Cladotheria is a clade (sometimes ranked as a

legion Legion may refer to: Military * Roman legion, the basic military unit of the ancient Roman army * Spanish Legion, an elite military unit within the Spanish Army * Legion of the United States, a reorganization of the United States Army from 179 ...

) of mammals. It contains modern

theria Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. C ...

n mammals (

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s and placentals) and several extinct groups, such as the dryolestoids, amphitheriids and

peramurid The family Peramuridae is a family of mammals that lived in the Late Jurassic and Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divis ...

s. 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 paleontol ...

. In 2002, it was defined as a

node-based taxon Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional approach, in which taxon names are defined by a ''type'', which c ...

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 Mus or MUS may refer to: Abbreviations * MUS, the NATO country code for Mauritius * MUS, the IATA airport code for Minami Torishima Airport * MUS, abbreviation for the Centre for Modern Urban Studies on Campus The Hague, Leiden University, Ne ...

'' (the house mouse) than to the " symmetrodont" ''

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 man ...

''.

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 have ...

). Their teeth differed from those of the " symmetrodonts" by the evolution of a talonid shelf ( hypoflexid) on the lower

molars The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone to ...

, which occluded with the paracone of the corresponding upper molars. A true

talonid basin The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone ...

, allowing for the crushing and grinding of food, was however absent in early-diverging groups like the dryolestoids, amphitheriids and

s. Cladotherians are also distinguished by a backwards-pointing

angular process Angular may refer to: Anatomy * Angular artery, the terminal part of the facial artery * Angular bone, a large bone in the lower jaw of amphibians and reptiles * Angular incisure, a small anatomical notch on the stomach * Angular gyrus, a region o ...

at the rear end of the

dentary bone In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable ...

, 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 this the incus and malleus are developed. 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. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...

connection may have been retained in early-diverging groups.

Phylogeny

The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below is simplified after a 2022 phylogenetic analysis by Lasseron and colleagues:

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