Cladotheria is a

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 ...

(sometimes ranked as a

legion Legion may refer to: Military * Roman legion, the basic military unit of the ancient Roman army * Aviazione Legionaria, Italian air force during the Spanish Civil War * A legion is the regional unit of the Italian carabinieri * Spanish Legion, ...

) of

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s. It contains modern

theria Theria ( or ; ) is a scientific classification, subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the Placentalia, placental mammals) and the metatherians (including the marsupials) but excludes the egg-lay ...

n mammals (

marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

s and

placentals Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguishe ...

) and several

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 ...

groups, such as the "

dryolestoid Dryolestida is an extinct order of mammals, known from the Jurassic and Cretaceous. They are considered Basal (phylogenetics), basal members of the clade Cladotheria, close to the ancestry of therian mammals. It is also believed that they develop ...

s", amphitheriids and peramurids. The clade was named in 1975 by

Malcolm McKenna Malcolm Carnegie McKenna (1930–2008) was an American paleontologist and author on the subject. Paleontologist McKenna began his paleontology career at the Webb School of California (grades 9-12) in Claremont, California, under noted paleontolo ...

. In 2002, it was defined as a

node-based taxon Phylogenetic nomenclature is a method of nomenclature for taxon, taxa in biology that uses phylogenetics, phylogenetic definitions for taxon names as explained below. This contrasts with Biological classification, the traditional method, by which ...

containing "the common ancestor of dryolestids and living therians, plus all its descendants". A different, stem-based definition was given in 2013, in which Cladotheria contains all taxa that are closer to ''

Mus musculus The house mouse (''Mus musculus'') is a small mammal of the rodent family Muridae, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus ''Mus (genu ...

'' (the house mouse) than to the "

symmetrodont Symmetrodonta is a group of Mesozoic mammals and mammal-like synapsids characterized by the triangular aspect of the molars when viewed from above, and the absence of a well-developed talonid. The traditional group of 'symmetrodonts' ranges in ...

" ''

Spalacotherium tricuspidens ''Spalacotherium'' is a genus of extinct mammal from the Early Cretaceous of Europe. The type species ''Spalacotherium tricuspidens'' was originally named by Richard Owen in 1854, and its material includes maxillary and dentary fragments and many ...

''. Cladotheria incorporates a set of nested mammal clades culminating in

Tribosphenida Tribosphenida is a clade of mammals that includes the ancestor of ''Hypomylos'', Aegialodontia and Theria (the last common ancestor of marsupials and placentals plus all of its descendants). It belongs to the group Zatheria. The current definitio ...

(also known as Boreosphenida), mammals with fully tribosphenic teeth such as therians and a few of their closest relatives. The clade Prototribosphenida includes "the common ancestor of '' Vincelestes'' and living therians, plus all of its descendants". Apart from tribosphenids, Prototribosphenida also includes amphitheriids and peramurids, as well as a few isolated genera such as ''Vincelestes''. It excludes the various basal cladotherian groups which have been combined under the label "dryolestoids". The clade Zatheria is even more exclusive, restricted to solely peramurids and tribosphenids. Zatheria is defined as "the common ancestor of ''

Peramus ''Peramus'' is an extinct genus of cladotherian mammal. It lived in the Late Jurassic and Early Cretaceous of Europe and North Africa. Species There are three known extinct species in the genus: * ''Peramus dubius'' Lulworth Formation, United ...

'' and living marsupials and placentals, plus all of its descendants".

Description

Representative jaws and molars of early cladotherians and their close relatives

Early cladotherians can be distinguished from other mammals by a number of derived traits (

apomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to hav ...

). Their teeth differed from those of the "

s" by the evolution of a talonid shelf (

hypoflexid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

) on the lower

molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

, which occluded with the paracone of the corresponding upper molars. A true talonid basin, allowing for the crushing and grinding of food, was however absent in early-diverging groups like the

s, amphitheriids and peramurids. Cladotherians are also distinguished by a backwards-pointing

angular process __NOTOC__ The angle of the mandible (a.k.a. gonial angle, Masseteric Tuberosity, and Masseteric Insertion) is located at the posterior border at the junction of the lower border of the ramus of the mandible. The angle of the mandible, which may ...

at the rear end of the

dentary bone In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

, below the jaw joint. The shape of this process indicates that early cladotherians had a more transverse (side-to-side) chewing motion than more basal mammal groups. The connection of the middle ear bones to the dentary through an ossified

Meckel's cartilage In humans, the cartilaginous bar of the mandibular arch is formed by what are known as Meckel's cartilages (right and left; also known as Meckelian cartilages), above which the incus and malleus are located. Meckel's cartilage arises from the fir ...

appears to have been lost in cladotherians, but a

cartilaginous Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

connection may have been retained in early-diverging groups.

Phylogeny

Cladogram after Panciroli et al. 2018: The

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 ...

after Lasseron et al 2022:Cladogram after Magallanes et al, 2024:

References

External links

MESOZOIC MAMMALS; Stem zatherians, zatherians & Peramuridae, an internet directory

Extant Middle Jurassic first appearances Taxa described in 1975 Taxa named by Malcolm McKenna {{Mammal-stub