User:Ankylosaur Enthusiast/sandbox2
| Ankylosaur Enthusiast/sandbox2 Temporal range: Late Cretaceous,
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Thyreophora |
| Clade: | †Ankylosauria |
| Family: | †Ankylosauridae |
| Subfamily: | †Ankylosaurinae |
| Genus: | †Tarchia Maryanska, 1977 |
| Type species | |
| †Tarchia kielanae Maryanska, 1977
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| Other species | |
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| Synonyms | |
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History and naming[edit]
In 1970, a Polish-Mongolian Palaeontological Expedition led by Professor Zofia Kielan-Jaworowska was sent to the Baruungoyot Formation (previously known as the 'Lower Nemegt Beds') of the Nemegt Basin of Mongolia. The expedition uncovered numerous specimens of lizards, diplopods, myriapods, tortoises, mammals, and dinosaurs. Among these finds was a partial skull collected from the Khulsan locality. In 1977, Polish palaeontologist Teresa Maryańska published a description of the skull material and named the type species Tarchia kielanae. The generic name is derived from the Mongolian word "tarkhi" (brain) and Latin word "~ia", in reference to its presumed large brain size. The holotype, designated as ZPAL MgD I/111, consists of a skull roof, braincase, and partial occiput.
Prior to the description of T. kielanae, Maleev (1956) named the species Dyoplosaurus giganteus based on a series of caudal vertebrae, metatarsals, phalanges, osteoderms and a partial tail club knob collected from the Nemegt Formation. Maleev attributed it to the genus Dyoplosaurus based on similarities with the free caudal and handle vertebrae. Tumanova (1977) would, however, synonymise Tarchia with “Dyoplosaurus” giganteus, forming the new combination Tarchia gigantea while also retaining T. kielanae as a separate species. Tarchia was used as the generic name, in spite of Dyoplosaurus having priority, because at the time Dyoplosaurus was considered a junior synonym of Euoplocephalus. A review of ankylosaurs from Mongolia published by Tumanova (1987) suggested that T. kielanae could be a synonym of T. gigantea but retained it as a separate species, noting that it was difficult to compare both species due to the fragmentary nature of the holotype of T. kielanae. Coombs and Maryańska (1990) would later recognsie T. kielanae to be a junior synonym of T. gigantea. A fragmentary skeleton (ZPAL MgD I/113) consisting of an incomplete postcranial skeleton preserving skin impressions and in situ osteoderms was referred to T. cf. gigantea in 2013 on the basis of stratigraphy. In 2014, a study published by Arbour et al. revived the name Tarchia kielanae based on a newly recognised autapomorphy, an accessory postorbital ossification with a surrounding furrow, and also deemed the combination T. gigantea to be unnecessary. The authors stated that “Dyoplosaurus” giganteus should be regarded as a nomen dubium as it lacked diagnostic characteristics. In the same publication, the authors noted similarities between the holotypes of Minotaurasaurus and T. kielanae, suggesting the former to be a junior synonym. Penkalski & Tumanova (2016), however, argued that Minotaurasaurus was distinct, noting differences between the two. In addition, the authors established a new species, T. teresae, on material collected from the Nemegt Formation that was previously assigned to “D”. giganteus and Saichania. In 2017, a paper was published detailing the description of the endocast of Talarurus and T. teresae material based on newly reported material collected by the 2007-2008 Korea-Mongolia International Dinosaur Expedition to Mongolia. The new material would, however, be referred to as a new species, T. tumanovae, by Park et al. (2021). A study on a pathology preserved in the type specimen of T. teresae was published in 2023.
Species[edit]
- T. kielanae
The type species T. kielanae is the oldest known species, living during the middle to late Campanian stage of the Upper Cretaceous (ca. ~72-71 Ma.). It was described in 1977 by Teresa Maryańska based on a partial skull. In 2016, Penkalksi and Tumanova referred ZPAL MgD I/114, a partial skull roof and osteoderms, to the species. Its remains have been collected from the Khulsan and Hermiin Tsav II localities of the Baruungoyot Formation. It can be distinguished from other species of Tarchia based on the foramen ovalis and cnn. (common foramen) IX-XI exiting through a single external opening, in addition to two separate exits for cn. XII, and the presence of an accessory postorbital osteoderm fused to the skull roof. The species name honours Professor Zofia Kielan-Jaworowska, the leader of the 1970 expedition that recovered the holotype material.
- T. teresae
T. teresae is the second species to be described and one of the youngest, known from the Hermiin Tsav I and Altan Uul IV localities of the Maastrichtian Nemegt Formation. The species is currently known from two specimens: PIN 3142/250, a skull, mandibles, and undescribed cervical vertebrae, scapula, sacrum, ischia, femur, ribs, and osteoderms; and ZPAL MgD I/43, vertebrae and tail club. Originally, the type specimen was assigned to “D”. giganteus, but then was later referred to Saichania. It was named in 2016 by Penkalski and Tumanova (2016). It differs from other Tarchia species in the lack of fusion of the accessory osteoderm to the skull roof, an unfused quadrate and paroccipital process, a deeply sculptured postfrontal skull roof, and a large, bifurcated opening for cnn. IX-XII.The species name honours Teresa Maryańska, for her work on Mongolian dinosaurs.
- T. tumanovae
The remains of T. tumanovae have been recovered from the same locality as T. teresae and were found in association with a Tarbosaurus fibula. The species was named by Park et al. (2021) and is known only from a skull, a few dorsal vertebrae, sacral vertebrae, caudal vertebrae, dorsal ribs and ilia, a partial ischium, free osteoderms, and a tail club (MPC-D 100/1353). It is unlike T. kielanae and T. teresae in having a moderate-sized basioccipital foramen, a quadrate-quadratojugal region positioned anteriorly (towards the front), a visible interpterygoid vacuity in occipital view, and a quadrate unfused to the exocciptal region. The species name honours Tatiana Tumanova, for her work on Mongolian ankylosaurs.
Description[edit]
Cranium[edit]
Postcrania[edit]
Osteoderms[edit]
he type specimen of T. tumanovae preserves isolated osteoderms which vary in morphology. One such osteoderm is sharply keeled dorsally, polygonal and has a thin wall. The osteoderm has damaged external surfaces, although the medial surface remains well preserved, and has a pitted surface texture. Also persevered are two osteoderms that are sub-circular, flattened dorsoventrally and have a slightly concave ventral surface. Like the previous osteoderm, the two osteoderms possess a rugose external surface and a thin wall. Forming the tail club knob are two major osteoderms and a single minor osteoderm that envelop the distal end of the tail. The major osteoderm is hemispherical, while the minor osteoderm is rhomboidal in shape
Classification[edit]
In its original description, Maryanska (1977) referred Tarchia to the clade Ankylosauridae and hypothesised that North American ankylosaurids may have descended from ankylosaurids similar to Talarurus and Pinacosaurus that migrated from Asia to North America. A 2018 study by Wiermas and Irmis further expanded upon this idea, suggesting that there may have been at least two faunal migrations between Asia and North America, created when sea levels dropped, allowing migrations between the continents via the Beringian Land Bridge during or earlier than the Campanian stage. In support of this, the authors found T. kielanae, and other Asian taxa (Shanxia, Minotaurasaurus), to be sister group to a southern Laramidian clade (Nodocephalosaurus, Akainacephalus). Furthermore, this southern Laramidian/Asian clade is sister to a clade containing all other known Laramidian taxa. However, Park et al. (2019) found both Akainacephalus and Nodocephalosaurus to be basal to Asian taxa such as Tarchia and Talarurus, suggesting that a migration occurred before the Cenomanian stage and that ankylosaurines dispersed at least twice from Asia to Western North America.
Paleontologist James Kirklind, in 1998, used a phylogenetic analysis to test the interrelationships of ankylosaurs and found Tarchia to be sister taxon to Saichainia. Numerous studies would find support for this relationship, including Arbour & Currie (2015), Penkalski & Tumanova (2016) and Park et al. (2021), who found the sister taxa to be deeply nested within a group containing other Asian taxa such as Minotaurasaurus and Zarapelta. This Asian clade is sister to the predominantly North American clade Ankylosaurini.
The following cladogram is based on a 2015 phylogenetic analysis of the Ankylosaurinae conducted by Arbour and Currie:
A limited phylogenetic analysis conducted in the 2016 redescription of Tarchia, focusing on the interrelationships between Tarchia, Saichania, and Minotaurasaurus, is reproduced below.
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Palaeobiology[edit]
Brain and senses[edit]
A 2017 study by Ariana Paulina-Carabajal and colleagues analysed the endocranium of T. tumanovae. They found that it, like other ankylosaurs, had a short forebrain with short olfactory tracts and small olfactory bulbs, cephalic and pontine flexures that are poorly marked, and a large pituitary that protrudes downwards. The authors also noted the presence of a floccular recess, a feature not seen in nodosaurids but in some stegosaurs and other ankylosaurids such as Talarurus and Euoplocephalus. This feature may have paleobiological implications, such as gaze stabilization during locomotion although it remains unknown. In addition, the inner ear has robust and low semicircular canals with a long lagena. This correlates to the ability to hear a greater range of sound frequencies in the lower range. Schade et al. (2022) proposed that the combination of features could be associated with more active defensive behaviours, involving digging and the ability to target their tail clubs.
Growth[edit]
The holotype skull of T. tumanovae shows the squamosal horns divided into the external layer and the proper, with the base of the external dermal layer having an irregular ventral margin which might be indicative of resorption. Arbour et al. (2014) originally suggested that the external layer and the underlying squamosal horn propers would fuse together into a single, large horn characterised by having a keel and smooth texture during ontogeny. However, Penkalski & Tumanova (2016) argued that instead the smooth textures signifies the beginning of resorption and the external layer of the squamosal horn disappears entirely in skeletally mature individuals. This implies that ankylosaurines underwent extreme remodelling of the squamosal horns during growth.
In 2019, a Canadian Society of Vertebrate Palaeontology abstract book briefly mentioned the discovery of hatchling material from the Hermiin Tsav locality of the Nemegt Formation. The authors considered that the material could either represent Tarchia or Saichania, although a confident taxonomic identification remains difficult as the juveniles are represented by postcranial material. At least two individuals were preserved and were found in close association with each other, suggesting that either this represents multiple eggs hatching within the same nest at the same time, or eggs that hatched at almost the same time but from multiple nests.
Feeding[edit]
Tarchia was a selective feeder, on the basis of its anteriorly protruded shovel-shaped muzzle. Sometime during the middle Campanian to lower Maastrichtian stages, there was a shift from bulk feeding to selective feeding in Mongolian ankylosaurids. Park et al. (2021) suggested that this may have been caused either by the change in climate from semi-arid and arid to humid, or competition with saurolophine hadrosaurids that immigrated from North America to Central Asia sometime during the Campanian stage.
It has been thought that Tarchia, and other Asian ankylosaurs, retained the basal condition of feeding without biphasal chewing, with their jaw movement being restricted to simple movements of the jaws in a vertical plane (orthal pulping). This likely relates to the consumption of different types of vegetation, compared to non-Asian Cretaceous ankylosaurs, such as succulent plants as they did not require complex chewing. In addition, they may have relied on hindgut fermentation more than oral processing to digest plant matter. Dental wear shows that these ankylosaurs, including Tarchia, dealt with more grit in their environment compared to ankylosaurs living in tropical to subtropical climates.
Paleopathology[edit]
A skull assigned to T. teresae (PIN 3142/250) exhibits an open hole on the dorsal (upper) surface of the right orbit. Additionally, CT scans have revealed a large, bony mass with an encompassing shell (an osteoma) in the right nasal cavity and a dozen smaller lesions within the left nasal cavity. It has been suggested that the open hole above the right orbit was likely caused by a traumatically induced puncture, either from a failed predation attempt from a tyrannosaur such as Tarbosaurus, as the anterior-most premaxillary teeth are of the right shape and size, or intraspecific combat. The osteoma was probably a result of new bone growth to heal a wound or as a response to infection, while the smaller lesions could either be artefacts of fossilization or calcified inflammatory debris. These lesions could have been chronic, lasting for an extensive period of time, and may have potentially been fatal. It is unknown if these pathologies are interrelated.
Park et al. (2022) reported evidence of pathologies in the holotype specimen of T. tumanovae. Both sides of the first dorsosacral ribs in the anterolateral part of the pelvic region show signs of fracture healing. The authors noted injuries localized to the pelvic region were likely the result of intraspecific combat. Furthermore, an ossified tendon of the tail club shows signs of healing and the tail club knob is asymmetric, with the left major knob osteoderm being shorter in mediolateral width than the right major knob osteoderm. This may relate to side preferences in tail use and further suggests that ankylosaurines used their tail clubs for agonistic behaviour.
Paleoenvironment[edit]
Baruungoyot Formation[edit]
The type species, T. kielanae, is known from the Khulsan and Hermiin Tsav II localities at the Baruungoyot Formation. The formation overlies the Djadokhta Formation and consists of a series of red beds, reddish-brown sandy claystones, light-brown siltstones and light-brown to yellowish-orange fine-grained sandstones. The upper Baruungoyot Formation and lower Nemegt Formation overlapped in time, and may have been a singular ecosystem. The sediments of the formation were deposited in various conditions, with the lower part consisting of alternating dune deposits and lakes that existed in interdune areas, while the upper part consisted of sediments that were deposited over a takyr-like area that was flooded at irregular intervals. Overall, the formation had an arid to semi-arid climate with significant rainfall. The formation dates to the middle to late Campanian stage of the Late Cretaceous period, ca. ~72-71 Ma. Arbour and colleagues (2014) noted that there was a great diversity of ankylosaurids in the Baruungoyot Formation and suggested that this may have either been due to the lack of direct competition for food resources with large herbivores, or through sexual selection. Although, the authors also noted that their relative niches were unclear and there is little indications of sexual dimorphism.
The Baruungoyot Formation has yielded specimens of the alvarezsaurids Ceratonykus, Khulsanurus, Ondogurvel and Parvicursor; the ceratopsians Bagaceratops and Breviceratops; the dromaeosaurids Kuru, Shri and an indeterminate velociraptorine; the halszkaraptorines Hulsanpes and Natovenator the pachycephalosaur Tylocephale; the oviraptorosaurs Conchoraptor, Heyuannia and Nemegtomaia; the ankylosaurids Saichania, Zaraapelta and an indeterminate ankylosaurid; and the sauropod Quaesitosaurus.
Nemegt Formation[edit]
Specimens attributable to T. teresae and T. tumanovae have been recovered from the Hermiin Tsav I and Altan Uul IV localities at the Nemegt Formation. The formation consists of a variety of sediments such as such as reddish-brown to grey-green mudstones, grey-to-brown sandstones, light grey to-tan coloured siltstones and granular beds. Stream and river channels, mudflats, and shallow lakes were present in the formation as indicated by the rock facies, although droughts periodically occurred as indicated by the presence of caliche deposits. Woodlands were also present in the Nemegt Formation and were represented by large, enclosed, Araucaria forests, as evidenced by the numerous petrified wood found in the outcrops of the formation. The formation had mean annual temperatures of 7.6 and 8.7 °C, and was influenced by monsoons with cold, dry winters and hot summers. It has been said that the environment was similar to the Okavango Delta of present-day Botswana. Due to the discontinuity of exposures, absence of microfossil biostratigraphy, and absence of datable volcanic rock facies, the precise age of the Nemegt Formation cannot be attained through radiometric dating. Although, it has been suggested to be of late Campanian to early Maastrichtian age based on the fauna present in the fossil record.
The Nemegt Formation has yielded specimens of the ankylosaurid Saichania; the alvarezsaurids Mononykus and Nemegtonykus; the dromaeosaurid Adasaurus; the hadrosaurids Saurolophus angustirostris and Barsboldia; the ornithomimosaurs Anserimimus, Deinocheirus and Gallimimus; the oviraptorosaurians Avimimus, Conchoraptor, Elmisaurus, Gobiraptor, Nemegtomaia, Oksoko and Rinchenia; the pachycephalosaurs Homalocephale and Prenocephale; the sauropods Nemegtosaurus and Opisthocoelicaudia; the therizinosaur Therizinosaurus; the troodontids Borgovia, Tochisaurus and Zanabazar; the tyrannosaurids Alioramus and Tarbosaurus; and an indeterminate azhdarchid.
See also[edit]
References[edit]
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