''Vigilius'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

brachyopid Brachyopidae is an extinct family of temnospondyl labyrintodonts. They evolved in the early Mesozoic and were mostly aquatic. A fragmentary find from Lesotho, Africa is estimated to have been long, the largest amphibian ever known to have lived ...

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

amphibian from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

. It is known from the single

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

''Vigilius wellesi''. The

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

specimen of ''Vigilius'' is a skull labelled UCMP 36199. The skull was found in an area alongside

Arizona State Route 64 State Route 64 (SR 64) is a state highway in the northern part of the US state of Arizona. It travels from its western terminus in Williams to its intersection with U.S. Route 89 (US 89) in Cameron. Route description S ...

overlooking the

Grand Canyon The Grand Canyon (, yuf-x-yav, Wi:kaʼi:la, , Southern Paiute language: Paxa’uipi, ) is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is long, up to wide and attains a depth of over a m ...

. It came from a layer of the Early Triassic

Moenkopi Formation The Moenkopi Formation is a geological formation that is spread across the U.S. states of New Mexico, northern Arizona, Nevada, southeastern California, eastern Utah and western Colorado. This unit is considered to be a group in Arizona. Part ...

. The skull was described by paleontologists Samuel Paul Welles and Richard Estes in 1969 and attributed to a new genus and species of brachyopid called '' Hadrokkosaurus bradyi''. The holotype of ''Hadrokkosaurus'' was an isolated lower jaw. In 2000, paleontologists Anne Warren and Claudia Marsicano suggested that the lower jaw and skull represent two different species, as they were found over apart and come from two animals of different size. Warren and Marsicano assigned the skull the a new genus and species ''Vigilius wellesi''. The genus name comes from the Latin word ''vigilia'' meaning "keeping watch," a reference to its large eye sockets and "to the fact that the skull was keeping vigil over the Grand Canyon." The species was named in honor of Welles. Several bones found around the Grand Canyon site were also attributed to ''Vigilius'', including a

pterygoid bone The pterygoid is a paired bone forming part of the palate of many vertebrates, behind the palatine bone In anatomy, the palatine bones () are two irregular bones of the facial skeleton in many animal species, located above the uvula in the th ...

that was described in 1971 as a scapulacoracoid. Additional remains were found west of Holbrook, Arizona.

Phylogeny

The material now assigned to ''Vigilius'' was first identified as remains of a brachyopoid. Warren and Marsicano conducted a phylogenetic analysis of many brachyopoids and found ''Vigilius'' to nest within the family Brachyopidae. Brachyopoidea is normally divided into the families Brachyopidae and

Chigutisauridae Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. Du ...

, but these families are not always considered closely related; in some studies, Chigutisauridae is placed in a group of mostly Mesozoic temnospondyls called Stereospondyli while Brachyopidae is classified within a group of temnospondyls called

Dvinosauria Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from t ...

, which includes

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

and

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

taxa that are older than ''Vigilius''. The relationship of dvinosaurians to other temnospondyls is uncertain, as they may or may not belong to Stereospondyli. Warren and Marsicano identified many features in ''Vigilius'' that are not seen in other brachyopoids but are common in dvinosaurians, including a narrow

vomer The vomer (; lat, vomer, lit=ploughshare) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxill ...

bone at the front of the palate and a very wide cultriform process at the front of the

parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived) ...

, a bone on the underside of the skull. They considered ''Vigilius'' to be a dvinosaur in spite of the results of their phylogenetic analysis.

References

{{Taxonbar, from=Q7928933 Brachyopids Early Triassic amphibians Triassic temnospondyls of North America Triassic Arizona Holbrook, Arizona Paleontology in Arizona Fossil taxa described in 2000