Editing Diprotodon (section)

==Paleobiology==

===Diet===
[[File:Diprotodon sculpture.jpg|thumb|''Diprotodon'' sculpture at the [[Australian Museum]]]]

Like modern megaherbivores, most evidently the [[African elephant]], Pleistocene Australian megafauna likely had a profound effect on the vegetation, limiting the spread of forest cover and woody plants.<ref>{{cite journal|first1=E. S.|last1=Bakker|first2=J. L.|last2=Gill|first3=C. N.|last3=Johnson|first4=F. W. M.|last4=Vera|first5=C. J.|last5=Sandom|first6=G. P.|last6=Asner|first7=J.-C.|last7=Svenning|year=2015|title=Combining paleo-data and modern exclosure experiments to assess the impact of megafauna extinctions on woody vegetation|journal=Proceedings of the National Academy of Sciences|volume=113|issue=4|pages=847–855|doi=10.1073/pnas.1502545112|pmid=26504223 |pmc=4743795 |doi-access=free }}</ref> [[Isotopes of carbon#Tracing food sources and diets|Carbon isotope analysis]] suggests ''Diprotodon'' fed on a broad range of foods and, like kangaroos, was consuming both [[C3 carbon fixation|C<sub>3</sub>]]—well-watered trees, shrubs, and grasses—and [[C4 carbon fixation|C<sub>4</sub>]] plants—arid grasses,<ref>{{cite journal|url=https://www.academia.edu/1099030|first=D. R.|last=Gröke|year=1997|title=Distribution of C3 and C4 plants in the Late Pleistocene of South Australia recorded by isotope biogeochemistry of collagen in megafauna|journal=Australian Journal of Botany|volume=45|issue=3|pages=607–617|doi=10.1071/BT96040|bibcode=1997AuJB...45..607G }}</ref> a finding replicated by calcium isotope analysis showing ''Diprotodon'' to have been a mixed feeder.<ref>{{Cite journal |last1=Koutamanis |first1=Dafne |last2=McCurry |first2=Matthew |last3=Tacail |first3=Theo |last4=Dosseto |first4=Anthony |date=22 November 2023 |title=Reconstructing Pleistocene Australian herbivore megafauna diet using calcium and strontium isotopes |journal=[[Royal Society Open Science]] |language=en |volume=10 |issue=11 |doi=10.1098/rsos.230991 |issn=2054-5703 |pmc=10663789 |pmid=38026016 |bibcode=2023RSOS...1030991K }}</ref> Carbon isotope analyses on ''Diprotodon'' excavated from the [[Cuddie Springs]] site in [[unit (geology)|unit]]s SU6 (possibly 45,000 years old) and SU9 (350,000 to 570,000 years old) indicate ''Diprotodon'' adopted a somewhat-more-varied seasonal diet as Australia's climate dried but any change was subtle. In contrast, contemporary kangaroos and wombats underwent major dietary shifts or specialisations towards, respectively, C<sub>3</sub> and C<sub>4</sub> plants.<ref>{{cite journal|first1=L. R. G.|last1=DeSantis|first2=J. H.|last2=Field|first3=S.|last3=Wroe|first4=J. R.|last4=Dodson|year=2017|title=Dietary responses of Sahul (Pleistocene Australia–New Guinea) megafauna to climate and environmental change|journal=Paleobiology|volume=43|issue=2|page=190|doi=10.1017/pab.2016.50|s2cid=13134989 |doi-access=free|bibcode=2017Pbio...43..181D }}</ref> The fossilised, incompletely digested gut contents of one 53,000-year-old individual from [[Lake Callabonna]] show its last meal consisted of young leaves, stalks, and twigs.<ref name=Gillespie2008>{{cite journal|last1=Gillespie|first1=R.|last2=Fifield|first2=L. K.|last3=Levchenko |first3=V.|last4=Wells|first4=R.|year=2008|title=New <sup>14</sup>C Ages on Cellulose from Diprotodon Gut Contents: Explorations in Oxidation Chemistry and Combustion|journal=Radiocarbon|volume=50|issue=1|pages=75–81|doi=10.1017/s003382220004337x|s2cid=54577642 |doi-access=free|bibcode=2008Radcb..50...75G }}</ref>

The molars of ''Diprotodon'' are a simple bilophodont shape. Kangaroos use their bilophodont teeth to grind tender, low-fibre plants as a [[browsing (herbivory)|browser]] as well as grass as a grazer. Kangaroos that predominantly graze have specialised molars to resist the abrasiveness of grass but such adaptations are not exhibited in ''Diprotodon'', which may have had a mixed diet similar to that of a browsing [[wallaby]]. It may also have chewed like wallabies, beginning with a vertical crunch before grinding transversely, as opposed to wombats, which only grind transversely. Similarly to many large [[ungulate]]s (hoofed mammals), the jaws of ''Diprotodon'' were better suited for crushing rather than grinding, which would have permitted it to process vegetation in bulk.<ref name=Sharp2014/>

In 2016, Australian biologists Alana Sharpe and Thomas Rich estimated the maximum-possible [[bite force]] of ''Diprotodon'' using [[finite element analysis]]. They calculated {{cvt|2374|N}} at the incisors and {{cvt|4118|to|11134|N}} across the molar series.<ref name=Sharpe2016/> For reference, the [[American alligator]] can produce forces upwards of {{cvt|9500|N}}.<ref>{{cite journal|first1=G. M.|last1=Erickson|first2=A. K.|last2=Lappin|first3=K.|last3=Vliet|year=2003|title=The ontogeny of bite-force performance in American alligator (''Alligator mississippiensis'')|journal=Journal of Zoology|volume=260|issue=6|pages=317–327|doi=10.1017/S0952836903003819}}</ref> Though these are likely overestimates,{{efn|[[Finite element analysis]] considers the skull's [[section modulus]]—an object's ability to resist bending—but the material properties of marsupial skulls are not well studied. Sharpe and Rich used what they considered a typical [[Young's modulus]] and [[Poisson's ratio]] for a mammalian skull—respectively {{cvt|20|GPa}} and 0.3—and unsafely assumed these properties were uniform across the entire skull. This likely would have made their model skull stiffer than the real thing.<ref name=Sharpe2016/>}} the jaws of ''Diprotodon'' were exceptionally strong, which would have allowed it to consume a broad range of plants, including tough, fibrous grasses.<ref name=Sharpe2016/>

===Migration and sociality===
[[File:Condamine River ChinchillaQLD 2012mar.JPG|thumb|left|One ''Diprotodon'' herd was making seasonal migrations along the [[Condamine River]] (above).<ref name="Price2017"/>]]

In 2017,  by measuring the [[Isotopes of strontium|strontium isotope]] ratio (<sup>87</sup>Sr/<sup>86</sup>Sr) at various points along the ''Diprotodon'' incisor QMF3452 from the Darling Downs, and matching those ratios to the ratios of sites across that region, Price and colleagues determined ''Diprotodon'' made seasonal migrations, probably in search of food or watering holes. This individual appears to have been following the [[Condamine River]] and, while apparently keeping to the Darling Downs during the three years this tooth had been growing, it would have been annually making a {{cvt|200|km}} northwest-southeast round trip. This trek parallels the [[List of mammals that perform mass migrations|mammalian mass migrations]] of modern-day East Africa.<ref name="Price2017">{{cite journal|last1= Price|first1=G.J.|last2= Ferguson|first2=K.J.|last3=Webb|first3=G.E.|last4= Feng|first4= Y.|last5= Higgins |first5= P.|last6= Nguyen |first6=A.D. |last7= Zhao|first7= J.|last8= Joannes-Boyau |first8= R. |last9= Louys |first9= J. |display-authors=6 |year= 2017 |title= Seasonal migration of marsupial megafauna in Pleistocene Sahul (Australia–New Guinea) |journal= Proceedings of the Royal Society B: Biological Sciences |volume= 284 |issue= 1863 |page= 20170785 |doi= 10.1098/rspb.2017.0785 |pmid=28954903 |pmc= 5627191}}</ref>

''Diprotodon'' is the only identified [[metatherian]]{{efn|Metatheria includes marsupials and all [[theria]]n mammals more closely related to marsupials than placentals.}} that seasonally migrated between two places. A few modern marsupials, such as the red kangaroo, have been documented making migrations when necessary but it is not a seasonal occurrence. Because ''Diprotodon'' could do it, it is likely other Pleistocene Australian megafauna also had seasonal migrations.<ref name="Price2017"/>

''Diprotodon'' apparently moved in large herds. Possible fossilised herds, which are most-commonly unearthed in south-eastern Australia, seem to be mostly or entirely female, and sometimes travelled with juveniles. Such [[Sexual segregation (biology)|sexual segregation]] is normally seen in [[polygyny in animals|polygynous]] species; it is a common social organisation among modern megaherbivores involving an entirely female herd save for their young and the dominant male, with which the herd exclusinvely breeds.<ref name=Price2008/> Similarly, the skull is adapted to handling much-higher stresses than that which resulted from bite alone so ''Diprotodon'' may have subjected its teeth or jaws to more-strenuous activities than chewing, such as fighting other ''Diprotodon'' for mates or fending off predators, using the incisors.<ref name=Sharpe2016/> Like modern red and grey kangaroos, which also sexually segregate, [[bachelor herd]]s of ''Diprotodon'' seem to have been less tolerant to drought conditions than female herds due to their larger size and nutritional requirements.<ref name=Price2008/>

===Gait===
[[File:VVP fossil tracks.png|thumb|upright=1.4|Fossil tracks from the [[Victorian Volcanic Plain grasslands|Victorian Volcanic Plain site]]: a) ''[[Protemnodon]]'', b) ''Diprotodon'' pes, c) ''Diprotodon'' overlain by a [[vombatid]], d) ''[[Thylacoleo]]'']]

The locomotion of an extinct animal can be inferred using [[fossil trackway]]s, which seldom preserve in Australia over the [[Cenozoic]]. Only the trackways of humans, kangaroos, vombatids, ''Diprotodon'', and the diprotodontid ''[[Euowenia]]'' have been identified.<ref name=Camens2009>{{cite journal|first1=A.|last1=Camens|first2=R.|last2=Wells|year=2009|title=Diprotodontid Footprints from the Pliocene of Central Australia|journal=Journal of Vertebrate Paleontology|volume=29|issue=3|pages=863–869|doi=10.1671/039.029.0316|bibcode=2009JVPal..29..863C |s2cid=128776520 |url=http://doc.rero.ch/record/208748/files/PAL_E3968.pdf |archive-url=https://web.archive.org/web/20170921220511/http://doc.rero.ch/record/208748/files/PAL_E3968.pdf |archive-date=2017-09-21 |url-status=live }}</ref> ''Diprotodon'' trackways have been found at Lake Callabonna<ref>{{cite journal|first=R. H.|last=Tedford|title=The diprotodons of Lake Callabonna|journal=Australian Natural History|volume=17|year=1973|page=354|url=https://museum-publications.australian.museum/aus-nat-hist-1973-v17-iss11/}}</ref> and the [[Victorian Volcanic Plain grasslands]].<ref name=Carey2011>{{cite journal|first1=S. P.|last1=Carey|first2=A. B.|last2=Camens|first3=M. L.|last3=Cupper|first4=R.|last4=Grün|first5=J. C.|last5=Hellstrom|first6=S. W.|last6=McKnight|first7=I.|last7=McLennan|first8=D. A.|last8=Pickering|first9=P.|last9=Trusler|first10=M.|last10=Aubert|year=2011|title=A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains, Australia|journal=Quaternary Science Reviews|volume=30|issue=5–6|pages=598–602|doi=10.1016/j.quascirev.2010.11.021|bibcode=2011QSRv...30..591C |hdl=1885/65964|hdl-access=free}}</ref><ref>{{cite journal|first1=A. B.|last1=Camens|first2=S. P.|last2=Carey|year=2013|title=Contemporaneous Trace and Body Fossils from a Late Pleistocene Lakebed in Victoria, Australia, Allow Assessment of Bias in the Fossil Record|journal=PLOS ONE|volume=8|issue=1|page=e52957|doi=10.1371/journal.pone.0052957 |doi-access=free |pmc=3534647|pmid=23301008|bibcode=2013PLoSO...852957C }}</ref> The diprotodontid manus (forepaw) print is semi-circular and the pes (hindpaw) is reniform (kidney-shaped).<ref name=Carey2011/> Owing to proportionally small digits, most of the weight was borne on the [[carpus]] and [[tarsus (skeleton)|tarsus]]—the bones connecting to respectively the wrist and the ankle. Diprotodontines seem to have had a much-more-erect gait, an adaptation to long-distance travel that is similar to that of elephants, rather than the more-sprawling posture of wombats and zygomaturines, though there are no fossil trackways of the latter to verify their reconstructed standing posture.<ref name=Camens2009/><ref name=Carey2011/>

At Lake Callabonna, the single ''Diprotodon'' responsible for the impressions had an average stride length of {{cvt|1500|mm|ftin|0}}, trackway width of {{cvt|430|mm|ftin|0}}, and track dimensions {{cvt|295x202|mm}} in length x width. The gleno-acetabular length—the distance between the shoulders and pelvis—could have been about {{cvt|1125|mm|ftin|0}}; assuming a hip height of {{cvt|900|mm|ftin}}, the maker of these tracks was probably moving at around {{cvt|6.3|kph}}.<ref name=Camens2009/>

The single ''Diprotodon'' responsible for the impressions at the volcanic plain had an average stride length of {{cvt|1310|mm|ftin|0}}, trackway width of {{cvt|660|mm|ftin|0}}, and pes length of {{cvt|450|mm|ftin|0}}. The gleno-acetabular length may have been about {{cvt|1080|mm|ftin|0}} and assuming a hip height of {{cvt|830|mm|ftin|0}}, the maker of the tracks was probably moving at around {{cvt|5.5|kph}}. Its posture was much-more-sprawled than the example from Callabonna, aligning more with what might be expected of ''Zygomaturus''. The animal may have been a female carrying a large joey in her pouch, the added weight on the stomach altering the gait. The first trackway continues for {{cvt|62.8|m}} in a south-easterly direction towards a palaeo-lake. The animal seems to have hesitated while stepping down from the first [[sand bar]] on its path with the right pes making three overlapping prints here while shuffling around. The trackway vanishes for a {{cvt|20|m}} stretch and reappears while the animal seemingly is stepping on wet sediment. Another diprotodontid trackway appears {{cvt|50|m}} away, moving southerly, which may have been left by the same individual.<ref name=Carey2011/>

===Life history===
The marsupial [[metabolic rate]] is about 30% lower than that of placentals due to a lower [[body temperature]] of {{cvt|34|to|36|C}}. Marsupials give birth at an earlier point in foetal development, relying on [[lactation]] to facilitate most of the joey's development; because pregnancy is much-more-energetically expensive, investing in lactation rather than longer gestation can be advantageous in a highly seasonal and unpredictable climate to minimise maternal nutritional requirements. Consequently, marsupials cannot support as large a litter size or as short a [[generation time]].<ref name=Tyndale2001>{{cite journal|last=Tyndale-Biscoe|first=C. H.|year=2001|title=Australasian marsupials—to cherish and to hold|journal=Reproduction, Fertility and Development|volume=13|issue=8|pages=477–485|doi=10.1071/RD01079|pmid=11999297 }}</ref>

Based on the relationship between female body size and life history in kangaroos, a {{cvt|1000|kg}} ''Diprotodon'' female would have gestated for six-to-eight weeks, and given birth to a single {{cvt|5|g}} joey. Given its massive size, ''Diprotodon'' may not have sat down to give birth as do smaller marsupials, possibly standing instead. Like koalas and wombats, the pouch may have faced backwards so the joey could crawl down across its mother's abdomen to enter and attach itself to a teat until it could see—perhaps 260 days—and [[thermoregulate]]. It would have permanently left the pouch after 860 days and suckled until reaching {{cvt|270|kg}} after four or five years.<ref name=Tyndale2001/>

In large kangaroos, females usually reach [[sexual maturity]] and enter [[estrous cycle|oestrus]] soon after weaning, and males need double the time to reach sexual maturity. A similar pattern could have been exhibited in ''Diprotodon''. Assuming a lifespan of up to 50 years, a female ''Diprotodon'' could have given birth eight times.<ref name=Tyndale2001/>