''Protome'' 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 ...

of parasuchid

phytosaur Phytosaurs (Φυτόσαυροι in Greek, meaning 'plant lizard') are an extinct group of large, mostly semiaquatic Late Triassic archosauriform or basal archosaurian reptiles. Phytosaurs belong to the order Phytosauria and are sometimes ref ...

from 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 ...

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, represented by 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), ...

, ''Protome batalaria''. It is known from a single

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 ...

incomplete, partially disarticulated

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 ...

and left

lower jaw In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

called PEFO 34034 from the Upper Lot's Wife beds, Sonsela Member of the

Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In ...

Petrified Forest National Park Petrified Forest National Park is a national park of the United States in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassing semi-desert shrub steppe as wel ...

. The skull was discovered in 2004 by Michelle Stocker and Bill Parker and was described by them as a specimen of '' Smilosuchus adamanensis'' (then a species of '' Leptosuchus''). It was placed in the new genus ''Protome'' in 2012. The genus name ''Protome'' is the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

word for an animal's face. The specific name ''batalaria'' is the

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

word for battleship, which is a reference to Battleship NW, the locality within Petrified Forest where the skull was found.

Description

''Protome'' has a long, narrow, tubular-shaped snout. It has a partial rostral crest at the back of the snout, a feature which it shares with phytosaurs like '' Smilosuchus adamanensis'', '' Pravusuchus'', and '' Leptosuchus'', but which is not as prominent as it is in other ''Smilosuchus'' species and some '' Pseudopalatus'' species. It lacks the

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry crest along the midline of the snout that is present in '' Leptosuchus studeri'' and ''

Mystriosuchus westphali ''Mystriosuchus'' (meaning "spoon-crocodile")
Retrieved on May 25th, 2008. is an extinct genus of phytosaur t ...

''. Many characteristics that associate ''Protome'' with other phytosaurs can be found in its

squamosal bone 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 ...

, which makes up the cheek region and extends behind the main portion of the skull. ''Protome'' was named on the basis of several unique characteristics, or

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

. The first autapomorphy is the flat shape of the basitubera, an area at the base of the skull in front of its attachment point with the neck. Another is that bony projections called exoccipital prongs at the back of the skull make up the top margin of the

foramen magnum The foramen magnum () is a large, oval-shaped opening in the occipital bone of the skull. It is one of the several oval or circular openings (foramina) in the base of the skull. The spinal cord, an extension of the medulla oblongata, passes thro ...

, the hole through which the spinal cord enters the skull. A third autapomorphy is a small depression or fossa surrounding the front tip of a hole in the lower jaw called the mandibular fenestra. These features were used to distinguish PEFO 34034 as a new genus and species, distinct from ''Leptosuchus adamanensis''. ''Protome'' and ''Leptosuchus'' are similar in that both have broad squamosals and holes called

supratemporal fenestrae Temporal fenestrae are openings in the Temple (anatomy), temporal region of the skull of some Amniote, amniotes, behind the Orbit (anatomy), orbit (eye socket). These openings have historically been used to track the evolution and affinities of re ...

that are located on top of the skull. When it was described in 2004, PEFO 34034 was thought to represent a small ''Leptosuchus'' individual, possibly a juvenile. The lack of a premaxillary crest has been used as evidence for it being a juvenile, although the absence of a crest has also been interpreted as a distinct characteristic of some species, and more recently as a possible characteristic of

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

. Most juvenile phytosaurs are identified on the basis of incomplete fusion of different parts of each

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

, but ''Protome'' is not known from any postcranial remains.

Phylogeny

When ''Protome'' was named in 2012, 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 was conducted to determine its evolutionary relationships. The analysis placed PEFO 34034 outside 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 ...

s containing species of ''Leptosuchus'' and ''Smilosuchus'', the two most likely genera to which the specimen could be referred. PEFO 34034's placement outside these groups justified the erection of a new genus and species. ''Protome'' was found to be a phytosaurid just outside the clade Leptosuchomorpha. As was the case in previous studies, species of ''Leptosuchus'' formed 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 ...

grouping, meaning that they did not represent one coherent genus. Many isolated phytosaur skull fragments from Petrified Forest have been assigned to ''Leptosuchus'' because they had broad squamosals, but the presence of this type of squamosal in the distinct taxon ''Protome'' suggests that not all of these fragments can be assigned with confidence to ''Leptosuchus''. 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 ...

showing the phylogenetic relationships of ''Protome'' from Stocker (2012):

References

{{Taxonbar, from1=Q28598688, from2=Q3280960 Phytosauria Late Triassic reptiles of North America Triassic Arizona Paleontology in Arizona Chinle fauna Fossil taxa described in 2012