Xixiasaurus: Difference between revisions
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==Discovery== |
==Discovery== |
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[[File:Xixiasaurus map.jpg|thumb|left|Map showing the type locality (★) in the [[Henan Province]] of China]] |
[[File:Xixiasaurus map.jpg|thumb|left|Map showing the type locality (★) in the [[Henan Province]] of China]] |
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The [[holotype specimen]] (catalogued as HGM 41HIII−0201 in Henan Geological Museum) was discovered near Songgou Village, in the northeast region of [[Xixia County]], in the [[Henan Province]] of central China. This area of the [[Xixia Basin]] is part of the [[Majiacun Formation]]. In [[2010 in paleontology|2010]] it was described as the new [[genus]] and [[species]] ''Xixiasaurus henanensis'', by the Chinese palaeontologist [[Lü Junchang]] and colleagues. The generic name refers to Xixia County coupled with ''saurus'', meaning "lizard", while the [[Specific name (zoology)|specific name]] refers to the Hennan Province, where the type locality is located. The full name can be translated as "Henan Xixia lizard".<ref name="Lüetal"/><ref name="mm">{{cite book|last=Martyniuk|first=M. P.|year=2012|title=A Field Guide to Mesozoic Birds and Other Winger Dinosaurs|publisher=Pan Aves|page=102|isbn=978-0-9885965-0-4}}</ref> |
The [[holotype specimen]] (catalogued as HGM 41HIII−0201 in Henan Geological Museum) was discovered near Songgou Village, in the northeast region of [[Xixia County]], in the [[Henan Province]] of central China. This area of the [[Xixia Basin]] is part of the [[Majiacun Formation]]. In [[2010 in paleontology|2010]] it was described as the new [[genus]] and [[species]] ''Xixiasaurus henanensis'', by the Chinese palaeontologist [[Lü Junchang]] and colleagues. The generic name refers to Xixia County coupled with ''saurus'', meaning "lizard", while the [[Specific name (zoology)|specific name]] refers to the Hennan Province, where the type locality is located. The full name can be translated as "Henan Xixia lizard". Remains of [[trodoontids]] are very rare compared to those of other small [[theropod]] [[dinosaurs]], and are mainly found in Asia.<ref name="Lüetal"/><ref name="mm">{{cite book|last=Martyniuk|first=M. P.|year=2012|title=A Field Guide to Mesozoic Birds and Other Winger Dinosaurs|publisher=Pan Aves|page=102|isbn=978-0-9885965-0-4}}</ref> |
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The holotype specimen is the only known ''Xixiasaurus'' fossil, and consists of an almost complete skull except for the hindmost portion, as well as a partial right forelimb. The connection between the |
The holotype specimen is the only known ''Xixiasaurus'' fossil, and consists of an almost complete skull except for the hindmost portion, as well as a partial right forelimb. The connection between the {{Dinogloss|frontal}} (forehead bone) and {{Dinogloss|nasal}} (bone running at the upper length of the snout) bones is displaced, and part of the {{Dinogloss|braincase}} is missing. Most of the snout is preserved, with the {{Dinogloss|dentition}} of the right side being well-preserved. The frontmost teeth there are missing, but their number can be determined since their sockets are preserved. Only the front part of the left {{Dinogloss|dentary bone}} (tooth-bearing bone of the mandible) and some of its broken teeth are preserved. The forelimb (of which all preserved parts are articulated) consists of the middle part of the {{Dinogloss|radius}} and {{Dinogloss|ulna}} (bones of the lower arm), the extremity of the second and third {{Dinogloss|metacarpals}} (hand bones), the complete first finger, and the first {{Dinogloss|phalanx bone}} of the second finger.<ref name="Lüetal"/> In 2014, the Japanese palaeontologist Takanobu Tsuihiji and colleagues stated that a bone Lü and colleagues had originally identified as the {{Dinogloss|vomer}} (part of the {{Dinogloss|palate}}) of ''Xixiasaurus'' was instead part of the {{Dinogloss|premaxillae}} or {{Dinogloss|maxillae}} (the main bones of the upper jaw), based on comparison with the vomer of the more complete troodontid ''[[Gobivenator]]''.<ref>{{cite journal |last1=Tsuihiji |first1=T. |last2=Barsbold |first2=R. |last3=Watabe |first3=M. |last4=Tsogtbaatar |first4=K. |last5=Chinzorig |first5=T. |last6=Fujiyama |first6=Y. |last7=Suzuki |first7=S. |title=An exquisitely preserved troodontid theropod with new information on the palatal structure from the Upper Cretaceous of Mongolia |journal=Naturwissenschaften |date=2014 |volume=101 |issue=2 |pages=131–142 |doi=10.1007/s00114-014-1143-9}}</ref> |
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==Description== |
==Description== |
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''Xixiasaurus'' is estimated to have been around {{convert|1.5|m}} long, and to have weighed about {{convert|8|kg}}.<ref name="paul2016">{{cite book | title=The Princeton Field Guide to Dinosaurs | publisher=[[Princeton University Press]] | last=Paul | first=G. S. | year=2016 | pages=155, 158 | isbn=978-0-691-16766-4}}</ref> As a troodontid [[maniraptoran]], it would have been a small, bird-like, and lightly built [[theropod]]. It would have had [[raptorial]] (grasping) hands, and an enlarged {{Dinogloss|sickle-claw}} on the hyper-extendible second toe of its foot.<ref name="Lüetal"/><ref name="Hendrickx">{{cite journal | last = Hendrickx | first = C. | last2 = Hartman | first2 = S.A. | last3 = Mateus | first3 = O. | title = An overview on non-avian theropod discoveries and classification | journal = PalArch's Journal of Vertebrate Palaeontology | series = | volume = 12 | issue = 1 | url = http://www.palarch.nl/2015/08/christophe-hendrickx-scott-a-hartman-octavio-mateus-2015-an-overview-of-non-avian-theropod-discoveries-and-classification-palarchs-journal-of-vertebrate-palaeontology-12-1-2015/ | pages = 1–73 | doi = | year = 2015}}</ref> Fossils of other troodontids show that members of the group were covered in [[pennaceous feathers]], with long feathers on the arms and legs, and frond-like feathering on the tail (similar to the [[avialan]] ''[[Archaeopteryx]]'').<ref name="Jianianhualong">{{cite journal |last1=Xu |first1=X. |last2=Currie |first2=P. |last3=Pittman |first3=M. |last4=Xing |first4=L. |last5=Meng |first5=Q. |last6=Lü |first6=J. |last7=Hu |first7=D. |last8=Yu |first8=C. |title=Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features |journal=Nature Communications |date=2017 |volume=8 |pages=14972 |doi=10.1038/ncomms14972}}</ref> |
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[[File:Xixiasaurus.jpg|thumb |
[[File:Xixiasaurus.jpg|thumb|Life [[paleoart|restoration]], showing an individual in bird-like resting pose]] |
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It was a [[troodontid]], a group of small, bird-like, [[wikt:gracile|gracile]] [[maniraptora]]ns. All troodontids have many unique features of the skull, such as large numbers of teeth, which in the lower jaw are closely spaced. Troodontids have sickle-claws and [[Velociraptor|raptor]]ial [[hands]].<ref name="Lüetal"/> It is one of few troodontids that have no [[serrated|serrations]] on their teeth, similar to its closest relative ''[[Byronosaurus]]''. ''Xixiasaurus'' has fewer teeth than ''Byronosaurus'' and ''[[Mei long|Mei]]'', but more than ''[[Sinornithoides]]'', ''[[Zanabazar junior|Zanabazar]]'' and ''[[Saurornithoides]]''. Like in ''Byronosaurus'', the [[palate]] of ''Xixiasaurus'' was extensive, and the teeth were [[heterodont]].<ref name="Lüetal">{{cite journal |last1=Lü |first1=J. |last2=Xu |first2=L. |last3=Liu |first3=Y. |last4=Zhang |first4=X. |last5=Jia |first5=S. |last6=Ji |first6=Q. |title=A New Troodontid Theropod from the Late Cretaceous of Central China, and the Radiation of Asian Troodontids |journal=Acta Palaeontologica Polonica |date=2010 |volume=55 |issue=3 |pages=381–388 |doi=10.4202/app.2009.0047}}</ref> |
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''Xixiasaurus'' is known from a mostly complete skull, only lacking the [[anatomical terms of location#Anterior and posterior|posterior]] portion. The top of the snout is slightly displaced, but overall, the skull resembles ''Byronosaurus''. As the [[nasal bones]] are very not and not completely fused, the [[holotype]] of ''Xixiasaurus'' may have died immature. Most of the [[braincase]] is preserved, as well as most teeth and all [[tooth socket]]s. Viewed from below, the tooth rows form a U-shaped curve. Some small pits are present of the [[anatomical terms of location#Lateral|lateral]] surface of the [[maxilla]]. The teeth on the maxilla are larger than those in the [[premaxilla]]. The hand and lower arm are also preserved. The claw of the first [[Digit (anatomy)|digit]] is very large, with a large [[tubercle|flexor tubercle]]. The first [[phalanges]] of the first two digits are {{convert|3.6|cm|in|abbr=on}} and {{convert|3|cm|in|abbr=on}} long, respectively.<ref name="Lüetal"/> |
''Xixiasaurus'' is known from a mostly complete skull, only lacking the [[anatomical terms of location#Anterior and posterior|posterior]] portion. The top of the snout is slightly displaced, but overall, the skull resembles ''Byronosaurus''. As the [[nasal bones]] are very not and not completely fused, the [[holotype]] of ''Xixiasaurus'' may have died immature. Most of the [[braincase]] is preserved, as well as most teeth and all [[tooth socket]]s. Viewed from below, the tooth rows form a U-shaped curve. Some small pits are present of the [[anatomical terms of location#Lateral|lateral]] surface of the [[maxilla]]. The teeth on the maxilla are larger than those in the [[premaxilla]]. The hand and lower arm are also preserved. The claw of the first [[Digit (anatomy)|digit]] is very large, with a large [[tubercle|flexor tubercle]]. The first [[phalanges]] of the first two digits are {{convert|3.6|cm|in|abbr=on}} and {{convert|3|cm|in|abbr=on}} long, respectively.<ref name="Lüetal"/> |
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==Classification== |
==Classification== |
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| ⚫ | The [[cladogram]] below follows a 2012 analysis by Turner, Makovicky and Norell.<ref name=TMN2012>{{Cite journal | last1 = Turner | first1 = Alan H. | last2 = Makovicky | first2 = Peter J. | last3 = Norell | first3 = Mark A. | title = A Review of Dromaeosaurid Systematics and Paravian Phylogeny | doi = 10.1206/748.1 | journal = Bulletin of the American Museum of Natural History | volume = 371 | pages = 1–206 | year = 2012 | pmid = | pmc = | hdl = 2246/6352 }}</ref> |
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[[File:Xixiasaurus hand bones.jpg|thumb|upright|Arm and hand bones of the holotype]] |
[[File:Xixiasaurus hand bones.jpg|thumb|upright|Arm and hand bones of the holotype]] |
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| ⚫ | The [[cladogram]] below follows a 2012 analysis by Turner, Makovicky and Norell.<ref name=TMN2012>{{Cite journal | last1 = Turner | first1 = Alan H. | last2 = Makovicky | first2 = Peter J. | last3 = Norell | first3 = Mark A. | title = A Review of Dromaeosaurid Systematics and Paravian Phylogeny | doi = 10.1206/748.1 | journal = Bulletin of the American Museum of Natural History | volume = 371 | pages = 1–206 | year = 2012 | pmid = | pmc = | hdl = 2246/6352 }}</ref> |
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{{clade|style=font-size:100%;line-height:100% |
{{clade|style=font-size:100%;line-height:100% |
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|label1=[[Paraves]] |
|label1=[[Paraves]] |
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|1=''[[Saurornithoides]]'' |
|1=''[[Saurornithoides]]'' |
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|2=''[[Zanabazar (dinosaur)|Zanabazar]]''}} }} }} }} }} }} }} }} }} }} }} }} |
|2=''[[Zanabazar (dinosaur)|Zanabazar]]''}} }} }} }} }} }} }} }} }} }} }} }} |
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==Palaeobiology== |
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''Xixiasaurus'' and other troodonts without serrated teeth may have been either herbivorous or omnivorous. Trodoonts had some of the highest non-[[Bird|avian]] [[encephalization quotient]]s, meaning they were behaviourally advanced and had keen senses.<ref name="Lüetal"/> |
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==Palaeoecology== |
==Palaeoecology== |
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''Xixiasaurus'' is from the middle region of the [[Majiacun Formation]], which dates to the [[Santonian]]-[[Coniacian]] [[Geological stage|stages]] of the [[Late Cretaceous]] [[Period (geologic time)|Period]] of [[China]], about 86 million years ago.<ref name="Lüetal"/> |
''Xixiasaurus'' is from the middle region of the [[Majiacun Formation]], which dates to the [[Santonian]]-[[Coniacian]] [[Geological stage|stages]] of the [[Late Cretaceous]] [[Period (geologic time)|Period]] of [[China]], about 86 million years ago.<ref name="Lüetal"/> |
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Revision as of 22:56, 4 December 2018
| Xixiasaurus Temporal range: Late Cretaceous,
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| Holotype skull shown from above, the right side, and below | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Family: | †Troodontidae |
| Genus: | †Xixiasaurus Lü et al., 2010 |
| Species: | †X. henanensis
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| Binomial name | |
| †Xixiasaurus henanensis Lü et al., 2010
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Xixiasaurus is a genus of troodontid dinosaur from the Late Cretaceous Period of modern-day China. It was first described as a new taxon in 2010. The type species is X. henanensis. Fossils of Xixiasaurus were discovered in central China, in the Majiacun Formation of Henan, and are believed to have been from the Santonian-Coniacian stages, about 86 million years ago. The remains were described by Lü Junchang and colleagues from the Chinese Academy of Geological Sciences and a second group from the Henan Geological Museum. They chose the name Xixiasaurus henanensis, translating as "lizard from Xixia, Henan".
Discovery
The holotype specimen (catalogued as HGM 41HIII−0201 in Henan Geological Museum) was discovered near Songgou Village, in the northeast region of Xixia County, in the Henan Province of central China. This area of the Xixia Basin is part of the Majiacun Formation. In 2010 it was described as the new genus and species Xixiasaurus henanensis, by the Chinese palaeontologist Lü Junchang and colleagues. The generic name refers to Xixia County coupled with saurus, meaning "lizard", while the specific name refers to the Hennan Province, where the type locality is located. The full name can be translated as "Henan Xixia lizard". Remains of trodoontids are very rare compared to those of other small theropod dinosaurs, and are mainly found in Asia.[1][2]
The holotype specimen is the only known Xixiasaurus fossil, and consists of an almost complete skull except for the hindmost portion, as well as a partial right forelimb. The connection between the frontal (forehead bone) and nasal (bone running at the upper length of the snout) bones is displaced, and part of the braincase is missing. Most of the snout is preserved, with the dentition of the right side being well-preserved. The frontmost teeth there are missing, but their number can be determined since their sockets are preserved. Only the front part of the left dentary bone (tooth-bearing bone of the mandible) and some of its broken teeth are preserved. The forelimb (of which all preserved parts are articulated) consists of the middle part of the radius and ulna (bones of the lower arm), the extremity of the second and third metacarpals (hand bones), the complete first finger, and the first phalanx bone of the second finger.[1] In 2014, the Japanese palaeontologist Takanobu Tsuihiji and colleagues stated that a bone Lü and colleagues had originally identified as the vomer (part of the palate) of Xixiasaurus was instead part of the premaxillae or maxillae (the main bones of the upper jaw), based on comparison with the vomer of the more complete troodontid Gobivenator.[3]
Description
Xixiasaurus is estimated to have been around 1.5 metres (4 ft 11 in) long, and to have weighed about 8 kilograms (18 lb).[4] As a troodontid maniraptoran, it would have been a small, bird-like, and lightly built theropod. It would have had raptorial (grasping) hands, and an enlarged sickle-claw on the hyper-extendible second toe of its foot.[1][5] Fossils of other troodontids show that members of the group were covered in pennaceous feathers, with long feathers on the arms and legs, and frond-like feathering on the tail (similar to the avialan Archaeopteryx).[6]
It was a troodontid, a group of small, bird-like, gracile maniraptorans. All troodontids have many unique features of the skull, such as large numbers of teeth, which in the lower jaw are closely spaced. Troodontids have sickle-claws and raptorial hands.[1] It is one of few troodontids that have no serrations on their teeth, similar to its closest relative Byronosaurus. Xixiasaurus has fewer teeth than Byronosaurus and Mei, but more than Sinornithoides, Zanabazar and Saurornithoides. Like in Byronosaurus, the palate of Xixiasaurus was extensive, and the teeth were heterodont.[1]
Xixiasaurus is known from a mostly complete skull, only lacking the posterior portion. The top of the snout is slightly displaced, but overall, the skull resembles Byronosaurus. As the nasal bones are very not and not completely fused, the holotype of Xixiasaurus may have died immature. Most of the braincase is preserved, as well as most teeth and all tooth sockets. Viewed from below, the tooth rows form a U-shaped curve. Some small pits are present of the lateral surface of the maxilla. The teeth on the maxilla are larger than those in the premaxilla. The hand and lower arm are also preserved. The claw of the first digit is very large, with a large flexor tubercle. The first phalanges of the first two digits are 3.6 cm (1.4 in) and 3 cm (1.2 in) long, respectively.[1]
Classification
The cladogram below follows a 2012 analysis by Turner, Makovicky and Norell.[7]
| Paraves |
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Palaeobiology
Xixiasaurus and other troodonts without serrated teeth may have been either herbivorous or omnivorous. Trodoonts had some of the highest non-avian encephalization quotients, meaning they were behaviourally advanced and had keen senses.[1]
Palaeoecology
Xixiasaurus is from the middle region of the Majiacun Formation, which dates to the Santonian-Coniacian stages of the Late Cretaceous Period of China, about 86 million years ago.[1]
See also
References
- ^ a b c d e f g h Lü, J.; Xu, L.; Liu, Y.; Zhang, X.; Jia, S.; Ji, Q. (2010). "A New Troodontid Theropod from the Late Cretaceous of Central China, and the Radiation of Asian Troodontids". Acta Palaeontologica Polonica. 55 (3): 381–388. doi:10.4202/app.2009.0047.
- ^ Martyniuk, M. P. (2012). A Field Guide to Mesozoic Birds and Other Winger Dinosaurs. Pan Aves. p. 102. ISBN 978-0-9885965-0-4.
- ^ Tsuihiji, T.; Barsbold, R.; Watabe, M.; Tsogtbaatar, K.; Chinzorig, T.; Fujiyama, Y.; Suzuki, S. (2014). "An exquisitely preserved troodontid theropod with new information on the palatal structure from the Upper Cretaceous of Mongolia". Naturwissenschaften. 101 (2): 131–142. doi:10.1007/s00114-014-1143-9.
- ^ Paul, G. S. (2016). The Princeton Field Guide to Dinosaurs. Princeton University Press. pp. 155, 158. ISBN 978-0-691-16766-4.
- ^ Hendrickx, C.; Hartman, S.A.; Mateus, O. (2015). "An overview on non-avian theropod discoveries and classification". PalArch's Journal of Vertebrate Palaeontology. 12 (1): 1–73.
- ^ Xu, X.; Currie, P.; Pittman, M.; Xing, L.; Meng, Q.; Lü, J.; Hu, D.; Yu, C. (2017). "Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features". Nature Communications. 8: 14972. doi:10.1038/ncomms14972.
- ^ Turner, Alan H.; Makovicky, Peter J.; Norell, Mark A. (2012). "A Review of Dromaeosaurid Systematics and Paravian Phylogeny". Bulletin of the American Museum of Natural History. 371: 1–206. doi:10.1206/748.1. hdl:2246/6352.
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