Biogeography of paravian dinosaurs: Difference between revisions

Paraves first appeared in the fossil record in early [[Late Jurassic]] (163–145 million years ago),<ref name=":1">{{Cite journal|last1=Zheng|first1=X.|last2=O'Connor|first2=J.|last3=Wang|first3=X.|last4=Wang|first4=M.|last5=Zhang|first5=X.|last6=Zhou|first6=Z.|date=2014-09-08|title=On the absence of sternal elements in Anchiornis (Paraves) and Sapeornis (Aves) and the complex early evolution of the avian sternum|journal=Proceedings of the National Academy of Sciences|volume=111|issue=38|pages=13900–13905|doi=10.1073/pnas.1411070111|pmid=25201982|pmc=4183337|issn=0027-8424|bibcode=2014PNAS..11113900Z|doi-access=free }}</ref><ref name=":2">{{Cite journal|last1=Hu|first1=Dongyu|last2=Hou|first2=Lianhai|last3=Zhang|first3=Lijun|last4=Xu|first4=Xing|date=2009-09-24|title=A pre-Archaeopteryx troodontid theropod from China with long feathers on the metatarsus|journal=Nature|volume=461|issue=7264|pages=640–643|doi=10.1038/nature08322|pmid=19794491|issn=0028-0836|bibcode=2009Natur.461..640H|s2cid=205218015 }}</ref> then rapidly diversified and dispersed during [[Cretaceous]] (145–66 million years ago).<ref name=":14">{{Cite journal|last1=Godefroit|first1=Pascal|last2=Cau|first2=Andrea|last3=Dong-Yu|first3=Hu|last4=Escuillié|first4=François|last5=Wenhao|first5=Wu|last6=Dyke|first6=Gareth|date=2013-05-29|title=A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds|journal=Nature|volume=498|issue=7454|pages=359–362|doi=10.1038/nature12168|pmid=23719374|issn=0028-0836|bibcode=2013Natur.498..359G|s2cid=4364892 }}</ref> They emerged during the [[Pangaea#Rifting and break-up|breakup of Pangea]] (since Early-Middle Jurassic),<ref name=":4">{{Cite journal|last=Scotese|first=Christopher R.|date=1991|title=Jurassic and cretaceous plate tectonic reconstructions|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=87|issue=1–4|pages=493–501|doi=10.1016/0031-0182(91)90145-h|issn=0031-0182|bibcode=1991PPP....87..493S}}</ref> which influenced the biogeographic processes such as [[speciation]], [[geodispersal]] and [[extinction]]. By the Late Cretaceous, Paraves reached global distribution with fossils found in modern Asia, Europe, Australia, Antarctica etc.<ref name=":7">{{Cite journal|title=The Biogeography of Coelurosaurian Theropods and its Impact on their Evolutionary History |last1=Ding |first1=Anyang |last2=Pittman |first2=Michael |date=2019-05-10 |last3=Upchurch |first3=Paul |last4=O’Connor |first4=Jingmai |last5=Field |first5=Daniel J.|last6=Xu|first6=Xing|doi = 10.1101/634170|doi-access=free |url=https://www.biorxiv.org/content/biorxiv/early/2019/05/10/634170.full.pdf}}</ref> Almost all Paravian dinosaurs died out before or during the [[Cretaceous–Paleogene extinction event|end-Cretaceous mass extinction]] (~66 million years ago), also called the Cretaceous-Paleogene (K-Pg) mass extinction.<ref name=":3" /><ref name=":15">{{Cite journal|last=Brusatte|first=Stephen L.|date=2016|title=Evolution: How Some Birds Survived When All Other Dinosaurs Died|journal=Current Biology|volume=26|issue=10|pages=R415–R417|doi=10.1016/j.cub.2016.03.043|pmid=27218848|issn=0960-9822|doi-access=free}}</ref><ref name=":9" />

There are limitations to be considered when studying the [[Biogeography|paleobiogeography]] of Paraves. Firstly, the fossil record may not represent the actual distribution of the three clades mainly due to [[Taphonomy|taphonomic bias]].<ref name=":25" /> Also, the fossil record may be incomplete, which may lead to misinterpretations.<ref name=":25">{{Citation|last1=Allison|first1=Peter A.|title=Taphonomy: Bias and Process Through Time|date=2010|work=Topics in Geobiology|pages=1–17|publisher=Springer Netherlands|isbn=9789048186426|last2=Bottjer|first2=David J.|series=Topics in Geobiology |volume=32 |s2cid=55502956|doi=10.1007/978-90-481-8643-3_1}}</ref>

[[File:Geodispersal at Bering Land Bridge.png|thumb|Fig. 3. The figure shows two maps viewed from the North Pole at early and mid-Late Cretaceous. It illustrates the concept of geodispersal through the formation of the Bering Land Bridge between Asia and North America. Modified from Wen et al. (2016).<ref>{{Cite journal|last1=Wen|first1=Jun|last2=Nie|first2=Ze-Long|last3=Ickert-Bond|first3=Stefanie M.|date=2016|title=Intercontinental disjunctions between eastern Asia and western North America in vascular plants highlight the biogeographic importance of the Bering land bridge from late Cretaceous to Neogene|journal=Journal of Systematics and Evolution|volume=54|issue=5|pages=469–490|doi=10.1111/jse.12222|s2cid=89438777 |issn=1674-4918|doi-access=free}}</ref>|alt=|338x338px]][[Vicariance]] is a biogeographic process that occurs when a population is forced to separate into two or more groups due to geographic constraints.<ref>{{Cite journal|last=Paterson|first=Hugh|date=2000|title=Endless Forms: Species and Speciation. Daniel J. Howard , Stewart H. Berlocher|journal=The Quarterly Review of Biology|volume=75|issue=3|pages=319|doi=10.1086/393533|issn=0033-5770}}</ref><ref name=":10">{{Cite encyclopedia|last=Trewick|first=Steve|s2cid=135155273|chapter=Plate Tectonics in Biogeography|date=2017-03-06|encyclopedia=International Encyclopedia of Geography: People, the Earth, Environment and Technology|pages=1–9|publisher=John Wiley & Sons, Ltd|isbn=9780470659632|doi=10.1002/9781118786352.wbieg0638|title=International Encyclopedia of Geography, 15 Volume Set: People, the Earth, Environment and Technology}}</ref> It is a key process in the biogeographic history of Paraves and one of the main hypotheses on the global distribution of dromaeosauridae in Late [[Mesozoic]].<ref>{{Cite journal|last1=Upchurch|first1=Paul|last2=Hunn|first2=Craig A|last3=Norman|first3=David B|date=2002-03-22|title=An analysis of dinosaurian biogeography: evidence for the existence of vicariance and dispersal patterns caused by geological events|journal=Proceedings of the Royal Society of London. Series B: Biological Sciences|volume=269|issue=1491|pages=613–621|doi=10.1098/rspb.2001.1921|pmid=11916478|pmc=1690931|issn=0962-8452}}</ref> Pangea broke up into [[Laurasia]] and [[Gondwana]], creating an oceanic barrier in between the two landmasses where terrestrial faunal exchange was near impossible. In a regional scale, the collapse of land bridges can also cause vicariance.<ref name=":7" />

During the [[Mesozoic|Early Mesozoic]], the supercontinent [[Pangaea|Pangea]] just finished its assembly and almost immediately started breaking apart.<ref name=":4" /> The [[rift]]ing began to take place during Early to Middle [[Jurassic]] (201–163 million years ago), and gradually formed two extensive landmasses&nbsp;– [[Laurasia]] and [[Gondwana]].<ref name=":12" /> The continents then continued to be ripped apart into smaller land that resembled modern continents throughout late [[Mesozoic]] and [[Cenozoic]].<ref name=":4" /> The breakup of continents did not happen uniformly, and modern continents were formed at different speeds while experiencing repeated collision and rifting.<ref>{{Cite journal|last1=Bortolotti|first1=Valerio|last2=Principi|first2=Gianfranco|date=2005|title=Tethyan ophiolites and Pangea break-up|journal=The Island Arc|volume=14|issue=4|pages=442–470|doi=10.1111/j.1440-1738.2005.00478.x|s2cid=129367872 |issn=1038-4871|doi-access=free}}</ref><ref name=":12">{{Cite journal|last1=Frizon de Lamotte|first1=Dominique|last2=Fourdan|first2=Brendan|last3=Leleu|first3=Sophie|last4=Leparmentier|first4=François|last5=de Clarens|first5=Philippe|date=2015|title=Style of rifting and the stages of Pangea breakup|journal=Tectonics|volume=34|issue=5|pages=1009–1029|doi=10.1002/2014tc003760|issn=0278-7407|bibcode=2015Tecto..34.1009F|doi-access=free}}</ref> This phenomenon is closely related to the dispersal and evolution of Paraves.<ref name=":7" />

|✓<ref name=":18">{{Cite journal|last1=Foth|first1=Christian|last2=Rauhut|first2=Oliver W. M.|date=2017|title=Re-evaluation of the Haarlem Archaeopteryx and the radiation of maniraptoran theropod dinosaurs|journal=BMC Evolutionary Biology|volume=17|issue=1|pages=236|doi=10.1186/s12862-017-1076-y|pmid=29197327|pmc=5712154|bibcode=2017BMCEE..17..236F |issn=1471-2148 |doi-access=free }}</ref>

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The iconic [[Jehol Biota]] found in [[Yixian Formation]] and [[Jiufotang Formation]] in [[Inner Mongolia]] yielded fossils of early avialans including [[enantiornithes]] (a subclass of birds)<ref>{{Cite journal|last1=Wang|first1=Xia|last2=Zhang|first2=Zihui|last3=Gao|first3=Chunling|last4=Hou|first4=Lianhai|last5=Meng|first5=Qingjin|last6=Liu|first6=Jinyuan|date=2010|title=A New Enantiornithine Bird From the Early Cretaceous of Western Liaoning, China|journal=The Condor|volume=112|issue=3|pages=432–437|doi=10.1525/cond.2010.090248|s2cid=83803657 |issn=0010-5422|doi-access=free}}</ref> and small dromaeosaurids (i.e. [[Microraptoria|microraptorians]]).<ref>{{Cite journal|last1=Gong|first1=En-Pu|last2=Martin|first2=Larry D.|last3=Burnham|first3=David A.|last4=Falk|first4=Amanda R.|last5=Hou|first5=Lian-Hai|date=2012|title=A new species of Microraptor from the Jehol Biota of northeastern China|journal=Palaeoworld|volume=21|issue=2|pages=81–91|doi=10.1016/j.palwor.2012.05.003|issn=1871-174X}}</ref> During the paravians' rapid diversification, some of the better-known dinosaurs came into existence, including the troodontid [[Mei long|''Mei'']].<ref>{{Cite journal|last1=Xu|first1=Xing|last2=Norell|first2=Mark A.|date=2004|title=A new troodontid dinosaur from China with avian-like sleeping posture|journal=Nature|volume=431|issue=7010|pages=838–841|doi=10.1038/nature02898|pmid=15483610|issn=0028-0836|bibcode=2004Natur.431..838X|s2cid=4362745 |url=http://doc.rero.ch/record/15284/files/PAL_E2583.pdf }}</ref>[[File:The distribution of paraves in Late Cretaceous.png|thumb|389x389px|Fig. 7. A map showing the distribution of Paraves in Late Cretaceous. The dotted lines indicate the position of the continents at the end of Early Cretaceous. Abbreviations: N, North America; S, South America; A, Asia; E, Europe; F, Africa; T, Antarctica; U, Australia; I, India; M, Madagascar. Modified from Ding et al. (2019).<ref name=":7" />]]

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The [[Cretaceous–Paleogene extinction event|Cretaceous-Paleogene mass extinction]] (~66 million years ago) is one of the most-studied extinction events. While not being the largest known mass extinction event, it is famous for its impact on dinosaurs.<ref name="Brusatte 628–642">{{Cite journal|last1=Brusatte|first1=Stephen L.|last2=Butler|first2=Richard J.|last3=Barrett|first3=Paul M.|last4=Carrano|first4=Matthew T.|last5=Evans|first5=David C.|last6=Lloyd|first6=Graeme T.|last7=Mannion|first7=Philip D.|last8=Norell|first8=Mark A.|last9=Peppe|first9=Daniel J.|last10=Upchurch|first10=Paul|last11=Williamson|first11=Thomas E.|date=2014-07-28|title=The extinction of the dinosaurs|journal=Biological Reviews|volume=90|issue=2|pages=628–642|doi=10.1111/brv.12128|pmid=25065505|issn=1464-7931|doi-access=free|hdl=20.500.11820/176e5907-26ec-4959-867f-0f2e52335f88|hdl-access=free}}</ref> Like all other dinosaurian species, almost all Paraves died out sometime between the latest Cretaceous ([[Maastrichtian]]) and the start of [[Paleogene]]&nbsp;– with one exception. Given the title "the most successful dinosaurs" by paleontologists, [[neornithine]]s managed to survive the [[Extinction event|mass extinction]] and continued to flourish in present days.<ref name=":3" /><ref name=":6" />

Another hypothesis suggested that the extinction of non-neornithines was unlikely a result of [[Extinction event|mass extinction]] but was instead caused by a change in vegetation pattern.<ref name=":6" /> It is found that a portion of non-neornithines was already extinct before the [[Chicxulub impactor|impact event]].<ref name=":6" /> This can be accounted for by the regional scale vegetation loss that occurred in North America,<ref>{{Cite book|title=Early Flowers and Angiosperm Evolution|last1=Friis|first1=Else Marie|last2=Crane|first2=Peter R.|last3=Pedersen|first3=Kaj Raunsgaard|date=2011|publisher=Cambridge University Press|isbn=978-0-511-98020-6|location=Cambridge|doi = 10.1017/cbo9780511980206}}</ref> which largely affected the atmospheric composition<ref>{{Cite journal|last1=Alegret|first1=L.|last2=Thomas|first2=E.|last3=Lohmann|first3=K. C.|date=2011-12-29|title=End-Cretaceous marine mass extinction not caused by productivity collapse|journal=Proceedings of the National Academy of Sciences|volume=109|issue=3|pages=728–732|doi=10.1073/pnas.1110601109|pmid=22207626|pmc=3271934|issn=0027-8424|doi-access=free }}</ref> and disrupted the food chain.<ref name=":6" />

Both hypotheses, along with any other possibilities, have yet to be proven with definitive evidence. One certain thing is that [[Bird|neornithines]] did not diversify much in Cretaceous compared to that in the early [[Cenozoic]], unlike other groups of birds.<ref name=":9">{{Cite journal|last=Feduccia|first=Alan|date=2014|title=Avian extinction at the end of the Cretaceous: Assessing the magnitude and subsequent explosive radiation|journal=Cretaceous Research|volume=50|pages=1–15|doi=10.1016/j.cretres.2014.03.009|bibcode=2014CrRes..50....1F |issn=0195-6671}}</ref><ref name=":8">{{Cite journal|last1=Longrich|first1=N. R.|last2=Tokaryk|first2=T.|last3=Field|first3=D. J.|date=2011-09-13|title=Mass extinction of birds at the Cretaceous-Paleogene (K-Pg) boundary|journal=Proceedings of the National Academy of Sciences|volume=108|issue=37|pages=15253–15257|doi=10.1073/pnas.1110395108|pmid=21914849|pmc=3174646|issn=0027-8424|bibcode=2011PNAS..10815253L|doi-access=free }}</ref> The fossil record for neornithines in [[Late Cretaceous]] was sparse, but there was an explosive increase in fossils in Early Cenozoic.<ref name=":9" /> As the radiation of neornithines happened together with the rise of mammals, it seems logical that the two events were related.

[[File:K-Pg boundary and Radiation of Neornithines.png|thumb|287x287px|Fig. 8. A diagram showing the diversification of avialans before and after the K-Pg mass extinction event. The size roughly represents the number of species in that group. Basal birds diversified into different groups in the Cretaceous, while neornithines only began their rapid diversification in Paleocene. Modified from Feduccia (2014).<ref name=":9" />|alt=]]As the UniverseEarth entered a new era, the continents started to move into their modern positions.<ref name=":23">{{Cite journal|last1=RONA|first1=P|last2=RICHARDSON|first2=E|date=1978|title=Early Cenozoic global plate reorganization|journal=Earth and Planetary Science Letters|volume=40|issue=1|pages=1–11|doi=10.1016/0012-821x(78)90069-9|issn=0012-821X|bibcode=1978E&PSL..40....1R}}</ref> Australia and South America finally separated from Antarctica<ref>{{Citation|last1=Wilford|first1=G. E.|title=Maps of late Mesozoic-Cenozoic Gondwana break-up: some palaeogeographical implications|date=2017-03-30|work=History of the Australian Vegetation: Cretaceous to Recent|pages=5–13|publisher=University of Adelaide Press|isbn=978-1-925261-47-9|last2=Brown|first2=P. J.|doi=10.20851/australian-vegetation-02|doi-access=free}}</ref> while the Indian subplate began its collision into Asia, creating the world's largest mountain range the [[Himalayas]].<ref>{{Cite journal|last1=van Hinsbergen|first1=D. J. J.|last2=Lippert|first2=P. C.|last3=Dupont-Nivet|first3=G.|last4=McQuarrie|first4=N.|last5=Doubrovine|first5=P. V.|last6=Spakman|first6=W.|last7=Torsvik|first7=T. H.|date=2012-04-30|title=Greater India Basin hypothesis and a two-stage Cenozoic collision between India and Asia|journal=Proceedings of the National Academy of Sciences|volume=109|issue=20|pages=7659–7664|doi=10.1073/pnas.1117262109|pmid=22547792|pmc=3356651|issn=0027-8424|bibcode=2012PNAS..109.7659V|doi-access=free }}</ref> At the same time, the global average temperature cooled down<ref>{{Cite journal|last1=Zachos|first1=James C|last2=Opdyke|first2=Bradley N|last3=Quinn|first3=Terrence M|last4=Jones|first4=Charles E|last5=Halliday|first5=Alex N|date=1999|title=Early cenozoic glaciation, antarctic weathering, and seawater 87Sr/86Sr: is there a link?|journal=Chemical Geology|volume=161|issue=1–3|pages=165–180|doi=10.1016/s0009-2541(99)00085-6|issn=0009-2541|bibcode=1999ChGeo.161..165Z}}</ref><ref>{{Cite journal|last1=Fletcher|first1=Benjamin J.|last2=Brentnall|first2=Stuart J.|last3=Anderson|first3=Clive W.|last4=Berner|first4=Robert A.|last5=Beerling|first5=David J.|s2cid=128436783|date=2007-12-09|title=Atmospheric carbon dioxide linked with Mesozoic and early Cenozoic climate change|journal=Nature Geoscience|volume=1|issue=1|pages=43–48|doi=10.1038/ngeo.2007.29|issn=1752-0894}}</ref> since [[Late Cretaceous]] with a [[Paleocene–Eocene Thermal Maximum|Thermal Maximum]] at [[Paleocene]]-[[Eocene]] boundary and [[Middle Miocene]] Climatic Optimum.<ref>{{Cite journal|last1=Mudelsee|first1=Manfred|last2=Bickert|first2=Torsten|last3=Lear|first3=Caroline H.|last4=Lohmann|first4=Gerrit|date=2014-08-11|title=Cenozoic climate changes: A review based on time series analysis of marine benthic δ18O records|journal=Reviews of Geophysics|volume=52|issue=3|pages=333–374|doi=10.1002/2013rg000440|issn=8755-1209|bibcode=2014RvGeo..52..333M|url=https://epic.awi.de/id/eprint/37401/1/Mudelsee_et_al-2014-Reviews_of_Geophysics.pdf|doi-access=free}}</ref> Between these warm episodes were periods of cooling ([[Oligocene]] global cooling),<ref name=":6" /> where seawater level fell and land bridges between Africa and Eurasia (i.e. [[Gomphotherium land bridge|Gomphotherium landbridge]]),<ref>{{Cite journal|last=Böhme|first=Madelaine|date=2003|title=The Miocene Climatic Optimum: evidence from ectothermic vertebrates of Central Europe|journal=Palaeogeography, Palaeoclimatology, Palaeoecology|volume=195|issue=3–4|pages=389–401|doi=10.1016/s0031-0182(03)00367-5|issn=0031-0182|bibcode=2003PPP...195..389B}}</ref> and Eurasia and North America (i.e. [[Beringia|Bering Land Bridge]])<ref name=":20" /> were formed.

Since the continents were almost entirely separated from each other,<ref name=":23" /> [[Bird|neornithines]] began to [[Speciation|speciate]] independently.<ref name=":6" /> Most of the [[mutation]]s occurred in birds without long-distance flight abilities, and the most prominent changes were found in birds living on isolated islands like New Zealand and Australia.<ref name=":6" /><ref name=":24" /> It is hypothesised that due to the lack of large [[carnivorous]] (meat-eating) [[Predation|predators]] on these islands due to the extinction of dinosaurs, birds were able to evolve and [[Adaptive radiation|adapt]] to the new environments.<ref name=":6" /> Such [[mutation]]s include an increase in body sizes but reduced wings and development of flightlessness, as found in birds like [[moa]]s (completely extinct by the year 1440<ref>{{Cite journal|last=Holdaway|first=R. N.|date=2000-03-24|title=Rapid Extinction of the Moas (Aves: Dinornithiformes): Model, Test, and Implications|journal=Science|volume=287|issue=5461|pages=2250–2254|doi=10.1126/science.287.5461.2250|pmid=10731144|issn=0036-8075|bibcode=2000Sci...287.2250H}}</ref>), [[Kiwi (bird)|kiwi]]s and [[Common ostrich|ostriches]].<ref name=":6" /> Though they were not closely related to one another, this evolution pattern indicates that birds evolve similarly in isolated environments without major threats of predators.<ref name=":24">{{Cite journal|last1=Cooper|first1=A.|last2=Mourer-Chauvire|first2=C.|last3=Chambers|first3=G. K.|last4=von Haeseler|first4=A.|last5=Wilson|first5=A. C.|last6=Paabo|first6=S.|date=1992-09-15|title=Independent origins of New Zealand moas and kiwis.|journal=Proceedings of the National Academy of Sciences|volume=89|issue=18|pages=8741–8744|doi=10.1073/pnas.89.18.8741|pmid=1528888|pmc=49996|issn=0027-8424|bibcode=1992PNAS...89.8741C|doi-access=free }}</ref>

There are some limitations in studying the biogeography of Paraves, including their development of [[flight]]. Flight capabilities in Paraves were developed since the Late Jurassic.<ref name=":6" /> While only several groups of [[Paraves|paravian]] dinosaurs have such abilities, it is certainly a possibility that it contributed to their dispersal in late Mesozoic.<ref name=":18"/> In these cases, the biogeographic record of Paraves cannot be interpreted solely by whether the land was connected or not. Modern [[migratory birds]] can travel covering long distances without relying much on land. This means that the development of long-distance flight occurred at some point between the first appearance of bird-like dinosaurs and present day.<ref name=":6" /> It is found that, at least until [[Early Cretaceous]], Paraves can only glide between trees instead of flying like modern birds.<ref>{{Cite journal|last1=Chatterjee|first1=S.|last2=Templin|first2=R. J.|date=2007-01-22|title=Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui|journal=Proceedings of the National Academy of Sciences|volume=104|issue=5|pages=1576–1580|doi=10.1073/pnas.0609975104|pmid=17242354|pmc=1780066|issn=0027-8424|bibcode=2007PNAS..104.1576C|doi-access=free }}</ref> Thus, their flight abilities do not affect the dispersal of Paraves.<ref name=":7" /> In [[Cenozoic]], avian flight abilities were more or less developed in [[Bird|neornithines]], though there are exceptions that are flightless birds mainly found in isolated islands.<ref name=":24" /> Since then, flight in avians had become a major factor contributing to the dispersal of birds.<ref name=":6" />

[[Taphonomic bias]] is caused by the difference in how organisms decay and fossilise. It is another challenge faced by paleontologists as the fossil records are often incomplete.<ref>{{Citation|last=Lyman|first=R. Lee|pages=1–11|publisher=Cambridge University Press|isbn=978-1-139-87830-2|doi=10.1017/cbo9781139878302.002|chapter=What is Taphonomy?|title=Vertebrate Taphonomy|year=1994}}</ref> Moreover, some localities have better-preserved record due to their geological history than the others, leading to misinterpretations in biogeography.<ref>{{Citation|last1=Allison|first1=Peter A.|title=Taphonomy: Bias and Process Through Time|date=2010|work=Topics in Geobiology|pages=1–17|publisher=Springer Netherlands|isbn=978-90-481-8642-6|last2=Bottjer|first2=David J.|series=Topics in Geobiology |volume=32 |s2cid=55502956|doi=10.1007/978-90-481-8643-3_1}}</ref> This is especially true for dinosaurian fossil records since localities in North America and China had a much higher abundance of fossils preserved in [[Sedimentary rock|sedimentary rocks]].<ref name=":7" /><ref name=":6" /> In fact, there is only one known rock formation that holds a relatively complete and dated record of the latest [[Cretaceous]] ([[Maastrichtian]]), named the [[Hell Creek Formation]] in western North America.<ref name="Brusatte 628–642"/> The fossils for birds (including basal [[Avialae|avialans]]) in [[Late Cretaceous]] are incomplete as well, given the sparse record discovered in Australia and Antarctica.<ref name=":8" />