Mesoeucrocodylia is the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

that includes Eusuchia and crocodyliforms formerly placed in the

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

group Mesosuchia. The group appeared during the Early Jurassic, and continues to the present day.

Diagnosis

It was long known that Mesosuchia was an

evolutionary grade A grade is a taxon united by a level of morphological or physiological complexity. The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit. Definition An evolutionary grade is a group of ...

, a hypothesis confirmed by the

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis of Benton and Clark (1988) which demonstrated that Eusuchia (which includes all living crocodylian species) was nested within Mesosuchia. Due to the paraphyly of Mesosuchia, Mesoeucrocodylia was erected to replace Mesosuchia. Several anatomical characteristics differentiate Mesoeucrocodylia from the other crocodylomorph clades. The

frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...

s of the skull are fused together into a single compound element, for example. Mesoeucrocodylians possess something of a secondary palate, formed by the posterior extension of sutured palatine bones. The

otic aperture Otic means pertaining to the ear. It can refer to: * Otic ganglion, nerve cells in ear * Otic polyp, benign growth in middle ear * Otic capsule, another name for bony labyrinth * Otic drops, another name for ear drops * Otic notch, notch in skull ...

of the members of this clade is blocked posteriorly by the squamosal bone.

Classification

Phylogeny

Below is a cladogram from Fiorelli and Calvo (2007).Fiorelli LE, Calvo JO. 2007. The first "protosuchian" (Archosauria: Crocodyliformes) from the Cretaceous (Santonian) of Gondwana. ''Arquivos do Museu Nacional, Rio de Janeiro'' 65 (4): 417-459.

References

Jurassic crocodylomorphs Cretaceous crocodylomorphs Paleogene crocodylomorphs Neogene crocodylomorphs Sinemurian first appearances Extant Early Jurassic first appearances {{archosaur-stub