Editing Megafauna (section)

==Evolution of large body size==
One observation that has been made about the evolution of larger body size is that rapid rates of increase that are often seen over relatively short time intervals are not sustainable over much longer time periods. In an examination of mammal body mass changes over time, the maximum increase possible in a given time interval was found to scale with the interval length raised to the 0.25 power.<ref name = "Evans2012"/> This is thought to reflect the emergence, during a trend of increasing maximum body size, of a series of anatomical, physiological, environmental, genetic and other constraints that must be overcome by evolutionary innovations before further size increases are possible. A strikingly faster rate of change was found for large decreases in body mass, such as may be associated with the phenomenon of [[insular dwarfism]]. When normalized to generation length, the maximum rate of body mass decrease was found to be over 30 times greater than the maximum rate of body mass increase for a ten-fold change.<ref name = "Evans2012"/>

===In terrestrial mammals===
[[File:Patagotitan vs Mammals Scale Diagram SVG Steveoc86.svg|thumb|upright=2|Large terrestrial mammals compared in size to one of the largest sauropod dinosaurs, ''[[Patagotitan]]'']]
Subsequent to the [[Cretaceous–Paleogene extinction event]] that eliminated the non-avian dinosaurs about {{period start|Paleogene}} [[Megaannum|Ma]] (million years) ago, terrestrial mammals underwent a nearly exponential increase in body size as they diversified to occupy the ecological niches left vacant.<ref name = "F.A.Smith">{{cite journal | last1=Smith|first1=F. A.|last2=Boyer|first2=A. G.|last3=Brown|first3=J. H.|last4=Costa|first4=D. P.|last5=Dayan|first5=T.|last6=Ernest|first6=S. K. M.|last7=Evans|first7=A. R.|last8=Fortelius|first8=M.|last9=Gittleman|first9=J. L.|last10=Hamilton|first10=M. J.|last11=Harding|first11=L. E.|last12=Lintulaakso|first12=K.|last13=Lyons|first13=S. K.|last14=McCain|first14=C.|last15=Okie|first15=J. G.|last16=Saarinen|first16=J. J.|last17=Sibly|first17=R. M.|last18=Stephens|first18=P. R.|last19=Theodor|first19=J.|last20=Uhen|first20=M. D.
  | title = The Evolution of Maximum Body Size of Terrestrial Mammals
  | journal = [[Science (journal)|Science]] | volume = 330 | issue = 6008 | pages = 1216–1219
  | date = 2010-11-26 | doi = 10.1126/science.1194830 |pmid=21109666|bibcode = 2010Sci...330.1216S|citeseerx=10.1.1.383.8581|s2cid=17272200}}</ref> Starting from just a few kg before the event, maximum size had reached ~{{Convert|50|kg|lb}} a few million years later, and ~{{Convert|750|kg|lb}} by the end of the [[Paleocene]]. This trend of increasing body mass appears to level off about 40 Ma ago (in the late [[Eocene]]), suggesting that physiological or ecological constraints had been reached, after an increase in body mass of over three orders of magnitude.<ref name = "F.A.Smith"/> However, when considered from the standpoint of rate of size increase per generation, the exponential increase is found to have continued until the appearance of ''[[Indricotherium]]'' 30 Ma ago. (Since generation time scales with ''body mass''<sup>0.259</sup>, increasing generation times with increasing size cause the log mass vs. time plot to curve downward from a linear fit.)<ref name = "Evans2012">{{cite journal
| last1=Evans|first1=A. R.|last2=Jones|first2=D.|last3=Boyer|first3=A. G.|last4=Brown|first4=J. H.|last5=Costa|first5=D. P.|last6=Ernest|first6=S. K. M.|last7=Fitzgerald|first7=E. M. G.|last8=Fortelius|first8=M.|last9=Gittleman|first9=J. L.|last10=Hamilton|first10=M. J.|last11=Harding|first11=L. E.|last12=Lintulaakso|first12=K.|last13=Lyons|first13=S. K.|last14=Okie|first14=J. G.|last15=Saarinen|first15=J. J.|last16=Sibly|first16=R. M.|last17=Smith|first17=F. A.|last18=Stephens|first18=P. R.|last19=Theodor|first19=J. M.|last20=Uhen|first20=M. D. 
 | title = The maximum rate of mammal evolution | journal = [[Proceedings of the National Academy of Sciences|PNAS]]
 | volume=109| issue=11| pages=4187–4190 | date = 2012-01-30
 | doi = 10.1073/pnas.1120774109 |pmid=22308461|pmc=3306709|bibcode=2012PNAS..109.4187E|doi-access=free}}</ref>

Megaherbivores eventually attained a body mass of over {{Convert|10,000|kg|lb}}. The largest of these, [[indricothere]]s and [[proboscid]]s, have been [[hindgut fermentation|hindgut fermenter]]s, which are believed to have an advantage over [[Foregut fermentation|foregut fermenter]]s in terms of being able to accelerate gastrointestinal transit in order to accommodate very large food intakes.<ref name = "Clauss">{{cite journal | last = Clauss | first = M. | author2 = Frey, R. | author3 = Kiefer, B. | author4 = Lechner-Doll, M. | author5 = Loehlein, W. | author6 = Polster, C. | author7 = Roessner, G. E. | author8 = Streich, W. J. | title = The maximum attainable body size of herbivorous mammals: morphophysiological constraints on foregut, and adaptations of hindgut fermenters | journal = [[Oecologia]] | volume = 136 | issue = 1 | pages = 14–27 | date = 2003-04-24 | doi = 10.1007/s00442-003-1254-z | pmid = 12712314 | bibcode = 2003Oecol.136...14C | s2cid = 206989975 | url = http://www.zora.uzh.ch/id/eprint/2393/2/Oecologia_body_size_2003V.pdf | access-date = 2019-07-13 | archive-date = 2019-06-08 | archive-url = https://web.archive.org/web/20190608152406/https://www.zora.uzh.ch/id/eprint/2393/2/Oecologia_body_size_2003V.pdf | url-status = dead }}</ref> A similar trend emerges when rates of increase of maximum body mass per generation for different mammalian [[clade]]s are compared (using rates averaged over [[macroevolution]]ary time scales). Among terrestrial mammals, the fastest rates of increase of ''body mass''<sup>0.259</sup> vs. time (in Ma) occurred in [[perissodactyl]]s (a slope of 2.1), followed by [[rodent]]s (1.2) and proboscids (1.1),<ref name = "Evans2012"/> all of which are hindgut fermenters. The rate of increase for [[artiodactyl]]s (0.74) was about a third of the perissodactyls. The rate for [[carnivora]]ns (0.65) was slightly lower yet, while [[primate]]s, perhaps constrained by their [[arboreal]] habits, had the lowest rate (0.39) among the mammalian groups studied.<ref name = "Evans2012"/>

Terrestrial mammalian carnivores from several [[eutheria]]n groups (the [[artiodactyl]] ''[[Andrewsarchus]]'' – formerly considered a [[Mesonychidae|mesonychid]], the [[oxyaenid]] ''[[Sarkastodon]]'', and the carnivorans ''[[Amphicyon]]'' and ''[[Arctodus]]'') all reached a maximum size of about {{Convert|1,000|kg|lb}}<ref name = "F.A.Smith"/> (the carnivoran ''[[Arctotherium]]'' and the [[hyaenodontid]] ''[[Simbakubwa]]'' may have been somewhat larger). The largest known [[metatheria]]n carnivore, ''[[Proborhyaena gigantea]]'', apparently reached {{Convert|600|kg|lb}}, also close to this limit.<ref name = "Sorkin"/> A similar theoretical maximum size for mammalian carnivores has been predicted based on the metabolic rate of mammals, the energetic cost of obtaining prey, and the maximum estimated rate coefficient of prey intake.<ref name = "Carbone">{{cite journal
  | last = Carbone | first = C. |author2=Teacher, A |author3=Rowcliffe, J. M.
  | title = The Costs of Carnivory | journal = [[PLOS Biology]]
  | volume = 5 | issue = 2, e22 | pages = 363–368
  | date = 2007-01-16 | doi = 10.1371/journal.pbio.0050022
  | pmid=17227145 | pmc=1769424 | doi-access = free }}</ref> It has also been suggested that maximum size for mammalian carnivores is constrained by the stress the [[humerus]] can withstand at top running speed.<ref name = "Sorkin">{{Cite journal
  | last = Sorkin | first = B.  | title = A biomechanical constraint on body mass in terrestrial mammalian predators
  | journal = [[Lethaia]] | volume = 41 | issue = 4 | pages = 333–347
  | date = 2008-04-10 | doi = 10.1111/j.1502-3931.2007.00091.x | bibcode = 2008Letha..41..333S }}</ref>

Analysis of the variation of maximum body size over the last 40 Ma suggests that decreasing temperature and increasing continental land area are associated with increasing maximum body size. The former correlation would be consistent with [[Bergmann's rule]],<ref name = "Ashton">{{cite journal
  | last = Ashton | first = K. G. |author2=Tracy, M. C. |author3=de Queiroz, A.
  | title = Is Bergmann's Rule Valid for Mammals?
  | journal = [[The American Naturalist]]
  | volume = 156 | issue = 4 | pages = 390–415
  | date = October 2000  | jstor = 10.1086/303400
  | doi = 10.1086/303400
  | pmid = 29592141 | s2cid = 205983729 }}</ref> and might be related to the [[Thermoregulation|thermoregulatory]] advantage of large body mass in cool climates,<ref name = "F.A.Smith"/> better ability of larger organisms to cope with seasonality in food supply,<ref name = "Ashton"/> or other factors;<ref name = "Ashton"/> the latter correlation could be explained in terms of range and resource limitations.<ref name = "F.A.Smith"/> However, the two parameters are interrelated (due to sea level drops accompanying increased glaciation), making the driver of the trends in maximum size more difficult to identify.<ref name = "F.A.Smith"/>

===In marine mammals===
[[File:Baleen whale sizes.JPG|thumb|upright=1.5|Baleen whale comparative sizes]]
Since tetrapods (first [[Marine reptile|reptiles]], later [[Marine mammal|mammals]]) returned to the sea in the [[Late Permian]], they have dominated the top end of the marine body size range, due to the more efficient intake of oxygen possible using lungs.<ref name = "Webb2015">{{Cite news | last = Webb | first = J. | title = Evolution 'favours bigger sea creatures' | publisher = [[BBC]] | date = 2015-02-19 | url = https://www.bbc.com/news/science-environment-31533744 | access-date = 2015-02-22 | work = BBC News | archive-date = 2015-02-22 | archive-url = https://web.archive.org/web/20150222044708/http://www.bbc.com/news/science-environment-31533744 | url-status = live }}</ref><ref name = "Helm2015">{{cite journal | last1 = Heim | first1 = N. A. | last2 = Knope | first2 = M. L. | last3 = Schaal | first3 = E. K. | last4 = Wang | first4 = S. C. | last5 = Payne | first5 = J. L. | title = Cope's rule in the evolution of marine animals | journal = Science | volume = 347 | issue = 6224 | pages = 867–870 | doi = 10.1126/science.1260065 | date = 2015-02-20 | pmid = 25700517 | bibcode = 2015Sci...347..867H | url = http://www.swarthmore.edu/NatSci/swang1/Publications/ | doi-access = free | access-date = 2019-07-13 | archive-date = 2019-07-05 | archive-url = https://web.archive.org/web/20190705023917/http://www.swarthmore.edu/NatSci/swang1/Publications/ | url-status = live }}</ref> The ancestors of [[cetacea]]ns are believed to have been the semiaquatic [[pakicetid]]s, no larger than dogs, of about 53 million years (Ma) ago.<ref name=poster>{{cite journal|last=Thewissen|first=J. G. M.|author2=Bajpai, S.|title=Whale Origins as a Poster Child for Macroevolution|journal=[[BioScience]]|date=1 January 2001|volume=51|issue=12|pages=1037–1049|doi=10.1641/0006-3568(2001)051[1037:WOAAPC]2.0.CO;2|issn=0006-3568|doi-access=free}}</ref> By 40 Ma ago, cetaceans had attained a length of {{cvt|20|m}} or more in ''[[Basilosaurus]]'', an elongated, serpentine whale that differed from modern whales in many respects and was not ancestral to them. Following this, the evolution of large body size in cetaceans appears to have come to a temporary halt and then to have backtracked, although the available fossil records are limited. However, in the period from 31 Ma ago (in the [[Oligocene]]) to the present, cetaceans underwent a significantly more rapid sustained increase in body mass (a rate of increase in ''body mass''<sup>0.259</sup> of a factor of 3.2 per million years) than achieved by any group of terrestrial mammals.<ref name = "Evans2012"/> This trend led to the largest animal of all time, the modern [[blue whale]]. Several reasons for the more rapid evolution of large body size in cetaceans are possible. Fewer [[Biomechanics|biomechanical]] constraints on increases in body size may be associated with suspension in water as opposed to standing against the force of gravity, and with [[Aquatic locomotion|swimming movements]] as opposed to [[terrestrial locomotion]]. Also, the greater heat capacity and thermal conductivity of water compared to air may increase the [[thermoregulation|thermoregulatory]] advantage of large body size in marine [[endotherm]]s, although diminishing returns apply.<ref name = "Evans2012"/>

Among the toothed whales, maximum body size appears to be limited by food availability. Larger size, as in [[sperm whale|sperm]] and [[beaked whale]]s, facilitates deeper diving to access relatively easily-caught, large cephalopod prey in a less competitive environment. Compared to odontocetes, the efficiency of baleen whales' [[filter feeding]] scales more favorably with increasing size when planktonic food is dense, making larger sizes more advantageous. The [[lunge feeding]] technique of [[rorqual]]s appears to be more energy efficient than the [[ram feeding]] of [[balaenid]] whales; the latter technique is used with less dense and patchy plankton.<ref name="Goldbogen2019">{{cite journal|last1= Goldbogen|first1=J. A.|last2= Cade|first2=D. E.|last3= Wisniewska|first3=D. M.|last4= Potvin|first4= J.|last5= Segre|first5=P. S.|last6= Savoca|first6=M. S.|last7= Hazen|first7=E. L.|last8= Czapanskiy|first8=M. F.|last9= Kahane-Rapport|first9=S. R.|last10= DeRuiter|first10=S. L.|last11= Gero|first11= S.|last12= Tønnesen|first12= P.|last13= Gough|first13=W. T.|last14= Hanson|first14=M. B.|last15= Holt|first15=M. M.|last16= Jensen|first16=F. H.|last17= Simon|first17= M.|last18= Stimpert|first18=A. K.|last19= Arranz|first19= P.|last20= Johnston|first20=D. W.|last21= Nowacek|first21=D. P.|last22= Parks|first22=S. E.|last23= Visser|first23= F.|last24= Friedlaender|first24=A. S.|last25= Tyack|first25=P. L.|last26= Madsen|first26=P. T.|author27-link=Nicholas Pyenson|last27= Pyenson|first27=N. D.|title= Why whales are big but not bigger: Physiological drivers and ecological limits in the age of ocean giants|journal= Science|volume= 366|issue= 6471|year= 2019|pages= 1367–1372|doi= 10.1126/science.aax9044|pmid=31831666|bibcode=2019Sci...366.1367G|hdl=10023/19285|s2cid=209339266|hdl-access= free}}</ref> The cooling trend in Earth's recent history may have generated more localities of high plankton abundance via wind-driven [[upwelling]]s, facilitating the evolution of gigantic whales.<ref name="Goldbogen2019" />

Cetaceans are not the only marine mammals to reach tremendous sizes.<ref>{{Cite journal |last1=Baker |first1=Joanna |last2=Meade |first2=Andrew |last3=Pagel |first3=Mark |last4=Venditti |first4=Chris |date=2015-04-21 |title=Adaptive evolution toward larger size in mammals |journal=Proceedings of the National Academy of Sciences |language=en |volume=112 |issue=16 |pages=5093–5098 |doi=10.1073/pnas.1419823112 |doi-access=free |issn=0027-8424 |pmc=4413265 |pmid=25848031|bibcode=2015PNAS..112.5093B }}</ref> The largest mammal [[carnivora]]ns of all time are marine [[pinniped]]s, the largest of which is the [[southern elephant seal]], which can reach more than {{cvt|6|m}} in length and weigh up to {{cvt|5,000|kg}}. Other large pinnipeds include the [[northern elephant seal]] at {{cvt|4,000|kg}}, [[walrus]] at {{cvt|2,000|kg}}, and [[Steller sea lion]] at {{cvt|1,135|kg}}.<ref>{{Cite journal |last1=Churchill |first1=Morgan |last2=Clementz |first2=Mark T. |last3=Kohno |first3=Naoki |date=2014-12-19 |title=Cope's rule and the evolution of body size in Pinnipedimorpha (Mammalia: Carnivora) |url=|journal=Evolution |volume=69 |issue=1 |pages=201–215 |doi=10.1111/evo.12560 |pmid=25355195 |issn=0014-3820}}</ref><ref>{{Cite journal |last1=Haley |first1=Michael P. |last2=Deutsch |first2=Charles J. |last3=Boeuf |first3=Burney J. Le |date=April 1991 |title=A method for estimating mass of large pinnipeds |url=|journal=Marine Mammal Science |language=en |volume=7 |issue=2 |pages=157–164 |doi=10.1111/j.1748-7692.1991.tb00562.x |bibcode=1991MMamS...7..157H |issn=0824-0469}}</ref> The [[sirenia]]ns are another group of marine mammals which adapted to fully aquatic life around the same time as the cetaceans did. Sirenians are closely related to elephants. The largest sirenian was the [[Steller's sea cow]], which reached up to {{cvt|10|m}} in length and weighed {{cvt|8,000|to|10,000|kg}}, and was hunted to extinction in the 18th century.<ref>{{Cite journal |last=Goldbogen |first=J. A. |date=2018-04-17 |title=Physiological constraints on marine mammal body size |journal=Proceedings of the National Academy of Sciences |language=en |volume=115 |issue=16 |pages=3995–3997 |doi=10.1073/pnas.1804077115 |doi-access=free |issn=0027-8424 |pmc=5910879 |pmid=29618615|bibcode=2018PNAS..115.3995G }}</ref>

===In flightless birds===
[[File:Dinornithidae SIZE 01.png|thumb|A size comparison between a human and 4 [[moa]] species: {{Clear}} '''1.''' ''[[Dinornis novaezealandiae]]'' {{Clear}} '''2.''' ''[[Emeus crassus]]'' {{Clear}} '''3.''' ''[[Anomalopteryx didiformis]]'' {{Clear}} '''4.''' ''[[Dinornis robustus]]'']]
Because of the small initial size of all mammals following the extinction of the non-avian dinosaurs, nonmammalian vertebrates had a roughly ten-million-year-long window of opportunity (during the Paleocene) for evolution of gigantism without much competition.<ref name = "Mitchell2014">{{Cite journal| doi = 10.1126/science.1251981| pmid = 24855267| title = Ancient DNA reveals elephant birds and kiwi are sister taxa and clarifies ratite bird evolution| journal = Science| volume = 344| issue = 6186| pages = 898–900| date = 2014-05-23| last1 = Mitchell| first1 = K. J.| last2 = Llamas| first2 = B.| last3 = Soubrier| first3 = J.| last4 = Rawlence| first4 = N. J.| last5 = Worthy| first5 = T. H.| last6 = Wood| first6 = J.| last7 = Lee| first7 = M. S. Y.| last8 = Cooper| first8 = A.| bibcode = 2014Sci...344..898M| hdl = 2328/35953| s2cid = 206555952| url = https://dspace.flinders.edu.au/xmlui/bitstream/2328/35953/1/Mitchell_AncientDNA_AM2014.pdf| hdl-access = free| access-date = 2019-09-24| archive-date = 2023-03-15| archive-url = https://web.archive.org/web/20230315211934/https://dspace.flinders.edu.au/xmlui/bitstream/2328/35953/1/Mitchell_AncientDNA_AM2014.pdf| url-status = live}}</ref> During this interval, [[apex predator]] niches were often occupied by reptiles, such as terrestrial [[crocodilian]]s (e.g. ''[[Pristichampsus]]''), large snakes (e.g. ''[[Titanoboa]]'') or [[varanid lizard]]s, or by flightless birds<ref name = "F.A.Smith"/> (e.g. ''[[Paleopsilopterus]]'' in South America). This is also the period when megafaunal flightless herbivorous [[gastornithid]] birds evolved in the Northern Hemisphere, while flightless [[paleognath]]s evolved to large size on [[Gondwana]]n land masses and [[Europe]]. Gastornithids and at least one lineage of flightless paleognath birds originated in Europe, both lineages dominating niches for large herbivores while mammals remained below {{Convert|45|kg|lb}} (in contrast with other landmasses like [[North America]] and [[Asia]], which saw the earlier evolution of larger mammals) and were the largest European tetrapods in the [[Paleocene]].<ref name="Buffetaut2014">{{cite journal|last1=Buffetaut|first1=E.|last2=Angst|first2=D.|title=Stratigraphic distribution of large flightless birds in the Palaeogene of Europe and its palaeobiological and palaeogeographical implications|journal=Earth-Science Reviews|volume=138|date=November 2014|pages=394–408|doi=10.1016/j.earscirev.2014.07.001|bibcode=2014ESRv..138..394B}}</ref>

Flightless paleognaths, termed [[ratite]]s, have traditionally been viewed as representing a lineage separate from that of their small flighted relatives, the [[Neotropic]] [[tinamou]]s. However, recent genetic studies have found that tinamous nest well within the ratite tree, and are the [[sister group]] of the extinct [[moa]] of New Zealand.<ref name = "Mitchell2014" /><ref name = "Phillips2010">{{cite journal |vauthors=Phillips MJ, Gibb GC, Crimp EA, Penny D |title=Tinamous and moa flock together: mitochondrial genome sequence analysis reveals independent losses of flight among ratites |journal=Systematic Biology |volume=59 |issue=1 |pages=90–107 |date=January 2010  |pmid=20525622 |doi=10.1093/sysbio/syp079|doi-access=free }}</ref><ref name = "Baker2014">{{Cite journal | doi = 10.1093/molbev/msu153| title = Genomic Support for a Moa-Tinamou Clade and Adaptive Morphological Convergence in Flightless Ratites| journal = Molecular Biology and Evolution| year = 2014| last1 = Baker | first1 = A. J.| last2 = Haddrath | first2 = O.| last3 = McPherson | first3 = J. D.| last4 = Cloutier | first4 = A.| volume=31 | issue = 7| pages=1686–1696 | pmid=24825849| doi-access = free}}</ref> Similarly, the small [[Kiwi (bird)|kiwi]] of New Zealand have been found to be the sister group of the extinct [[elephant bird]]s of Madagascar.<ref name = "Mitchell2014" /> These findings indicate that [[Flightless bird|flightlessness]] and gigantism arose independently multiple times among ratites via [[parallel evolution]].<ref name="Murray 2004" />

Predatory megafaunal flightless birds were often able to compete with mammals in the early [[Cenozoic]]. Later in the Cenozoic, however, they were displaced by advanced carnivorans and died out. In North America, the [[bathornithids]] ''[[Paracrax]]'' and ''[[Bathornis]]'' were apex predators but became extinct by the [[Early Miocene]]. In South America, the related [[phorusrhacid]]s shared the dominant predatory niches with metatherian [[Sparassodonta|sparassodont]]s during most of the Cenozoic but declined and ultimately went extinct after eutherian predators arrived from North America (as part of the [[Great American Interchange]]) during the [[Pliocene]]. In contrast, large herbivorous flightless ratites have survived to the present.<ref name="Murray 2004" />

However, none of the flightless birds of the Cenozoic, including the predatory ''[[Brontornis]]'', possibly omnivorous ''[[Dromornis stirtoni]]''<ref name = "Murray 2004">{{cite book
  | last1 = Murray | first1 = Peter F.
  | last2 = Vickers-Rich | first2 = Patricia
  | year = 2004
  | title = Magnificent Mihirungs: The Colossal Flightless Birds of the Australian Dreamtime
  | url=https://books.google.com/books?id=-t6cQHdVEggC&pg=PA51
  | publisher = Indiana University Press | pages = 51, 314
  | isbn = 978-0-253-34282-9 | access-date=7 January 2012
}}</ref> or herbivorous ''[[Aepyornis]]'', ever grew to masses much above {{Convert|500|kg|lb}}, and thus never attained the size of the largest mammalian carnivores, let alone that of the largest mammalian herbivores. It has been suggested that the increasing thickness of avian eggshells in proportion to egg mass with increasing egg size places an upper limit on the size of birds.<ref name = "Murray 2004b">{{cite book
  | last1 = Ibid | url=https://books.google.com/books?id=-t6cQHdVEggC&pg=PA212
  | title = p. 212| isbn=978-0-253-34282-9
  | year=2004
  | publisher=Indiana University Press }}</ref>{{refn | Nonavian dinosaur size was not similarly constrained because they had a different relationship between body mass and egg size than birds. The {{Convert|400|kg|lb}} ''[[Aepyornis]]'' had larger eggs than nearly all dinosaurs.<ref name="Carpenter1999">{{cite book|author=Kenneth Carpenter|title=Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction|url=https://archive.org/details/isbn_9780253334978|url-access=registration|page=[https://archive.org/details/isbn_9780253334978/page/100 100]|access-date=6 May 2013|year=1999|publisher=[[Indiana University Press]]|isbn=978-0-253-33497-8|oclc= 42009424}}</ref><ref name="JacksonVarricchio2008">{{cite journal|last1=Jackson|first1=F. D.|last2= Varricchio|first2=D. J.|last3=Jackson|first3=R. A.|last4=Vila|first4= B.|last5=Chiappe |first5=L. M.|title=Comparison of water vapor conductance in a titanosaur egg from the Upper Cretaceous of Argentina and a ''Megaloolithus siruguei'' egg from Spain|journal=Paleobiology|volume= 34|issue=2|year=2008|pages= 229–246|issn=0094-8373|doi= 10.1666/0094-8373(2008)034[0229:COWVCI]2.0.CO;2|s2cid=85880201 }}</ref>| group = note}} The largest species of ''Dromornis'', ''D. stirtoni'', may have gone extinct after it attained the maximum avian body mass and was then outcompeted by marsupial [[diprotodon]]ts that evolved to sizes several times larger.<ref name = "Murray 2004c">{{cite book
  | last1 = Ibid | url=https://books.google.com/books?id=-t6cQHdVEggC&pg=PA277
  | title = p. 277| isbn=978-0-253-34282-9
  | year=2004
  | publisher=Indiana University Press }}</ref>

===In giant turtles===
[[Giant tortoise]]s were important components of late [[Cenozoic]] megafaunas, being present in every nonpolar continent until the arrival of [[hominina]]ns.<ref name="Hansen">{{Cite journal
 |last=Hansen
 |first=D. M.
 |author2=Donlan, C. J.
 |author3=Griffiths, C. J.
 |author4=Campbell, K. J.
 |title=Ecological history and latent conservation potential: large and giant tortoises as a model for taxon substitutions
 |journal=[[Ecography (journal)|Ecography]]
 |volume=33
 |issue=2
 |pages=272–284
 |date=April 2010
 |url=http://www.advancedconservation.org/library/hansen_etal_2010.pdf
 |doi=10.1111/j.1600-0587.2010.06305.x
 |bibcode=2010Ecogr..33..272H
 |access-date=2011-02-26
 |archive-url=https://web.archive.org/web/20110724224354/http://www.advancedconservation.org/library/hansen_etal_2010.pdf
 |archive-date=July 24, 2011
}}</ref><ref name="Cione">{{Cite journal
 |last=Cione
 |first=A. L.
 |author2=Tonni, E. P.
 |author3=Soibelzon, L.
 |title=The Broken Zig-Zag: Late Cenozoic large mammal and tortoise extinction in South America
 |journal=Rev. Mus. Argentino Cienc. Nat. |series=Nueva Serie
 |volume=5
 |issue=1
 |pages=1–19
 |year=2003
 |issn=1514-5158
 |doi= 10.22179/REVMACN.5.26
 |doi-access=free
 }}</ref> The largest known terrestrial tortoise was ''[[Megalochelys atlas]]'', an animal that probably weighed about {{cvt|1,000|kg}}.<ref>{{Citation |last1=Gordon |first1=Iain J. |title=The Ecology of Browsing and Grazing in Other Vertebrate Taxa |date=2019 |work=The Ecology of Browsing and Grazing II |pages=339–404 |editor-last=Gordon |editor-first=Iain J. |url=|place=Cham |publisher=Springer International Publishing |language=en |doi=10.1007/978-3-030-25865-8_15 |isbn=978-3-030-25865-8 |last2=Prins |first2=Herbert H. T. |last3=Mallon |first3=Jordan |last4=Puk |first4=Laura D. |last5=Miranda |first5=Everton B. P. |last6=Starling-Manne |first6=Carolina |last7=van der Wal |first7=René |last8=Moore |first8=Ben |last9=Foley |first9=William |editor2-last=Prins |editor2-first=Herbert H. T.}}</ref>

Some earlier aquatic Testudines, e.g. the marine ''[[Archelon]]'' of the Cretaceous<ref>{{Cite journal |last1=Jaffe |first1=Alexander L. |last2=Slater |first2=Graham J. |last3=Alfaro |first3=Michael E. |date=2011-08-23 |title=The evolution of island gigantism and body size variation in tortoises and turtles |journal=Biology Letters |language=en |volume=7 |issue=4 |pages=558–561 |doi=10.1098/rsbl.2010.1084 |issn=1744-9561 |pmc=3130210 |pmid=21270022}}</ref> and freshwater ''[[Stupendemys]]'' of the Miocene, were considerably larger, weighing more than {{cvt|2,000|kg}}.<ref>{{Cite journal |last1=Cadena |first1=Edwin-Alberto |last2=Link |first2=Andrés |last3=Cooke |first3=Siobhán B. |last4=Stroik |first4=Laura K. |last5=Vanegas |first5=Andrés F. |last6=Tallman |first6=Melissa |date=December 2021 |title=New insights on the anatomy and ontogeny of the largest extinct freshwater turtles |url=|journal=Heliyon |volume=7 |issue=12 |pages=e08591 |doi=10.1016/j.heliyon.2021.e08591 |doi-access=free |pmid=35005268 |pmc=8717240 |bibcode=2021Heliy...708591C |issn=2405-8440}}</ref>