Editing Dinosaur (section)

===Physiology===
{{Main|Physiology of dinosaurs}}
Because both modern crocodilians and birds have four-chambered hearts (albeit modified in crocodilians), it is likely that this is a trait shared by all archosaurs, including all dinosaurs.<ref name=CH04/> While all modern birds have high metabolisms and are [[endotherm]]ic ("warm-blooded"), a vigorous debate has been ongoing since the 1960s regarding how far back in the dinosaur lineage this trait extended. Various researchers have supported dinosaurs as being endothermic, [[ectotherm]]ic ("cold-blooded"), or somewhere in between.<ref name="pontzer2009">{{cite journal |last1=Pontzer |first1=H. |last2=Allen |first2=V. |last3=Hutchinson |first3=J.R. |year=2009 |title=Biomechanics of running indicates endothermy in bipedal dinosaurs |journal=PLOS ONE |volume=4 |issue=11 |page=e7783 |doi=10.1371/journal.pone.0007783 |doi-access=free |pmc=2772121 |pmid=19911059 |bibcode=2009PLoSO...4.7783P |issn=1932-6203}}</ref> An emerging consensus among researchers is that, while different lineages of dinosaurs would have had different metabolisms, most of them had higher metabolic rates than other reptiles but lower than living birds and mammals,<ref name="benson2018">{{cite journal |last1=Benson |first1=R.B.J. |year=2018 |title=Dinosaur Macroevolution and Macroecology |journal=Annual Review of Ecology, Evolution, and Systematics |volume=49 |pages=379–408 |doi=10.1146/annurev-ecolsys-110617-062231|s2cid=92837486 |doi-access=free }}</ref> which is termed [[mesotherm]]y by some.<ref name="grady2014">{{cite journal |last1=Grady |first1=J.M. |last2=Enquist |first2=B.J. |last3=Dettweiler-Robinson |first3=E. |last4=Wright |first4=N.A. |last5=Smith |first5=F.A. |year=2014 |title=Evidence for mesothermy in dinosaurs |journal=Science |volume=344 |issue=6189 |pages=1268–1272 |doi=10.1126/science.1253143|pmid=24926017 |bibcode=2014Sci...344.1268G |s2cid=9806780 }}</ref> Evidence from crocodiles and their extinct relatives suggests that such elevated metabolisms could have developed in the earliest archosaurs, which were the common ancestors of dinosaurs and crocodiles.<ref name="legendre2016">{{cite journal |last1=Legendre |first1=L.J. |last2=Guénard |first2=G. |last3=Botha-Brink |first3=J. |last4=Cubo |first4=J. |title=Palaeohistological Evidence for Ancestral High Metabolic Rate in Archosaurs |journal=Systematic Biology |year=2016 |volume=65 |issue=6 |pages=989–996 |doi=10.1093/sysbio/syw033|pmid=27073251 |doi-access=free }}</ref><ref name="seymour2004">{{cite journal |last1=Seymour |first1=R.S. |last2=Bennett-Stamper |first2=C.L. |last3=Johnston |first3=S.D. |last4=Carrier |first4=D.R. |last5=Grigg |first5=G.C. |year=2004 |title=Evidence for endothermic ancestors of crocodiles at the stem of archosaur evolution |journal=Physiological and Biochemical Zoology |volume=77 |issue=6 |pages=1051–1067 |doi=10.1093/sysbio/syw033|pmid=27073251 |doi-access=free }}</ref>

[[File:Pasta-Brontosaurus.jpg|thumb|left|This 1897 restoration of ''[[Brontosaurus]]'' as an aquatic, tail-dragging animal, by [[Charles R. Knight]], typified early views on dinosaur lifestyles.]]
After non-avian dinosaurs were discovered, paleontologists first posited that they were ectothermic. This was used to imply that the ancient dinosaurs were relatively slow, sluggish organisms, even though many modern reptiles are fast and light-footed despite relying on external sources of heat to regulate their body temperature. The idea of dinosaurs as ectothermic remained a prevalent view until [[Robert T. Bakker]], an early proponent of dinosaur endothermy, published an influential paper on the topic in 1968. Bakker specifically used anatomical and ecological evidence to argue that sauropods, which had hitherto been depicted as sprawling aquatic animals with their tails dragging on the ground, were endotherms that lived vigorous, terrestrial lives. In 1972, Bakker expanded on his arguments based on energy requirements and predator-prey ratios. This was one of the seminal results that led to the dinosaur renaissance.<ref name="bakker1968">{{cite journal |last1=Bakker |first1=R.T. |author-link=Robert T. Bakker |year=1968 |title=The Superiority of Dinosaurs |journal=Discovery: Magazine of the Peabody Museum of Natural History |volume=3 |issue=2 |pages=11–22 |issn=0012-3625 |oclc=297237777}}</ref><ref name="bakker1972">{{cite journal |last1=Bakker |first1=R.T. |author-link=Robert T. Bakker |year=1972 |title=Anatomical and Ecological Evidence of Endothermy in Dinosaurs |journal=Nature |volume=238 |issue=5359 |pages=81–85 |doi=10.1038/238081a0|bibcode=1972Natur.238...81B |s2cid=4176132 }}</ref><ref name="taylor2010"/><ref name="parsons2001"/>

One of the greatest contributions to the modern understanding of dinosaur physiology has been [[histology|paleohistology]], the study of microscopic tissue structure in dinosaurs.<ref name="erickson2014">{{cite journal |last1=Erickson |first1=G.M. |year=2014 |title=On dinosaur growth |journal=Annual Review of Earth and Planetary Sciences |volume=42 |issue=1 |pages=675–697 |doi=10.1146/annurev-earth-060313-054858|bibcode=2014AREPS..42..675E }}</ref><ref name="bailleul2019">{{cite journal |last1=Bailleul |first1=A.M. |last2=O'Connor |first2=J. |last3=Schweitzer |first3=M.H. |year=2019 |title=Dinosaur paleohistology: review, trends and new avenues of investigation |journal=PeerJ |volume=7 |page=e7764 |doi=10.7717/peerj.7764|pmid=31579624 |pmc=6768056 |doi-access=free }}</ref> From the 1960s forward, [[Armand de Ricqlès]] suggested that the presence of fibrolamellar bone—bony tissue with an irregular, fibrous texture and filled with blood vessels—was indicative of consistently fast growth and therefore endothermy. Fibrolamellar bone was common in both dinosaurs and pterosaurs,<ref name="dericqles1974">{{cite journal |last1=De Ricqlès |first1=A. |year=1974 |title=Evolution of endothermy: histological evidence |journal=Evolutionary Theory |volume=1 |issue=2 |pages=51–80 |url=http://www.stuartsumida.com/BIOL622/Ricqles1974.pdf |archive-url=https://web.archive.org/web/20210417055907/http://www.stuartsumida.com/BIOL622/Ricqles1974.pdf |archive-date=2021-04-17 |url-status=live}}</ref><ref name="dericqles1980">{{cite book |last1=De Ricqlès |first1=A. |year=1980 |chapter=Tissue structures of dinosaur bone, functional significance and possible relation to dinosaur physiology |editor-last1=Thomas |editor-first1=R.D.K. |editor-last2=Olson |editor-first2=E.C. |title=A Cold Look at the Warm-Blooded Dinosaurs |location=New York |publisher=American Association for the Advancement of Science |pages=103–139}}</ref> though not universally present.<ref name="padian2004">{{cite journal |last1=Padian |first1=K. |last2=Horner |first2=J.R. |last3=de Ricqlès |first3=A. |year=2004 |title=Growth in small dinosaurs and pterosaurs: the evolution of archosaurian growth strategies |journal=Journal of Vertebrate Paleontology |volume=24 |issue=3 |pages=555–571 |doi=10.1671/0272-4634(2004)024[0555:GISDAP]2.0.CO;2 |s2cid=86019906 |url=http://doc.rero.ch/record/15191/files/PAL_E2467.pdf |archive-date=February 4, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230204094637/https://doc.rero.ch/record/15191/files/PAL_E2467.pdf |url-status=live }}</ref><ref name="desouza2020">{{cite journal |last1=de Souza |first1=G.A. |last2=Bento Soares |first2=M. |last3=Souza Brum |first3=A. |last4=Zucolotto |first4=M. |last5=Sayão |first5=J.M. |last6=Carlos Weinschütz |first6=L. |last7=Kellner |first7=A.W.A. |year=2020 |title=Osteohistology and growth dynamics of the Brazilian noasaurid ''Vespersaurus paranaensis'' Langer et al., 2019 (Theropoda: Abelisauroidea) |journal=PeerJ |volume=8 |pages=e9771 |doi=10.7717/peerj.9771 |pmid=32983636 |pmc=7500327 |s2cid=221906765 |doi-access=free }}</ref> This has led to a significant body of work in reconstructing [[growth curve (biology)|growth curves]] and modeling the evolution of growth rates across various dinosaur lineages,<ref name="physiologyrefs">For examples of this work conducted on different dinosaur lineages, see

* {{cite journal |last1=Erickson |first1=G.M. |last2=Tumanova |first2=T.A. |year=2000 |title=Growth curve of ''Psittacosaurus mongoliensis'' Osborn (Ceratopsia: Psittacosauridae) inferred from long bone histology |journal=Zoological Journal of the Linnean Society |volume=130 |issue=4 |pages=551–566 |doi=10.1111/j.1096-3642.2000.tb02201.x |s2cid=84241148}}
* {{cite journal |last1=Erickson |first1=G. |last2=Rogers |first2=K. |last3=Yerby |first3=S. |year=2001 |title=Dinosaurian growth patterns and rapid avian growth rates |journal=Nature |volume=412 |issue=429–433 |pages=429–433 |bibcode=2001Natur.412..429E |doi=10.1038/35086558 |pmid=11473315 |s2cid=4319534}}{{Erratum|doi=10.1038/nature16488|pmid=26675731|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''|checked=yes}}
* {{cite journal |last1=Erickson |first1=G. |last2=Makovicky |first2=P. |last3=Currie |first3=P. |last4=Norell |first4=M.A. |last5=Yerby |first5=S.A. |last6=Brochu |first6=C.A. |year=2004 |title=Gigantism and comparative life-history parameters of tyrannosaurid dinosaurs |url=http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |url-status=live |journal=Nature |volume=430 |issue=7001 |pages=772–775 |bibcode=2004Natur.430..772E |doi=10.1038/nature02699 |pmid=15306807 |s2cid=4404887 |archive-url=https://web.archive.org/web/20200714024211/http://doc.rero.ch/record/15279/files/PAL_E2578.pdf |archive-date=2020-07-14 }}{{Erratum|doi=10.1038/nature16487|pmid=26675726|http://retractionwatch.com/2016/03/01/high-profile-critic-slams-nature-letters-about-dinosaur-growth-following-corrections/ ''Retraction Watch''|checked=yes}}
* {{cite journal |last1=Lehman |first1=T.M. |last2=Woodward |first2=H.N. |year=2008 |title=Modeling growth rates for sauropod dinosaurs |url=http://doc.rero.ch/record/16723/files/PAL_E3766.pdf |journal=Paleobiology |volume=34 |issue=2 |pages=264–281 |doi=10.1666/0094-8373(2008)034[0264:MGRFSD]2.0.CO;2 |s2cid=84163725 |archive-date=February 4, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230204092325/https://doc.rero.ch/record/16723/files/PAL_E3766.pdf |url-status=live }}
* {{cite journal |last1=Horner |first1=J.R. |last2=de Ricqles |first2=A. |last3=Padian |first3=K. |last4=Scheetz |first4=R.D. |year=2009 |title=Comparative long bone histology and growth of the "hypsilophodontid" dinosaurs ''Orodromeus makelai'', ''Dryosaurus altus'', and ''Tenontosaurus tillettii'' (Ornithischia: Euornithopoda) |journal=Journal of Vertebrate Paleontology |volume=29 |issue=3 |pages=734–747 |bibcode=2009JVPal..29..734H |doi=10.1671/039.029.0312 |s2cid=86277619}}
* {{cite journal |last1=Woodward |first1=H. |last2=Freedman Fowler |first2=E. |last3=Farlow |first3=J. |last4=Horner |first4=J. |year=2015 |title=''Maiasaura'', a model organism for extinct vertebrate population biology: A large sample statistical assessment of growth dynamics and survivorship |journal=Paleobiology |volume=41 |issue=4 |pages=503–527 |bibcode=2015Pbio...41..503W |doi=10.1017/pab.2015.19 |s2cid=85902880}}</ref> which has suggested overall that dinosaurs grew faster than living reptiles.<ref name="bailleul2019"/> Other lines of evidence suggesting endothermy include the presence of feathers and other types of body coverings in many lineages (see {{section link||Feathers}}); more consistent ratios of the isotope [[oxygen-18]] in bony tissue compared to ectotherms, particularly as latitude and thus air temperature varied, which suggests stable internal temperatures<ref name="amiot2006">{{cite journal |last1=Amiot |first1=R. |last2=Lécuyer |first2=C. |last3=Buffetaut |first3=E. |last4=Escarguel |first4=G. |last5=Fluteau |first5=F. |last6=Martineau |first6=F. |year=2006 |title=Oxygen isotopes from biogenic apatites suggest widespread endothermy in Cretaceous dinosaurs |journal=Earth and Planetary Science Letters |volume=246 |issue=1–2 |pages=41–54 |doi=10.1016/j.epsl.2006.04.018|bibcode=2006E&PSL.246...41A |url=http://doc.rero.ch/record/14262/files/PAL_E2159.pdf }}</ref><ref name="amiot2010">{{cite journal |last1=Amiot |first1=R. |last2=Wang |first2=X. |last3=Lécuyer |first3=C. |last4=Buffetaut |first4=E. |last5=Boudad |first5=L. |last6=Cavin |first6=L. |last7=Ding |first7=Z. |last8=Fluteau |first8=F. |last9=Kellner |first9=A.W.A. |last10=Tong |first10=H. |last11=Zhang |first11=F. |year=2010 |title=Oxygen and carbon isotope compositions of middle Cretaceous vertebrates from North Africa and Brazil: ecological and environmental significance |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=297 |issue=2 |pages=439–451 |doi=10.1016/j.palaeo.2010.08.027|bibcode=2010PPP...297..439A }}</ref> (although these ratios can be altered during fossilization<ref name="kolodny1996">{{cite journal |last1=Kolodny |first1=Y. |last2=Luz |first2=B. |last3=Sander |first3=M. |last4=Clemens |first4=W.A. |year=1996 |title=Dinosaur bones: fossils or pseudomorphs? The pitfalls of physiology reconstruction from apatitic fossils |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=126 |issue=1–2 |pages=161–171 |doi=10.1016/S0031-0182(96)00112-5 |bibcode=1996PPP...126..161K |url=http://doc.rero.ch/record/14443/files/PAL_E1627.pdf |archive-date=February 4, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230204094527/https://doc.rero.ch/record/14443/files/PAL_E1627.pdf |url-status=live }}</ref>); and the discovery of [[South Polar region of the Cretaceous#Dinosaurs|polar dinosaurs]], which lived in Australia, Antarctica, and Alaska when these places would have had cool, temperate climates.<ref name="paul1988">{{cite journal |last1=Paul |first1=G.S. |year=1988 |title=Physiological, migratorial, climatological, geophysical, survival, and evolutionary implications of Cretaceous polar dinosaurs |journal=Journal of Paleontology |volume=62 |issue=4 |pages=640–652 |jstor=1305468|ref=none}}</ref><ref name="clemens1993">{{cite journal |last1=Clemens |first1=W.A. |last2=Nelms |first2=L.G. |year=1993 |title=Paleoecological implications of Alaskan terrestrial vertebrate fauna in latest Cretaceous time at high paleolatitudes |journal=Geology |volume=21 |issue=6 |pages=503–506 |doi=10.1130/0091-7613(1993)021<0503:PIOATV>2.3.CO;2|bibcode=1993Geo....21..503C }}</ref><ref name="rich2002">{{cite journal |last1=Rich |first1=T.H. |last2=Vickers-Rich |first2=P. |last3=Gangloff |first3=R.A. |year=2002 |title=Polar dinosaurs |journal=Science |volume=295 |issue=5557 |pages=979–980 |doi=10.1126/science.1068920|pmid=11834803 |s2cid=28065814 }}</ref><ref name="buffetaut2004">{{cite journal |last1=Buffetaut |first1=E. |year=2004 |title=Polar dinosaurs and the question of dinosaur extinction: a brief review |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=214 |issue=3 |pages=225–231 |doi=10.1016/j.palaeo.2004.02.050|url=http://doc.rero.ch/record/15383/files/PAL_E2734.pdf |archive-url=https://web.archive.org/web/20200608120307/http://doc.rero.ch/record/15383/files/PAL_E2734.pdf |archive-date=2020-06-08 |url-status=live }}</ref>

[[File:Dino bird h.jpg|thumb|Comparison between the [[air sac]]s of an [[abelisaur]] and a bird]]
In saurischian dinosaurs, higher metabolisms were supported by the evolution of the avian respiratory system, characterized by an extensive system of [[air sac]]s that extended the lungs and invaded many of the bones in the skeleton, making them hollow.<ref name=Sereno2008/> Such respiratory systems, which may have appeared in the earliest saurischians,<ref name="oconnor2009">{{cite journal |last1=O'Connor |first1=P.M. |year=2009 |title=Evolution of archosaurian body plans: skeletal adaptations of an air-sac-based breathing apparatus in birds and other archosaurs |journal=Journal of Experimental Zoology Part A: Ecological Genetics and Physiology |volume=311 |issue=8 |pages=629–646 |doi=10.1002/jez.548|pmid=19492308 |bibcode=2009JEZA..311..629O }}</ref> would have provided them with more oxygen compared to a mammal of similar size, while also having a larger resting [[tidal volume]] and requiring a lower breathing frequency, which would have allowed them to sustain higher activity levels.<ref name="sander2011"/> The rapid airflow would also have been an effective cooling mechanism, which in conjunction with a lower metabolic rate<ref name="eagle2011">{{cite journal |last1=Eagle |first1=R.A. |last2=Tütken |first2=T. |last3=Martin |first3=T.S. |last4=Tripati |first4=A.K. |last5=Fricke |first5=H.C. |last6=Connely |first6=M. |last7=Cifelli |first7=R.L. |last8=Eiler |first8=J.M. |year=2011 |title=Dinosaur body temperatures determined from isotopic (<sup>13</sup>C-<sup>18</sup>O) ordering in fossil biominerals |journal=Science |volume=333 |issue=6041 |pages=443–445 |pmid=21700837 |doi=10.1126/science.1206196 |bibcode=2011Sci...333..443E |s2cid=206534244}}</ref> would have prevented large sauropods from overheating. These traits may have enabled sauropods to grow quickly to gigantic sizes.<ref name="wedel2003">{{cite journal |last1=Wedel |first1=M.J. |year=2003 |title=Vertebral pneumaticity, air sacs, and the physiology of sauropod dinosaurs |journal=Paleobiology |volume=29 |issue=2 |pages=243–255 |doi=10.1017/S0094837300018091 |bibcode=2003Pbio...29..243W |url=http://doc.rero.ch/record/14872/files/PAL_E2010.pdf |archive-date=May 18, 2023 |access-date=January 3, 2024 |archive-url=https://web.archive.org/web/20230518003816/https://doc.rero.ch/record/14872/files/PAL_E2010.pdf |url-status=live }}</ref><ref name="perry2009">{{cite journal |last1=Perry |first1=S.F. |last2=Christian |first2=A. |last3=Breuer |first3=T. |last4=Pajor |first4=N. |last5=Codd |first5=J.R. |year=2009 |title=Implications of an avian-style respiratory system for gigantism in sauropod dinosaurs |journal=Journal of Experimental Zoology Part A: Ecological Genetics and Physiology |volume=311 |issue=8 |pages=600–610 |doi=10.1002/jez.517 |pmid=19189317|bibcode=2009JEZA..311..600P }}</ref> Sauropods may also have benefitted from their size—their small surface area to volume ratio meant that they would have been able to thermoregulate more easily, a phenomenon termed [[gigantothermy]].<ref name="sander2011"/><ref name="alexander1998">{{cite journal |last1=Alexander |first1=R.M. |year=1998 |title=All-time giants: the largest animals and their problems |journal=Palaeontology |volume=41 |pages=1231–1245 |url=https://www.palass.org/publications/palaeontology-journal/archive/41/6/article_pp1231-1245 |archive-date=September 27, 2016 |access-date=January 2, 2021 |archive-url=https://web.archive.org/web/20160927060250/https://www.palass.org/publications/palaeontology-journal/archive/41/6/article_pp1231-1245 |url-status=live }}</ref>

Like other reptiles, dinosaurs are primarily [[uricotelic]], that is, their [[kidney]]s extract nitrogenous wastes from their bloodstream and excrete it as [[uric acid]] instead of [[urea]] or [[ammonia]] via the ureters into the intestine. This would have helped them to conserve water.<ref name="benson2018"/> In most living species, uric acid is excreted along with feces as a semisolid waste.<ref name="tsahar2005">{{cite journal |last1=Tsahar |first1=E. |last2=Martínez del Rio |first2=C. |last3=Izhaki |first3=I. |last4=Arad |first4=Z. |year=2005 |title=Can birds be ammonotelic? Nitrogen balance and excretion in two frugivores |journal=[[The Journal of Experimental Biology]] |volume=208 |issue=6 |pages=1025–1034 |url= https://jeb.biologists.org/content/jexbio/208/6/1025.full.pdf |url-status=live |doi=10.1242/jeb.01495 |issn=0022-0949 |pmid=15767304 |bibcode=2005JExpB.208.1025T |s2cid=18540594 |archive-url=https://web.archive.org/web/20191017110333/https://jeb.biologists.org/content/jexbio/208/6/1025.full.pdf |archive-date=October 17, 2019 |access-date=October 31, 2019}}</ref><ref name="skadhauge2003">{{cite journal |last1=Skadhauge |first1=E. |last2=Erlwanger |first2=K.H. |last3=Ruziwa |first3=S.D. |last4=Dantzer |first4=V. |last5=Elbrønd |first5=V.S. |last6=Chamunorwa |first6=J.P. |year=2003 |title=Does the ostrich (''Struthio camelus'') coprodeum have the electrophysiological properties and microstructure of other birds? |journal=[[Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology]] |volume=134 |issue=4 |pages=749–755 |doi=10.1016/S1095-6433(03)00006-0 |issn=1095-6433 |pmid=12814783}}</ref> However, at least some modern birds (such as [[hummingbird]]s) can be facultatively [[ammonotelic]], excreting most of the nitrogenous wastes as ammonia.<ref name="preest1997">{{cite journal |last1=Preest |first1=M.R. |last2=Beuchat |first2=C.A. |year=1997 |title=Ammonia excretion by hummingbirds |journal=Nature |volume=386 |issue=6625 |pages=561–562 |bibcode=1997Natur.386..561P |doi=10.1038/386561a0 |s2cid=4372695 |issn=0028-0836}}</ref> This material, as well as the output of the intestines, emerges from the [[cloaca]].<ref name="mora1965">{{cite journal |last1=Mora |first1=J. |last2=Martuscelli |first2=J. |last3=Ortiz Pineda |first3=J. |last4=Soberon |first4=G. |year=1965 |title=The Regulation of Urea-Biosynthesis Enzymes in Vertebrates |journal=[[Biochemical Journal]] |volume=96 |issue=1 |pages=28–35 |issn=0264-6021 |doi=10.1042/bj0960028 |pmc=1206904 |pmid=14343146}}</ref><ref name="packard1966">{{cite journal |last=Packard |first=G.C. |year=1966 |title=The Influence of Ambient Temperature and Aridity on Modes of Reproduction and Excretion of Amniote Vertebrates |journal=The American Naturalist |volume=100 |issue=916 |pages=667–682 |doi=10.1086/282459 |issn=0003-0147 |jstor=2459303 |bibcode=1966ANat..100..667P |s2cid=85424175}}</ref> In addition, many species regurgitate [[Pellet (ornithology)|pellets]],<ref name="balgooyen1971">{{cite journal |last=Balgooyen |first=T.G. |year=1971 |title=Pellet Regurgitation by Captive Sparrow Hawks (''Falco sparverius'') |journal=[[The Condor (journal)|Condor]] |volume=73 |issue=3 |pages=382–385 |jstor=1365774 |url=https://sora.unm.edu/sites/default/files/journals/condor/v073n03/p0382-p0385.pdf |doi=10.2307/1365774 |archive-url=https://web.archive.org/web/20190404001957/https://sora.unm.edu/sites/default/files/journals/condor/v073n03/p0382-p0385.pdf |archive-date=April 4, 2019 |access-date=October 30, 2019}}</ref> and fossil pellets are known as early as the Jurassic from ''[[Anchiornis]]''.<ref name="xu2018">{{cite journal |last1=Xu |first1=X. |last2=Li |first2=F. |last3=Wang |first3=Y. |last4=Sullivan |first4=C. |last5=Zhang |first5=F. |last6=Zhang |first6=X. |last7=Sullivan |first7=C. |last8=Wang |first8=X. |last9=Zheng |first9=X. |year=2018 |title=Exceptional dinosaur fossils reveal early origin of avian-style digestion |journal=Scientific Reports |volume=8 |issue=1 |page=14217 |doi=10.1038/s41598-018-32202-x |pmid=30242170 |issn=2045-2322 |pmc=6155034 |bibcode=2018NatSR...814217Z}}</ref>

{{anchor|intelligence}}The size and shape of the brain can be partly reconstructed based on the surrounding bones. In 1896, Marsh calculated ratios between brain weight and body weight of seven species of dinosaurs, showing that the brain of dinosaurs was proportionally smaller than in today's crocodiles, and that the brain of ''Stegosaurus'' was smaller than in any living land vertebrate. This contributed to the widespread public notion of dinosaurs as being sluggish and extraordinarily stupid. Harry Jerison, in 1973, showed that proportionally smaller brains are expected at larger body sizes, and that brain size in dinosaurs was not smaller than expected when compared to living reptiles.<ref name="russell1997"/> Later research showed that relative brain size progressively increased during the evolution of theropods, with the highest intelligence – comparable to that of modern birds – calculated for the troodontid ''Troodon''.<ref name="brusatte2012"/>