Achillobator
Encyclopedia
Achillobator is a genus
of dromaeosaurid theropod dinosaur
from the late Cretaceous
Period of what is now Mongolia
, about 90 million years ago. It was probably an active bipedal predator, hunting with the large sickle-shaped claw
on the second toe of each hind foot. It was a large dromaeosaurid: the holotype and only known individual of Achillobator is estimated at 6 metres (19.7 ft) long.
The generic name comes from Achilles
, a famous ancient Greek
warrior of the Trojan War
, and the Mongolian
word bator ("warrior" or "hero"). It refers to the large Achilles tendon
needed to use the sickle claw on the foot, which was the major combat organ of dromaeosaurids. The one species
is named A. giganticus because it is much larger than most other dromaeosaurids.
n field expedition in 1989, though it was not described and named until ten years later, in 1999, by Mongolian paleontologist Altangerel Perle
, and Americans
Mark Norell and Jim Clark, although the description was not complete and was actually published without the knowledge of the latter two authors.
Fossil
bones of Achillobator were found mostly disarticulated, but associated, including a fragment of the upper jaw with teeth, as well as vertebrae from all sections of the spinal column, rib
s, and bones from the shoulder, pelvis
, forelimbs and hindlimbs. These remains were found in the Bayan Shireh Formation
of Dornogovi Province
, Mongolia, which dates to the Late Cretaceous
epoch. The exact age is uncertain, with two competing hypotheses; based on comparisons with other formations, the Bayan Shireh fauna
seems to correspond best with the Turonian
through early Campanian
stages of the Late Cretaceous, about 93 to 80 million years ago. However, examination of the magnetostratigraphy
of the formation seems to confirm that the entire Bayan Shireh lies within the Cretaceous Long Normal, which lasted only until the end of the Santonian
stage, giving a possible Cenomanian
through Santonian age, or between 98 and 83 million years ago. Other dinosaurs found in the Bayan Shireh include Alectrosaurus
, Segnosaurus
, Talarurus
, and Bactrosaurus
.
, a family
of dinosaurs currently thought to be very closely related to birds. While the relationship of dromaeosaurids to other theropods (including birds) is relatively well-understood, the phylogeny within the family itself is not. The most recent analysis shows Achillobator as a member of the subfamily
Dromaeosaurinae
, most closely related to North America
n forms like Utahraptor
and Dromaeosaurus
. Deinonychus
and Velociraptor
are also dromaeosaurids, but appear to represent a different branch of the family.
n characteristics compared to other dromaeosaurids. For instance, the pubis
is aligned vertically and has a large pubic boot (a wide expansion at the end), unlike most other dromaeosaurids, where there is a much smaller boot, if any, and the pubis points backwards in the same direction as the ischium (a condition called opisthopuby, which is also seen in the unrelated therizinosaur
s and ornithischia
ns, as well as in birds).
The above differences and others have led to suggestions that Achillobator represents a paleontological chimera
. However, other studies have attempted to refute this, noting that many pieces were found semi-articulated, and that Achillobator routinely comes out as a dromaeosaurid in cladistic analyses, even taking into account the differences.
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 dromaeosaurid theropod 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 late Cretaceous
Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...
Period of what is now Mongolia
Mongolia
Mongolia is a landlocked country in East and Central Asia. It is bordered by Russia to the north and China to the south, east and west. Although Mongolia does not share a border with Kazakhstan, its western-most point is only from Kazakhstan's eastern tip. Ulan Bator, the capital and largest...
, about 90 million years ago. It was probably an active bipedal predator, hunting with the large sickle-shaped claw
Claw
A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
on the second toe of each hind foot. It was a large dromaeosaurid: the holotype and only known individual of Achillobator is estimated at 6 metres (19.7 ft) long.
The generic name comes from Achilles
Achilles
In Greek mythology, Achilles was a Greek hero of the Trojan War, the central character and the greatest warrior of Homer's Iliad.Plato named Achilles the handsomest of the heroes assembled against Troy....
, a famous ancient Greek
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...
warrior of the Trojan War
Trojan War
In Greek mythology, the Trojan War was waged against the city of Troy by the Achaeans after Paris of Troy took Helen from her husband Menelaus, the king of Sparta. The war is among the most important events in Greek mythology and was narrated in many works of Greek literature, including the Iliad...
, and the Mongolian
Mongolian language
The Mongolian language is the official language of Mongolia and the best-known member of the Mongolic language family. The number of speakers across all its dialects may be 5.2 million, including the vast majority of the residents of Mongolia and many of the Mongolian residents of the Inner...
word bator ("warrior" or "hero"). It refers to the large Achilles tendon
Achilles tendon
The Achilles tendon , also known as the calcaneal tendon or the tendo calcaneus, is a tendon of the posterior leg. It serves to attach the plantaris, gastrocnemius and soleus muscles to the calcaneus bone.- Anatomy :The Achilles is the tendonous extension of 3 muscles in the lower leg:...
needed to use the sickle claw on the foot, which was the major combat organ of dromaeosaurids. The one species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
is named A. giganticus because it is much larger than most other dromaeosaurids.
Discovery and species
The fossil remains of Achillobator were first discovered during a Mongolian and RussiaRussia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n field expedition in 1989, though it was not described and named until ten years later, in 1999, by Mongolian paleontologist Altangerel Perle
Altangerel Perle
Altangerel Perle is a Mongolian palaeontologist.He is employed at the National University of Mongolia. He has described species such as Goyocephale lattimorei, Achillobator giganticus and Erlikosaurus andrewsi. He has been honored by Polish palaeontologist Halszka Osmólska, who named the species...
, and Americans
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
Mark Norell and Jim Clark, although the description was not complete and was actually published without the knowledge of the latter two authors.
Fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
bones of Achillobator were found mostly disarticulated, but associated, including a fragment of the upper jaw with teeth, as well as vertebrae from all sections of the spinal column, rib
Rib
In vertebrate anatomy, ribs are the long curved bones which form the rib cage. In most vertebrates, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the chest cavity. They serve to protect the lungs, heart, and other internal organs of the thorax...
s, and bones from the shoulder, pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
, forelimbs and hindlimbs. These remains were found in the Bayan Shireh Formation
Bayan Shireh Formation
The Bayan Shireh Formation is a geological formation in Burkhant, Mongolia, that dates to the late Cretaceous period...
of Dornogovi Province
Dornogovi Province
Dornogovi is one of the 21 Aimags of Mongolia. It is located in the southeast of the country.-Administrative Subdivision:* - tosgon .** - The aimag capital Sainshand-References:...
, Mongolia, which dates to the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
epoch. The exact age is uncertain, with two competing hypotheses; based on comparisons with other formations, the Bayan Shireh fauna
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
seems to correspond best with the Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
through early Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stages of the Late Cretaceous, about 93 to 80 million years ago. However, examination of the magnetostratigraphy
Magnetostratigraphy
Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization , that is, the...
of the formation seems to confirm that the entire Bayan Shireh lies within the Cretaceous Long Normal, which lasted only until the end of the Santonian
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 85.8 ± 0.7 mya and 83.5 ± 0.7 mya...
stage, giving a possible Cenomanian
Cenomanian
The Cenomanian is, in the ICS' geological timescale the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series. An age is a unit of geochronology: it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding...
through Santonian age, or between 98 and 83 million years ago. Other dinosaurs found in the Bayan Shireh include Alectrosaurus
Alectrosaurus
Alectrosaurus is a genus of tyrannosaurid theropod dinosaur from the Late Cretaceous Period of Inner Mongolia. It was a bipedal carnivore with a body shape similar to its much larger relative, Tyrannosaurus rex...
, Segnosaurus
Segnosaurus
Segnosaurus is a genus of herbivorous theropod dinosaur belonging to the Therizinosauridae from the Cretaceous of Mongolia.-Discovery and naming:...
, Talarurus
Talarurus
Talarurus is a genus of hippopotamus-sized ankylosaurid dinosaur with heavy armour and a club tail. It was named by Evgeny Maleev in 1952.-Age and location:...
, and Bactrosaurus
Bactrosaurus
Bactrosaurus is a genus of herbivorous dinosaur that lived in east China during the late Cretaceous, about 70 mya. The position Bactrosaurus occupies in the Cretaceous makes it one of the earliest known hadrosaurs, and although it is not known from a full skeleton, Bactrosaurus is one of the best...
.
Classification
Achillobator is probably a dromaeosauridDromaeosauridae
Dromaeosauridae is a family of bird-like theropod dinosaurs. They were small- to medium-sized feathered carnivores that flourished in the Cretaceous Period. The name Dromaeosauridae means 'running lizards', from Greek dromeus meaning 'runner' and sauros meaning 'lizard'...
, a family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of dinosaurs currently thought to be very closely related to birds. While the relationship of dromaeosaurids to other theropods (including birds) is relatively well-understood, the phylogeny within the family itself is not. The most recent analysis shows Achillobator as a member of the subfamily
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Dromaeosaurinae
Dromaeosaurinae
Dromaeosaurinae is a subfamily of Dromaeosauridae. Most dromaeosaurines lived in what is now the USA and Canada, , as well as Mongolia, , and possibly Denmark, , as well. Isolated teeth that may belong to African dromaeosaurines have also been discovered in Ethiopia...
, most closely related to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
n forms like Utahraptor
Utahraptor
Utahraptor is a genus of theropod dinosaurs, including the largest known members of the family Dromaeosauridae. Fossil specimens date to the upper Barremian stage of the early Cretaceous period...
and Dromaeosaurus
Dromaeosaurus
Dromaeosaurus was a genus of theropod dinosaur which lived during the Late Cretaceous period , sometime between 76.5 and 74.8 million years ago, in the western United States and Alberta, Canada. The name means 'running lizard'....
. Deinonychus
Deinonychus
Deinonychus was a genus of carnivorous dromaeosaurid dinosaur. There is one described species, Deinonychus antirrhopus. This 3.4 meter long dinosaur lived during the early Cretaceous Period, about 115–108 million years ago . Fossils have been recovered from the U.S...
and Velociraptor
Velociraptor
Velociraptor is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 million years ago during the later part of the Cretaceous Period. Two species are currently recognized, although others have been assigned in the past. The type species is V. mongoliensis; fossils...
are also dromaeosaurids, but appear to represent a different branch of the family.
Chimera hypothesis
The pelvis of Achillobator seems to show plesiomorphic ("primitive") saurischiaSaurischia
Saurischia meaning 'lizard' and ischion meaning 'hip joint') is one of the two orders, or basic divisions, of dinosaurs. In 1888, Harry Seeley classified dinosaurs into two orders, based on their hip structure...
n characteristics compared to other dromaeosaurids. For instance, the pubis
Pubis (bone)
In vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
is aligned vertically and has a large pubic boot (a wide expansion at the end), unlike most other dromaeosaurids, where there is a much smaller boot, if any, and the pubis points backwards in the same direction as the ischium (a condition called opisthopuby, which is also seen in the unrelated therizinosaur
Therizinosaur
Therizinosaurs are theropod dinosaurs belonging to the clade Therizinosauria. Therizinosaur fossils have been found in Early through Late Cretaceous deposits in Mongolia, the People's Republic of China and Western North America...
s and ornithischia
Ornithischia
Ornithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
ns, as well as in birds).
The above differences and others have led to suggestions that Achillobator represents a paleontological chimera
Chimera (paleontology)
In paleontology, a chimera is a fossil which was reconstructed with elements coming from more than a single species of animal. A now classic example of chimera is Protoavis.-List of paleontological chimeras:*Brontosaurus*Lametasaurus...
. However, other studies have attempted to refute this, noting that many pieces were found semi-articulated, and that Achillobator routinely comes out as a dromaeosaurid in cladistic analyses, even taking into account the differences.