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{{Short description|Extinct genus of dinosaurs}}
{{Short description|Extinct genus of dinosaurs}}
{{speciesbox
{{speciesbox
| fossil_range = [[Late Cretaceous]], {{fossilrange|75|70}}
| fossil_range = [[Late Cretaceous]], {{fossilrange|75|71}}
| image = Minotaurasaurus skull cast.jpg
| image = Minotaurasaurus skull cast.jpg
| image_caption = Skull of ''Minotaurasaurus''
| image_caption = Cast of the holotype skull of ''Minotaurasaurus''.
| display_parents = 3
| display_parents = 3
| genus = Minotaurasaurus
| genus = Minotaurasaurus
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| authority = Miles & Miles, 2009
| authority = Miles & Miles, 2009
}}
}}
'''''Minotaurasaurus''''' (meaning “[[Minos]]'-bull reptile”) is a [[monospecific]] [[genus]] of [[ankylosaurid]] [[dinosaur]] that lived in [[Mongolia]] during the [[Late Cretaceous]] (late [[Campanian]] stage, ~75-71 Ma) in what is now the [[Djadochta Formation]]. The type and only species, '''''Minotaurasaurus ramachandrani''''', is known from two [[skulls]], a [[cervical vertebra]] and a cervical half ring. It was named and described in [[2009 in paleontology|2009]] by Clifford Miles and Clark Miles. The first fossils of ''Minotaurasaurus'' were illegally exported out of Mongolia.{{Citation needed|date=January 2023}}It has been suggested to be a synonym of ''[[Tarchia]]'' but more recent publications consider it as a distinct genus.


''Minotaurasaurus'' was a medium-sized ankylosaurid, with an estimated length of 4.2 metres (13.8 feet), although it may have reached larger sizes as the type specimen represents an immature individual. Although not a lot of postcranial material is known, it would have had a tail club that may have been used for protection against predators or interspecific combat and would have been covered in protective [[osteoderms]]. It would have also had a barrel-like body, and short, robust limbs based on close relatives.
'''''Minotaurasaurus''''' (meaning “Man-bull reptile”) is a monospecific genus of [[ankylosauridae|ankylosaurid]] [[dinosaur]] that lived in [[Mongolia]] during the [[Late Cretaceous]] ([[Campanian]], ~75-71 Ma) in what is now the [[Djadochta Formation]].


==Discovery and Naming==
==Discovery and Naming==
[[File:Cretaceous-aged dinosaur fossil localities of Mongolia.PNG|250px|thumb|left|Fossil localities in [[Mongolia]]. ''Minotaurasaurus'' fossils have been collected at '''Uhkaa Tolgod''' (area B)]]
[[File:Tondo_Minotaur_London_E4_MAN.jpg|200px|thumb|left|[[Minotaur]], mythological namesake of the species.]]
In 2003, a skull of an ankylosaurid was purchased for US$10,000 by the private fossil collector and neuroscientist [[Vilayanur S. Ramachandran]] while accompanied by Clifford Miles at the [[Tucson Gem & Mineral Show|Tucson Gem, Mineral and Fossil Showcase]], [[Arizona]]. The skull was put on display by Robert Gaston for the fossil poacher Hollis Butts, who Ramachandran purchased it from{{Citation needed|date=January 2023}}. The stratigraphic position was stated as being from the [[Gobi Desert]] of either [[Mongolia]] or [[China]] due to the provenance being unknown at the time. In 2006, Clifford Miles and his brother Clark Miles attempted to publish the description of the skull in a Polish Journal but was promptly rejected as the specimen was seemingly obtained illegally from Mongolia. Two years later, the authors stated that the specimen had come from the [[Barun Goyot Formation]] but later stated that they could not confirm its origin. The skull would later be described and named in [[2009_in_paleontology|2009]]. The publication was later criticised by palaeontologists such as [[Mark Norell]], [[Phillip J. Currie]] and [[Bolortsetseg Minjin]] due to the questionable origins of the specimen.<ref name="Dalton2009">{{Cite news|author=Rex Dalton|title=Paper sparks fossil fury|url=https://www.nature.com/articles/news.2009.60|work=Nature|date=2 February 2009 |access-date=27 June 2011}}</ref> The [[holotype]] specimen, '''INBR21004''', consists of a skull with [[mandible|lower jaws]] and predentary. The type specimen is currently housed at the [[Victor Valley Museum]] in [[Apple Valley, California]].<ref name="Miles2009">{{cite journal |last1=Miles |first1=Clifford A. |last2=Miles |first2=Clark J. |year=2009 |title=Skull of ''Minotaurasaurus ramachandrani'', a new Cretaceous ankylosaur from the Gobi Desert |url=https://www.jurassic-world.com/wp-content/uploads/2015/02/pdf_65.pdf |journal=Current Science |volume=96 |issue=1 |pages=65–70}}</ref>
The holotype, '''INBR21004''', was obtained by the private fossil collector [[Vilayanur S. Ramachandran]] for $10,000 from the fossil poacher Hollis Butts at the Tucson Gem, Mineral and Fossil Showcase in Arizona.<ref name=naturenews2009>[http://www.nature.com/news/2009/090202/full/news.2009.60.html?s=news_rss naturenews, February 2, 2009]</ref> The specimen consists of a skull with complete lower jaws and predentary.<ref name=MM09>{{cite journal |last1=Miles |first1=Clifford A. |last2=Miles |first2=Clark J. |year=2009 |title= Skull of ''Minotaurasaurus ramachandrani'', a new Cretaceous ankylosaur from the Gobi Desert |journal=Current Science|volume= 96 |issue=1 |pages=65–70|url= http://www.dinosaures-web.com/sites/default/files/publications/65.pdf%7D%7D}}</ref> The provenance of the holotype became controversial amongst palaeontologists after the paper describing the specimen was published as it was illegally taken from the [[Gobi Desert]].<ref name=naturenews2009/> V. S. Ramachandran says that he would be happy to repatriate the fossil to the appropriate nation, if someone shows him "evidence it was exported without permit".<ref name=naturenews2009/> The specimen itself is currently housed at the Victor Valley Museum in [[Apple Valley, California]].<ref name=MM09/><ref name=naturenews2009/>


The generic name ''Minotaurasaurus'' is derived from the mythical creature the [[Minotaur]], that had a body of a man and the head of a bull.<ref name=MM09/> This is in reference to the bull-like appearance of the holotype skull.<ref name=MM09/> The specific name, ''ramachandrani'', honours V. S. Ramachandran as they made sure that the holotype was described and made available to science.<ref name=MM09/>
The [[genus|generic]] name, ''Minotaurasaurus'', is derived from the [[Minotaur]] and the [[Ancient Greek|Greek]] word "''sauros''" (lizard), in reference to the bull-like appearance of the holotype skull. The [[species|specific]] name, ''ramachandrani'', honours V. S. Ramachandran, who purchased the type specimen.<ref name="Miles2009"/>


In 2013, a [[Society of Vertebrate Paleontology]] abstract book mentioned the discovery of a second specimen of ''Minotaurasaurus'' (MAE 98 179) from the Uhkaa Tolgod locality of the late Campanian [[Djadochta Formation]] in the [[Nemegt Basin]]. The specimen consists of a skull, [[Axis (anatomy)|axis]] and first cervical half-ring, and it is part of the collection of the [[Mongolian Academy of Sciences]]. MAE 98 179 was reported as having insect burrows that continues into a pattern which is only seen in [[Late Cretaceous]] Gobi deposits.<ref name="Alicea2013">{{Cite journal|last1=Alicea|first1=Justy|last2=Loewen|first2=Mark|date=2013|title=New ''Minotaurasaurus'' material from the Djodokta Formation establishes new taxonomic and stratigraphic criteria for the taxon|url=https://vertpaleo.org/wp-content/uploads/2021/03/SVP-2013-merged-book-10-15-2013.pdf|journal=Journal of Vertebrate Paleontology|volume=33|pages=76}}</ref> Penkalski & Tumanova (2016) would later describe the specimen, which was used to establish the [[Stratigraphy|stratigraphic position]] of the type specimen and the validity of the taxon, as before it was suggested by Arbour et al. (2014) and Arbour & Currie (2015) to be from the Barun Goyot Formation and a junior synonym of ''[[Tarchia|Tarchia kielanae]]''.<ref name=Penkalski2016>{{cite journal|last1=Penkalski|first1=P.|last2=Tumanova|first2=T.|date=2017|title=The cranial morphology and taxonomic status of Tarchia (Dinosauria: Ankylosauridae) from the Upper Cretaceous of Mongolia|journal=Cretaceous Research|volume=70|pages= 117–12|doi=10.1016/j.cretres.2016.10.004|bibcode=2017CrRes..70..117P }}</ref><ref name="Arbour2014II">{{cite journal|last1=Arbour|first1=V.M.|last2=Currie|first2=P.J.|last3=Badamgarav|first3=D.|year=2014|title=The ankylosaurid dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia|journal=Zoological Journal of the Linnean Society|volume=172|issue=3|pages=631–652|doi=10.1111/zoj.12185}}</ref><ref name="Arbour2015">{{cite journal|author1=Arbour, V. M. |author2=Currie, P. J. |year=2015|title=Systematics, phylogeny and palaeobiogeography of the ankylosaurid dinosaurs|journal=Journal of Systematic Palaeontology|volume=14 |issue=5 |pages=1–60|doi=10.1080/14772019.2015.1059985|bibcode=2016JSPal..14..385A |s2cid=214625754 }}</ref> Its validity was also tested by Arbour & Currie (2012) by using a retrodeformation and finite element analysis, which found that many of its diagnostic features were likely not caused by deformation.<ref>{{Cite journal | last1 = Arbour | first1 = V. M. | last2 = Currie | first2 = P. J. | doi = 10.1371/journal.pone.0039323 | editor1-last = Dodson | editor1-first = Peter | title = Analyzing Taphonomic Deformation of Ankylosaur Skulls Using Retrodeformation and Finite Element Analysis | journal = PLOS ONE | volume = 7 | issue = 6 | pages = e39323 | year = 2012 | pmid = 22761763| pmc = 3382236| doi-access = free | bibcode = 2012PLoSO...739323A }}</ref>
In 2016, a second specimen, ''MAE 98 179'', consisting of a skull, axis, and first cervical half-ring was assigned to ''Minotaurasaurus'' from the [[Djadochta Formation]] at Ukhaa Tolgod locality, establishing the provenance of this taxon.<ref name=Tarchia/>


==Description==
==Description==
===Size and distinguishing traits===
The holotype skull measures 30 centimetres (7.9 inches) long and represents an individual with a total length of 4.2 metres (13.8 feet), although it may have reached larger sizes as the holotype specimen probably represents an immature individual based on the unfused osteoderms on the skull.<ref name=MM09/>
[[File:Minotaurasaurus Skull.png|thumb|right|Diagram of the holotype skull]]
Miles & Miles (2009) gave ''Minotaurasaurus'' an estimated length of at least 4.2 metres (13.8 feet), although it may have attained larger sizes as the type specimen, and only known specimen at the time, represents an immature individual based on the unfused osteoderms.<ref name="Miles2009"/>


Penkalski & Tumanova (2016) established numerous distinguishing traits of ''Minotaurasaurus''. The paroccipital processes are not present laterally to the squamosal horns due to presence of a small and dorsoventrally shallow [[Occipital bone|occiput]]. The [[skull roof]] possessing an unfused occiput. Basioccipital foramen that are either small or absent. Highly sculptured squamosal horns that are dorsoventrally narrow and cylindrical in shape. Non prominent nuchal caputegulae that angle caudolaterally. The presence of two distinct supraorbital apices. Frontal caputegulae that aren't arranged at right angles but with nasofrontal caputegulae that are elongated transversely and are ridge-like. The presence of a deep notch in the [[Lacrimal bone|lacrimal]]. The presence of two pairs of internarial osteoderms, unlike the presence of a single osteoderm as in ''Tarchia'' and ''Saichania''. An overall small skull that is broad. A more horizontal [[Pterygoid bone|pterygoid]] body. A mandibular osteoderm that extends towards the front end of the tooth row. Other distinguishing traits include the occiput being more visible in dorsal view, an [[occipital condyle]] that is protrudes less towards the underside in caudal view and a skull that is proportionally lower and wider than that of ''Tarchia''.<ref name=Penkalski2016/>
[[File:Minotaurasaurus BW.jpg|thumb|left|Restoration]]
Although no postcranial material belonging to ''Minotaurasaurus'' has been recovered, besides a cervical half-ring, it would have had a tail club that may have been used for intraspecific or interspecific combat, numerous osteoderms running across its body, a barrel-like body, and short, robust limbs based on close relatives. Its skull is ornamented with pyramid-shaped osteoderms and is roughly bi-symmetrically arranged on the skull.<ref name=MM09/> The squamosal horns form the widest point of the skull roof which are more gracile and tapering than any other ankylosaurid.<ref name=MM09/> The skull also shows a blend of characters seen in other ankylosaurids like the presence of a quadratojugal horn. <ref name=MM09/> The braincase has features that are more primitive than those of other ankylosaurids from the Gobi Desert. <ref name=MM09/> The bilateral symmetry and lack of deformation of both the left and right jugal horns show that the jugal horns thrust more laterally than ventrally, a feature not seen in other ankylosaurs such as [[Tarchia]] and [[Saichania]].<ref name=MM09/> The teeth are leaf-shaped and bear vertical striations dividing the crown surface into eight cusps.<ref name=MM09/> Some of the teeth show apical wear, which is unusual as ankylosaurids typically have wear on the crown face. <ref name=MM09/>


==Classification==
===Skull===
[[File:Ankylosaurin skulls.jpg|left|thumb|Skull of ''Minotaurasaurus'' (far right) compared to other ankylosaurids]]
A 2014 study by [[Victoria Arbour]], [[Philip J. Currie|Philip Currie]] and Demchig Badamgarav suggested that ''Minotaurasaurus'' was probably a junior synonym of [[Tarchia]], and the holotype was from the [[Barun Goyot Formation]].<ref name=A14>{{cite journal |last=Arbour |first=Victoria M. |author2=Currie, Philip J. |author3=Badamgarav, Demchig |year=2014 |title=The ankylosaurid dinosaurs of the Upper Cretaceous Baruungoyot and Nemegt formations of Mongolia |journal=Zoological Journal of the Linnean Society|volume=172 |issue=3 |pages=631–652 |doi=10.1111/zoj.12185}}</ref> However, a 2016 paper Paul Penkalski and Tatiana Tumanova redescribed the cranial anatomy of ''Tarchia'' and concluded that ''Minotaurasaurus'' was a valid taxon.<ref name=Tarchia>{{cite journal|last1=Penkalski|first1=P.|last2=Tumanova|first2=T.|date=2017|title=The cranial morphology and taxonomic status of Tarchia (Dinosauria: Ankylosauridae) from the Upper Cretaceous of Mongolia|journal=Cretaceous Research|volume=70|pages= 117–12|doi=10.1016/j.cretres.2016.10.004}}</ref>
The holotype skull measures 30 centimetres (11.8 inches) long and has a width of 43 centimetres (17 inches). Excluding the squamosal horns, the skull is longer than wide. The [[skull roof]] has its widest point formed by the squamosal horns. Unlike other ankylosaurids, the squamosal horns are more gracile and tapering. Pyramid-shaped caputegulae cover most of the surface of the skull, with the exception of an area of the skull roof that is near the [[Orbit (anatomy)|orbits]]. The caputegulae are arranged roughly bi-symmetrically on the skull, with two sharp-keeled caputegulae projecting laterally above the orbits and similar caputegulae being present near the prefrontal. Partially fused to unfused caputegulae are present on parts of the skull.<ref name="Miles2009"/> Present near the squamosal horn is a furrow, or unfused caputegulum, that is also seen in ''Tarchia kielanae''. The furrow is an artefact of the postorbital osteoderm being within the postorbital fossa. However, unlike ''Tarchia'', the supraoccipital is co-ossified to the [[Parietal bone|parietals]].<ref name=Penkalski2016/> The skull's orbit is tear drop-shaped with a tapered end that points towards the front. The osteoderms of the narial region create a flared look due to how large and ornamented they are, and project towards the front and sides. Present in the narial region are three apertures and the external nasal cavity, which is bound by a single osteoderm. The surface of the premaxillary beak is covered partially by secondary dermal ossifications. An inverted, triangular osteoderm is coossified to the [[premaxilla]] along the ventral margin of the narial opening. A sharp premaxillary beak is present as a result of the palatal portions of the premaxillae changing shape from the front end to the back end. Unlike most ankylosaurids, the vomer extends below the maxillary tooth crowns. All teeth are leaf-shaped. There are a total of 17 teeth and alveoli in the left maxilla and 16 in the right maxilla. The maxillary teeth are up to 25% larger than the dentary teeth and have crowns that are variable.<ref name="Miles2009"/>
[[File:Tarchia gigantea skull front 4.JPG|thumb|upright|Front view of the holotype of Tarchia teresae, which was a close relative of Minotaurasaurus.]]

A limited phylogenetic analysis conducted in the 2016 redescription of ''Tarchia'', focusing on the interrelationships between ''Tarchia'', ''Saichania'', and ''Minotaurasaurus'', is reproduced below.<ref name=Tarchia/>
The [[epipterygoid]], a small, triangular structure, separates the pterygoid from the [[maxilla]]. Instead of being vertical or even slightly overturned as seen in most ankylosaurids, the main body of the pterygoids is near horizontal which, as a result, makes the interpterygoid vacuity in palatal view. The occipital condyle lacks a neck and is heart-shaped. The occiput is low and rectangular in shape. The paroccipital processes fall well short of the medial edge of the squamosal horn. Both the basisphenoid and basioccipital are fused together, with the sutural area being expanded as a ridge. This ridge marks the insertion for the rectus capitis and longus capitis muscles. Both the left and right [[jugal]] horns thrust more towards the sides than towards the underside. Towards the sides of the tooth row is a broad maxillary shelf that extends beneath the middle of the orbit. A long, narrow [[osteoderm]] is partially fused along each side of the mandible but does not extend dorsally onto the lateral surface. The tooth row is positioned along the margins of the [[dentary]]. The ventral half of the [[mandible]] has a rough texture on the lateral surface, while the dorsal half of the mandible has a smooth texture. The position of the cheeks on the lower jaws is marked by the boundary between the smooth and the textured surfaces during occlusion as it is opposite to the lateral edge of the maxillary shelf. The coronoid process is small and low, and is present towards the front of the base of the process. The [[predentary]] is subtriangular in cross-section and bears numerous nutrient foramina to serve the [[Beak#Rhamphotheca|rhamphotheca]] on the dorsal surface. The left dentary preserves 15 teeth and alveoli in the left dentary and 16 in the right dentary.<ref name="Miles2009"/>
{{clade | style=font-size:85%; line-height:85%

==Classification==
[[File:Череп_тархии.jpg|thumb|right|Type specimen of ''Tarchia teresae'', a taxon closely related to ''Minotaurasaurus'']]
Miles & Miles (2009) interpreted ''Minotaurasaurus'' as an ankylosaurid, but did not conduct a [[phylogenetic tree|phylogenetic analysis]].<ref name="Miles2009"/> A phylogenetic analysis performed by Thomas ''et al.'' (2012) recovered it as [[Sister group|sister taxon]] to ''[[Pinacosaurus|Pinacosaurus grangeri]]'', a position also recovered by Han ''et al.'' (2014).<ref name=Thompson2012>Richard S. Thompson, Jolyon C. Parish, Susannah C. R. Maidment and Paul M. Barrett, 2012, "Phylogeny of the ankylosaurian dinosaurs (Ornithischia: Thyreophora)", ''Journal of Systematic Palaeontology'' '''10'''(2): 301–312</ref><ref name=Han2014>{{cite journal |author1=Han, F. |author2=Zheng, W. |author3=Hu, D. |author4=Xu, X. |author5=Barrett, P.M. |year=2014 |title=A New Basal Ankylosaurid (Dinosauria: Ornithischia) from the Lower Cretaceous Jiufotang Formation of Liaoning Province, China |journal=PLOS ONE |volume=9 |issue=8 |pages=e104551 |doi=10.1371/journal.pone.0104551 |pmid=25118986 |pmc=4131922|bibcode=2014PLoSO...9j4551H |doi-access=free }}</ref> Arbour ''et al.'' (2014) considered ''Minotaurasaurus'' as a junior synonym of ''[[Tarchia|Tarchia kielanae]]'' due to the shared presence of a furrow near the squamosal horn, a conclusion also met by Arbour & Currie (2015).<ref name="Arbour2014II"/><ref name="Arbour2015"/> However, Penkalski & Tumanova (2016) noted that it differs from ''Tarchia'' by a number of characteristics, such as differences in the squamosal horns and caputegulae, and stated that it should therefore be considered as a valid taxon. Penkalski & Tumanova (2016) also conducted a phylogenetic analysis which found ''Minotaurasaurus'' as being at the base of a clade containing ''[[Zaraapelta]]'', ''[[Saichania]]'' and ''Tarchia''.<ref name=Penkalski2016/> Park ''et al.'' (2021) also had similar results to Penkalski & Tumanova (2016), while Wiersma & Irmis (2018) recovered it within a [[polytomy]] with ''Tarchia kielanae'' and ''[[Shanxia]]''.<ref name="Park"/><ref name=wiersma2018>{{Cite journal|author1=Jelle P. Wiersma |author2=Randall B. Irmis |year=2018 |title=A new southern Laramidian ankylosaurid, ''Akainacephalus johnsoni'' gen. et sp. nov., from the upper Campanian Kaiparowits Formation of southern Utah, USA |journal=PeerJ |volume=6 |pages=e5016 |doi=10.7717/peerj.5016 |pmc=6063217 |pmid=30065856 |doi-access=free }}</ref>

A limited phylogenetic analysis conducted Penkalski & Tumanova (2016) is reproduced below.<ref name=Penkalski2016/>
{{clade | style=font-size:85%; line-height:95%
|1={{clade
|1={{clade
|1=''Minotaurasaurus''
|1='''''Minotaurasaurus'''''
|2={{clade
|2={{clade
|1=''[[Zaraapelta]]''
|1=''[[Zaraapelta]]''
Line 39: Line 48:
|1=''[[Saichania]]''
|1=''[[Saichania]]''
|2={{clade
|2={{clade
|1='''''T. kielanae'''''
|1=''[[Tarchia|T. kielanae]]''
|2='''''T. teresae'''''}}}}}}
|2=''[[Tarchia|T. teresae]]''}}}}}}
|3=''[[Pinacosaurus]]''}}}}
|3=''[[Pinacosaurus]]''}}}}

The results of an earlier analysis by Thompson ''et al.'' (2012) are reproduced below.<ref name=Thompson2012/>
{{clade| style=font-size:85%;line-height:85%
|1={{clade
|1={{clade
|1=''[[Huayangosaurus taibaii]]''
|2=''[[Stegosaurus armatus]]'' }}
|2={{clade
|1=[[Nodosauridae]]
|label2=[[Ankylosauridae]]
|2={{clade
|1=''[[Minmi paravertebra]]''
|2={{clade
|1=''[[Liaoningosaurus paradoxus]]''
|2={{clade
|1=''[[Cedarpelta bilbeyhallorum]]''
|2={{clade
|1=''[[Gobisaurus domoculus]]''
|2={{clade
|1=''[[Shamosaurus scutatus]]''
|2={{clade
|1=''[[Zhongyuansaurus|Zhongyuansaurus luoyangensis]]''
|2=''[[Tsagantegia longicranialis]]''
|3={{clade
|1={{clade
|1=''[[Shanxia tianzhensis]]''
|2={{clade
|1=''[[Crichtonpelta|"Crichtonsaurus" benxiensis]]''
|2={{clade
|1=''[[Dyoplosaurus acutosquameus]]''
|2=''[[Pinacosaurus mephistocephalus]]'' }} }} }}
|2={{clade
|1={{clade
|1=''[[Ankylosaurus magniventris]]''
|2=''[[Euoplocephalus tutus]]'' }}
|2={{clade
|1={{clade
|1='''''Minotaurasaurus ramachandrani'''''
|2=''[[Pinacosaurus grangeri]]'' }}
|2={{clade
|1=''[[Nodocephalosaurus kirtlandensis]]''
|2={{clade
|1={{clade
|1=''[[Talarurus plicatospineus]]''
|2=''[[Tianzhenosaurus youngi]]'' }}
|2={{clade
|1=''[[Saichania chulsanensis]]''
|2=''[[Tarchia gigantea]]'' }} }} }} }} }} }} }} }} }} }} }} }} }} }} }}

==Paleobiology==
===Feeding===
[[File:Mongolian ankylosaurines diet.png|thumb|left|upright|Snout morphology and diet of Mongolian ankylosaurids; ''M. ramachandrani'' in left]]
''Minotaurasaurus'' was, like other Mongolian ankylosaurines, [[herbivore|herbivorous]] and a low-level bulk feeder based on its sub-rectangular broad muzzle.<ref name="Park">{{cite journal | vauthors = Park JY, Lee YN, Kobayashi Y, Jacobs LL, Barsbold R, Lee HJ, Kim N, Song KY, Polcyn MJ | title = A new ankylosaurid from the Upper Cretaceous Nemegt Formation of Mongolia and implications for paleoecology of armoured dinosaurs | journal = Scientific Reports | volume = 11 | issue = 1 | pages = Article number 22928 | year = 2021 | doi = 10.1038/s41598-021-02273-4 | pmid = 34824329 | pmc = 8616956 | doi-access = free | bibcode = 2021NatSR..1122928P }}</ref> Instead of oral processing, ankylosaurids living in dry environments such as ''Minotaurasaurus'' may have relied more on [[hindgut fermentation]] for digestion or, alternatively, consumed succulent plants that did not require complex chewing. These ankylosaurids may have also been restricted to simple orthal pulping and might have had to deal with more grit during feeding compared to ankylosaurs that lived in tropical to subtropical climates, as indicated by the [[Dental microwear|microwear pits]].<ref name="Ősi2016">{{Cite journal |last1=Ősi |first1=Attila |last2=Prondvai |first2=Edina |last3=Mallon |first3=Jordan |last4=Bodor |first4=Emese Réka |date=2016-07-20 |title=Diversity and convergences in the evolution of feeding adaptations in ankylosaurs (Dinosauria: Ornithischia) |url=http://www.tandfonline.com/action/showCitFormats?doi=10.1080/08912963.2016.1208194 |journal=Historical Biology |language=en |volume=29 |issue=4 |pages=539–570 |doi=10.1080/08912963.2016.1208194 |s2cid=55372674 |issn=0891-2963}}</ref> Park ''et al.'' (2021) suggested that there was a shift from bulk feeding to selective feeding in Mongolian ankylosaurines during the Campanian and Maastrichtian stages which may have either been caused by the change in habitat, as the climate changed from semi-arid and arid to humid, or interspecific competition with [[saurolophine]] [[hadrosaurids]] that immigrated from [[North America]] to [[Central Asia]] during the Campanian stage.<ref name="Park"/>

The type specimen of ''Minotaurasaurus'' may have had a pair of small [[osteoderms]] below the orbits that were [[Homology (biology)|homologous]] to the posterior cheek plates of [[nodosaurids]] such as ''[[Panoplosaurus]]'' and ''[[Edmontonia]]''. The presence of these osteoderms at the level of the last three maxillary teeth suggests that either the [[cheek|bucca]] did not extend as anteriorly as in ''Panoplosaurus and Edmontonia'' or an anteriorly extended bucca was present but did not embed extensive cheek plates.<ref name="Ősi2016"/>


==Paleoenvironment==
==Paleoenvironment==
[[File:Minotaurasaurus BW.jpg|thumb|Restoration of ''Minotaurasaurus'' in paleoenvironment]]
[[File:Saichania_skeleton.jpg|thumb|left|Skeleton of cf. [[Pinacosaurus]], another ankylosaurid from the Djadochta Formation.]]
The remains of ''Minotaurasaurus'' were likely recovered from the Ukhaa Tolgod locality at the [[Djadochta Formation]].<ref name="Alicea2013"/><ref name=Penkalski2016/> The formation is divided into two members, the lower Bayn Dzak Member and the upper Turgrugyin Member. The Bayn Dzak Member consists of moderate reddish orange, crossbedded, and structureless [[sandstones]], with subordinate deposits of brown [[siltstone]] and [[mudstone]]. The mudstone and siltstone represents an interdune facies deposited by [[Fluvial processes|fluvial action]], while the crossbedded and structureless sandstones represent eolian dunes and fluvial deposits or sandslides that occurred on the [[dune]] faces. The Turgrugyin Member consists of very pale orange to light gray sands, which also represents a crossbedded dune facies and a structureless sandslide facies. [[Magnetostratigraphy|Magnetostratigraphic]] datings from the Bayn Dzak and Tugriken Shireh localities suggest that the formation dates to the late Campanian stage of the Late Cretaceous, ca. ~75-71 Ma.<ref name=Dashzeveg2005>{{cite journal|last1=Dashzeveg|first1=D.|last2=Dingus|first2=L.|last3=Loope|first3=D. B.|last4=Swisher III|first4=C. C.|last5=Dulam|first5=T.|last6=Sweeney|first6=M. R.|date=2005|title=New Stratigraphic Subdivision, Depositional Environment, and Age Estimate for the Upper Cretaceous Djadokhta Formation, Southern Ulan Nur Basin, Mongolia|journal=American Museum Novitates|number=3498|pages=1−31|doi=10.1206/0003-0082(2005)498[0001:NSSDEA]2.0.CO;2|hdl=2246/5667|s2cid=55836458 |hdl-access=free|url=http://digitallibrary.amnh.org/bitstream/handle/2246/5667/N3498.pdf?sequence=1&isAllowed=y}}</ref> Based on the strata, rock facies, sedimentation and coeval units, the Djadochta Formation represents an arid environment consisting of sand dunes and short-lived water bodies with a warm, semiarid climate.<ref>{{cite journal|last1=Dingus|first1=L.|last2=Loope|first2=D. B.|last3=Dashzeveg|first3=D.|last4=Swisher III|first4=C. C.|last5=Minjin|first5=C.|last6=Novacek|first6=M. J.|last7=Norell|first7=M. A.|date=2008|title=The Geology of Ukhaa Tolgod (Djadokhta Formation, Upper Cretaceous, Nemegt Basin, Mongolia)|journal=American Museum Novitates|number=3616|pages=1−40|doi=10.1206/442.1|hdl=2246/5916|s2cid=129735494 |hdl-access=free|url=https://core.ac.uk/download/pdf/189860633.pdf}}</ref>
The fossil remains of ''Minotaurasaurus'' were likely recovered from sediments of the [[Djadochta Formation]], which dates to the [[Campanian]] stage of the [[Late Cretaceous]], 75 to 71 million years ago. ''Minotaurasaurus'' would have been contemporary with various species of terrestrial [[Turtles]], [[Crocodilians]], [[Lizards]], [[Mammals]] and [[Dinosaurs]], such as the [[alvarezsauridae|alvarezsaurid]] [[Shuvuuia]], the [[ceratopsia|ceratopsians]] [[Protoceratops]] and [[Udanoceratops]], the [[dromaeosauridae|dromaeosaurids]] [[Tsaagan]] and [[Velociraptor]], the [[halszkaraptorinae|halszkaraptorine]] [[Halszkaraptor]] and [[Mahakala]], the [[oviraptorosauria|oviraptorosaurs]] [[Citipati]] and [[Oviraptor]], and the ankylosaurid [[Pinacosaurus]]. Based on strata, rock facies, sedimentation and coeval units, the Djadochta Formation represents an arid environment consisting of sand dunes and short-lived water bodies with a warm semiarid climate.


Specimens of ''Minotaurasaurus'' likely originated from the lower Bayn Dzak Member of the Djadochta Formation, which have also yielded specimens of the [[dromaeosaurids]] ''[[Velociraptor mongoliensis]]'' and ''[[Tsaagan]]'';<ref name=Norel1999>{{cite journal|last1=Norell|first1=M. A.|last2=Makovicky|first2=P. J.|date=1999|title=Important Features of the Dromaeosaurid Skeleton II: Information from Newly Collected Specimens of Velociraptor mongoliensis|journal=American Museum Novitates|number=3282|pages=1−45|hdl=2246/3025|hdl-access=free|oclc=802169086}}</ref><ref>{{cite journal|last1=Norell|first1=M. A.|last2=Clark|first2=J. M.|last3=Turner|first3=A. H.|last4=Makovicky|first4=P. J.|last5=Barsbold|first5=R.|last6=Rowe|first6=T.|date=2006|title=A New Dromaeosaurid Theropod from Ukhaa Tolgod (Ömnögov, Mongolia)|journal=American Museum Novitates|number=3545|pages=1–51|doi=10.1206/0003-0082(2006)3545[1:ANDTFU]2.0.CO;2|hdl=2246/5823|hdl-access=free|url=https://www.researchgate.net/publication/232678611}}</ref> the [[halszkaraptorine]] ''[[Halszkaraptor]]'';<ref>{{cite journal|last1=Cau|first1=A.|last2=Beyrand|first2=V.|last3=Voeten|first3=D. F. A. E.|last4=Fernandez|first4=V.|last5=Tafforeau|first5=P.|last6=Stein|first6=K.|last7=Barsbold|first7=R.|last8=Tsogtbaatar|first8=K.|last9=Currie|first9=P. J.|last10=Godefroit|first10=P.|date=2017|title=Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs|journal=Nature|volume=552|issue=7685|pages=395−399|bibcode=2017Natur.552..395C|doi=10.1038/nature24679|pmid=29211712|s2cid=4471941 |url=https://www.researchgate.net/publication/321609878}}</ref> the [[troodontids]] ''[[Byronosaurus]]'' and ''[[Saurornithoides]]'';<ref name="Norell2000">Norell, M.A., Makovicky, P.J. & Clark, J.M., 2000, "A new troodontid theropod from Ukhaa Tolgod, Mongolia", ''Journal of Vertebrate Paleontology'' '''20'''(1): 7-11</ref><ref>{{cite journal|last1=Norell|first1=M. A.|last2=Makovicky|first2=P. J.|last3=Bever|first3=G. S.|last4=Balanoff|first4=A. M.|last5=Clark|first5=J. M.|last6=Barsbold|first6=R.|last7=Rowe|first7=T.|date=2009|title=A review of the Mongolian Cretaceous dinosaur Saurornithoides (Troodontidae, Theropoda)|journal=American Museum Novitates|number=3654|pages=1−63|doi=10.1206/648.1|hdl=2246/5973|hdl-access=free|url=https://www.biodiversitylibrary.org/itempdf/280747}}</ref> the [[oviraptorids]] ''[[Citipati]]'', ''[[Oviraptor]]'' and ''[[Khaan]]'';<ref name=Clark2001>{{cite journal|last1=Clark|first1=J. M.|last2=Norell|first2=M. A.|last3=Barsbold|first3=R.|date=2001|title=Two new oviraptorids (Theropoda: Oviraptorosauria) from the Late Cretaceous Djadokta Formation, Ukhaa Tolgod|journal=Journal of Vertebrate Paleontology|volume=21|issue=2|pages=209–213|doi=10.1671/0272-4634(2001)021[0209:TNOTOU]2.0.CO;2|jstor=20061948|s2cid=86076568 |url=https://www.researchgate.net/publication/232685671}}</ref><ref name="osborn1924">{{cite journal|last1=Osborn|first1=H. F.|date=1924|title=Three new Theropoda, Protoceratops zone, central Mongolia|journal=American Museum Novitates|number=144|pages=1−12|hdl=2246/3223|hdl-access=free|oclc=40272928}}</ref> the [[alvarezsaurid]] ''[[Shuvuuia]]'';<ref name="chiappe98">Chiappe, L.M., Norell, M. A., and Clark, J. M. (1998). "The skull of a relative of the stem-group bird ''Mononykus''." ''Nature'', '''392'''(6673): 275-278.</ref> the [[ankylosaurid]] ''[[Pinacosaurus|Pinacosaurus grangeri]]'';<ref>{{cite journal|last=Gilmore|first=C. W.|title=Two new dinosaurian reptiles from Mongolia with notes on some fragmentary specimens|journal=American Museum Novitates|issue=679|pages=1–20|date=1933|hdl=2246/2076}}</ref> the [[ceratopsian]] ''[[Protoceratops]]'';<ref>{{cite journal|last1=Brown|first1=B.|last2=Schlaikjer|first2=E. M.|date=1940|title=The Structure and Relationships of Protoceratops|journal=Annals of the New York Academy of Sciences|volume=40|number=3|pages=133−266|bibcode=1940NYASA..40..133B|doi=10.1111/j.2164-0947.1940.tb00068.x|oclc=1673730|url=https://drive.google.com/file/d/1EM9A8LG5eqbQ5_Ho16QJx0_MebAqLjLQ/view}}</ref> an indeterminate [[hadrosauroid]];<ref>{{cite journal|last1=Barsbold|first1=R.|last2=Perle|first2=A.|date=1983|title=On taphonomy of joint burial of juvenile dinosaurs and some aspects of their ecology|journal=Transactions of the Joint Soviet-Mongolian Paleontological Expedition|volume=24|pages=121−125|language=ru}}</ref> and an indeterminate [[azhdarchid]].<ref>{{cite journal | last1 = Hone | first1 = D. | last2 = Tsuihiji | first2 = T. | last3 = Watabe | first3 = M. | last4 = Tsogtbaatr | first4 = K. | title = Pterosaurs as a food source for small dromaeosaurs | doi = 10.1016/j.palaeo.2012.02.021 | journal = Palaeogeography, Palaeoclimatology, Palaeoecology | volume = 331-332 | page = 27 | year = 2012 | bibcode = 2012PPP...331...27H }}</ref> The upper Turgrugyin Member has yielded the dromaeosaurid ''Velociraptor mongoliensis'';<ref name=Norel1999/> the halszkaraptorine ''[[Mahakala]]'';<ref>{{cite journal|last1=Turner|first1=A. H.|last2=Pol|first2=D.|last3=Clarke|first3=J. A.|last4=Erickson|first4=G. M.|last5=Norell|first5=M. A.|date=2007|title=A Basal Dromaeosaurid and Size Evolution Preceding Avian Flight|journal=Science|volume=317|issue=5843|pages=1378−1381|bibcode=2007Sci...317.1378T|doi=10.1126/science.1144066|doi-access=free|pmid=17823350}}</ref> the [[ornithomimosaurs]] ''[[Aepyornithomimus]]'' and an indeterminate ornithomimosaur;<ref>{{cite journal|last1=Chinzorig|first1=T.|last2=Kobayashi|first2=Y.|last3=Tsogtbaatar|first3=K.|last4=Currie|first4=P. J.|last5=Watabe|first5=M.|last6=Barsbold|first6=R.|date=2017|title=First Ornithomimid (Theropoda, Ornithomimosauria) from the Upper Cretaceous Djadokhta Formation of Tögrögiin Shiree, Mongolia|journal=Scientific Reports|volume=7|issue=5835|page=5835|bibcode=2017NatSR...7.5835C|doi=10.1038/s41598-017-05272-6|doi-access=free|pmc=5517598|pmid=28724887}}</ref><ref>{{cite journal | last1 = Makovicky | first1 = P. J. | last2 = Norell | first2 = Mark A. | year = 1998 | title=A partial ornithomimid briancase from Ukhaa Tolgod (Upper Cretaceous, Mongolia) | journal = American Museum Novitates | issue = 3247 | pages = 1–16}}</ref><ref>{{cite journal | last1 = Ksepka | first1 = Daniel T. | last2 = Norell | first2 = Mark A. | year = 2004 | title=Ornithomimosauria cranial material from Ukhaa Tolgod (Omnogov, Mongolia) | journal = American Museum Novitates | issue = 3448 | pages = 1–4 | issn = 0003-0082 | doi=10.1206/0003-0082(2004)448<0001:ocmfut>2.0.co;2| hdl = 2246/2813 | s2cid = 55019144 | url = https://www.biodiversitylibrary.org/item/292382 }}</ref> the [[oviraptorosaur]] ''[[Avimimus]]'';<ref>{{cite journal|last1=Kurzanov|first1=S. M.|date=1981|title=An unusual theropod from the Upper Cretaceous of Mongolia|journal=Transactions, Joint Soviet–Mongolian Palaeontological Expedition|volume=15|pages=39−49|language=ru}}</ref> the ceratopsians ''Protoceratops'' and ''[[Udanoceratops]]'';<ref>{{cite journal|last1=Chiba|first1=K.|last2=Ryan|first2=M. J.|last3=Saneyoshi|first3=M.|last4=Konishi|first4=S.|last5=Yamamoto|first5=Y.|last6=Mainbayar|first6=B.|last7=Tsogtbaatar|first7=K.|date=2020|title=Taxonomic re-evaluation of Protoceratops (Dinosauria: Ceratopsia) specimens from Udyn Sayr, Mongolia|journal=Journal of Vertebrate Paleontology|volume=Program and Abstracts|url=https://vertpaleo.org/wp-content/uploads/2021/03/SVP_2020_Program-Abstracts-Volume-FINAL-for-Publishing-1.27.2021.pdf}}</ref><ref>{{cite journal|last1=Kurzanov|first1=S. M.|date=1992|title=A giant protoceratopsid from the Upper Cretaceous of Mongolia|journal=Paleontological Journal|pages=81−93|language=ru}}</ref> and an indeterminate [[tyrannosaurid]].<ref name="Longrichetal10">{{cite journal|last1=Longrich|first1=N. R.|last2=Currie|first2=P. J.|last3=Dong|first3=Z.|date=2010|title=A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia|journal=Palaeontology|volume=53|issue=5|pages=945−960|doi=10.1111/j.1475-4983.2010.00968.x|doi-access=free|bibcode=2010Palgy..53..945L }}</ref>
==See also==
{{Portal|Dinosaurs}}
* [[Timeline of ankylosaur research]]


==References==
==References==
{{Reflist}}
{{Reflist}}

==See also==
{{Portal|Dinosaurs}}
* [[Timeline of ankylosaur research]]


{{Thyreophora|A.}}
{{Thyreophora|A.}}
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[[Category:Fossil taxa described in 2009]]
[[Category:Fossil taxa described in 2009]]
[[Category:Ornithischian genera]]
[[Category:Ornithischian genera]]


{{ankylosaurian stub}}

Latest revision as of 23:24, 22 August 2024

Minotaurasaurus
Temporal range: Late Cretaceous, 75–71 Ma
↓
Cast of the holotype skull of Minotaurasaurus.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Thyreophora
Clade: †Ankylosauria
Family: †Ankylosauridae
Subfamily: †Ankylosaurinae
Genus: †Minotaurasaurus
Miles & Miles, 2009
Species:
†M. ramachandrani
Binomial name
†Minotaurasaurus ramachandrani
Miles & Miles, 2009

Minotaurasaurus (meaning “Minos'-bull reptile”) is a monospecific genus of ankylosaurid dinosaur that lived in Mongolia during the Late Cretaceous (late Campanian stage, ~75-71 Ma) in what is now the Djadochta Formation. The type and only species, Minotaurasaurus ramachandrani, is known from two skulls, a cervical vertebra and a cervical half ring. It was named and described in 2009 by Clifford Miles and Clark Miles. The first fossils of Minotaurasaurus were illegally exported out of Mongolia.[citation needed]It has been suggested to be a synonym of Tarchia but more recent publications consider it as a distinct genus.

Minotaurasaurus was a medium-sized ankylosaurid, with an estimated length of 4.2 metres (13.8 feet), although it may have reached larger sizes as the type specimen represents an immature individual. Although not a lot of postcranial material is known, it would have had a tail club that may have been used for protection against predators or interspecific combat and would have been covered in protective osteoderms. It would have also had a barrel-like body, and short, robust limbs based on close relatives.

Discovery and Naming

[edit]
Fossil localities in Mongolia. Minotaurasaurus fossils have been collected at Uhkaa Tolgod (area B)

In 2003, a skull of an ankylosaurid was purchased for US$10,000 by the private fossil collector and neuroscientist Vilayanur S. Ramachandran while accompanied by Clifford Miles at the Tucson Gem, Mineral and Fossil Showcase, Arizona. The skull was put on display by Robert Gaston for the fossil poacher Hollis Butts, who Ramachandran purchased it from[citation needed]. The stratigraphic position was stated as being from the Gobi Desert of either Mongolia or China due to the provenance being unknown at the time. In 2006, Clifford Miles and his brother Clark Miles attempted to publish the description of the skull in a Polish Journal but was promptly rejected as the specimen was seemingly obtained illegally from Mongolia. Two years later, the authors stated that the specimen had come from the Barun Goyot Formation but later stated that they could not confirm its origin. The skull would later be described and named in 2009. The publication was later criticised by palaeontologists such as Mark Norell, Phillip J. Currie and Bolortsetseg Minjin due to the questionable origins of the specimen.[1] The holotype specimen, INBR21004, consists of a skull with lower jaws and predentary. The type specimen is currently housed at the Victor Valley Museum in Apple Valley, California.[2]

The generic name, Minotaurasaurus, is derived from the Minotaur and the Greek word "sauros" (lizard), in reference to the bull-like appearance of the holotype skull. The specific name, ramachandrani, honours V. S. Ramachandran, who purchased the type specimen.[2]

In 2013, a Society of Vertebrate Paleontology abstract book mentioned the discovery of a second specimen of Minotaurasaurus (MAE 98 179) from the Uhkaa Tolgod locality of the late Campanian Djadochta Formation in the Nemegt Basin. The specimen consists of a skull, axis and first cervical half-ring, and it is part of the collection of the Mongolian Academy of Sciences. MAE 98 179 was reported as having insect burrows that continues into a pattern which is only seen in Late Cretaceous Gobi deposits.[3] Penkalski & Tumanova (2016) would later describe the specimen, which was used to establish the stratigraphic position of the type specimen and the validity of the taxon, as before it was suggested by Arbour et al. (2014) and Arbour & Currie (2015) to be from the Barun Goyot Formation and a junior synonym of Tarchia kielanae.[4][5][6] Its validity was also tested by Arbour & Currie (2012) by using a retrodeformation and finite element analysis, which found that many of its diagnostic features were likely not caused by deformation.[7]

Description

[edit]

Size and distinguishing traits

[edit]
Diagram of the holotype skull

Miles & Miles (2009) gave Minotaurasaurus an estimated length of at least 4.2 metres (13.8 feet), although it may have attained larger sizes as the type specimen, and only known specimen at the time, represents an immature individual based on the unfused osteoderms.[2]

Penkalski & Tumanova (2016) established numerous distinguishing traits of Minotaurasaurus. The paroccipital processes are not present laterally to the squamosal horns due to presence of a small and dorsoventrally shallow occiput. The skull roof possessing an unfused occiput. Basioccipital foramen that are either small or absent. Highly sculptured squamosal horns that are dorsoventrally narrow and cylindrical in shape. Non prominent nuchal caputegulae that angle caudolaterally. The presence of two distinct supraorbital apices. Frontal caputegulae that aren't arranged at right angles but with nasofrontal caputegulae that are elongated transversely and are ridge-like. The presence of a deep notch in the lacrimal. The presence of two pairs of internarial osteoderms, unlike the presence of a single osteoderm as in Tarchia and Saichania. An overall small skull that is broad. A more horizontal pterygoid body. A mandibular osteoderm that extends towards the front end of the tooth row. Other distinguishing traits include the occiput being more visible in dorsal view, an occipital condyle that is protrudes less towards the underside in caudal view and a skull that is proportionally lower and wider than that of Tarchia.[4]

Skull

[edit]
Skull of Minotaurasaurus (far right) compared to other ankylosaurids

The holotype skull measures 30 centimetres (11.8 inches) long and has a width of 43 centimetres (17 inches). Excluding the squamosal horns, the skull is longer than wide. The skull roof has its widest point formed by the squamosal horns. Unlike other ankylosaurids, the squamosal horns are more gracile and tapering. Pyramid-shaped caputegulae cover most of the surface of the skull, with the exception of an area of the skull roof that is near the orbits. The caputegulae are arranged roughly bi-symmetrically on the skull, with two sharp-keeled caputegulae projecting laterally above the orbits and similar caputegulae being present near the prefrontal. Partially fused to unfused caputegulae are present on parts of the skull.[2] Present near the squamosal horn is a furrow, or unfused caputegulum, that is also seen in Tarchia kielanae. The furrow is an artefact of the postorbital osteoderm being within the postorbital fossa. However, unlike Tarchia, the supraoccipital is co-ossified to the parietals.[4] The skull's orbit is tear drop-shaped with a tapered end that points towards the front. The osteoderms of the narial region create a flared look due to how large and ornamented they are, and project towards the front and sides. Present in the narial region are three apertures and the external nasal cavity, which is bound by a single osteoderm. The surface of the premaxillary beak is covered partially by secondary dermal ossifications. An inverted, triangular osteoderm is coossified to the premaxilla along the ventral margin of the narial opening. A sharp premaxillary beak is present as a result of the palatal portions of the premaxillae changing shape from the front end to the back end. Unlike most ankylosaurids, the vomer extends below the maxillary tooth crowns. All teeth are leaf-shaped. There are a total of 17 teeth and alveoli in the left maxilla and 16 in the right maxilla. The maxillary teeth are up to 25% larger than the dentary teeth and have crowns that are variable.[2]

The epipterygoid, a small, triangular structure, separates the pterygoid from the maxilla. Instead of being vertical or even slightly overturned as seen in most ankylosaurids, the main body of the pterygoids is near horizontal which, as a result, makes the interpterygoid vacuity in palatal view. The occipital condyle lacks a neck and is heart-shaped. The occiput is low and rectangular in shape. The paroccipital processes fall well short of the medial edge of the squamosal horn. Both the basisphenoid and basioccipital are fused together, with the sutural area being expanded as a ridge. This ridge marks the insertion for the rectus capitis and longus capitis muscles. Both the left and right jugal horns thrust more towards the sides than towards the underside. Towards the sides of the tooth row is a broad maxillary shelf that extends beneath the middle of the orbit. A long, narrow osteoderm is partially fused along each side of the mandible but does not extend dorsally onto the lateral surface. The tooth row is positioned along the margins of the dentary. The ventral half of the mandible has a rough texture on the lateral surface, while the dorsal half of the mandible has a smooth texture. The position of the cheeks on the lower jaws is marked by the boundary between the smooth and the textured surfaces during occlusion as it is opposite to the lateral edge of the maxillary shelf. The coronoid process is small and low, and is present towards the front of the base of the process. The predentary is subtriangular in cross-section and bears numerous nutrient foramina to serve the rhamphotheca on the dorsal surface. The left dentary preserves 15 teeth and alveoli in the left dentary and 16 in the right dentary.[2]

Classification

[edit]
Type specimen of Tarchia teresae, a taxon closely related to Minotaurasaurus

Miles & Miles (2009) interpreted Minotaurasaurus as an ankylosaurid, but did not conduct a phylogenetic analysis.[2] A phylogenetic analysis performed by Thomas et al. (2012) recovered it as sister taxon to Pinacosaurus grangeri, a position also recovered by Han et al. (2014).[8][9] Arbour et al. (2014) considered Minotaurasaurus as a junior synonym of Tarchia kielanae due to the shared presence of a furrow near the squamosal horn, a conclusion also met by Arbour & Currie (2015).[5][6] However, Penkalski & Tumanova (2016) noted that it differs from Tarchia by a number of characteristics, such as differences in the squamosal horns and caputegulae, and stated that it should therefore be considered as a valid taxon. Penkalski & Tumanova (2016) also conducted a phylogenetic analysis which found Minotaurasaurus as being at the base of a clade containing Zaraapelta, Saichania and Tarchia.[4] Park et al. (2021) also had similar results to Penkalski & Tumanova (2016), while Wiersma & Irmis (2018) recovered it within a polytomy with Tarchia kielanae and Shanxia.[10][11]

A limited phylogenetic analysis conducted Penkalski & Tumanova (2016) is reproduced below.[4]

The results of an earlier analysis by Thompson et al. (2012) are reproduced below.[8]

Paleobiology

[edit]

Feeding

[edit]
Snout morphology and diet of Mongolian ankylosaurids; M. ramachandrani in left

Minotaurasaurus was, like other Mongolian ankylosaurines, herbivorous and a low-level bulk feeder based on its sub-rectangular broad muzzle.[10] Instead of oral processing, ankylosaurids living in dry environments such as Minotaurasaurus may have relied more on hindgut fermentation for digestion or, alternatively, consumed succulent plants that did not require complex chewing. These ankylosaurids may have also been restricted to simple orthal pulping and might have had to deal with more grit during feeding compared to ankylosaurs that lived in tropical to subtropical climates, as indicated by the microwear pits.[12] Park et al. (2021) suggested that there was a shift from bulk feeding to selective feeding in Mongolian ankylosaurines during the Campanian and Maastrichtian stages which may have either been caused by the change in habitat, as the climate changed from semi-arid and arid to humid, or interspecific competition with saurolophine hadrosaurids that immigrated from North America to Central Asia during the Campanian stage.[10]

The type specimen of Minotaurasaurus may have had a pair of small osteoderms below the orbits that were homologous to the posterior cheek plates of nodosaurids such as Panoplosaurus and Edmontonia. The presence of these osteoderms at the level of the last three maxillary teeth suggests that either the bucca did not extend as anteriorly as in Panoplosaurus and Edmontonia or an anteriorly extended bucca was present but did not embed extensive cheek plates.[12]

Paleoenvironment

[edit]
Restoration of Minotaurasaurus in paleoenvironment

The remains of Minotaurasaurus were likely recovered from the Ukhaa Tolgod locality at the Djadochta Formation.[3][4] The formation is divided into two members, the lower Bayn Dzak Member and the upper Turgrugyin Member. The Bayn Dzak Member consists of moderate reddish orange, crossbedded, and structureless sandstones, with subordinate deposits of brown siltstone and mudstone. The mudstone and siltstone represents an interdune facies deposited by fluvial action, while the crossbedded and structureless sandstones represent eolian dunes and fluvial deposits or sandslides that occurred on the dune faces. The Turgrugyin Member consists of very pale orange to light gray sands, which also represents a crossbedded dune facies and a structureless sandslide facies. Magnetostratigraphic datings from the Bayn Dzak and Tugriken Shireh localities suggest that the formation dates to the late Campanian stage of the Late Cretaceous, ca. ~75-71 Ma.[13] Based on the strata, rock facies, sedimentation and coeval units, the Djadochta Formation represents an arid environment consisting of sand dunes and short-lived water bodies with a warm, semiarid climate.[14]

Specimens of Minotaurasaurus likely originated from the lower Bayn Dzak Member of the Djadochta Formation, which have also yielded specimens of the dromaeosaurids Velociraptor mongoliensis and Tsaagan;[15][16] the halszkaraptorine Halszkaraptor;[17] the troodontids Byronosaurus and Saurornithoides;[18][19] the oviraptorids Citipati, Oviraptor and Khaan;[20][21] the alvarezsaurid Shuvuuia;[22] the ankylosaurid Pinacosaurus grangeri;[23] the ceratopsian Protoceratops;[24] an indeterminate hadrosauroid;[25] and an indeterminate azhdarchid.[26] The upper Turgrugyin Member has yielded the dromaeosaurid Velociraptor mongoliensis;[15] the halszkaraptorine Mahakala;[27] the ornithomimosaurs Aepyornithomimus and an indeterminate ornithomimosaur;[28][29][30] the oviraptorosaur Avimimus;[31] the ceratopsians Protoceratops and Udanoceratops;[32][33] and an indeterminate tyrannosaurid.[34]

References

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See also

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