Arcusaurus
Encyclopedia
Arcusaurus is an extinct genus
of sauropodomorph dinosaur
from the Early Jurassic
(Hettangian
to Sinemurian
stages) of South Africa
.
Arcusaurus was first named by Adam Yates
, Matthew Bonnan
and Johann Neveling in 2011
and the type species
is Arcusaurus pereirabdalorum. The generic name is derived from Latin
arcus, "rainbow", a reference to the Rainbow Nation
. The specific epithet honours Lucille Pereira and Fernando Abdala who discovered the fossils .
Arcusaurus is known from two fragmentary skeletons collected in March 2006 at the Spion Kop Heelbo site from the upper Elliot Formation
in Senekal
in Free State
. The holotype
, BP/1/6235, consists of a partial skull. Some limb bones and vertebrae are included in the material. Both specimens represented juvenile individuals. From detailed features the describers concluded these were not the young of either Aardonyx
or Massospondylus
.
A phylogenetic study of Arcusaurus found it to be a basal
sauropodomorph, placing it as the sister taxon of Efraasia
and all of the more derived sauropodomorphs. Since Efraasia is known from the Norian
stage of the Late Triassic
, the close relationship with Arcusaurus implies that there was a 35-million-year ghost lineage
of sauropodomorphs stretching from Late Triassic forms to Arcusaurus. However, Arcusaurus possesses many features unique to more advanced groups included in the clade
Plateosauria
, raising doubts about the results of the phylogenetic analysis.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of sauropodomorph dinosaur
Dinosaur
Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
from the Early Jurassic
Early Jurassic
The Early Jurassic epoch is the earliest of three epochs of the Jurassic period...
(Hettangian
Hettangian
The Hettangian is the earliest age or lowest stage of the Jurassic period of the geologic timescale. It spans the time between 199.6 ± 0.6 Ma and 196.5 ± 1 Ma . The Hettangian follows the Rhaetian and is followed by the Sinemurian.In Europe stratigraphy the Hettangian is a part of the time span in...
to Sinemurian
Sinemurian
In the geologic timescale, the Sinemurian is an age or stage in the Early or Lower Jurassic epoch or series. It spans the time between 196.5 ± 2 Ma and 189.6 ± 1.5 Ma...
stages) of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
.
Arcusaurus was first named by Adam Yates
Adam Yates
Adam Paul Yates is an English footballer who plays for League Two side Port Vale as a full back. He is a former semi-pro international with England....
, Matthew Bonnan
Matthew Bonnan
Matthew Bonnan is an American paleobiologist and an associate professor of biological sciences at Western Illinois University. His research combines traditional descriptive and anatomical study with computer-aided morphometric analysis and modeling of vertebrate skeletons. Dr...
and Johann Neveling in 2011
2011 in paleontology
-Lobopods:-Arachnids:-Insects:-Newly named jawless vertebrates:-Newly named acanthodian:-Newly named cartilaginous fishes:-Newly named bony fishes:-Newly named lepospondyls:-Newly named temnospondyls:-Newly named lissamphibians:...
and the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is Arcusaurus pereirabdalorum. The generic name is derived from Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
arcus, "rainbow", a reference to the Rainbow Nation
Rainbow Nation
Rainbow Nation is a term coined by Archbishop Desmond Tutu to describe post-apartheid South Africa, after South Africa's first fully democratic election in 1994....
. The specific epithet honours Lucille Pereira and Fernando Abdala who discovered the fossils .
Arcusaurus is known from two fragmentary skeletons collected in March 2006 at the Spion Kop Heelbo site from the upper Elliot Formation
Elliot Formation
The Elliot Formation is a geological formation dating to roughly 210 to 190 million years ago and covering the Norian to Sinemurian stages. The Elliot Formation is found in South Africa and Lesotho and is a member of the Stormberg Group. It consists mainly of limestone, sandstone, and mudstone...
in Senekal
Senekal
Senekal is a town situated on the banks of the Klipspruit River in the eastern part of the Free State province of South Africa. It was named after Commodant-General FP Senekal. Senekal lies on the N5 national...
in Free State
Free State
The Free State is a province of South Africa. Its capital is Bloemfontein, which is also South Africa's judicial capital. Its historical origins lie in the Orange Free State Boer republic and later Orange Free State Province. The current borders of the province date from 1994 when the Bantustans...
. The holotype
Holotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
, BP/1/6235, consists of a partial skull. Some limb bones and vertebrae are included in the material. Both specimens represented juvenile individuals. From detailed features the describers concluded these were not the young of either Aardonyx
Aardonyx
Aardonyx is a genus of prosauropod dinosaur. It is known from the type species Aardonyx celestae found from the Lower Jurassic Elliot Formation of South Africa. A. celestae was named after Celeste Yates, who prepared much of the first known fossil material of the species...
or Massospondylus
Massospondylus
Massospondylus and ) is a genus of prosauropod dinosaur from the early Jurassic Period . It was described by Sir Richard Owen in 1854 from remains found in South Africa, and is thus one of the first dinosaurs to have been named...
.
A phylogenetic study of Arcusaurus found it to be a basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
sauropodomorph, placing it as the sister taxon of Efraasia
Efraasia
Efraasia is a genus of basal sauropodomorph dinosaur. It was a herbivore which lived during the middle Norian stage of the Late Triassic, around 210 million years ago, in what is now Germany...
and all of the more derived sauropodomorphs. Since Efraasia is known from the Norian
Norian
The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in...
stage of the Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
, the close relationship with Arcusaurus implies that there was a 35-million-year ghost lineage
Ghost lineage
A ghost lineage is a phylogenetic lineage that is inferred to exist but has no fossil record....
of sauropodomorphs stretching from Late Triassic forms to Arcusaurus. However, Arcusaurus possesses many features unique to more advanced groups included in the clade
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...
Plateosauria
Plateosauria
Plateosauria is a clade of sauropodomorph dinosaurs which lived during the Late Triassic to the Late Cretaceous. The name Plateosauria was first coined by Gustav Tornier in 1913. The name afterwards fell out of use until the 1980s, when a new generation of paleontologists began using the name...
, raising doubts about the results of the phylogenetic analysis.