dolgopol de Saez, 1949 * '' Pseudoasthenocormus'' * '' Sauropsis'' Agassiz, 1843 * Hypsocorminae Vetter, 1881 ** '' Australopachycormus'' Kear, 2007 ** '' Hypsocormus'' Wagner, 1860 ** '' Kaykay'' Gouiric-Cavalli & Arratia, 2022 ** ''

Orthocormus ''Orthocormus'' is an extinct genus of prehistoric pachycormiform bony fish. It is known from three species found in Late Jurassic (Kimmeridgian) aged plattenkalk deposits in Bavaria, Germany. The species "'' Hypsocormus" tenuirostris'' Woodwar ...

'' Weitzel, 1930 ** ''

Protosphyraena ''Protosphyraena'' is a fossil genus of swordfish-like marine fish, that thrived worldwide during the Cretaceous period (Albian-Maastrichtian). Fossil remains of this taxon are mainly discovered in North America and Europe, and potential specime ...

'' Leidy, 1857 ** '' Simocormus'' Maxwell ''et al.'', 2020 * Asthenocorminae Cooper ''et al.'', 2022 ** '' Germanostomus'' Cooper ''et al.'', 2022 ** '' Ohmdenia'' Hauff, 1953 ** '' Pachycormus''? Agassiz, 1833 ** '' Saurostomus'' Agassiz, 1843 ** Suspension-feeding clade *** '' Asthenocormus'' Woodward, 1895 *** ''

Bonnerichthys ''Bonnerichthys'' is a genus of fossil fishes within the family Pachycormidae that lived during the Coniacian to Maastrichtian stage of the Late Cretaceous. Fossil remains of this taxon were first described from the Smoky Hill Member of the N ...

'' Friedman ''et al.'', 2010 *** ''

'' Woodward, 1889 *** '' Martillichthys'' Liston, 2008 *** '' Rhinconichthys'' Friedman ''et al.'', 2010 Cladistics according to Friedman ''et al.'' (2010).

References

{{Taxonbar, from=Q1227671 Late Triassic first appearances Maastrichtian extinctions Prehistoric ray-finned fish orders Monotypic vertebrate orders