Mesoeucrocodylia
Encyclopedia
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
that includes Eusuchia
Eusuchia
Eusuchia is a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. All living crocodilian species are eusuchians, as are many extinct forms.-Description:...
and the paraphyletic group Mesosuchia
Mesosuchia
"Mesosuchia" is an obsolete name for a group of terrestrial, semi-aquatic, or fully aquatic crocodylomorph reptiles. The marine crocodile Metriorhynchus had paddle-like forelimbs, Dakosaurus andiniensis had a skull that was adapted to eat large sea reptiles, and Shamosuchus was adapted for eating...
. The group appeared during the Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
, and continues to the present day.
It was long known that Mesosuchia was an evolutionary grade
Evolutionary grade
In alpha taxonomy, a grade refers to 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:...
, a hypothesis confirmed by the phylogenetic analysis of Benton and Clark, 1988 which demonstrated that Eusuchia
Eusuchia
Eusuchia is a clade of crocodylomorphs that first appears in the Early Cretaceous with Hylaeochampsa. All living crocodilian species are eusuchians, as are many extinct forms.-Description:...
(which includes all living crocodylian species) was nested within Mesosuchia. As the authors did not accept paraphyletic groups, Mesoeucrocodylia was erected to replace Mesosuchia.
Several anatomical characteristics differentiate Mesoeucrocodylia from the other crocodylomorph clades. The frontal bone
Frontal bone
The frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
s of the skull are fused together into a single compound element, for example. Mesoeucrocodylians possess somewhat of a secondary palate
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 medially and their mutual fusion in the midline...
, formed by the posterior extension of sutured palatine
Palatine bone
The palatine bone is a bone in many species of the animal kingdom, commonly termed the palatum .-Human anatomy:...
bones. The otic aperture of the members of this clade is blocked posteriorly by the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
bone.