''Amtosaurus'' () is a

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 ...

ornithischia Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

based on a fragmentary skull collected from the Upper

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

Bayan Shireh Formation (

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

Santonian The Santonian is an age in the geologic timescale or a chronostratigraphic stage. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series. It spans the time between 86.3 ± 0.7 mya ( million years ago) and 83.6 ± 0.7 m ...

) of

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

and originally believed to represent an ankylosaurid.

Hadrosaurid Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fami ...

affinities have also been suggested. However, per Parish and Barrett, this specimen is too fragmentary to be reliably classified beyond an indeterminate ornithischian. A second species assigned to the genus, ''A. archibaldi'', has become the basis of a valid ankylosaurid taxon, ''

Bissektipelta ''Bissektipelta'' (meaning " Bissekty shield") is a genus of ankylosaurine thyreophoran dinosaurs that lived in Asia during the Late Cretaceous in what is now the Bissekty Formation of Uzbekistan. ''Bissektipelta'' is a monospecific genus, cont ...

''.

Discovery and species

The Soviet-Mongolian Paleontological Expedition of 1975 discovered two partial

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful l ...

in the Baynshire Formation of the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, one from the locality Bayshin Tsav and the other from Amtgai. In

1978 Events January * January 1 – Air India Flight 855, a Boeing 747 passenger jet, crashes off the coast of Bombay, killing 213. * January 5 – Bülent Ecevit, of Republican People's Party, CHP, forms the new government of Turkey (42nd ...

, Soviet paleontologists Sergei Kurzanov and Tatiana Tumanova described these braincases, which represented the first description of the region of the skull in ankylosaurs since the description of '' Silvisaurus'' in 1960. While the braincase from Bayshin Tsav, PIN 3780/1, was referred to the existing taxon '' Talarurus plicatospineus'', the braincase from Amtgai (PIN 3780/2) was named as the new taxon ''Amtosaurus magnus'', with the genus name referencing the type locality and the species name derived from 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 ''magnus'' for "large". While the location, age, and general anatomy of ''Amtosaurus'' was most similar to ''Talarurus'', it could be separated from it and other ankylosaurs by details of the . During the 1998 expedition of the Uzbek-Russian-British-American-Canadian project a braincase of an ankylosaur was discovered in the

Turonian The Turonian is, in the International Commission on Stratigraphy, ICS' geologic timescale, the second age (geology), age in the Late Cretaceous epoch (geology), Epoch, or a stage (stratigraphy), stage in the Upper Cretaceous series (stratigraphy), ...

to Coniacian

Bissekty Formation The Bissekty Formation (sometimes referred to as Bissekt) is a formation (geology), geologic formation and Lagerstätte which outcrop, crops out in the Kyzyl Kum desert of Uzbekistan, and dates to the Late Cretaceous Period (geology), Period. Laid ...

of Dzarakuduk locality in

Uzbekistan , image_flag = Flag of Uzbekistan.svg , image_coat = Emblem of Uzbekistan.svg , symbol_type = Emblem of Uzbekistan, Emblem , national_anthem = "State Anthem of Uzbekistan, State Anthem of the Republ ...

. This braincase was the first diagnostic ankylosaur element discovered in the Bissekty Formation, allowing comparisons to many other taxa. The braincase, ZIN PH 1/16, was described in

2002 The effects of the September 11 attacks of the previous year had a significant impact on the affairs of 2002. The war on terror was a major political focus. Without settled international law, several nations engaged in anti-terror operation ...

by Russian paleontologist Alexander Averianov, who named it as a second species of ''Amtosaurus'', ''A. archibaldi'', after URBAC project leader J. David Archibald. From ''A. archibaldi'', ''Amtosaurus'' was identified as an intermediate genus between earlier and later members of

Ankylosauridae Ankylosauridae () is a family of armored dinosaurs within Ankylosauria, and is the sister group to Nodosauridae. The oldest known ankylosaurids date to around 122 million years ago and went extinct 66 million years ago during the Cretaceous–Pal ...

. The status of ''Amtosaurus magnus'' and ''A. archibaldi'' was revisited in

2004 2004 was designated as an International Year of Rice by the United Nations, and the International Year to Commemorate the Struggle Against Slavery and Its Abolition (by UNESCO). Events January * January 3 – Flash Airlines Flight 60 ...

by British paleontologists Joylon Parrish and Paul Barrett. They found that ''A. magnus'' lacked any clear diagnostic features of

Ankylosauria Ankylosauria is a group of herbivorous dinosaurs of the clade Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs ...

, or even any dinosaur clade. It has been suggested that ''Amtosaurus'' could represent a

hadrosaurid Hadrosaurids (), also hadrosaurs or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod fami ...

, but no features of the braincase distinguish that group, so Parrish and Barrett could only classify ''Amtosaurus'' as an indeterminate member of

Ornithischia Ornithischia () is an extinct clade of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek ...

. As a result of the dubious nature of ''A. magnus'', ''A. archibaldi'' was revisited, showing clearly diagnostic features of Ankylosauria and anatomy to suggest it was a member of Ankylosauridae or Polacanthidae. As a result, ''A. archibaldi'' was moved into its own genus ''

''.

References

{{Taxonbar, from=Q422864 Ornithischia Dinosaur genera Turonian dinosaurs Cenomanian dinosaurs Paleontology in Mongolia Fossil taxa described in 1978