Talarurus

Talarurus Temporal range: Late Cretaceous, 90 Ma PreЄ Є O S D C P T J K Pg N ↓
Front view of skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Ornithischia
Family:	†Ankylosauridae
Subfamily:	†Ankylosaurinae
Genus:	†Talarurus Maleev, 1952
Species:	† T. plicatospineus
Binomial name
Talarurus plicatospineus Maleev, 1952

Talarurus (/ˌtæləˈrʊərəs/ TAL-ə-ROOR-əs) is an extinct genus of ankylosaurid dinosaur that lived approximately 90 million years ago during the latter part of the Cretaceous Period in what is now Mongolia. Talarurus was a hippopotamus-sized, heavily built, ground-dwelling, quadrupedal herbivore, that could grow up to an estimated 6 m (19.7 ft) long. Like other ankylosaurs it had heavy armour and a club on its tail. Along with Tsagantegia, Talarurus is one of the oldest known ankylosaurines from Asia and one of the better-known ankylosaurs from Mongolia.

Etymology

The genus name Talarurus means "basket tail", and is derived from the Greek word talaros (τάλαρος) meaning "wicker basket", and the Latinized form "urus" of the Greek word οὐρά, oura, meaning "tail". The genus name is a reference to the club end of the tail which bears resemblance to a wicker basket, and the length of the tail which consists of interlaced bony struts, reminiscent of the weave that is employed when making wicker baskets. The type and only valid species known today is Talarurus plicatospineus. The specific name "plicatospineus" is derived from the Latin words plicatus which means "folded" and spineus which means "thorny". This is a reference to the corrugated spines which are present on the surface of its armor plates.^[1][2] Talarurus was described and named by Russian paleontologist Evgeny Maleev in 1952.^[3]

Discovery and age

The skull of the PIN mount; only the top is authentic

Talarurus remains have been discovered in the southeastern parts of the Gobi Desert in what is now Mongolia. The type specimen PIN 557-91 was discovered in 1948 by a joint Soviet-Mongolian Paleontological Expedition, and recovered from sandy, red calcareous claystone at the Bayn Shire locality of the Bayan Shireh Formation. Sediments found in this rock formation, are thought to date from the late Turonian or early Santonian stage of the Late Cretaceous period, about 90 to 85 million years ago. The age of these sediments has been determined by trying to find comparable remains in layers elsewhere. Specimen PIN 557, the original holotype designated by Maleev, included a fragmentary skull with the posterior part of the skull roof, including the occipital region and the basicranium, numerous vertebrae, several ribs, a scapulocoracoid, a humerus, a radius, an ulna, a nearly complete manus, a partial ilium, an ischium, a femur, a tibia, a fibula, a nearly complete pes, and assorted armor and scutes. In fact it consisted of fragmentary remains of six individuals discovered at the site. Elements of all these specimens were combined into a skeletal mount exhibited at the Moscow Palaeontological Institute. The skull was restored after the model of Pinacosaurus. In some respects the mount is outdated: e.g. it shows the forelimbs as strongly splayed. Elements were also incorrectly combined: segments of the halfrings protecting the neck were added to the side of the rump, on the ribcage, and the composite foot was restored with four toes, though likely only three were present.^[4] In 1977, Teresa Maryańska chose PIN 557-91, the rear of the skull, as the lectotype.^[5]

Skeleton

Specimen PIN 3780/1 was collected from terrestrial sediments at the Bayshin-Tsav locality of the Bayan Shireh Formation, by a joint Soviet-Mongolian Paleontological Expedition in 1975 and is now reposited at the Paleontological Institute, Russian Academy of Sciences, in Moscow.^[6] This material was assigned to Talarurus and is also considered to date from the Turonian stage of the Cretaceous. This specimen consists of the top of a skull and a fragmentary skeleton.

Since 2006, in the context of the Korea-Mongolia Joint International Dinosaur Project, numerous additional specimens have been referred to Talarurus, found at the Bayan Shireh and at Shine Us Khudag. These in 2014 were still undescribed.^[4]

Talarurus is now known from at least a dozen individual specimens, from various localities at the Bayan Shireh Formation. Specimen PEN AN SSR 557 consists of a dorsal vertebra with an attached rib, and a dermal scute. Another specimen referred to this genus from the Bayshin-Tsav locality is composed of an (undescribed) incomplete skull with cranial roof, occipital part and braincase. A second undescribed specimen, collected at the Baga Tarjach locality, consists of a fragment of a maxilla with eight teeth.

In 1977, Maryańska renamed Syrmosaurus disparoserratus (Maleev, 1952) into a second species: Talarurus disparoserratus.^[5] In 1987, this was made the separate genus Maleevus.^[7]

Description

Tail

The skull of Talarurus measured approximately 24 centimetres (9.4 in) in length by approximately 22 centimetres (8.7 in) wide, and its body length has been estimated at 4 to 6 metres (13 to 20 ft). In 2010, Gregory S. Paul estimated the length at five metres, the weight at two tonnes.^[8]

Talarurus was described by Malejev as having had five fingers on the hand and four toes on the foot. However, a four-toed foot was not found in articulation; the mounted foot is a composite and three is the more likely number as all other known ankylosaurids show three toes; earlier reports that Pinacosaurus also possessed four are incorrect.^[4] Another presumed diagnostic characteristics: that the osteoderms had a furrowed ornamentation, making for a specially formidable armour, with each plate adorned with additional pleated spines, was also based on a misunderstanding. These were segments of the halfrings protecting the neck, with their typical low keels. The mount has the further peculiarity that it shows Talarurus as built like a hippopotamus, with a barrel-shaped thorax, not with the characteristic ankylosaurid low and wide body type. This was caused by an incorrect positioning of the ribs as if they were appending instead of sticking out sideways; this mistake also prevented a mounting of the wide upper pelvic elements.

Authentic traits of Talarurus include dorsal vertebrae with transversely broad hypapophyses, swellings of the lower front centrum rims. There is a sacral rod of four rear dorsal vertebrae, connected to the true sacrum consisting of four sacrals and a caudo-sacral. The tail club of the mount is rather small.

Distinguishing anatomical features

The skull of the mount shows the V-shaped zone between the eyes, the only known autapomorphy of Talarurus

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism.

Diagnoses provided by Malejev in 1956 and Tumanova in 1987, were of limited utility as they largely listed traits shared with many other ankylosaurids.^[4]

According to Coombs and Maryańska (1990), Talarurus can be distinguished based on the following characteristics:^[9]

• The skull is relatively long and narrow
• The occipital condyle is partially visible when observed from above, meaning the back of the head is not strongly inclined to the rear
• The maxillary teeth, of the upper jaw, have swollen bases cut on the labial, outer, side by W-shaped furrows
• The presence of a pentadactyl manus, and a tetradactyl pes, thus of five fingers in the hand and four toes in the foot
• The postcranial bones, those behind the skull, are wide relative to their length
• The armor plates are ribbed
• The tail club is relatively small

Arbour noted in 2014 that the foot in fact had three toes. She established a single autapomorphy: on the frontals, at the middle skull roof, a raised V- shaped region is present. Also she determined that Talarurus differed from all known ankylosaurids with the exception of the American Nodocephalosaurus in the possession of caputegulae, head armour tiles, on the frontals and nasals, that are cone-shaped with a circular base.^[4]

Classification and phylogeny

Talarurus was assigned to the Ankylosauridae by Maleev in its original description in 1952. In 1978, Walter Preston Coombs posited that it was the same dinosaur as Euoplocephalus although subsequent study did not support this assertion.^[10] Maryańska in 1977 demonstrated that it differed from Euoplocephalus, citing the shape of the skull, the morphology of the palate, and the presence of four pedal digits.^[5]

Ankylosaurid phylogenetic relations are hard to determine because many taxa are only partially known, the exact armour configuration has rarely been preserved, fused osteoderms obscure many details of the skull and the Ankylosauridae are conservative in their postcranial skeleton, showing little variation in their vertebrae, pelves and limbs. Previously it was assumed that as one of the oldest known ankylosaurids, Talarurus possessed some basal characters that are shared with nodosaurids but were later lost in more advanced ankylosaurs, such as the presence of four toes. However, the presumed "primitive" traits proved to be largely artefacts of the initial skeletal restoration. Recent phylogenetic analysis provides evidence for an assignment of Talarurus to the Ankylosaurinae, a derived ankylosaurid group. This can be reconciled with its relatively old geological age by the possibility that the Ankylosauridae as a whole appeared much earlier during the Early Jurassic, which must have been true if they were the sister group of the Nodosauridae in the sense proposed by Coombs in 1978; i.e. if all polacanthines were nodosaurids.

The following cladogram is based on the phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie (2013):^[11]

Vickaryous et al. (2004) note the presence of two distinct ankylosaurid clades during the Late Cretaceous, "one consisting of North American taxa and the other restricted to Asian taxa. The oldest member of the Asian clade...is Talarurus plicatospineus."^[12] However, Arbour in 2014 recovered trees in which Talarurus was more closely related to North-American forms than to Asian ankylosaurids. In some of these Talarurus was the sister species of Nodocephalosaurus.^[4]

Paleoecology

Existing evidence suggests that the habitat that Talarurus lived in were lowland floodplains. It shared its paleoenvironment with carnivorous dromaeosaurids, therizinosaurs, and other ankylosaurians, like Tsagantegia

In the media

Talarurus had a small part in the beginning of the Disney computer-animated film Dinosaur.

See also

• Timeline of ankylosaur research

References