Unieke skildery van uitgestorwe reuse luiaard wat in Madagaskar -grot ontdek is

Unieke skildery van uitgestorwe reuse luiaard wat in Madagaskar -grot ontdek is

'N Span wetenskaplikes wat 'n grot in die weste van Madagaskar verken het, het 'n antieke skildery ontdek wat hulle die "enigste bekende tekening van 'n uitgestorwe reuse -lemur" noem wat tot ten minste 1000 jaar gelede in die afgeleë westelike woude van die eiland gewoon het.

Navorsers van die Natuurhistoriese museum verduidelik op die webwerf van die museum dat Madagaskar vroeër die tuiste van reuse -lemore was, wat volgens hulle tot die grootte van silwerrug -gorilla's kan groei. Behalwe vir die ontdekking van 'n paar bene, het daar geen tasbare bewyse bestaan ​​van hoe hierdie reuse -diere werklik gelyk het nie, wat die ontdekking van hierdie nuwe grotverf veral opwindend maak.

Verken die eiland Prehistoriese Megafauna

Die eiland Madagaskar is aan die suidoostelike kus van kontinentale Afrika geleë en is vandag nog die tuiste van 'n uiteenlopende reeks lemurs. Argeologiese vondste, soos snymerke op bene wat in die noordweste gevind is, en klipwerktuie in die noordooste, vertel argeoloë dat Madagaskar omstreeks 2000 vC deur voerders besoek is. 'N 2018 -koerant gepubliseer in Wetenskaplike vooruitgang verduidelik dat 'vroeë Holoseen -mense 10 500 jaar gelede op die eiland kon bestaan' toe 'n groot verskeidenheid megafauna, wat vandag nie meer bestaan ​​nie, die eiland oorheers het. Hierdie groep megafauna bevat die grootste voëls wat ooit bestaan ​​het, olifantvoëls, sowel as reuse-skilpaaie, die Malgassiese havikarend en dwerg-seekoeie.

Navorsing het bevind dat toe vroeë Holoseen -mense die eerste keer op die eiland gewoon het, dit ook bewoon is deur 'n wye reeks megafauna wat nou uitgesterf het, waaronder die reuse luiaard, olifantvoëls, reuse -skilpaaie en dwerg -seekoeie. (Beeld: ©Julian Hume )

In 'n nuwe koerant gepubliseer in die Journal of Island and Coastal Archaeology , Museumnavorser Julian Hume , wat die uitgestorwe diere van die Indiese Oseaan bestudeer, beskryf die skildery as die "enigste bekende tekening van 'n reuse luiaardmemor" wat in die grotte van Wes -Madagaskar gevind is. In 'n tweede koerant, gepubliseer in Kwartêrnavorsing , Beskryf Hume ook 'n nuwe fossielterrein wat bepaal dat reuse -lemurs op Madagaskar bestaan ​​het tot minstens 1000 jaar gelede, 'n lang tyd nadat mense die eiland die eerste keer gevestig het.

Verskeie kenners is dit eens dat die enigste wese wat die grottekening kan voorstel, die nou uitgestorwe reuse luiaard is wat na bewering slegs in Madagaskar bestaan ​​het. ( © Burney et al. 2020 / tandfonline)

Bizarre antieke dier het gedink om die nou uitgestorwe reuse -luiaard te verteenwoordig

Hume het tot die gevolgtrekking gekom dat Madagaskar die tuiste is van verskeie spesies reuse -lemurs, sommige volgens 'n artikel op die webwerf van die Natural History Museum "die grootte van silwerrug -gorilla's was wat waarskynlik 'n groot deel van hul tyd op die bosvloer deurgebring het." Alhoewel die beeld in die grotskildery nie lyk soos u sou verwag nie, het verskeie kenners almal saamgestem dat dit die enigste wese is kon verteenwoordig die nou uitgestorwe reuse luiaard wat na bewering nêrens anders ter wêreld gevind is nie.

Die papier in die Journal of Island and Coastal Archaeology sê luiaardlemore was hoogs gespesialiseerde diere wat tot by die grootte van skape kom, wat aan boomtakke sou gehang het en stadig deur die afdakke van die bos sou kom, en dat die luiaardmemor Babakotia was ''n werklik bisarre spesie' in vergelyking met moderne luiaards wat hul kloue onderstebo hang. Inteendeel, die Babakotia's die vingers is verleng en aan die een kant gebuig en vorm 'starre hake' wat die lemurs in staat stel om hul hande vir enigiets anders te gebruik.

Links, 'n lewensherstel van die reuse luiaardmaki. ( CC BY-SA 3.0 ) Aan die regterkant is 'n mannetjie met 'n mannetjie gekroon wat in die spesiale reservaat Ankarana in Madagaskar gefotografeer is. (Beeld: CC BY-SA 3.0 )

Die span wetenskaplikes het die fossiele van vier verskillende spesies reuse -maki ontdek, tesame met bene uit die uitgestorwe Madagaskaanse erdvark, of bibimalagasie, en ook die oorblyfsels van uitgestorwe reuse -koekoeke en reuse -fossa, wat ongeveer twee derdes groter was as die spesie wat vandag oorleef. Koolstofdatums vir hierdie bene toon dat reuse lemurs tot in die laaste millennium oorleef het. Die navorsers het tot die gevolgtrekking gekom dat een van die hoofoorsake vir die uitsterwing van die meeste van hierdie groot diere 'mense' was, en dat die grot, wat in 'n afgeleë droë woud geleë is, een van die laaste oorblyfsels was vir sommige van die megafauna.

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Skedel van die uitgestorwe reuse luiaardmaki, Babakotia radofilai. ( CC BY-SA 3.0 )

Verbasende ontdekking van komplekse matriks van antieke simbole

Wat die navorsers gesê het, was "verstommend" dat die grotkuns abstrakte simbole bevat wat slegs voorheen gevind is op 'n grotte op die eiland Borneo, ongeveer 7.500 kilometer daarvandaan, en dateer uit "2000 jaar gelede." Dit is ongeveer dieselfde tyd as wat die eerste Indonesiërs in Madagaskar aangekom het, en dit is baie waarskynlik dat hulle hierdie simbole by hulle gehad het, 'n teorie wat, indien korrek, die grot en die skildery van 1000 tot 2000 jaar oud maak.

Die grotkuns wat gevind is, bevat ook abstrakte simbole wat slegs voorheen op 'n grot op die eiland Borneo, 7.500 kilometer daarvandaan gesien is. (Burney et al. 2020 / tandfonline)

Die kuns wat in die grot ontdek is, bevat ook letters wat lyk soos antieke Arabiese skrif uit Ethiopië, en menslike figure met kopvorme wat, volgens die koerant, 'n verbygaande ooreenkoms met die ou Egiptiese gode toon '. En hoewel hierdie vermenging van Indonesiese, Afrikaanse en Malgassiese kulturele simbole van duisende jare gelede ongelooflik aanloklik en suggestief is, het die navorsers gesê dat dit alles nog steeds spekulatief is.


Unieke skildery van uitgestorwe reuse luiaard wat in Madagaskar -grot ontdek is - geskiedenis

LONDEN .- Madagaskar was vroeër die tuiste van 'n verskeidenheid spesies wat vandag nie meer oorleef nie. Dit sluit nie net die reuse -olifantvoëls in nie, maar ook reuse -lemurs, waarvan sommige die grootte van gorilla's was.

Afgesien van die bene van hierdie diere en moontlike ooggetuieverslae wat deur die generasies oorgedra is, was daar min bewyse van hoe hierdie diere in die werklike lewe gelyk het. Maar die ontdekking van nuwe grotkuns kan dit verander.

Julian Hume is 'n navorser by die museum wat werk aan die uitgestorwe diere van die Indiese Oseaan. In 'n nuwe koerant wat in die Journal of Island and Coastal Archaeology gepubliseer is, het Julian en sy kollegas beskryf wat vermoedelik die enigste bekende tekening is van 'n reuse luiaardmaki uit grotte in die weste van Madagaskar.

Die span het die beelde aan verskeie kenners gewys, wat almal saamstem dat die enigste ding wat dit kan voorstel, die nou uitgestorwe reuse luiaardlemors is. Burney et al. 2020

'Daar is tonele van wat ons sien as die jag van 'n reuse luiaardmaki met honde en wapens,' verduidelik Julian. 'Dit is die enigste beeld van die oorspronklike megafauna.

'Daar is niks anders wat wys hoe hierdie diere in die lewe gelyk het nie.'

Daarbenewens het Julian ook gehelp met die skrywer van 'n ander artikel in Quaternary Research wat 'n nuwe fossielwebwerf beskryf, wat toon dat hierdie reuse -lemure ten minste 1000 jaar gelede op Madagaskar oorleef het, lank nadat mense die eiland die eerste keer gevestig het.

'N Land van reuse
Die eiland Madagaskar, aan die suidoostelike kus van kontinentale Afrika, huisves 'n uiteenlopende verskeidenheid lemurs.

Hierdie primate van klein grootte kom nêrens anders ter wêreld voor nie. Aangesien hulle ongeveer 60 miljoen jaar van ape en ape geskei is, is daar tans tot 100 spesies lemurs wat in die tropiese en droë woude, savanne en stekelige woude van die eiland woon.

Deesdae weeg die lemurs slegs 'n paar kilogram, maar as ons net 'n duisend jaar gelede sou teruggaan, was die prentjie baie anders.

Madagaskar was vroeër die tuiste van verskeie spesies reuse -lemurs. Daar was die grootte van silwerrug -gorilla's wat waarskynlik 'n groot deel van hul tyd op die bosvloer deurgebring het. Sommige reuse lemurs sou hulle soos bobbejane gedra het, terwyl ander aanpassings gehad het, soos om voete vas te gryp wat vergelyk is met dié van kolas.

Een van die mees fassinerende groepe reuse -lemurs was die luiaardlemore. Dit was hoogs gespesialiseerde diere wat so groot was as skape wat aan boomtakke sou gehang het en stadig deur die afdakke van die bos sou kom.

'Die luiaardmaki Babakotia was regtig 'n bisarre spesie', verduidelik Julian. 'Terwyl moderne luiaards hul kloue gebruik om onderstebo te hang, het die Babakotia se vingers eerder verleng geraak. Die bene self was geboë om hierdie stewige hake te word sodat die lemurs nie hul hande vir iets anders kon gebruik nie.

'Dit was regtig ongelooflike diere.'

Die reuse lemurs was nie alleen nie. Terselfdertyd drom die groot primate om die Malgassiese woude, so was 'n hele klomp ander, nou uitgestorwe megafauna. Dit sluit in die grootste voëls wat ooit bestaan ​​het, die olifantvoëls, sowel as reuse-skilpaaie, die Malgassiese havikarend en dwergie-seekoeie.

In 'n nuwe subfossiele terrein uit die droë woude van Wes-Madagaskar, het Julian en sy kollegas 'n reeks van hierdie uitgestorwe wesens gedokumenteer.

Hulle het die fossiele van vier verskillende spesies reuse -maki gevind, tesame met bene van die nou uitgestorwe bibymalagasy, ook bekend as die Madagaskaanse erdvark, die oorblyfsels van uitgestorwe reuse -koekoeke en selfs dié van die uitgestorwe reuse -fossa, wat ongeveer twee sou gewees het derdes groter as die spesie wat vandag oorleef.

'Die belangrikste is dat ons die koolstofdatums vir hierdie bene gekry het,' sê Julian. 'Die datums het getoon dat hierdie reuse -lemurs tot in die laaste millennium op hierdie plek oorleef het, wat die jongste datum is vir die dier wat nog gerapporteer is.

'Dit is waarskynlik ten minste 1000 jaar nadat mense Madagaskar die eerste keer beset het.'

Dit is beduidend, want daar word gedink dat een van die dryfvere vir die uitsterwing van baie van hierdie groot diere die koms van mense was. Hierdie bene toon egter dat sommige bevolkings van die reuse -lemore moontlik in duisende jare in afgeleë toevlugsoord in die ontoeganklike woude vasgehou het.

Die koms van mense
Dit is nog nie presies bekend wanneer mense op Madagaskar aangekom het nie. Sommige het voorgestel dat dit ten minste 10 000 jaar gelede die eerste keer plaasgevind het, hoewel hierdie bewyse onlangs meer bevraagteken is.

Wat nie betwyfel word nie, is waar hierdie eerste inwoners vandaan kom. Daar word geglo dat hierdie mense van Indonesië oor die Indiese Oseaan gevaar het eerder as om die relatief kort reis van die vasteland van Afrika te maak.

Verbasend genoeg bevat die grotkuns wat deur Julian en sy kollegas beskryf is, abstrakte simbole wat slegs voorheen gevind is op 'n grot op die eiland Borneo, ongeveer 7.500 kilometer daarvandaan.

'Die simbole in Borneo dateer uit 2 000 jaar gelede', verduidelik Julian. 'Dit word vermoedelik ongeveer dieselfde tyd as wat die eerste Indonesiërs in Madagaskar aangekom het, wat beteken dat hulle moontlik hierdie simbole saamgedra het. Dit beteken dat die grotterrein in Madagaskar van 1 000 tot 2 000 jaar oud kan wees. '

Hierdie spesifieke simbole is interessant, aangesien die enigste ander simbole op die eiland Borneo gevind kan word Burney et al. 2020

Dit pas by die grotkuns -toneel wat die jag van die luiaardmemor uitbeeld, veral as dit gekombineer word met die datering van die fossielmemorbene. Daarbenewens kan ander tekeninge ook uitgestorwe megafauna soos die olifantvoël en die reuse -skilpad toon.

Daar is ook 'n paar tekeninge wat die effens latere invloed van die Afrika -kolonisasiegebeure kan toon. Die grotte -kuns bevat ook letters wat lyk op ou Arabiese skrif uit Ethiopië en menslike figure met koppe wat 'n verbygaande ooreenkoms met die ou Egiptiese gode het.

Die navorsers bespiegel dat dit die vermenging van die Indonesiese, Afrikaanse en Malgassiese kulture tydens die eerste paar honderd jaar van menslike nedersetting duisende jare gelede kan verteenwoordig, hoewel hulle ook versigtig is om aan te hou dat dit nogal spekulatief is.


Wetenskaplike indeling

Koninkryk Animalia
Filum Chordata
Clade Mammalia
Orde Pilosa
Familie † Megatheriidae
Subtribe † Megatheriina
Geslag † Megatherium

EXTINCT DIERES IN ROCK ART - MADAGASCAR ’S SLOTH LEMUR:

Foto van die grotwand van Madagaskar met piktogramme, regs bo. Internetfoto - Publieke domein.

Een van die opwindendste dinge van rotskuns is dat dit kan dien as 'n venster op die verlede, 'n manier om dinge te sien wat nie meer bestaan ​​nie, of dit nou die lewenswyse van antieke mense is, of antieke wesens wat die mense uitgebeeld het wat nou is uitgesterf.

'N Internasionale span wetenskaplikes het stilistiese unieke antieke tekeninge ontdek, insluitend die enigste bekende prehistoriese voorstelling van 'n uitgestorwe reuse luiaard, op die mure van 'n rotsskuiling in die weste van Madagaskar. Die tekeninge is ontdek deur dr David Burney uit die National Tropical Botanical Garden van Hawaii en sy kollegas uit die Verenigde Koninkryk, Madagaskar en die Verenigde State in die Andriamamelo -grot naby die klein dorpie Anahidrano. ” (Prostak 2020)

Die diversiteit van lemurs was in die verlede groter - baie groter. Waar Afrika sy gorilla's en Borneo en Sumatra hul orang-oetans het, het Madagaskar sy reuse luiaardlemors (Archaeoindris fontoynonti), wat tot 244 kg geweeg het en die grootte van manlike gorilla's was. ” (Van der Geer 2017)

Luiaard Lemur -skedel (Archaeoindris fontoynontii), Internetfoto wikipedia.com - Publieke domein.

Die luiaardlemore (familie Palaeopropithecidae) is 'n groep uitgestorwe reuse -lemurs wat vier genera insluit. Die algemene naam kan misleidend wees, aangesien hierdie wesens nie nou verwant was aan Suid -Amerikaanse luiaards nie. Soos die naam aandui, is luiaardlemors ontwerp vir boomtoppe, met lang arms en bene, lenige gewrigte en haakagtige hande en voete. Hierdie aanpassings het hulle in staat gestel om beide spring en klim te wees. ” (Prostak 2020)

Beperkte vakkundigheid is geposuleer vir t hy is 'n gorilla-grootte Archaeoindris wat vergelyk word met 'n luiaard. Die baie hoë hoek van die femorale nek-as en ander hoogs afgeleide postkraniale kenmerke wat slegs met Palaeopropithecus gedeel word, dui egter op meer toegewyde arborealiteit. ” (Godfrey en Jungers 2003: 256) (LET WEL: Scansorial word gedefinieer as in staat, of aangepas vir, klim.>

Wat die vermeende antieke skepping van hierdie beelde betref, moet ons onthou dat Madagaskar een van die laaste plekke op aarde is waarop die mensdom die uitwissing van die inheemse megafauna bereik het. 'N Paar het moontlik baie onlangs beswyk. 'N Voorbeeld Palaeopropithecus ingens uit Ankilitelo in die suidweste van Madagaskar is onlangs met radiokoolstof gedateer op 510-80 PB. Vertroue perke op hierdie datum sluit die historiese tydperk in. ” (Godfrey en Jungers 2003: 257) Alhoewel die Madagaskar Sloth Lemur inderdaad uitgesterf het, beteken dit egter nie dat die rotskuns oud is nie, omdat die uitsterwing van hierdie dier blykbaar gedurende die vroeë historiese tydperk plaasgevind het.

Alhoewel dit werklik opwindend sou wees om die uitgestorwe dier te verteenwoordig wat aangewys is, het ek 'n paar probleme om te verklaar dat dit beslis 'n voorstelling is van Madagaskar se uitgestorwe luiaardlemoer. Eerstens het nie een van die skrywers van die koerant ervaring in rotskuns of publikasies in hul verlede nie, wat ek kon bepaal. Tweedens, hoewel die betrokke beeld baie lyk soos 'n luiaard wat onderstebo hang, word hierdie pose byna algemeen aanvaar deur rotskunsstudente om aan te dui dat die dier op die foto oorlede is, nie 'n luiaard wat aan 'n boom hang nie. En as dit nie 'n luiaard is nie, maar 'n viervoetige dooie, is 'n groot ouderdom vir hierdie rotstekening nie so waarskynlik nie. Ek voel daarom dat die positiewe identifisering van hierdie beeld as die uitgestorwe luiaardmemor van Madagaskar regtig op 'n ledemaat gaan.

OPMERKING: die towenaars in hierdie plasing is van die internet gehaal met 'n soektog na foto's in die publieke domein. As een van hierdie beelde nie as 'n openbare domein bedoel is nie, vra ek om verskoning en sal ek graag die foto -krediete verskaf as die eienaar my daarmee sal kontak. Vir meer inligting oor hierdie verslae, lees die oorspronklike verslae op die onderstaande webwerwe.

Godfrey, Laura en William Jungers,

2003 Die Uitgestorwe Luiaard Lemurs van Madagaskar , Evolusionêre Antropologie 12: 252 � (2003)

2020 Navorsers vind unieke antieke rotstekeninge van uitgestorwe luiaardmaki , 7 September 2020, http://www.sci-news.com/archaeology/sloth-lemur-drawing-08820.html

2017 Die laat oorlewing van Madagaskar se Megafauna , 22 September 2017, https://beta.capeia.com/paleobiology/2017/09/22/the -late-survival-of-madagascars-megafauna

2020 Rotskuns uit die Andriamamelo -grot in die Beanka -beskermde gebied van Wes -Madagaskar, Journal of Island and Coastal Archaeology , aanlyn gepubliseer 26 Mei 2020 doi: 10.1080/15564894.2020.1749735


Vroeë wanopvattings

Alhoewel ons gereeld hoor hoe Thomas Jefferson Megalonyx vernoem het, is die geskiedenisboeke nie so nuut as dit kom by alles wat hy verkeerdelik met hierdie prehistoriese soogdier gemaak het nie. Ten minste 50 jaar voor die publikasie van Charles Darwin's Oor die oorsprong van spesies, Jefferson (saam met die meeste ander natuurkundiges van daardie tyd) het geen idee gehad dat diere kan uitsterf nie en het geglo dat pakke Megalonyx nog steeds in die Amerikaanse weste rondloop, en hy het selfs die beroemde pioniersduo Lewis en Clark gevra om 'n kyk uit vir enige waarnemings! Miskien nog erger, Jefferson het ook nie 'n idee gehad dat hy te doen het met 'n wese wat so eksoties soos 'n luiaard was nie, die naam wat hy gegee het, Grieks vir 'reuse -klou', bedoel was om te eer wat hy gedink het 'n buitengewoon groot leeu was.


10 groot feite oor reuse grond luiaards

Vandag word die ses lewende luiaardsoorte gewoonlik aan boomtakke hang of op YouTube versprei. Maar luiaards was vroeër baie meer uiteenlopend - en baie groter. Die uitgestorwe luiaards het allerhande verskillende lewensstyle nagestreef en kom in omtrent elke denkbare vorm en grootte. Sommige was koei-agtige weidings, ander was dalk 'n graafgraaf en, glo dit of nie, 'n paar het selfs onder die seegolwe geëet.

1. DIE GROOTSTE WAS ELEFANT-GROOT.

Megatherium (hierbo) beteken 'reuse -dier' ​​- 'n gepaste naam vir 'n wese wat 'n paar ton weeg, 'n lengte van 20 voet bereik het, en - as dit op sy agterpote opgehef is - meer as 12 voet lank was. Die grootste luiaard van alle tye, Megatherium americanum, Suid -Amerika tussen vyf miljoen en elfduisend jaar gelede beset. Bo die ewenaar, sy effens kleiner neef, die 6000 pond Eremotherium, daarin geslaag om so ver noord as New Jersey te versprei.

2. DIE MEESTE LOPEND OP DIE KANTTE VAN HULLE VOETE.

Alle luiaards was oorwegend viervoetig. Alhoewel hulle meer as twee bene kon staan ​​(meer hieroor later), het die diere verkies om op vier rond te kom - maar individuele spesies verskil baie van mekaar ten opsigte van die liggaamshouding.

Wetenskaplikes het grondluiwe in vier erkende gesinne verdeel, en slegs een - die megalonychids - het plat op hul agtervoete gestaan ​​soos mense doen. As gevolg van die vorms van hul enkel- en/of agterkloue, moes luiaards van die megatheriid-, mylodontid- en nothrotheriid -gesinne saamtrek deur gewig aan die buitekant van hul voete te plaas.

3. TEN MINSTE HET PANTE GEDEEL.

Begrawe in die vel van die mylodontide gemaalde luiaards - insluitend die Harlan se grondluiaard, waarvan die reikwydte van Florida tot die staat Washington strek - was 'n reeks klein, skyfies. Hierdie knoppies (bekend as 'osteoderms'), was meestal om die rug, skouers en nek gegroepeer en sou soos 'n beskermende ketting gedra het.

Hierdie eienskap is nie so ongewoon nie. 'N Paar moderne diere, insluitend gordeldiere en krokodille, het ook osteoderms van een of ander aard - net soos baie dinosourusse.

4. BAIE GEBRUIK HUL STERTE OM “TRIPODS” TE VORM.

Vir hierdie diere het 'n paar ekstra stabiliteit nodig om op twee ledemate op te staan. Elke keer as 'n luiaard dit doen, sal sy gespierde stert soos 'n ander been optree, wat sy aansienlike liggaamsgewig kan ondersteun.

5. EEN SPESIE WORD GENOEM NA THOMAS JEFFERSON.

Die belangrikheid van Sage of Monticello vir die Amerikaanse paleontologie kan nie onderskat word nie. In 1796 het Jefferson - 'n gerespekteerde leunstoel -natuurkundige - 'n paar nuuskierige bene van Wes -Virginia (moderne Wes -Virginia) ontvang. Hierdie vonds was nie so ongewoon nie-fossiele met dieselfde voorkoms het ook na vore gekom in Kentucky en ander dele van Virginia. Tog het Jefferson tydens 'n byeenkoms van die American Philosophical Society in Philadelphia in 1797 uitgebrei gepraat oor die grootklou raaiseldier. Die toekomstige president het hierdie wese genoem Megalonyx, of 'groot klou'. Alhoewel ons nou weet dat dit 'n groot luiaard is, het Jefferson die dier oorspronklik as 'n enorme leeu of tieragtige karnivoor beskou.

Tans is vier verskillende spesies van Megalonyx word die bekendste erken, Megalonyx jeffersonii, is ter ere van Jefferson genoem. Op 8 Maart 2008 erken West Virginia die dier as sy amptelike staatsfossiel.

6. MENSLIKE HET HULLE WAARLIKS AANGEET.

Wat het die wollerige mammoet, die koggelkat en die ander ystydperk-mega-soogdiere van Noord-Amerika doodgemaak? Homo sapiens kry gewoonlik 'n goeie deel van die skuld. Wetenskaplikes het lank bespiegel dat mense grondluiaards doodgemaak en verslind het - maar daar was jare lank geen fisiese bewyse om hierdie idee te ondersteun nie. Toe, in 2008, is inkriminerende letsels op die femur van 'n Ohio gevind Megalonyx. Die 13 000 jaar oue fossiel is deurspek met 41 ongewone snitte wat blykbaar deur mensgemaakte gereedskap agtergelaat is.

Soos die argeoloog Haskel Greenfield uitwys, sal ons waarskynlik nooit weet of vroeë Amerikaners hierdie dier doodgemaak het of net die oorskot daarvan verwyder het nie. 'Die enigste ding wat duidelik is,' het hy in 2012 gesê, 'is dat daar ontwykingsmerke is: hulle skei die ledemate van mekaar en sny die gewrigte. En 'n paar merke toon dat hulle die vleis van die been af ​​gevul het. "

7. DAAR WAS OPGESLUIT "GROND" SLOTS.

Stel jou voor 'n luiaard wat hard probeer om 'n mariene leguaan te wees. U het pas 'n lid van die Thalassocnus genus. Hierdie Peruaanse herbivore, wat 8 tot 4 miljoen jaar gelede geleef het, duik in die see vir hul aandete. Haak kloue het hulle gehelp om vas te klou op ondergedompelde, met seewier bedekte rotse wat een keer veranker was, a Thalassocnus mariene alge kan verteer. Met verloop van tyd het evolusie die amfibiese luiaards toegerus met toenemend digte ribbes en ledemate. Daarom was jonger spesies minder lewendig - en waarskynlik meer in die water - as wat hul voorouers was.

8. ONS HET 'N VERMUITIGE GRONDSLOTTE VIND.

Met 'n swart beer in grootte, Nothrotheriops sou verdwerg gewees het deur behemotte soos Megatherium. Tog weet ons meer daarvan as enige ander luiaard danksy 'n wonderlike vonds. Elfduisend jaar gelede, 'n New Mexican Nothrotheriops beland in 'n vulkaniese gasopening en sterf. Toe, in 1927 of 1928 (bronne verskil), kom 'n groep ontdekkingsreisigers op die ongelooflik goed bewaarde liggaam. Byna al sy ligamente en bene was ongeskonde, maar ook dit Nothrotheriops kom ook met 'n paar spiervesels. Nog interessanter, die monster het 'n oorspronklike vel behou - bedek met growwe, gelerige hare. Die kersie bo -op was 'n gepaardgaande misbal, wat dit help bevestig het Nothrotheriops het 'n uiteenlopende verskeidenheid plante geëet - insluitend kaktusvrugte, yuccas en soutbosse.

In 1928 het Yale's Peabody Museum of Natural History die mummie gekry, en vandag kan besoekers die wesens in Mammal Hall vind.

9. VEILIGE SLOTS IS MAG REGTIG GOEIE DIGGERS.

Jou gemiddelde grond luiaard was - na alle waarskynlikheid - 'n blaaiende herbivoor wat boomtakke afgetrek het met sy sterk voorpote. Die mylodontiede het egter moontlik ook voedsel ingesamel deur daarvoor te grawe. Kenners voer aan dat hul wye, afgeplatte kloue soos ideale gereedskap lyk om wortels en knolle uit te grawe [PDF].

Glo dit of nie, mylodontiede was selfs grawe. Verskeie reuse, prehistoriese tonnels is in Argentinië gevind [PDF]. Dit is iewers gemaak tydens die Pleistoseen -tydperk (tussen 2,6 miljoen en 11,700 jaar gelede), dit was natuurlike wonderwerke, met die langste strek van 130 voet van einde tot einde. Wat kon hulle moontlik gegrawe het? Twee topverdagtes is Scelidotherium en Glossotherium: 'n paar mylodonts met kloue wat ooreenstem met krapmerke wat in die gate gevind word.

10. EEN UITHOUDING HET NIE UITGESLUIT TOT RAADLIK NIE.

Die Karibiese eilande lyk na 'n onwaarskynlike plek waar grondluiaards hul laaste standpunt kon neem - maar dit is presies waar dit gebeur het [PDF]. Noord-Amerika op die vasteland het ongeveer 11 000 jaar gelede al sy inheemse spesies verloor, en 'n halwe millennium later het Suid-Amerika ook 'n luiaardvrye vasteland geword.

Maar ten spyte van hierdie uitwissings, het sommige grondluiaards eers baie later uitgesterf. Hispaniola en Kuba was die tuiste van verskillende dwergspesies. Hierdie soogdiere, wat afkomstig was van hul eweknieë op die vasteland, was veerkragtig. Uiteindelik, Megaloncus rodens was die laaste luiaard: Radiokoolstofdatering dui aan dat hierdie vegetariër van 200 pond so 4200 jaar gelede oor Kuba gewikkel het.


Unieke skildery van uitgestorwe reuse luiaard wat in Madagaskar -grot ontdek is - geskiedenis

Isolasie en biodiversiteit
Deur Dr Laurie Godfrey

Ongeveer 300 kilometer oos van suidelike Afrika, oorkant die Mosambiekse kanaal, lê die eiland Madagaskar. Die bekendste vir sy lemurs (primitiewe familielede van ape, ape en mense), kleurvolle verkleurmannetjies, pragtige orgideë en toring kremetartbome, is 'n paar van die wêreld se mees unieke flora en fauna. Byna al die reptiel- en amfibiese spesies van Madagaskar, die helfte van sy voëls en al die lemurs is endemies vir die eiland, wat beteken dat hulle nêrens anders op aarde gevind kan word nie.

Madagaskar is ongewoon, nie net vir sy endemiese spesies nie, maar ook vir die spesies wat opvallend afwesig is. As gevolg van die geografiese isolasie van Madagaskar, is baie groepe plante en diere heeltemal afwesig van die eiland. Sommige groepe word slegs verteenwoordig deur spesies wat baie onlangs deur mense bekendgestel is. Die vele spesies groot soogdiere en#151 wildsbokke, olifante, sebras, kamele, kameelperde, hiënas, leeus en jagluiperds wat tans op kontinentale Afrika rondbeweeg, ontbreek op die eiland. Die enigste groot Afrika -soogdier wat dit 'n paar duisend jaar gelede na Madagaskar gemaak het, was die seekoei. Seekoeie, soortgelyk aan dié wat vandag die Nylrivier beset, het blykbaar gedurende die tersiêre era na Madagaskar geswem. Hulle afstammelinge het verdwerg en ontwikkel tot spesies wat uniek is vir die eiland.

Hierdie kenmerkende biodiversiteit is die gevolg van die geografiese isolasie van Madagaskar. Geoloë glo dat Madagaskar 165 miljoen jaar gelede aan Afrika verbonde was, maar dat dit iewers gedurende die volgende 15 miljoen jaar van die vasteland begin wegdryf het. Paleontoloë wat die afsettings van die Mesozoïese era in Madagaskar ondersoek, het die bene van dinosourusse, vroeë voëls en soogdiere gevind. Die meeste soogdiere en ander aardlewe wat vandag op Madagaskar goed verteenwoordig word, het egter nie ontwikkel toe Madagaskar die eerste keer van kontinentale Afrika geskei het nie.

Daar word geglo dat die voorouers van hierdie diere (insluitend ten minste een spesie primitiewe primate) op hierdie groot eiland aangekom het nadat hulle groot dele van die oseaan oorgesteek het deur vlot te dryf op drywende stompe of gekapte plantegroei. Die daaropvolgende adaptiewe straling van hierdie taksonomiese groepe maak Madagaskar so besonders. Die dier- en plantlewe van hierdie groot eiland is grotendeels die gevolg van 'n natuurlike eksperiment in evolusie op 'n aparte land, maar baie soos ons eie.

Die aankoms van mense

Mense het ongeveer 2000 jaar gelede die eerste keer in bote na Madagaskar gekom. Die oudste mens-gemodifiseerde bene van uitgestorwe spesies verskyn tans in die fossielrekord. Houtskoolseine, en#148 in sedimente in die meer, het gedurende hierdie tydperk dramaties toegeneem - wat dui op 'n toename in brande. Stuifmeelprofiele, gelees uit sedimentkerne in die meer, onthul die koms van ingevoerde plante, insluitend dagga. Argeoloë glo dat Madagaskar moontlik 'n belangrike stoppunt was langs 'n handelsroete wat van Suidoos -Asië na Oos -Afrika geloop het.

Die kulturele praktyke van die Malgassiese mense weerspieël hul gemengde Asiatiese en Afrikaanse wortels. Hierdie dubbele wortels blyk duidelik uit die seremonie van die opgrawing, herverpakking en herbegraafing van die skeletreste van eerbiedige voorouers rysvleisboerdery en die Malgassiese taal self, wat deur mense wat in die binneland van Borneo woon, gepraat word.

Ontwikkel in vergetelheid

Toe mense die eerste keer op Madagaskar aankom, het daar ten minste 50 maki -spesies op die eiland gewoon, waarvan die grootste teen die liggaamsmassa van 'n manlike gorilla of orangoetang was. Nie een van die 33 lemursoorte wat nog op die eiland oorleef is so groot soos die kleinste lemurs wat gedurende die afgelope paar millennia van Madagaskar verdwyn het nie. Saam met die reuse -lemurs is Madagaskar bevolk deur ander megafauna's wat ook sedertdien verdwyn het. Daar was groot skilpaaie, reuse roofvoëls en dwerg -seekoeie. Daar was reuse vluglose voëls wat olifantvoëls genoem word. Hierdie voëls was groter as enige ander voël - lewend of uitgesterf. Hulle was swaarder as die beroemde moas van 10 voet lank in Nieu-Seeland. Die eiers van olifantvoëls kan die vloeistofinhoud van ongeveer 180 hoendereiers bevat! Daar was geen katte of honde op Madagaskar nie, maar daar was vreemde primitiewe vleiseters (mangoeste, saaiers en kriptoproste), waaronder een wat meer as 10 kilogram geweeg het.

Gedurende die afgelope 2000 jaar het al die groot endemiese diere van Madagaskar uitgesterf, en daar word beraam dat minder as 3% van wat vroeër 'n groot uitgestrekte westelike bladwisselende woud was, vandag bestaan.

Madagaskar se ongewone endemisme maak dit een van die grootste bewaringsprioriteite ter wêreld. Maar sy endemiese plante en diere ly steeds aan praktyke soos sny-en-brand-landbou en die oes van houtagtige plante vir houtskool en hout. Grasse word dikwels doelbewus verbrand om die groei van vars lemme te stimuleer om die beeste te voed. Wilde diere word soms ook gejag. Vanweë die geweldige endemisiteit en rykdom van plant- en diersoorte op Madagaskar, glo natuurbewaarders dat die vernietiging van bos hier 'n groter negatiewe impak op die globale biodiversiteit kan hê as op enige ander plek op aarde.

Subfossiel vind

Grot-, moeras- en stroomplekke het die bene van diere opgelewer wat op die groot eiland geleef het voor kolonisering deur mense en gedurende die afgelope twee millennia. These subfossil sites, so-called because the bones are too fresh to have become fossilized, provide some direct evidence of the history of the long and slow decimation of Madagascar's wildlife following the arrival of humans.

Recent explorations of some of these subfossil sites by a team from Duke University (North Carolina) and associated scientists (from the University of Massachusetts, Amherst the State University of New York at Stony Brook, and the University of Madagascar in Antananarivo) have added enormously to our knowledge of the anatomy and adaptations of Madagascar's paleofauna. These scientists have explored, among other sites, the 110 kilometers of caves at the Ankarana mountains in northern Madagascar, and a pit called Ankilitelo that descends almost 500 feet deep in southwestern Madagascar. The subfossil sites contain the bones of elephant birds, pygmy hippopotamuses, giant tortoises and at least 17 species of extinct lemurs. The oldest radiocarbon-dated bones of extinct lemurs are about 12,000-26,000 years old. The most recent are only 1000-500 years old -- proof that giant lemurs survived human occupation of the island by at least 1,500 years. There is also some circumstantial evidence that pygmy hippos may have been alive as recently as 100 years ago.

Extinct Giants

Fossil studies have concluded that the giant extinct lemurs of Madagascar were an extraordinarily diverse group. There was a giant aye-aye, a relative of the living aye-aye, but three to five times as heavy. Both living and extinct aye-ayes possess an elongated third digit and enormous rodent-like incisors — adaptations for extracting grubs and insect larvae from tunnels in dead wood. The robust extinct aye-aye is the only extinct lemur that clearly belongs to a non-extinct genus.

Megaladapis was an orangutan-sized lemur with teeth very like those of the living sportive lemur (Lepilemur). Unlike the Lepilemur, however, Megaladapis had a long muzzle and widely separated eyes --very uncharacteristic of primates! Its feet were enormous pincer-like grasping devices. Its forelimbs were long and robust. Paleontologists believe that it climbed trees like koalas and subsisted almost entirely on a diet of leaves.

The “Sloth” lemurs, so named because of its remarkable convergences with tree-dwelling sloth of South and Central America, had crania and teeth that suggest a close relationship with some living lemurs (indris, sifakas, and avahis). The largest of the sloth lemurs was the gorilla-sized Archaeoindris, which probably spent a large amount of time on the ground. The most specialized was Palaeopropithecus, a chimpanzee-sized lemur with teeth like those of the sifaka, but bodies like those of arboreal sloths. These upside-down animals had long forelimbs and short hindlimbs, and enormous, hook-like hands and feet.

Advancing the Research

Thanks to the development of the Polymerase Chain Reaction (PCR) techniques, it is now possible to extract ancient DNA from the bones of subfossil lemurs. DNA samples are currently being analyzed in a laboratory at Northwestern University in Chicago. These methods will be used to test hypotheses of evolutionary relationship that were derived from the analysis of the skeletal morphology of extant and extinct lemurs.

Dr. Laurie Godfrey has been involved with paleontological fieldwork in Madagascar since the mid-1980's. She received her PhD in biological anthropology at Harvard University in 1977, and currently teaches anthropology at the University of Massachesetts in Amherst.


Habitat

Giant ground sloths evolved in South America around 35 million years ago. Around 8 million years ago, they migrated into North America, according to the San Diego Natural History Museum.

Giant ground sloths preferred forests along rivers or lakes, but they also lived during the Pleistocene period, also known as the Great Ice Age. At its peak, as much as 30 percent of the Earth's surface was covered by glaciers and parts of the northern oceans were frozen, according to the San Diego Natural History Museum. This made for a very cold environment that few animals could endure.

By the end of the Great Ice Age, around 11,700 years ago, many believe that the giant ground sloths had become extinct. Some argue that they were around for many more thousands of years, though, surviving on islands in the Caribbean.

Ground sloths were herbivores, meaning they ate vegetation. Their peg-like teeth were ideal for this diet, but they also had other body parts that played a large part in their meals. "They had long curved claws, likely an adaptation for foraging for grabbing branches and stripping foliage from tree limbs, as well as for protection from predators," Wilkins told Live Science.

Their hind foot structure and posture of the ground sloths also helped it with meal time. They likely relied on their robust hind feet, in combination with a stout tail, to support their massive bodies when rearing on their hindquarters to reach high into trees for forage, Wilkins explained.


Inhoud

Megafauna – in the sense of the largest mammals and birds – are generally K-strategists, with high longevity, slow population growth rates, low mortality rates, and (at least for the largest) few or no natural predators capable of killing adults. [7] These characteristics, although not exclusive to such megafauna, make them vulnerable to human overexploitation, in part because of their slow population recovery rates. [8] [9]

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. [10] 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. [10]

In terrestrial mammals Edit

Subsequent to the Cretaceous–Paleogene extinction event that eliminated the non-avian dinosaurs about 66 Ma (million years) ago, terrestrial mammals underwent a nearly exponential increase in body size as they diversified to occupy the ecological niches left vacant. [11] Starting from just a few kg before the event, maximum size had reached

50 kg a few million years later, and

750 kg 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. [11] 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 0.259 , increasing generation times with increasing size cause the log mass vs. time plot to curve downward from a linear fit.) [10]

Megaherbivores eventually attained a body mass of over 10,000 kg. The largest of these, indricotheres and proboscids, have been hindgut fermenters, which are believed to have an advantage over foregut fermenters in terms of being able to accelerate gastrointestinal transit in order to accommodate very large food intakes. [12] A similar trend emerges when rates of increase of maximum body mass per generation for different mammalian clades are compared (using rates averaged over macroevolutionary time scales). Among terrestrial mammals, the fastest rates of increase of body mass 0.259 vs. time (in Ma) occurred in perissodactyls (a slope of 2.1), followed by rodents (1.2) and proboscids (1.1), [10] all of which are hindgut fermenters. The rate of increase for artiodactyls (0.74) was about a third that of perissodactyls. The rate for carnivorans (0.65) was slightly lower yet, while primates, perhaps constrained by their arboreal habits, had the lowest rate (0.39) among the mammalian groups studied. [10]

Terrestrial mammalian carnivores from several eutherian groups (the artiodactyl Andrewsarchus - formerly considered a mesonychid, the oxyaenid Sarkastodon, and the carnivorans Amphicyon en Arctodus) all reached a maximum size of about 1000 kg [11] (the carnivoran Arctotherium and the hyaenodontid Simbakubwa may have been somewhat larger). The largest known metatherian carnivore, Proborhyaena gigantea, apparently reached 600 kg, also close to this limit. [13] 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. [14] It has also been suggested that maximum size for mammalian carnivores is constrained by the stress the humerus can withstand at top running speed. [13]

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, [15] and might be related to the thermoregulatory advantage of large body mass in cool climates, [11] better ability of larger organisms to cope with seasonality in food supply, [15] or other factors [15] the latter correlation could be explained in terms of range and resource limitations. [11] 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. [11]

In marine mammals Edit

Since tetrapods (first reptiles, later 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. [16] [17] The ancestors of cetaceans are believed to have been the semiaquatic pakicetids, no larger than dogs, of about 53 million years (Ma) ago. [18] By 40 Ma ago, cetaceans had attained a length of 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 0.259 of a factor of 3.2 per million years) than achieved by any group of terrestrial mammals. [10] 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 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 swimming movements as opposed to terrestrial locomotion. Also, the greater heat capacity and thermal conductivity of water compared to air may increase the thermoregulatory advantage of large body size in marine endotherms, although diminishing returns apply. [10]

Among toothed whales, maximum body size appears to be limited by food availability. Larger size, as in sperm and beaked whales, 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 size more advantageous. The lunge feeding technique of rorquals appears to be more energy efficient than the ram feeding of balaenid whales the latter technique is used with less dense and patchy plankton. [19] The cooling trend in Earth's recent history may have generated more localities of high plankton abundance via wind-driven upwellings, facilitating the evolution of gigantic whales. [19]

Cetaceans are not the only marine mammals to reach tremendous sizes. The largest carnivorans of all time are marine pinnipeds, the largest of which is the southern elephant seal, which can reach 6 meters in length and weigh up to 5,000 kilograms (11,000 lb). Other large pinnipeds include the northern elephant seal at 4,000 kilograms (8,800 lb), walrus at 2,000 kilograms (4,400 lb), and Steller sea lion at 1,135 kilograms (2,502 lb). The sirenians 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 10 meters in length and weighed 8,000 to 10,000 kilograms (18,000 to 22,000 lb), and was hunted to extinction in the 18th century. The semi-aquatic hippopotamus, which is the terrestrial mammal most closely related to cetaceans, can reach 3,200 kilograms (7,100 lb).

In flightless birds Edit

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. [20] During this interval, apex predator niches were often occupied by reptiles, such as terrestrial crocodilians (e.g. Pristichampsus), large snakes (e.g. Titanoboa) or varanid lizards, or by flightless birds [11] (e.g. Paleopsilopterus in South America). This is also the period when megafaunal flightless herbivorous gastornithid birds evolved in the Northern Hemisphere, while flightless paleognaths evolved to large size on Gondwanan 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 45 kg (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. [21]

Flightless paleognaths, termed ratites, have traditionally been viewed as representing a lineage separate from that of their small flighted relatives, the Neotropic tinamous. 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. [20] [22] [23] Similarly, the small kiwi of New Zealand have been found to be the sister group of the extinct elephant birds of Madagascar. [20] These findings indicate that flightlessness and gigantism arose independently multiple times among ratites via parallel evolution.

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 en Bathornis were apex predators but became extinct by the Early Miocene. In South America, the related phorusrhacids shared the dominant predatory niches with metatherian sparassodonts 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.

However, none of the flightless birds of the Cenozoic, including the predatory Brontornis, possibly omnivorous Dromornis stirtoni [24] or herbivorous Vorombe, ever grew to masses much above 500 kg, 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. [25] [note 1] 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 diprotodonts that evolved to sizes several times larger. [28]

In giant turtles Edit

Giant tortoises were important components of late Cenozoic megafaunas, being present in every nonpolar continent until the arrival of homininans. [29] [30] The largest known terrestrial tortoise was Megalochelys atlas, an animal that probably weighed about 1,000 kg.

Some earlier aquatic Testudines, e.g. the marine Archelon of the Cretaceous and freshwater Stupendemys of the Miocene, were considerably larger, weighing more than 2,000 kg.

Timing and possible causes Edit

The Holocene extinction (see also Quaternary extinction event), occurred at the end of the last ice age glacial period (a.k.a. the Würm glaciation) when many giant ice age mammals, such as woolly mammoths, went extinct in the Americas and northern Eurasia. An analysis of the extinction event in North America found it to be unique among Cenozoic extinction pulses in its selectivity for large animals. [31] ( Fig. 10 ) Various theories have attributed the wave of extinctions to human hunting, climate change, disease, a putative extraterrestrial impact, or other causes. However, this extinction near the end of the Pleistocene was just one of a series of megafaunal extinction pulses that have occurred during the last 50,000 years over much of the Earth's surface, with Africa and southern Asia (where the local megafauna had a chance to evolve alongside modern humans) being comparatively less affected. The latter areas did suffer a gradual attrition of megafauna, particularly of the slower-moving species (a class of vulnerable megafauna epitomized by giant tortoises), over the last several million years. [32] [33]

Outside the mainland of Afro-Eurasia, these megafaunal extinctions followed a highly distinctive landmass-by-landmass pattern that closely parallels the spread of humans into previously uninhabited regions of the world, and which shows no overall correlation with climatic history (which can be visualized with plots over recent geological time periods of climate markers such as marine oxygen isotopes or atmospheric carbon dioxide levels). [34] [35] Australia [36] and nearby islands (e.g., Flores [37] ) were struck first around 46,000 years ago, followed by Tasmania about 41,000 years ago (after formation of a land bridge to Australia about 43,000 years ago), [38] [39] [40] Japan apparently about 30,000 years ago, [41] North America 13,000 years ago, [note 2] South America about 500 years later, [43] [44] Cyprus 10,000 years ago, [45] [46] the Antilles 6,000 years ago, [47] [48] New Caledonia [49] and nearby islands [50] 3,000 years ago, Madagascar 2,000 years ago, [51] New Zealand 700 years ago, [52] the Mascarenes 400 years ago, [53] and the Commander Islands 250 years ago. [54] Nearly all of the world's isolated islands could furnish similar examples of extinctions occurring shortly after the arrival of humans, though most of these islands, such as the Hawaiian Islands, never had terrestrial megafauna, so their extinct fauna were smaller. [34] [35]

An analysis of the timing of Holarctic megafaunal extinctions and extirpations over the last 56,000 years has revealed a tendency for such events to cluster within interstadials, periods of abrupt warming, but only when humans were also present. Humans may have impeded processes of migration and recolonization that would otherwise have allowed the megafaunal species to adapt to the climate shift. [55] In at least some areas, interstadials were periods of expanding human populations. [56]

An analysis of Sporormiella fungal spores (which derive mainly from the dung of megaherbivores) in swamp sediment cores spanning the last 130,000 years from Lynch's Crater in Queensland, Australia, showed that the megafauna of that region virtually disappeared about 41,000 years ago, at a time when climate changes were minimal the change was accompanied by an increase in charcoal, and was followed by a transition from rainforest to fire-tolerant sclerophyll vegetation. The high-resolution chronology of the changes supports the hypothesis that human hunting alone eliminated the megafauna, and that the subsequent change in flora was most likely a consequence of the elimination of browsers and an increase in fire. [57] [58] [59] [60] The increase in fire lagged the disappearance of megafauna by about a century, and most likely resulted from accumulation of fuel once browsing stopped. Over the next several centuries grass increased sclerophyll vegetation increased with a lag of another century, and a sclerophyll forest developed after about another thousand years. [59] During two periods of climate change about 120,000 and 75,000 years ago, sclerophyll vegetation had also increased at the site in response to a shift to cooler, drier conditions neither of these episodes had a significant impact on megafaunal abundance. [59] Similar conclusions regarding the culpability of human hunters in the disappearance of Pleistocene megafauna were derived from high-resolution chronologies obtained via an analysis of a large collection of eggshell fragments of the flightless Australian bird Genyornis newtoni, [61] [62] [60] from analysis of Sporormiella fungal spores from a lake in eastern North America [63] [64] and from study of deposits of Shasta ground sloth dung left in over half a dozen caves in the American southwest. [65] [66]

Continuing human hunting and environmental disturbance has led to additional megafaunal extinctions in the recent past, and has created a serious danger of further extinctions in the near future (see examples below). Direct killing by humans, primarily for meat, is the most significant factor in contemporary megafaunal decline. [67] [68]

A number of other mass extinctions occurred earlier in Earth's geologic history, in which some or all of the megafauna of the time also died out. Famously, in the Cretaceous–Paleogene extinction event the non-avian dinosaurs and most other giant reptilians were eliminated. However, the earlier mass extinctions were more global and not so selective for megafauna i.e., many species of other types, including plants, marine invertebrates [69] and plankton, went extinct as well. Thus, the earlier events must have been caused by more generalized types of disturbances to the biosphere.

Consequences of depletion of megafauna Edit

Effect on nutrient transport Edit

Megafauna play a significant role in the lateral transport of mineral nutrients in an ecosystem, tending to translocate them from areas of high to those of lower abundance. They do so by their movement between the time they consume the nutrient and the time they release it through elimination (or, to a much lesser extent, through decomposition after death). [70] In South America's Amazon Basin, it is estimated that such lateral diffusion was reduced over 98% following the megafaunal extinctions that occurred roughly 12,500 years ago. [71] [72] Given that phosphorus availability is thought to limit productivity in much of the region, the decrease in its transport from the western part of the basin and from floodplains (both of which derive their supply from the uplift of the Andes) to other areas is thought to have significantly impacted the region's ecology, and the effects may not yet have reached their limits. [72] In the sea, cetaceans and pinnipeds that feed at depth are thought to translocate nitrogen from deep to shallow water, enhancing ocean productivity, and counteracting the activity of zooplankton, which tend to do the opposite. [73]

Effect on methane emissions Edit

Large populations of megaherbivores have the potential to contribute greatly to the atmospheric concentration of methane, which is an important greenhouse gas. Modern ruminant herbivores produce methane as a byproduct of foregut fermentation in digestion, and release it through belching or flatulence. Today, around 20% of annual methane emissions come from livestock methane release. In the Mesozoic, it has been estimated that sauropods could have emitted 520 million tons of methane to the atmosphere annually, [74] contributing to the warmer climate of the time (up to 10 °C warmer than at present). [74] [75] This large emission follows from the enormous estimated biomass of sauropods, and because methane production of individual herbivores is believed to be almost proportional to their mass. [74]

Recent studies have indicated that the extinction of megafaunal herbivores may have caused a reduction in atmospheric methane. This hypothesis is relatively new. [76] One study examined the methane emissions from the bison that occupied the Great Plains of North America before contact with European settlers. The study estimated that the removal of the bison caused a decrease of as much as 2.2 million tons per year. [77] Another study examined the change in the methane concentration in the atmosphere at the end of the Pleistocene epoch after the extinction of megafauna in the Americas. After early humans migrated to the Americas about 13,000 BP, their hunting and other associated ecological impacts led to the extinction of many megafaunal species there. Calculations suggest that this extinction decreased methane production by about 9.6 million tons per year. This suggests that the absence of megafaunal methane emissions may have contributed to the abrupt climatic cooling at the onset of the Younger Dryas. [76] The decrease in atmospheric methane that occurred at that time, as recorded in ice cores, was 2-4 times more rapid than any other decrease in the last half million years, suggesting that an unusual mechanism was at work. [76]

The following are some notable examples of animals often considered as megafauna (in the sense of the "large animal" definition). This list is not intended to be exhaustive:


Last of the giants: What killed off Madagascar's megafauna a thousand years ago?

A modern mouse lemur Microcebus sits upon the cranium of an extinct Megaladapis lemur. Credit: Dao Van Hoang www.daovanhoang.com

Giant 10-foot-tall elephant birds, with eggs eight times larger than an ostrich's. Sloth lemurs bigger than a panda, weighing in at 350 pounds. A puma-like predator called the giant fosa.

They sound like characters in a child's fantasy book, but along with dozens of other species, they once really roamed the landscape of Madagascar. Then, after millions of years of evolution in the middle of the Indian Ocean, the populations crashed in just a couple of centuries.

Scientists know that over the past 40,000 years, most of Earth's megafauna – that is, animals human-size or larger – have gone extinct. Woolly mammoths, sabre tooth tigers and countless others no longer roam the planet.

What's remarkable about the megafaunal crash in Madagascar is that it occurred not tens of thousands of years ago but just over 1,000 years ago, between A.D. 700 and 1000. And while some small populations survived a while longer, the damage was done in a relatively short amount of time. Hoekom?

Over the last three years, new investigations into climate and land use patterns, human genetic diversity on the island and the dating of hundreds of fossils have fundamentally changed scientists' understanding of the human and natural history of Madagascar. As two paleoclimatologists and a paleontologist, we brought together this research with new evidence of megafaunal butchery. In doing so we've created a new theory of how, why and when these Malagasy megafauna went extinct.

Malagasy graduate student and team member Peterson Faina with stalagmites in a cave in Madagascar. Credit: Laurie Godfrey, CC BY-ND

Climate at the time of the crash

The first job is to understand exactly when the megafauna died out.

Radiocarbon dating of over 400 recent fossils demonstrates that animals under 22 pounds lived on Madagascar throughout the last 10,000 years. For animals over 22 pounds, there are abundant fossils up to 1,000 years ago, but relatively few since. The biggest decline in number of large animals occurred rapidly between A.D. 700 and 1000 – practically instantaneous given the long history of their existence on the island.

What was the climate doing at that time? One popular theory for the megafaunal extinction has blamed island-wide drying. To test this idea, our team has been exploring the caves of Madagascar, collecting and analyzing stalagmites. As stalagmites grow upwards from the cave floor, layer by layer, differences in the chemistry of each layer document changes in the climate outside the cave.

By analyzing chemical composition and comparing ratios of various isotopes in these stalagmites, we created new high-resolution records of changes in the Malagasy ecosystems and climate. We found minor fluctuations in the strength of the summer rains throughout the last 2,000 years, but no significant drying over that period. In fact, A.D. 780-960 was one of the wettest periods of the last 2,000 years. Chemical analyses of fossils back up this claim.

Malagasy graduate student and team member Peterson Faina with stalagmites in a cave in Madagascar. Credit: Laurie Godfrey, CC BY-ND

So it looks like there was no significant drying around the time the megafauna disappeared.

Instead, the stalagmite records indicated a rapid and dramatic change in the landscape. Changing ratios of the isotopes carbon-12 to carbon-13 reveal a switch from forests to grassland right around A.D. 900, the same time as the megafaunal population crash. Clearly something big happened around this time.

Cut marks and evidence of butchery

With no significant change in the climate, some point to the arrival of humans on the island as a possible cause of the megafauna population crash. It seems logical that once people arrived on Madagascar, they might have hunted the big animals into extinction. New data suggest that this timing doesn't add up, though.

According to new dates on fossil bones with cut marks on them, humans arrived on Madagascar 10,500 years ago, much earlier than previously believed. But whoever these early people were, there's no genetic evidence of them left on the island. New analysis of the human genetic diversity in modern Madagascar suggests the current population derives primarily from two waves of migration: first from Indonesia 3,000 to 2,000 years ago, and later from mainland Africa 1,500 years ago.

One of two chop marks on the head of a femur of an extinct lemur, Pachylemur. This individual’s hind limb was removed from the trunk at the hip joint, probably with a machete. Credit: Lindsay Meador, CC BY-ND

So it seems that people lived alongside the megafauna for thousands of years. How did the humans interact with the large animals?

Our new study found dozens of fossils with butchery marks. Cut and chop marks provide compelling evidence as to which species people were hunting and eating. Evidence of butchery of animals that are now extinct continues right up to the time of the megafaunal crash. Some people on Madagascar hunted and ate the megafauna for millennia without a population crash.

Evidence for a change in land use

If there was no obvious climate shift and humans lived alongside and sustainably hunted the megafauna for up to 9,000 years, what could have triggered the population crash?

The abrupt land use change might hold some clues. The transition from a forest-dominated ecosystem to a grassland-dominated ecosystem appears to be widespread. Scientists have identified this switch not only in the chemical signature of stalagmites but also in pollen grains buried in layers of mud at the bottom of lakes. Ancient lake sediments reveal two other changes occurred at the same time as the shift to grass species: an increase in charcoal from fires and an increase in the fungus Sporormiella, which is associated with the dung of large herbivores such as cows.

Some Malagasy farmers plow agricultural fields in the traditional way. Credit: Damian Ryszawy/Shutterstock.com

Evidence for simultaneous increases in grassland, fires, and cows and other domesticated animals points to a sudden change in Malagasy lifestyle: the introduction of cattle husbandry and slash-and-burn agriculture known locally as Tavy. Here, forests are cut down to make space for rice paddies, and grassland burned to promote the growth of nutritious seedlings for cow fodder.

This move away from foraging and hunting toward farming meant the land could support more people. The result was a rapid rise in the size of the human population – and that's what we conclude spelled disaster for the megafauna.

Here lies the contradiction of the situation: Hunting megafauna for survival became less important as people could rely on their agriculture and livestock. But cut marks on fossil bones indicate that hunting didn't altogether stop just because people had other food sources. It turns out that the impact on the megafauna of larger human populations hunting just to supplement their diet was greater than the impact of smaller human populations relying more heavily on the native animals as a vital food source.

Bringing together new data on land use changes, climatic histories, genetics, fossil ages and butchery of the megafauna, we call this change "the subsistence shift hypothesis." Both the habitat loss and increase in human population arose out of a fundamental change in the way humans lived on Madagascar, from a more nomadic hunter-gatherer lifestyle to an agrarian society. We argue that it was this reorganization on Madagascar around A.D. 700-1000 that led to the crash in the megafaunal population.

Small populations of megafauna lived on in isolated pockets for another few centuries, but their fate was likely already sealed. The majority of the giant birds and animals that were once common across our planet have gone extinct. Many of the remaining giants, such as elephants and rhinos, are threatened or endangered. Will they go the same way as the Malagasy megafauna, casualties of humans' changing lifestyles?

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