Mesoeucrocodylia is the clade that includes

Eusuchia Eusuchia is a clade of crocodylomorphs that first appeared in the Early Cretaceous with '' Hylaeochampsa''. Along with Dyrosauridae and Sebecosuchia, they were the only crocodyliformes who survived the K-T extinction. Since the other two clades ...

and crocodyliforms formerly placed in the paraphyletic group Mesosuchia. The group appeared during 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-J ...

, 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 sp ...

, 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

(which includes all living

crocodylia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period (Cenomanian stage) and are the closest living ...

n 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, pa ...

s of the skull are fused together into a single compound element, for example. Mesoeucrocodylians possess something of a

secondary palate The secondary palate is an anatomical structure that divides the nasal cavity from the oral cavity in many vertebrates. In human embryology, it refers to that portion of the hard palate that is formed by the growth of the two palatine shelves medi ...

, formed by the posterior extension of sutured

palatine A palatine or palatinus (in Latin; plural ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman times.

bones. The otic aperture of the members of this clade is blocked posteriorly by the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal bones form the cheek series of the skull. The bone forms an ancestral co ...

bone.

Classification

Phylogeny

Below is a

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 ...

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