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''Zaraapelta'' is an
extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial no ...
of herbivorous
ankylosaurid 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–Pa ...
thyreophoran Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of body ...
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23  million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is ...
from the
Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', t ...
of
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million ...
. The
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( ...
is ''Zaraapelta nomadis'', named and described by Arbour ''et al'' in 2014. ''Zaraapelta'' is known from a single skull from the
Barun Goyot Formation The Barun Goyot Formation (also known as Baruungoyot Formation or West Goyot Formation) is a geological formation dating to the Late Cretaceous Period. It is located within and is widely represented in the Gobi Desert Basin, in the Ömnögovi Pro ...
. It was found to be closest to ''
Tarchia ''Tarchia'' (meaning "brainy one") is a genus of herbivorous ankylosaurid dinosaur from the late Cretaceous of Mongolia. Discovery and naming In 1970, a Polish-Mongolian expedition discovered an ankylosaurian skull near Khulsan. In 1977, Ter ...
'' in the
phylogenetic analysis In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
within its description.


Discovery and naming

In 2000, Robert Gabbard, member of a team headed by Philip John Currie, found an ankylosaur skull in the
Gobi Desert The Gobi Desert ( Chinese: 戈壁 (沙漠), Mongolian: Говь (ᠭᠣᠪᠢ)) () is a large desert or brushland region in East Asia, and is the sixth largest desert in the world. Geography The Gobi measures from southwest to northeast ...
near Hermiin Tsav at the Baruungoyot. In 2014, Victoria Megan Arbour named and described the find as the species ''Zaraapelta nomadis'', but at first it remained an invalid ''nomen ex dissertatione''.Arbour, Victoria Megan, 2014, ''Systematics, evolution, and biogeography of the ankylosaurid dinosaurs'' Ph.D thesis, University of Alberta Later that year, however, it was validly named as the type species ''Zaraapelta nomadis'' by Arbour, Currie and, posthumously, the female Mongolian paleontologist Demchig Badamgarav. The generic name is derived from Mongolian ', "hedgehog", in reference to the prickly appearance of ankylosaurs, and the Greek , ', "small shield", a common component of ankylosaurian names in view of their
body armour Body armor, also known as body armour, personal armor or armour, or a suit or coat of armor, is protective clothing designed to absorb or deflect physical attacks. Historically used to protect military personnel, today it is also used by variou ...
. The specific name ' is the
genitive In grammar, the genitive case ( abbreviated ) is the grammatical case that marks a word, usually a noun, as modifying another word, also usually a noun—thus indicating an attributive relationship of one noun to the other noun. A genitive can ...
of the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
', "nomad" and refers to the ''Nomadic Expeditions''
travel agency A travel agency is a private retailer or public service that provides travel and tourism-related services to the general public on behalf of accommodation or travel suppliers to offer different kinds of travelling packages for each destinatio ...
that has organised many palaeontological expeditions to Mongolia. 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 ...
, MPC D-100/1388, was found in a layer of the Barun Goyot Formation, dating from the mid to late
Campanian The Campanian is the fifth of six ages of the Late Cretaceous Epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campani ...
, about seventy-five million years old. It consists of a skull lacking the snout tip. No elements of the lower jaws were discovered. The specimen probably represents a subadult individual.


Description

The preserved skull has, lacking the
praemaxilla 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 mammal has b ...
e, about a length of forty centimetres, indicating that ''Zaraapelta'' was a medium-sized ankylosaurian. ''Zaraapelta'' differs from all other
Ankylosauria Ankylosauria is a group of herbivorous dinosaurs of the order 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 ...
in the possession of a squamosal horn with a very smooth bone texture along the upper cutting edge, abruptly changing into a rough surface at the inner and the outer side; and in the presence of an intricate pattern of a large number of osteoderms behind the eye socket. Beside these
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 ...
, ''Zaraapelta'' differs from its close relative ''
Saichania ''Saichania'' (Mongolian meaning "beautiful one") is a genus of herbivorous ankylosaurid dinosaur from the Late Cretaceous period of Mongolia and China. The first fossils of ''Saichania'' were found in the early 1970s in Mongolia. In 1977 t ...
'' in having a large number of osteoderms in front of the eye socket; by a notch in the rim above the eye socket, causing the two supraorbital osteoderms there to have separate peaks; by the lack of distinct ', head armour tiles, behind the rear of the middle supraorbital; by less protruding osteoderms on the rear edge of the skull roof; and by the rear of the skull and the
occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anter ...
being visible in top view. ''Zaraapelta'' differs from the relative ''
Tarchia ''Tarchia'' (meaning "brainy one") is a genus of herbivorous ankylosaurid dinosaur from the late Cretaceous of Mongolia. Discovery and naming In 1970, a Polish-Mongolian expedition discovered an ankylosaurian skull near Khulsan. In 1977, Ter ...
'' in having a less sideways protruding ' on the prefrontal; in the presence of a(n ossified) scroll-shaped turbinate bone in the nasal cavity, at the underside of the
frontal bone The frontal bone is a bone in the human skull. The bone consists of two portions.''Gray's Anatomy'' (1918) These are the vertically oriented squamous part, and the horizontally oriented orbital part, making up the bony part of the forehead, par ...
; by the lack of distinct ', head armour tiles, behind the rear of the middle supraorbital; and by the fusion of the quadrate with the paroccipital process. The main difference with ''Tarchia'' resided in the unique squamosal horn shape. However, ''Tarchia'' itself has also a unique squamosal horn configuration in that an accessory osteoderm is present in front of it. It might thus in principle be possible that ''Zaraapelta'' simply represents an old ''Tarchia'' individual in which this osteoderm has shifted on top of the squamosal horn, creating the strange double-layered structure. This possibility was rejected by the authors however, because from other ankylosaurian species no comparably large
ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...
changes of the squamosal horn shape are known. The squamosal horn, on the top rear corner of the skull, is robust and pyramid-shaped. There is a sharp cutting edge on top of the horn, bordered by smooth strips; these abruptly change into deeper rugose areas, so that rims are present on both sides. The quadratojugal cheeks horn is large with a concave rear edge. The cheek area between these large horns, behind the eye socket, is filled by flat osteoderms, separated by deep grooves, creating a delicate "dried mud" pattern. The eye socket itself is surrounded by a narrow bone ring. On its rear edge six osteoderms are present, those above rectangular in shape, the lower ones gradually becoming smaller and more triangular. Behind these are seven smaller tiles, roughly square-shaped, in an irregular pattern. The rear of this configuration is formed by a large triangular osteoderm. Just below the squamosal horn and above the cheek horn a row of small bumps is present.


Phylogeny

''Zaraapelta'' was placed in the
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–Pa ...
. A
cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived c ...
analysis recovered it as the
sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A a ...
of ''Tarchia''.


Paleobiology

Arbour pointed out that ''Saichania'', ''Tarchia'' and ''Zaraapelta'' shared the same habitat. She assumed that this relative ankylosaurian abundance in species had been caused by their being the main herbivores in the area, enough crop thus being available to feed three populations, although their relative niches were unclear. The differences in head ornamentation would then have served species recognition. She saw no indications of
sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most an ...
. However, she also assumed that
sexual selection Sexual selection is a mode of natural selection in which members of one biological sex choose mates of the other sex to mate with (intersexual selection), and compete with members of the same sex for access to members of the opposite sex ( ...
had been a factor in the evolution of the typical ''Zaraapelta'' head ornamentation.


See also

* Timeline of ankylosaur research


References

{{Taxonbar, from=Q18435455 Ankylosaurids Late Cretaceous dinosaurs of Asia Maastrichtian life Fossils of Mongolia Barun Goyot Formation Fossil taxa described in 2014 Taxa named by Philip J. Currie Ornithischian genera