crocodilian biology database - faq - what's the difference between a crocodile and an alligator

8/9/2019 Crocodilian Biology Database - FAQ - What's the Difference Between a Crocodile and an Alligator

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What's the difference between a crocodile and an alligator?

AMERICAN ALLIGATOR

Crocodilesandalligators-twocreaturesthatsharemanysimilarities.Butwhataretherealdifferencesbetweenthem?Thisisprobablythemostfrequentlyaskedquestionwhenitcomestocrocodilians,andwhiletheanswermayappearstraightforwardtherealtruthslieinthedetails.

SIAMESECROCODILE

1.Differentfamilies:Therearethreegroups families ofcrocodilians:thealligatoridae,whichincludesthealligatorandthecaimans;thecrocodylidae,whichincludesthe"true"crocodiles;andthegavialidae,whichcontainsonlythegharial.So,thefirstdifferenceisthatalligatorsandcrocodilesareactuallyindifferentfamilies.

2.Shapeofthejaw:Theeasiestwayoftellingapartcrocodilesfromalligators,however,istolookattheirnoses.Alligators andcaimans haveawide"U"-shaped,roundedsnout likeashovel ,whereascrocodilestendtohavelongerandmorepointed"V"-shapednoses.Thisisillustratedinthediagramtotheleft C=alligator,D=crocodile .Thebroadsnoutof

alligatorsisdesignedforstrength,capableofwithstandingthestresscausedtobone

whenmassiveforceisappliedtocrackopenturtlesandhard-shelledinvertebrateswhichformpartoftheirdiet.Ofcourse,alligatorseatsofterpreytoo,buthard-shelledpreyareubiquitousintheirenvironmentandit'sabigadvantagetobeabletoeatthem.Conversely,thepointedsnoutofacrocodileisn'tquiteasstrongasthealligatorineshape,butthecrocodileisstillcapableofexertingmassivebitingpower.Crocodilejawscanbethoughtofasbeingmoregeneralised-idealforawidevarietyofprey.Thefullextentofthewayjawshapeinfluencesdietisn'tparticularlywellstudiedincrocodilians,butit'sobviousthataverythinnoselikeagharial'sismuchbetteratdealingwithafishthanaturtle!Thereare23speciesofcrocodilians,though,andthissimplebroadvs.narrowruledoesn'talwayswork.

3.Placementofteeth:Inalligators,theupperjawiswiderthanthelowerjawandcompletelyoverlapsit.Therefore,theteethinthelowerjawarealmostcompletelyhiddenwhenthemouthcloses,fittingneatlyintosmalldepressionsor

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socketsintheupperjaw.Thisisparticularlyapparentwiththelargefourthtoothinthelowerjaw see[A]indiagramonright .Incrocodiles,theupperjawandlowerjawareapproximatelythesamewidth,andsoteethinthelowerjawfitalongthemarginoftheupperjawwhenthemouthisclosed.Therefore,theupperteethinterlock and"interdigitate" withthelowerteethwhenthemouthshuts.Asthelargefourthtoothinthelowerjawalsofitsoutsidetheupperjaw,thereisawell-definedconstrictionintheupperjawbehindthenostrilstoaccommodateitwhenthemouthisclosed see[B]indiagramonright .Thisconstrictionoccursattheboundaryofthepremaxillaandthemaxillaintheupperjaw.

4.Lingualsaltglands:Crocodilesandgharialsalsodifferfromalligatorsandcaimansinhavingfunctioningsaltglandsontheirtongue.Structurally,theseareactuallymodifiedsalivaryglands,andwhilealligatorsandcaimansalsohavethesestructurestheyappeartohavelosttheabilitytousethemforexcretingsignificantamountsofsalt.Thismakescrocodilesmoretoleranttolifeinsalinewater,includingseawaterinsomespecies.Moreover,itsuggeststhatcrocodileshaveamorerecentmarineancestry:theabilitytomigrateacrosswidemarinebodies,andevenlivethereforextendedperiods,wouldcertainlyexplaintheircurrentwidedistribution

acrossdifferentcontinents.Ifancestralspeciescouldliveinmarineenvironments,thisabilityhasnotbeencompletelylostinmoderncrocodiles.Speciessuchassaltwatercrocodiles C.porosus cansurviveforextendedperiodsintidalestuaries,aroundthecoast,andevenouttosea.Alligatorsandcaimanshavelostmuchofthisosmoticabilitytosecreteexcesssaltthroughthetongueglands,andcanonlytolerateitforshortperiodsoftime,preferingtoremaininfreshwaterareaswhenpossible.However,itisnotunknownforlargealligatorstofindtheirwayintotidalmangrovesandveryrarelyintocoastalareas.

5.Integumentarysenseorgans:Bothcrocodilesandalligatorshavesmall,sensorypitsdottedaroundtheupperandlowerjaws-takeacloselookonaphotograph,andyou'llseesmall,blackspecklesalmostlikeunshavenstubble.Thesearecapableof detectingsmallpressurechangesinwater,andassistinlocatingandcapturingprey.ThesewereoriginallycalledISOs,orIntegumentarySenseOrgans,althoughrecentresearchhasrenamedthemDPRs DermalPressureReceptors .Crocodileshavesimilarorganscoveringvirtuallyeveryscaleontheirbody,butalligatorsandcaimansonlyhavethosearoundthejaws.Althoughit'sbeenknownforyearsthatsenseorgansonthejawsareinvolvedinpressuredetection,nobodyisquitesurewhatthoseorganscoveringtherestofthebodyincrocodilesactuallydo.Theyprobablyextendthesensorysurfaceoverthecrocodile'sentirebody,butpreviousresearchershavesuggestedtheymay

assistinchemicalreception,orevensalinitydetection.Theconfusionliesoverwhycrocodileshavethem,butnotalligatorsandcaimans.Regardlessoftheirrole,they'reverygoodattellingapartcrocodileskinfromalligatorskin.Crocodileandalligatorskinwallets,handbags,bootsetcareeasytotellapart-ifthescaleshaveasmallspotordimpleclosetotheedge,youknowtheskinisfromacrocodileandnotanalligatororcaiman.Thisisillustratedbelow-thealligatorontheleftdoesnothaveanysenseorgans,butthecrocodileontherightdoes.



GULAR REGION (NECK)OF AMERICAN

ALLIGATOR

GULAR REGION (NECK)OF AMERICANCROCODILE

Otherdifferences:Theabovepointsareamongstthemostobviousdifferencesbetweencrocodilesandalligatorsintermsofexternalappearance.However,eachspeciesisunique,andtolistallthepossibledifferenceswouldbelikecomparinga jaguarwithalion.Differencesinbehaviourarealsoapparent.Mostpeopleregardcrocodilesasmoreaggressivethanalligators,andthisistrueofsomespecies.Forexample,alligatorsarerelativelydocilenexttosaltwatercrocodiles,buttherearemanyspecieswithmanydiffererentkindsofbehavioursandtemperaments.Ageneralrulethatcrocodilesaremoreaggressivethanalligatorsjustisn'tpossibletomake. Alligatorscanoftenreachatleast14or15feetinlength,whichislargerthansomecrocodilespecies,butnotothers.Thelargestcrocodilespeciesisthesaltwatercrocodile,whichcangettoatleast17or18feet-somerareindividualsexceeding20feetaftermanyyears.TheAfricandwarfcrocodile,asacontrast,doesn'tgrowlargerthan4or5feet.

Thetwoimagesbelowshowanexceptiontothe"jawshape"rule.TheIndianmugger Crocodyluspalustris breaksthecrocodileconventionofhavingnarrowjaws-itsjawsaresuperficiallyverysimilarinshapetothoseofanalligator,althoughthefourthlowertoothisstillvisible.Whenalltheabovecriteriaareconsidered,themuggerisdefinitelyacrocodile.Alwaysbearthedetailsinmindwhenfacedwithgeneralquestionslikewhat'sthedifferencebetweencrocodilesandalligators.Asyoucanhopefullysee,thesimpleanswerisnotalwaysthemostinteresting!

AMERICAN ALLIGATOR

INDIAN MUGGER

Do you have a question about crocodiles? If so, drop me aline and I'll answer it.

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