Editing Alvarezsauridae

{{Short description|Family of extinct long-legged dinosaurs}}
{{Automatic taxobox
| name = Alvarezsaurids
| fossil_range = [[Late Cretaceous]],<br/> {{fossilrange|97|66}}
| image = Mononykus.jpg
| image_caption = Mounted holotype of ''[[Mononykus]]''
| image2 = Alvarezsaurus.jpg
| image2_caption = Skeletal mount of ''[[Alvarezsaurus]]''
| image_upright = 1.2
| taxon = Alvarezsauridae
| authority = [[José Bonaparte|Bonaparte]], 1991
| type_species = {{extinct}}''[[Alvarezsaurus calvoi]]''
| type_species_authority = Bonaparte, 1991
| subdivision_ranks = Subgroups
| subdivision = 
*{{extinct}}''[[Achillesaurus]]''?
*{{extinct}}''[[Alnashetri]]''?
*{{extinct}}''[[Alvarezsaurus]]''
*{{extinct}}''[[Bradycneme]]''
*{{extinct}}''[[Heptasteornis]]''
*{{extinct}}'''Patagonykinae'''?
**{{extinct}}''[[Bonapartenykus]]''
**{{extinct}}''[[Patagonykus]]''
*{{extinct}}'''Parvicursorinae'''
**{{extinct}}''[[Dzharaonyx]]''
**{{extinct}}''[[Jaculinykus]]''
**{{extinct}}''[[Khulsanurus]]''
**{{extinct}}''[[Kol ghuva|Kol]]''
**{{extinct}}''[[Nemegtonykus]]''
**{{extinct}}''[[Ondogurvel]]''
**{{extinct}}''[[Parvicursor]]''
**{{extinct}}''[[Qiupanykus]]''
**{{extinct}}''[[Trierarchuncus]]''
**{{extinct}}'''Ceratonykini'''
***{{extinct}}''[[Albinykus]]''
***{{extinct}}''[[Ceratonykus]]''
***{{extinct}}''[[Xixianykus]]''
**{{extinct}}'''Mononykini'''
***{{extinct}}''[[Albertonykus]]''
***{{extinct}}''[[Linhenykus]]''
***{{extinct}}''[[Mononykus]]''
***{{extinct}}''[[Shuvuuia]]''
| synonyms =
*'''Bradycnemidae'''? <small>[[Colin Harrison (ornithologist)|Harrison]] & [[Cyril Walker (ornithologist)|Walker]], 1975 (in part)</small>
*'''Parvicursoridae''' <small>[[A.A. Karhu|Karhu]] & [[Rautian]], 1996</small>
*'''Mononykidae''' <small>Chiappe ''et al.'', 1998</small>
}}

'''Alvarezsauridae''' is a [[family (biology)|family]] of small, long-legged [[dinosaur]]s. Although originally thought to represent the earliest known flightless [[bird]]s, they are now thought to be an early diverging branch of [[maniraptora]]n [[theropod]]s. Alvarezsaurids were highly specialized. They had tiny but stout forelimbs, with compact, bird-like hands. Their skeletons suggest that they had massive breast and arm muscles, possibly adapted for digging or tearing. They had long, tube-shaped snouts filled with tiny teeth. They have been interpreted as [[Myrmecophagy|myrmecophagous]], adapted to prey on colonial insects such as [[termites]], with the short arms acting as effective digging instruments to break into nests. 

''[[Alvarezsaurus]]'', the [[type genus]] of the family, was named for the [[historian]] [[Gregorio Álvarez (historian)|Gregorio Álvarez]].<ref>i.e. not the more familiar [[physicist]] [[Luis Walter Alvarez|Luis Alvarez]], who proposed that the [[Cretaceous–Paleogene extinction event]] was caused by an [[impact event]]</ref>

==History of study==
Bonaparte (1991) described the first alvarezsaurid, ''[[Alvarezsaurus calvoi]]'', from an incomplete skeleton found in Patagonia, Argentina. Bonaparte also named a [[Family (biology)|family]], Alvarezsauridae, to contain it. He argued that ''Alvarezsaurus'' might be most closely related to the [[Ornithomimosauria|ornithomimosaurs]].<ref name="Bonaparte1991">{{cite journal |last1=Bonaparte |first1=José F. |title=Los vertebrados fósiles de la formación Río Colorado, de la ciudad de Neuquén y cercanías, Cretácico Superior, Argentina |journal=Revista del Museo Argentino de Ciencias Naturales "Bernardino Rivadavia". Paleontología |date=1991 |volume=4 |issue=3 |pages=15–123 |oclc=29480292 }}</ref>

In 1993, Perle ''et al.'' described the next alvarezsaur to be discovered, naming it ''Mononychus olecranus'' (meaning "one claw"). A month later they changed the genus name to ''[[Mononykus]]'', because the earlier spelling was already the genus name of an extant beetle.<ref name="Perleetal1993b">{{cite journal |last1=Altangerel |first1=Perle |last2=Norell |first2=Mark A. |last3=Chiappe |first3=Luis M. |last4=Clark |first4=James M. |title=Flightless bird from the Cretaceous of Mongolia |journal=Nature |date=April 1993 |volume=362 |issue=6421 |pages=623–626 |doi=10.1038/362623a0 |bibcode=1993Natur.362..623A |s2cid=4252852 }}</ref> Perle ''et al.'' mistakenly described ''[[Mononykus]]'' as a member of [[Avialae]], one more advanced than ''[[Archaeopteryx]]''. They argued that the family Alvarezsauridae was actually a group of Mesozoic flightless birds on the basis of several features that were supposedly unique to birds.<ref name="Perleetal1993a">{{cite journal |last1=Altangerel |first1=Perle |last2=Norell |first2=Mark A. |last3=Chiappe |first3=Luis M. |last4=Clark |first4=James M. |title=Flightless bird from the Cretaceous of Mongolia |journal=Nature |date=15 April 1993 |volume=362 |issue=6421 |pages=623–626 |doi=10.1038/362623a0 |bibcode=1993Natur.362..623A |s2cid=4252852 }}</ref>

In 1996, Novas described another member of the group called ''[[Patagonykus puertai]]''.<ref name="Novas1996">{{cite journal |id={{BHL page|40091128}} |last1=Novas |first1=Fernando E. |title=Alvarezsauridae, Cretaceous basal birds from Patagonia and Mongolia |journal=Memoirs of the Queensland Museum |date=1996 |volume=39 |pages=675–702 }}</ref> Karhu and Rautian (1996) described a Mongolian member of the family; ''[[Parvicursor]] remotus''.<ref name="Karhu&Rautian1996">{{cite journal |last1=Karhu |first1=A. A. |last2=Rautian |first2=A. S. |title=A new family of Maniraptora (Dinosauria: Saurischia) from the Late Cretaceous of Mongolia |journal=Paleontological Journal |volume=30 |issue=5 |year=1996 |pages=583–592 }}</ref> Chiappe ''et al.''(1998) described another Mongolian member, ''[[Shuvuuia]] deserti'', and found it to be a bird as in Perle et al.'s analysis.<ref name="Chiappeetal1998">{{cite journal |last1=Chiappe |first1=Luis M. |last2=Norell |first2=Mark A. |last3=Clark |first3=James M. |title=The skull of a relative of the stem-group bird Mononykus |journal=Nature |date=March 1998 |volume=392 |issue=6673 |pages=275–278 |doi=10.1038/32642 |bibcode=1998Natur.392..275C |s2cid=4426807 }}</ref>

[[Image:Patagonykus.jpg|thumb|left|Reconstructed skeleton of ''[[Patagonykus puertai]]'']] 
These mistaken assignments of alvarezsaurids to birds were caused primarily by features that are strikingly, or even uniquely, avian. The sternum, for example, is elongated and deeply keeled for an enlarged pectoralis muscle, as it is in [[neognathous]] birds and [[Flying and gliding animals|volant]] [[ratite]]s. One bone in the skull of ''[[Shuvuuia]]'' appeared to be an ectethmoid fused to a prefrontal. The ectethmoid is an ossification known only in [[Neornithes]]. Other birdlike characters included the palatine, foramen magnum, cervical and caudal vertebrae, and many others.<ref name="Sereno2001">{{cite book |last1=Sereno |first1=Paul |year=2001 |chapter=Alvarezsaurids: Birds or ornithomimosaurs? |editor1-last=Gauthier |editor1-first=Jacques |editor2-last=Ostrom |editor2-first=John H. |title=New Perspectives on the Origin and Early Evolution of Birds |publisher=Peabody Museum of Natural History Yale University |isbn=978-0-912532-57-8 }}</ref>

Several researchers disagreed with Perle ''et al.'' (1993) and Chiappe ''et al.'' (1998), Feduccia (1994), Ostrom (1994), Wellnhofer (1994), Kurochkin (1995), Zhou (1995), and Sereno (1997) considered it unlikely that alvarezsaurids were members of [[Avialae]]. Martin (1997) performed a cladistic analysis  but Sereno criticized it strongly, finding it flawed by incorrect codings, use of only select data, and results that did not support his conclusions. Sereno (1999) performed a new analysis, revising the anatomical interpretations and clarifying the characters. He found that alvarezsaurids were more parsimoniously related to the [[Ornithomimosauria]].<ref name="Sereno2001"/>

As the more primitive members of the Alvarezsauridae were better characterized, the monophyly of the clade was strongly supported,<ref name="Novas1996"/> but the more primitive members lacked the most birdlike traits. Some of these traits had been misinterpreted, also. The remaining similarities between birds and alvarezsaurs, like the keeled sterna, are another case of [[homoplasy]]; where the derived alvarezsaurids developed birdlike characters  through convergent evolution, rather than inheriting them from a common ancestor with birds.<ref name="Sereno2001"/>

==Description==
[[File:Alvarezsaurid scale martyniuk.png|thumb|left|Size comparison of several parvicursorines: ''Parvicursor remotus'' (green), ''Ceratonykus oculatus'' (red), ''Shuvuuia deserti'' (blue), and ''Mononykus olecranus'' (violet).]]
Alvarezsaurids ranged from {{convert|50|cm|in}} to {{convert|2|m|ft}} in length, although some possible members may have been larger, including the European ''[[Heptasteornis]]'' that may have reached {{convert|2.5|m|ft}} long. Fossils attributed to alvarezsaurids have also been found in [[North America|North]] and [[South America]] and [[Asia]], and range in age from about 86 to 66 million years ago.<ref>{{cite journal | last1 = Hutchinson | last2 = Chiappe | year = 1998 | title = The first known alvarezsaurid (Theropoda: Aves) from North America | journal = Journal of Vertebrate Paleontology | volume = 18 | issue = 3| pages = 447–450 | doi=10.1080/02724634.1998.10011073}}</ref>

===Feathers===
At least one specimen of alvarezsaurid, from the [[species]] ''[[Shuvuuia|Shuvuuia deserti]]'', preserved down-like, [[feather]]y, [[integument]]al structures covering the fossil. Schweitzer ''et al.'' (1999) subjected these filaments to microscopic, morphological, mass spectrometric, and immunohistochemical studies and found that they consisted of [[beta-keratin]], which is the primary protein in [[feather]]s.<ref name="Schweitzeretal1999">{{cite journal |last1=Schweitzer |first1=M. H. |last2=Watt |first2=J. A. |last3=Avci |first3=R. |last4=Knapp |first4=L. |last5=Chiappe |first5=L. |last6=Norell |first6=M. |last7=Marshall |first7=M. |title=Beta-keratin specific immunological reactivity in feather-like structures of the Cretaceous Alvarezsaurid, Shuvuuia deserti |journal=Journal of Experimental Zoology |date=1999 |volume=285 |issue=2 |pages=146–157 |doi=10.1002/(SICI)1097-010X(19990815)285:2<146::AID-JEZ7>3.0.CO;2-A |pmid=10440726 }}</ref>

==Lifestyle==
The lifestyle of alvarezsaurids has been debated since the nature of these dinosaurs was established. It has been suggested by numerous palaeontologists that they used their claws to break into ant and termite colonies, though the arm anatomy of an alvarezsaurid would require the animal to lie on its chest against a termite nest. It is also possible that the alvarezsaurids filled some ecological niche that has not yet been considered.<ref name=Holtz>{{cite book |last=Holtz |first=Thomas R. Jr. |year=2007 |title=Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages |chapter=Ornithomimosaurs and Alvarezsaurs |publisher=Random House Children's Books |isbn=978-0-375-82419-7 |chapter-url-access=registration |chapter-url=https://archive.org/details/dinosaursmostcom00holt }}</ref> Studies of the tails in various alvarezsaur genera also suggest they were possessed of an incredible ability to change their rotational inertia, and combined with their forelimbs, this suggests their ecological niches were similar to those of aardvarks, pangolins, and anteaters.<ref>{{cite journal |last1=Meso |first1=J.G. |last2=Qin |first2=Z. |last3=Pittman |first3=M. |last4=Canale |first4=J.I. |last5=Salgado |first5=L. |last6=Díez Díaz |first6=V. |title=Tail anatomy of the Alvarezsauria (Theropoda, Coelurosauria), and its functional and behavioural implications |journal=Cretaceous Research |date=March 2021 |volume=124 |pages=104830 |doi=10.1016/j.cretres.2021.104830 |s2cid=233858300 }}</ref>

Additionally, it is known that alvarezsaurids, with their long legs, appear to be built for speed. What implications this has on possible lifestyle is unknown.<ref name=Holtz/> The discovery of ''[[Qiupanykus]]'' in association with [[oviraptorid]] eggs, indicates that the advanced alvarezsaurids may also have been specialists in nest raiding, using their robust thumb claws to crack open eggshells.<ref name=lu>{{cite journal |last1=Lü |first1=Jun-chang |last2=Xu |first2=Li |last3=Chang |first3=Hua-li |last4=Jia |first4=Song-hai |last5=Zhang |first5=Ji-ming |last6=Gao |first6=Dian-song |last7=Zhang |first7=Yi-yang |last8=Zhang |first8=Cheng-jun |last9=Ding |first9=Fang |title=A new alvarezsaurid dinosaur from the Late Cretaceous Qiupa Formation of Luanchuan, Henan Province, central China |journal=China Geology |date=2018 |volume=1 |issue=1 |pages=28–35 |doi=10.31035/cg2018005 |doi-access=free }}</ref>

==Classification== 
[[Image:Shuvuuia.jpg|thumb|right|Life restoration of ''Shuvuuia deserti'']]
Turner ''et al.'' (2007) place the alvarezsaurs as the most basal group in the [[Maniraptora]], one step more derived than ''[[Ornitholestes]]'' and two more derived than the [[Ornithomimosauria]]. The alvarezsaurs are more primitive than the [[Oviraptorosauria]].<ref name="Turneretal07">{{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. |title=A Basal Dromaeosaurid and Size Evolution Preceding Avian Flight |journal=Science |date=7 September 2007 |volume=317 |issue=5843 |pages=1378–1381 |doi=10.1126/science.1144066 |pmid=17823350 |bibcode=2007Sci...317.1378T |doi-access=free }}</ref>

Novas' 1996 description of ''[[Patagonykus]]'', demonstrated that it was a link between the more primitive (basal) ''Alvarezsaurus'' and the more advanced (derived) ''Mononykus'', and reinforced their monophyly. ''[[Parvicursor]]'' was discovered shortly after, and placed in its own family Parvicursoridae, and then ''Shuvuuia'' in 1998. Everything has since been lumped into Alvarezsauridae, with Mononykinae surviving as a [[subfamily]].

There may be a relationship between the alvarezsaurids and the [[Ornithomimosauria]] as sister clades within either [[Thomas Holtz]]'s [[Arctometatarsalia]] or [[Paul Sereno]]'s [[Ornithomimiformes]]. The discovery of ''[[Haplocheirus]]'', which exhibits transitional features between the more derived alvarezsaurs and other [[maniraptora]]ns, particularly in relation to the skull structure and development of the hand, has provided further support for that relationship.<ref>Choiniere, J. (2010). [http://archosaurmusings.wordpress.com/2010/01/29/guest-post-haplocheirus-%E2%80%93-the-skilful-one/ Guest Post: ''Haplocheirus'', the Skillful One] Dave Hone's Archosaur Musings, April 23, 2011.</ref>

The taxonomy of the alvarezsaurs has been somewhat confused, due to different authors using different names for groups with the same definition. The [[Family (biology)|family]] Alvarezsauridae was first coined by Jose Bonaparte in 1991, but given no specific phylogenetic definition. Novas later defined the group as the most recent common ancestor of ''[[Alvarezsaurus]]'' and ''[[Mononykus]]'' plus all its descendants, though others, such as [[Paul Sereno]], used a more inclusive definition, such as all dinosaurs closer to ''[[Shuvuuia]]'' than to modern birds. In 2009, Livezey and Zusi used the name Alvarezsauroidea for the total group of all alvarezsaurs, restricting the name Alvarezsauridae to the clade defined by ''Alvarezsaurus'' + ''Mononykus''. This was followed by Choiniere and colleagues in 2010, who described the first non-alvarezsaurid alvarezsauroid, ''[[Haplocheirus]]''.<ref name=haplocheirus>{{cite journal |last1=Choiniere |first1=J. N. |last2=Xu |first2=X. |last3=Clark |first3=J. M. |last4=Forster |first4=C. A. |last5=Guo |first5=Y. |last6=Han |first6=F. |title=A Basal Alvarezsauroid Theropod from the Early Late Jurassic of Xinjiang, China |journal=Science |date=29 January 2010 |volume=327 |issue=5965 |pages=571–574 |doi=10.1126/science.1182143 |pmid=20110503 |bibcode=2010Sci...327..571C |s2cid=36904501 }}</ref> Some authors have used the name Mononykinae for the sub-group of alvarezsaurs including the advanced Mongolian species. However, Choiniere and colleagues argued that Parvicursorinae has priority, since its coordinate name under the [[International Code of Zoological Nomenclature|ICZN Code]], Parvicursoridae, was named earlier.<ref name=haplocheirus/> Another subfamily, Patagonykinae, has been named to include the South American ''Patagonykus'' and ''Bonapartenykus'', but a few recent studies have placed them just outside Alvarezsauridae, some of which do not even recover them in a single clade, making Patagonykinae turn out to be paraphyletic.<ref name="agnolinetal2012">{{cite journal |last1=Agnolin |first1=Federico L. |last2=Powell |first2=Jaime E. |last3=Novas |first3=Fernando E. |last4=Kundrát |first4=Martin |date=June 2012 |title=New alvarezsaurid (Dinosauria, Theropoda) from uppermost Cretaceous of north-western Patagonia with associated eggs |journal=Cretaceous Research |volume=35 |pages=33–56 |doi=10.1016/j.cretres.2011.11.014}}</ref><ref name="Xu2018">{{cite journal|doi=10.1016/j.cub.2018.07.057|title=Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution|journal=Current Biology|year=2018|last1=Xu|first1=Xing|last2=Choiniere|first2=Jonah|last3=Tan|first3=Qingwei|last4=Benson|first4=Roger B.J|last5=Clark|first5=James|last6=Sullivan|first6=Corwin|last7=Zhao|first7=Qi|last8=Han|first8=Fenglu|last9=Ma|first9=Qingyu|last10=He|first10=Yiming|last11=Wang|first11=Shuo|last12=Xing|first12=Hai|last13=Tan|first13=Lin|pmid=30146153|volume=28|issue=17 |pages=2853–2860.e3|doi-access=free}}</ref><ref>{{cite journal|first1=Zichuan |last1=Qin |first2=James |last2=Clark |first3=Jonah |last3=Choiniere |first4=Xing |last4=Xu |year=2019 |title= A new alvarezsaurian theropod from the Upper Jurassic Shishugou Formation of western China|journal=Scientific Reports |volume=9 |issue=1 |page=11727 |doi=10.1038/s41598-019-48148-7 |pmid=31409823 |pmc=6692367 |bibcode=2019NatSR...911727Q }}</ref><ref name=Fowler2020>{{cite journal |author1=Denver W. Fowler |author2=John P. Wilson |author3=Elizabeth A. Freedman Fowler |author4=Christopher R. Noto |author5=Daniel Anduza |author6=John R. Horner |year=2020 |title=''Trierarchuncus prairiensis'' gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana |journal=Cretaceous Research |volume=116 |pages=Article 104560 |doi=10.1016/j.cretres.2020.104560 |s2cid=225630913 |doi-access=free }}</ref><ref name="Averianov">{{cite journal| vauthors = Averianov AO, Lopatin AV |title=A re-appraisal of ''Parvicursor remotus'' from the Late Cretaceous of Mongolia: implications for the phylogeny and taxonomy of alvarezsaurid theropod dinosaurs |journal=Journal of Systematic Palaeontology |year=2022 |volume=19 |issue=16 |pages=1097–1128 |doi=10.1080/14772019.2021.2013965 |s2cid=247222017 }}</ref><ref name=Dzharaonyx>{{Cite journal |vauthors=Averianov AO, Sues HD |year=2022 |title=New material and diagnosis of a new taxon of alvarezsaurid (Dinosauria, Theropoda) from the Upper Cretaceous Bissekty Formation of Uzbekistan |journal=Journal of Vertebrate Paleontology |volume=41 |issue=5 |pages=e2036174  |doi=10.1080/02724634.2021.2036174 |s2cid=247391327 }}</ref>

The cladogram below is the latest and most comprehensive analysis of alvarezsaurid evolution, following Meso et al. (2024).<ref>{{Cite journal |last=Meso |first=Jorge Gustavo |last2=Pol |first2=Diego |last3=Chiappe |first3=Luis |last4=Qin |first4=Zichuan |last5=Díaz-Martínez |first5=Ignacio |last6=Gianechini |first6=Federico |last7=Apesteguía |first7=Sebastián |last8=Makovicky |first8=Peter J. |last9=Pittman |first9=Michael |title=Body size and evolutionary rate analyses reveal complex evolutionary history of Alvarezsauria |url=https://onlinelibrary.wiley.com/doi/10.1111/cla.12600 |journal=Cladistics |language=en |volume=n/a |issue=n/a |doi=10.1111/cla.12600 |issn=1096-0031|pmc=11811816 }}</ref>{{clade|{{clade
|1={{clade
|label1='''Patagonykinae'''
|1={{clade
|1=''[[Bonapartenykus ultimus]]''
|2=''[[Patagonykus puertai]]'' }}
|2={{clade
|1=''[[Achillesaurus manazzonei]]''
|2=''[[Alvarezsaurus calvoi]]'' }} }}
|label2='''Parvicursorinae'''
|2={{clade
|1=''[[Ceratonykus oculatus]]''
|2={{clade
|1=''[[Khulsanurus magnificus]]''
|2={{clade
|1=''[[Qiupanykus zhangi]]''
|2={{clade
|1=''[[Dzharaonyx eski]]''
|2={{clade
|1={{clade
|1=''[[Linhenykus monodactylus]]''
|2=''[[Parvicursor remotus]]'' }}
|label2='''Mononykini'''
|2={{clade
|1=''[[Shuvuuia deserti]]''
|2={{clade
|1=''[[Mononykus olecranus]]''
|2={{clade
|1=''[[Ondogurvel alifanovi]]''
|2=''[[Albinykus baatar]]'' }} }} }} }} }} }} }} }} }}|style=font-size:85%; line-height:75%;|label1='''Alvarezsauridae'''}}

==References==
{{Reflist}}

==External links==
* [http://dml.cmnh.org/2001Jan/msg00181.html RE: Alvarezsauridae splitting] {{Webarchive|url=https://web.archive.org/web/20160806154139/http://dml.cmnh.org/2001Jan/msg00181.html |date=2016-08-06 }}, by [[Thomas R. Holtz Jr.]], from the Dinosaur Mailing List.
* [http://dml.cmnh.org/2004Oct/msg00189.html The Holy of Holies... Dinosauria II] {{Webarchive|url=https://web.archive.org/web/20160806024439/http://dml.cmnh.org/2004Oct/msg00189.html |date=2016-08-06 }}, by Thomas R. Holtz Jr., from the Dinosaur Mailing List (mentions in passing the alvarezsaurid ''[[Rapator]]'' hypothesis seeing print for the first time; it had been rumored on the list for several years prior)

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[[Category:Alvarezsauridae]]
[[Category:Dinosaur families]]
[[Category:Late Cretaceous dinosaurs]]