''Almadasuchus'' is an

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 ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

crocodylomorph Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. Extinct crocodylomorphs were considerably mor ...

known from the early

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

(early Oxfordian stage) Puesto Almada Member of the e Cañadón Calcáreo Formation of

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

. It contains a single

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, ''Almadasuchus figarii''. It is known from the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

MPEF-PV 3838, a well-preserved posterior region of the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

as well as other skull and

postcranial The postcranium ("behind the cranium"; plural: postcrania) or postcranial skeleton in zoology and vertebrate paleontology is the skeleton apart from the skull. The postcranium encompasses the axial skeleton, which includes the entirety of the verte ...

remains. Almadasuchus was recovered from Puesto Almada , 30 m above the fish beds, dated as Oxfordian in age.

Description

According to a

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis that accompanied the first description of the species, ''A. figarii'' is the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

or closest relative of the

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 ...

Crocodyliformes Crocodyliformes is a clade of crurotarsan archosaurs, the group often traditionally referred to as "crocodilians". They are the first members of Crocodylomorpha to possess many of the features that define later relatives. They are the only pseu ...

, a large group that originated in the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

and includes modern

crocodilian Crocodilia () is an Order (biology), order of semiaquatic, predatory reptiles that are known as crocodilians. They first appeared during the Late Cretaceous and are the closest living relatives of birds. Crocodilians are a type of crocodylomorp ...

s. It is also a close relative of "

sphenosuchia Sphenosuchia is a suborder of basal crocodylomorphs that first appeared in the Triassic and occurred into the Middle Jurassic. Most were small, gracile animals with an erect limb posture. They are now thought to be ancestral to crocodyliforms ...

ns", a

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

group of more basal non-crocodyliform crocodylomorphs. ''Almadasuchus'' is most closely related to the "sphenosuchian" ''

Junggarsuchus ''Junggarsuchus'' () is an extinct genus of sphenosuchian crocodylomorpha, crocodylomorph from the Middle Jurassic, Middle or Late Jurassic period of China. The type species, type and only species is ''J. sloani''. The Genus, generic name of ''Ju ...

'' from the

Middle Jurassic The Middle Jurassic is the second Epoch (geology), epoch of the Jurassic Period (geology), Period. It lasted from about 174.1 to 161.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relativel ...

of China. ''Almadasuchus'' is one of only four non-crocodyliform crocodylomorphs known from after 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� ...

, the others being ''Junggarsuchus'' and two "sphenosuchians" from the

Morrison Formation The Morrison Formation is a distinctive sequence of Upper Jurassic sedimentary rock found in the western United States which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltston ...

in the western United States, ''

Hallopus ''Hallopus'' was a prehistoric reptile, named in 1877 as a species of ''Nanosaurus'' and classified as a genus by Othniel Charles Marsh, O. C. Marsh in 1881 from the Late Jurassic Morrison Formation. Today though the animal is thought to be a pse ...

'' and ''

Macelognathus ''Macelognathus'' is an extinct genus of sphenosuchian crocodylomorph from the Late Jurassic. Originally it was believed be a turtle and later a dinosaur. It lived in what is now Wyoming, in North America.Moodie, R.L. 1908. The relationship of th ...

''. Crocodyliforms appeared in the Late Triassic and began a major

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. A significantly large and diverse radiation within ...

in the Jurassic, making ''Almadasuchus'' one of the last non-crocodyliform crocodylomorphs. ''Almadasuchus'' is considered a

transitional form A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross ...

between crocodyliforms and earlier archosaurs with respect to its

braincase In human anatomy, the neurocranium, also known as the braincase, brainpan, brain-pan, or brainbox, is the upper and back part of the skull, which forms a protective case around the brain. In the human skull, the neurocranium includes the calv ...

. In nearly all

diapsid Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The earliest traditionally identified diapsids, the araeosc ...

reptiles the braincase is weakly connected to other bones that make up the back of the skull, making this region flexible or kinetic. In crocodyliforms, the braincase is strongly sutured to a bone called the quadrate, making the skull completely immovable or akinetic. The quadrate of ''Almadasuchus'' is not completely fused to the braincase, but makes connections with two braincase bones, the basisphenoid and the exoccipital. These two attachment points probably made the skull of ''Almadasuchus'' completely akinetic. ''Jungarrsuchus'', which is the second most closely related non-crocodyliform crocodylomorph to crocodyliforms, has a quadrate that only attaches to the exoccipital.

Phylogeny

Below is a

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 ...

modified from Pol ''et al.'' (in press).

References

{{Taxonbar, from=Q8196026 Late Jurassic crocodylomorphs of South America Oxfordian life Jurassic Argentina Fossils of Argentina Cañadón Asfalto Formation Fossil taxa described in 2013 Prehistoric pseudosuchian genera