1

NREM/ZOOL4464–OrnithologyDr.TimO’Connell

Lectures12–1411,13,&14February2019

Modernhierarchyoflifeonearth:•Domain•Kingdom•Phylum(plural“phyla”)•Class

•Order•Family•Genus(plural“genera”)•Species(plural“species”)

•Prokaryotes–nonucleusandnosubcellularorganelles.Theseareexceedinglytiny0.1–10micronsdiameter.•Eukaryotes–largercells(10–100microns)withDNAcontainedinanucleusandnumerousmembrane-boundorganelleslikemitochondria,Golgiapparatus.FourkingdomsoftheEukarya:•Protista-mostunicellular,hetero-orautotrophicorboth•Plantae-multicellular,photosyntheticautotrophs

•Fungi-multicellularheterotrophsthatfeedbyabsorption•Animalia-multicellularheterotrophsthatfeedbyingestion

WithinAnimalia:

•PhylumChordata•SubphylumVertebrata

•ClassAvesPaleontologistPhilCurrie,commentingonrecentfossilfindsinChinaofdinosaurswithfeathers:"Thisshowsthatdinosaursarenotextinct,butarewell-representedby10,000speciesofbirds."Whatdidhemean?Arebirdbirds,orarebirdsreallydinosaurs?Theissue:

•Birdsareobviouslyalliedwithreptiles,andspecificallytodinosaurs.Ancestryambiguous,however.•DidbirdsdescendfromancientreptilesthatwereNOTdinosaurs,ordidbirdsdescendDIRECTLYFROMdinosaurs?•Ifthelatter,thenbirdsaretechnicallyconsidereddinosaursaccordingtoamoderncladisticanalysis.Thatis,dinosaursdidNOTdieoutattheendoftheCretaceous!

Adaptiveradiation-processthroughwhichonetaxongivesrisetomanyothersthatexploitavailableniches.WeneedtogobacktothePaleozoic–theriseoftheTetrapods!~450millionyearsago(MYA),bonyfishwithcartilaginousraysintheirfinsappear.~420(blazeit!)MYA,somefishdevelopfleshyfinswithboneandmuscleinside,e.g.,Coelacanth.~410MYA,some“lobe-finned”fishdevelopastructureofoneproximallimbbonearticulatingwithtwodistallimbbonesineachlimb.Thisisthebeginningofhumerus-radius/ulna.~385MYA,Tiktaalikshowsadevelopmentofthepectoralgirdlesufficienttobearitsweightwithoutthebuoyancyofwater!~380MYA,Acanthostegahasdigitsattheendofits4limbs.~370MYA,amphibiansappear–5digitson4limbs–thesearetheancestralTetrapods.KingdomAnimalia,PhylumChordata,(SubphylumVertebrata),ClassReptilia–adaptiveradiationofreptilesintheMesozoicEra,~250–65mya.

2

Fromthebasalstockofreptiles(cotylosaurs),atleastSIXmajorgroupsdeveloped:• Turtles• Plesiosaurs(long-neckedmarinereptiles)• Icthyosaurs(dolphin-shapedmarine

reptiles)• Pelycosaurs(ancestraltothetherapsids

fromwhichwemammalsdescended)

• Eusuchians(ancestraltolizards,snakes,andthetuatara)

• Pseudosuchians(a.k.a.“thecodonts”,so-namedbecausetheirteethsitinindividualsocketsinthejaw).

Thepseudosuchiansareancestraltocrocodilians,pterosaurs(flyingreptiles),andthedinosaurs–thegroupthatunderwentoneofthemostdramaticadaptiveradiationstheworldhaseverseen.

Dino-diversity:Thedinosaurradiationledtothedevelopmentofmanywildlydifferentforms.Alldinosaurshadtheirlimbsrotatedtosupportthebodyfrombeneath–likemammallimbs–ratherthansplayedouttothesidesasinlizards,turtles,andcrocodilians.Significantly,dinosaursradiatedintoancestralquadrapedalformsandderivedbipedalforms.Thebigsplitindino-diversityinvolvestheorientationofthebonesinthepelvis:ilium,ischium,andpubis.IntheORNITHISCHIANS,thepubisbonepointsbackwards,asitdoesinmodernbirds(althoughaswe’llsee,birdsdidn’tdescendfromtheornithischians).

TheornithischiansincludesuchfamiliardinosaursasStegosaurus,Ankylosaurus,theceratopsianslikeTriceratops,andthehadrosaurs,i.e.,the“duck-billeddinosaurs”likeTrachodon.Iguanodon Stegosaurus

3

OppositetheornithischiansweretheSAURISCHIANS,the“lizard-hipped”dinosaurswiththepubisbonepointedforward:TheSaurischiansradiatedintothemassivelong-neckedsauropodslikeBrachiosaurusandthemeat-eating,bipedaltheropods.ThebigtheropodslikeTyrannosauruswerethe“carnosaurs”andthelittleviciousoneslikeVelociraptorwerethe“coelurosaurs.”Seismosaurus Megalosaurus

Thestructureofmodernbirdshasbeendramaticallyshapedbythedemandsofefficient,poweredflight.Thatsaid,therearenumeroussimilaritiesbetweenbirdsanddinosaurs,especiallythosecoelurosaurs.That’stheissue:Didbirdsdescenddirectlyfromsomebasalstockofreptileslikethepseudosuchians,ordidtheyariselater,descendingdirectlyfromthecoelurosaurdinosaurs?

Ifbirdsdescendeddirectlyfromthepseudosuchians,thentheprincipleofmonpohyleticismwoulddictatethatbirdsbeincludedwithreptilesintheclassReptilia.Ifbirdsdescendeddirectlyfromthecoelurosaurs,thenbirdsarenotjust“reptiles,”theyareaspecifictypeofreptile–dinosaurs!ThisisonlyreallyabigdealifweconsiderdinosaurstohavegoneextinctattheendoftheCretaceous.Ifbirdsaredinosaurs,thatmeansthatthedinosaursDIDNOTdieoutattheendoftheCretaceous;thousandsofthemarestillwithustoday.Toexaminethisissue,weneedtoconsidertheanatomyofbirdsandreptiles–specificallydinosaurs.

4

Okay,tobegintounderstandbirds,wemustfirstunderstandthefirstTetrapods–ourdeepancestors,too.

BasalreptilesofthePermian–theCotylosaurs:

Whenyouconsidertheanatomyofbirds,thinkaboutmodificationsfromthisbasicreptilianbodyplan.Thisistheancestralconditionofthebasalreptiles.NextconsiderEuparkeria,agenusofTriassicpseudosuchianthecodontreptilesthatpredatethedinosaurs,fromabout345mya.Thisisamorederivedbodyplanthanthecotylosaurs.

Let’slookatitsskeleton:AxialskeletonIncludesskull,allvertebrae(cervical,dorsal{thoracic,lumbar},sacralandcaudal),ribcage,andsternum.AppendicularskeletonIncludeslimbbonesplusscapula,coracoid,claviclesandpelvis.Euparkeria’sancestralconditionshowsalong,bonytail,teethinthejaw,atleast13pairsofribs,andinthelimbs,asolidbone(femurandhumerus)proximallyanddistallypairedbones(tibiaandfibulainthehindlimbs;radiusandulnaintheforelimbs)thatendinfeetwithfivedigits.Arealtheropoddinosaur:Compsognathus.ThisisamuchmorederivedskeletonthanthatofEuparkeria.

Modificationsincludeagreaterspecializationinlocomotionwithafullybipedalgaitandlengtheningofthehindlimbs.Phalangesinthehindlimbsnumber4–withonly3makingcontactwiththeground–andintheshortenedforelimbstherearebut3digits.Thenumberofribsnowreducedto10pairs.

5

Modernbirdsaremodifiedstillfurther.Infact,mostofthedifferenceswemightseebetweenapluckedturkeyandaCompsognathusarespecificmodificationsformoreefficientflight.Withoutthesemodificationsforthedemandsofflight,birdsareremarkablyreptilian.Scales,layeggs,singleurogenitalopening...FEATHERSarethekey:Ifit’sgotfeathers,thenit’sabird.Exceptionalbirds:Hoatzin-(extantinSouthAmerica)nestlingshaveclawsontheirwings.ThoughHoatzinclawsarebestdeveloped,youcanalsofindwingclawsinwaterfowl,owls,NewWorldvultures,etc.Hesperornisregalis:ACretaceousbirdthatwasstructurallysimilartoaloonorcormorant,thoughflightless.Itsbonybeakhadteeth.

CharlesDarwinpublisheshis‘OriginofSpecies’inwhichhedescribeshistheoryofevolutionbynaturalselection-1859.Predictedbythattheory:“intermediate”formsinthefossilrecord(andaroundtoday).

ThomasHenryHuxley,citingskeletalsimilaritiesbetweendinosaursandmodernbirdswasthefirsttopublishhisideathatbirdsdescendedfromdinosaurs.[Notjustreptiles,butspecificallydescendedfromthedinosaurs.]EnterArchaeopteryxlithographicain1862-afterHuxley’sproclamation:

6

SkeletonsofArchaeopteryx(left)andamodernpigeon(Columba)(right).

Skeletally,almostidenticaltosmallcoelurosaurs.Oneimportantdifference,though...Archaeopteryxhadfeathers.Fullyformedandmodernfeathers-includingasymmetricalvanesontheflightfeathersthatarepresumedtobeanadvancedcharactercompatiblewithflight.

Birdsandfeathereddinosaurs.ThesereconstructionsfromMatthewMartyniuk:Here’swhatourmostadvancedreconstructionsofArchaeopteryxsuggestitprobablylookedlike:

7

AgroupofcoelurosaurscalledthemaniraptorswereskeletallysimilartoArchaeopteryx:sickle-clawtoe,semi-lunatecarpal,posteriororientationofpubis,largeeyes&braincase,hollowbones,3-fingeredhand,4-toedfoot,fusedclavicles,bladelikescapula,secondarybonypalate,and...Feathers!

Someofthesynapomorphiesbetweenmodernbirds,Archaeopteryx,andmaniraptors:*Secondarypalate*3-fingeredhand,4-toedfoot*Semi-lunatecarpal*Furcula*Bladelikescapula

*Hingelikeankle-nolateralmovement*Highmetabolism*Bigeyes,bigbrains*FEATHERS!

BasedmostlyonspectacularfossilfindsfromquarriesinChina,wenowhaveatleast13differentgeneraofcoelurosaursknowntohavehadfeathersor“protofeathers”andmanyotherspecies,e.g.,Velociraptor,aresuspectedofhavingbeenfeatheredaswell.Sinornithosaurus:

Gigantoraptorandrelatedfeathereddinosaurs(CretaceousPeriod):-!Here’swhatVelociraptorprobablyreallylookedlike:

So,accordingtoJohnOstrom,PhilCurrie,JackHorner,BobBakker,andeverythinkingcladistoutthere,birdsmustshareacommonancestorwiththecoelurosaurs,i.e.,birdsaredescendedfromdinosaursandthereforeAREdinosaurs.

Asmall,butvocalgroupstandsinopposition:•AlanFeduccia,SankarChatterjee,PeterDodson•Concernedabouttimelineprimarily,butalsodisputesomeofthefeatheredfossils:

8

•ArethoseREALLYfeathers?•Whichspecificdigitswerelost/retainedonthe3-fingeredhand?•PresenceoffeathersonALLmaniraptorsisstillconjectural.•Maybebirdsaren’tdinosaurs,maybethosefeathereddinosaursarereallyflightlessbirds...Areabirds’handbonesdigits2,3,and4or–likealltheropods–1,2,and3?Timelineofmodernbirds, Archaeopteryx,andfeatheredmaniraptors:•Modernbirdsappear~60 mya•Archaeopteryx~150mya•Earliestcoelurosaurs~165mya•Feathereddinosaurs,“raptors”~135-80mya•IfArchaeopteryxisolderthantheCretaceousfeathereddinosaurs,andunequivocallyatruebird,thentheREALintermediatereptile/birdmustbemucholderthanArchaeopteryx!•Contrarytothemediafrenzy,NONEofthefeathereddinosaursdiscoveredtodatewasancestraltobirds!Themediaimpressioncreatedbythesediscoveriesisthatthefeathereddinosaurswereancestorstobirds.Thatcan’tbebecauseArchaeopteryxfromtheJurassicPeriodwasalreadymorebirdlikethatthefeathereddinosaursthatappearedlater.Arethereanycandidatesforbird-likereptilesmucholderthanArchaeopteryx?ButnooneseriouslyconsidersLongisquamaancestraltobirdsbecauseitisotherwisesodifferentinstructureandsomuchmoresimilartolizards.Themostwidelyheldancestryofbirdsthesedayslookssomethinglikethis:

9

Evenmorerecentdiscoveries,however,starttofillinsomeoftheblanks:olderthanArchaeopteryx.•Manymorefeathereddinosaursnowdiscovered,includinghundredsofindividualspecimens•Xiaotingia,155MYA

•Epidexipteryx,160MYA•Anchiornis,160MYA•Unlikelythatallthebird/coelurosaursynapomorphiesaremistakes,lies,orconvergence•Tosuggestthatcoelurosaursarederivedbirdsignoresthesynapomorphiesbetweenthefeatheredandnon-featheredtheropods-thatis,ifComposgnathuswasabird,thenTyrannosauruswastoo.•Littleevidenceforanearlier“proto-bird”thanArchaeopteryx-Longisquamaistoodistanttoforgeadefensiblelinktomodernbirds•Parsimonyandcladisticsdictatethatbirdsareindeed,livingdinosaurs.