Bio$200$Lecture$22$$Sister$group$of$Amphibians$are$Amniotes:$$Reptiles:$• Solve$the$problem$of$living$on$land$• They$have$a$new$leg$arrangement$of$legs$that$help$them$support$heavier$bodies$and$run$more$efficiently$on$land$• Reptile$lungs$and$lungs$have$improved$in$efficiently$allowing$for$a$complete$take$over$of$oxygen$by$the$lungs,$and$increased$delivery$by$the$heart$• Water$tight$covering$that$has$evolved$to$not$only$protect$the$embryos$but$also$water$tight$skin$that$protects$the$reptiles$from$drying$out$$Four$defining$reptile$traits:$• Amniotic$eggs$(shared$with$humans)$o What$united$the$amniotes$are$all$the$amniotes$have$amniotic$eggs$o Amnion$in$greekG$a$thin$tough$membranous$sac$that$encloses$the$embryo$filled$with$fluid.$o The$eggs$store$a$large$quantity$of$food$in$the$form$of$yolk$o This$allows$the$embryo$to$obtain$an$advance$state$of$development$before$it$hatches$o The$egg,$It$has$4$internal$membranes$that$allow$for$gas$exchange$and$waste$removal$o These$membranes$make$the$egg$an$independent$life$support$system$that$eliminate$the$need$for$water$o In$the$reptiles,$as$well$as$the$birds,$the$egg$is$covered$by$a$water$tight$shell$that$will$retard$the$evaporation$of$the$fluids$inside$the$egg,$but$it$still$permits$passages$of$oxygen$and$carbon$dioxide.$$o Amniotic$eggs$make$external$fertilization$IMPOSSIBLE,$because$sperm$in$unable$to$penetrate$the$egg$.$$o In$all$amniotes,$sperm$is$placed$inside$the$female$where$it$fertilize$the$egg$before$the$membranes$fully$form$o After$fertilization$and$membranes$form,$the$reptiles$and$birds,$they$have$external$gestation,$while$mammals$have$internal$gestation,$meaning$it$develops$inside$the$mother.$$o Most$mammals$have$lost$both$the$shell$and$yolk$found$in$the$typical$amniotic$egg,$allowed$for$internal$gestation…$allowing$the$embryo$to$develop$inside$and$get$nutrition$from$mother.$$o What$has$the$yolk$been$replaced$with$in$the$mammals?$The$placenta$o The$placenta$takes$the$function$of$the$yolk.$$• Dried$skin$o Have$dry$water$tight$skin$o Layer$of$keratin$rich$scaled$that$cover$the$body$ a nd$prevent$water$loss$o Keratin$is$the$same$material$that$forms$humans$fingernails$and$hair,$and$bird$feathers$o We$know$that$these$are$not$homologous$features,$the$keratin$types$are$very$different$and$development$is$different$of$these$structures.$o These$scales$make$the$skin$unable$for$gas$exchange,$therefore$reptiles$exchange$gasses$almost$entirely$through$the$lungs$o Hugely$expanded$lung$capacity$to$do$this$o This$increased$lung$capacity$calls$for$a$new$pattern$of$breathingG$Thoracic$breathing$$• Thoracic$breathing$o Greatly$increases$oxygen$intake$o The$lungs$are$pairs$of$thin$wall$sacs,$connected$to$the$mouth$through$an$opening$called$the$glottis.$o The$lungs$are$inflated$filling$the$mouth$with$air,$closing$the$mouth,$closing$the$openings$to$the$nose,$opening$the$glottis…$and$then$raising$the$floor$of$the$mouth$and$forcing$the$air$into$the$lungs$o This$method$limits$the$air$intake$to$the$size$of$the$mouth$o In$the$reptiles,$lungs$have$a$much$greater$surface$area$than$the$amphibians$o They$are$inflated$and$deflated$by$expansion$and$contraction$by$the$ribcage/muscles$o It$sucks$air$into$the$lungs$and$pushes$it$out.$o All$lungs$have$different$structures$but$this$is$how$humans$breath$as$well.$$o In$reptiles,$the$lungs$are$less$complex$than$humans$and$reptiles,$don’t$possess$a$diaphragm$o Evolved$to$send$blood$to$the$lungs$when$they$are$breathing$(flue$flow$in$diagram),$The$blue$flow$goes$into$the$lungs$from$the$heart$but$when$they$aren’t$breathing…$they$can$bypass$the$lungs$and$pump$all$the$mixed$blood$to$the$body$(purple$flow)$o This$ability$is$highly$adaptive$to$reptiles$for$their$breathing$$• Improved$kidneys$o All$amniotes$have$vastly$improved$kidneys$o Allows$for$excretion$for$concentrated$urine,$expels$nitrogenous$waste$without$high$level$of$water$loss$o Water$conservation$has$become$important$in$land$animals$o $$$$Reptiles$are$ectothermic$vertebrates$o Their$metabolic$is$much$lower$than$the$resting$metabolic$rate$of$birds$and$mammals$o Their$body$temperature$changes$with$the$environment,$unlike$endotherms$which$maintain$their$temps$through$eternal$metabolism$$o Mammals$are$endotherms,$we$keep$one$standard$temp$o If$your$temp$moves$away$from$one$temp,$you$wont$surviveG$humans$o Reptiles$being$ectothermic,$does$not$mean$reptiles$cant$control$a$temperature.$Many$can$maintain$the$temp$in$a$very$narrow$range$simply$by$moving$in$and$out$of$the$sun.$$$Reptile$Jaw$musclesG$$o Their$jaw$muscles$are$characterized$by$the$number$of$openings$in$the$skull$bone$behind$the$eye.$o Their$anchors$of$their$jaw$connect$in$the$skull$bone$behind$their$eyes$o These$muscles$connections$form$strong$bonds$and$allow$reptiles$to$bite$their$prey$much$more$effectively$than$what$we$see$in$amphibians.$o Synapsid$SkullG$single$hole$o Diapsid$SkullG$two$wholes$o All$the$amniotes$either$arose$from$the$diapsid$or$synapside$line$$o Some$reptiles$and$some$mammals$are$synapsid,$$o other$reptiles$including$the$crocs$and$dinosaurs$are$diapsid$o Birds$are$diapsid$o Birds$are$not$only$considered$reptiles,$but$dinosaurs$o The$first$reptiles$synapsid$$Pelycosaurs:$o Some$of$the$first$successful$synapsids$o Animals$like$this$were$dominate$land$animals$for$about$50$million$years$o They$gradually$replaced$the$amphibians$o These$animals$had$long$steakGknive$teeth$o Able$to$kill$animals$their$own$saws$o The$turtles,$the$snakes$evolved$from$these$early$synapsids$$Therapsid:$o About$250$MYA,$they$evolved$o These$were$definitely$reptiles,$but$some$evidence$that$they$had$fur,$and$even$endothermic$o Therapisid$dominated$land$for$20$Million$years$o During$this$time$they$would$have$been$far$more$active$than$other$vertebrates$because$longer$winters$because$endothermic$and$hair$characteristics$o $During$the$rise$of$the$dinosaurs,$diapsids,$most$therapsids$died$out$with$just$one$exception.$o This$group$that$survived$was$very$small$and$gave$rise$to$the$mammals.$$$DiapsidsG$o Two$wholes$behind$ocular$openings$o Having$these$two$skull$openings$allow$for$attachment$allow$for$a$larger$and$strong$jaw$muscles$that$allow$the$jaw$to$open$more$widely$o They$came$to$dominate$the$earth$around$230$MYA$o Monophyletic$consisting$of$crocodilians$dinosaurs$and$birds$o We$also$call$them$Archosaurs$o The$ancient$archosaurs,$the$largest$animals$the$world$had$witness,$first$to$walk$on$two$legs.$o
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