Archived version from NCDOCKS Institutional Repository http://libres.uncg.edu/ir/asu/

The Late Triassic Archosauromporph Trilophosaurus as an Arboreal Climber

By: Andrew Heckert, Justin A. Spielmann & Spencer G. Lucas

Abstract Two species of the unusual archosauromorph Trilophosaurus, T buettneri Case and T jacobsi Murry, are known from diverse localities in the Upper Triassic Chinle Group in the southwestern USA. Both species likely occupied similar ecological niches, based on morphological similarities in the postcrania, which are essentially identical. Trilophosaurus occurrences in the Chinle Group are relatively rare, but individual sites are exceptionally rich, suggesting that Trilophosaurus lived in a different paleoenvironment than more typical Chinle vertebrates, which lived in or near streams (phytosaurs, metoposaurs) or on floodplains (aetosaurs, rauisuchians, and dinosaurs). Two potential interpretations are that Trilophosaurus was either an arboreal climber or a fossorial digger. However, the gross skeletal features of Trilophosaurus are not compatible with a fossorial mode of life: the limbo are too long and gracile, proximal limb elements are longer than distal ones, and the claws are laterally compressed, not transversely broadened. The intermittent study of Trilophosaurus has caused the theory of it being arboreal, originally proposed by Gregory, to receive little mention in subsequent studies. We reexamined the functional morphology of Trilophosaurus using a qualitative functional morphological analysis of the skeleton, a quantitative examination of claw curvature, and a quantitative examination of manus/trunk and pes/ trunk rarios. Claw morphology of Trilophosaurus shows similarities to the arboreal drepanosaurs Drepanosaurus and Megalancosaurus. Our analysis provides ample evidence to suggest that Trilophosaurus was arboreal.

Andrew Heckert, Justin A. Spielmann & Spencer G. Lucas (2005) " The Late Triassic Archosauromporph Trilophosaurus as an Arboreal Climber" Rivista Italiana Di Paleontologia e Stratigrafa Volume 111 Issue 3 pp. 395-412 (open access) Version of Record Available From (www.riviste.unimi.it.com)

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†—r—nus s—lv—tor @wƒ w ƒrF QQTHA

those of fossori—l —nim—ls —nd —re not —d—pted to digE

wuseum of ƒouthwestern fiology @wƒfG xwA

gingFFFit seems most pro˜—˜le th—t they served prin™iE

gonolophus su˜™rsit—tus @ xw SVTTVGb xw SVTTUA

p—lly to se™ure the —nim—l9s feet in lo™omotionF „he

gtenos—ur— pe™tin—t— @ xw QVTWTA flexor mus™les of the —rm h—d strong origins on the

hipsos—urus dors—lis @ xw RISPRA humerusF „he toes ™ould h—ve gr—sped ˜r—n™hes or held

ƒ—urom—lus v—rius @ xw QVTWRA rough surf—™es in ™lim˜ingF99 elthough qregory —™E

†—r—nus indi™us @wƒf RRQWUA knowledged th—t „rilophos—urusD —t IEP m longD —ppe—rs

†—r—nus timorensis @ xw QVTWSA l—rge for —n —r˜ore—l —nim—lD he st—tedD ––‘s“t is not imE

possi˜le th—t they were ‘—r˜ore—l“F v—rge spe™ies of

„—˜F I E gomp—r—tive reptile spe™imens used in this studyF

sgu—n— —re —r˜ore—l in h—˜it99 @pF QPSAF „his is the m—E

jority of eviden™e th—t qregory presented to support his

gomp—r—tive —nd fun™tion—l morphology

interpret—tionD —ndD while su™h eviden™e is ™ompellingD it

is f—r from ™on™lusiveF hue —t le—st in p—rt to the l—™k of „he initi—l interpret—tion of —lmost —ny fossil tetE

™on™lusive support for his —r˜ore—l interpret—tionD su˜E r—pod found in fluvi—l sediments is th—t it is terrestri—lD

sequent —uthors h—ve not investig—tedD or even menE or semiE—qu—ti™F „he ex™eptions to this —re —nim—ls with

QWV ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF

pigF I E eD „rilophos—urus ˜uettneri

restor—tion in — w—lking pose

@from qregory IWRSAF fD left

m—nus of „rilophos—urus

˜uettneri @from qregory

IWRSAF gD left pes of „riloE

phos—urus ˜uettneri @from

qregory IWRSAF xote the orE

ient—tion of the digitsD espeE

™i—lly the medi—lly proje™tE

ing first digit of the m—nus

—nd the l—ter—lly diverging

fifth digit of the pesF elso

note the in™re—se in length

from the proxim—l to the peE

nultim—te ph—l—nges in most

of the digitsF e˜˜revi—tionsX

—st E —str—g—lusD ™—l ± ™—l™—E

neumD ™ent ± ™entr—leD int E

intermediumD r—d E r—di—leD

ul E uln—reD IER ± dist—l ™—rE

p—lsGt—rs—lsD v E fifth met—E

t—rs—lF

„he —r™hos—uromorphs used for ™omp—risonD ˜—sed on

qenus w—nusG„runk ‚—tio €esG„runk ‚—tio

pu˜lished figuresD —reX the rhyn™hos—urs ytis™h—lki— elE

€roterosu™hus HFIPHH HFIWPH

der—e @ilder IWUVY runt 8 vu™—s IWWIY vong 8 wurry

†jushkovi— HFIHVH HFIWTH

IWWSAD ryperod—pedon gordoni @fenton IWVQAD —nd

‚utiodon HFHWUT HFIQHI

‚hyn™hos—urus —rti™eps @fenton IWWHAY the erythrosuE

ƒt—gonolepis HFHVIQ HFIUHU

™hid irythrosu™hus —fri™—nus @qower IWWTD PHHQAY the

ƒ—urosu™hus HFHUSV HFPISR —r™hos—uriform iup—rkeri— ™—pensis @iwer IWTSAY the

€ostosu™hus HFHVSR HFPSPH —r™hos—ur irpetosu™hus gr—nti @fenton 8 ‡—lker

€seudhesperosu™hus HFITTU HFQQQQ PHHPAY the —etos—urs vongosu™hus me—dei —nd hesm—toE

su™hus h—plo™erus @vong —nd wurry IWWSAY the popoE iup—rkeri— HFIRRH HFPTRH

s—urid €ostosu™hus kirkp—tri™ki @gh—tterjee IWVSY vong ‚ioj—su™hus HFHVHH HFPRVH

8 wurry IWWSAY the ™ro™odylomorph hromi™osu™hus

„rilophos—urus HFPRHH HFQIPS

gr—ll—tor @ƒues et —lF PHHQAY —nd the sphenosu™hid „erriE

strisu™hus gr—™ilis @grush IWVRAF g—sts —nd spe™imens of „—˜F P E €roportion r—tios —mong v—te „ri—ssi™ er™hos—uroE

morphsF the popos—urid €ostosu™hus kirkp—tri™kiD the —etos—ur

hesm—tos™uhus h—plo™erusD —nd the phytos—ur €seudoE

p—l—tus ˜u™eros were —lso ex—mined for ™omp—r—tive

skelet—l spe™i—liz—tions spe™ifi™—lly —d—pted to — p—rti™uE purposesF „he re™onstru™tions in €—rrish @IWVTAD espeE

™i—lly of €seudhesperosu™husD were used in the m—nus l—r mode of lifeD eFgF extended digits supporting — p—t—E

—nd pes proportion —n—lysisF gium in pteros—ursF „hereforeD we ™omp—re the skelet—l

stru™ture of „rilophos—urus to th—t of other —r™hos—urE

omorphs to ™onstru™t — null hypothesisD n—mely th—t fody proportionsF „he most striking fe—ture of

„rilophos—urus is — typi™—l —r™hos—uromorph —nd shows the —ppendi™ul—r skeleton of „rilophos—urus is the size

morphologi™—l ™h—r—™ters th—t —re ™omp—r—˜le to other of its m—nus —nd pesD espe™i—lly ™omp—red to the trunk

terrestri—l „ri—ssi™ —r™hos—uromorphsF „o test this hyE @pigF IeAF sing the —n—tomi™—l re™onstru™tions of terE

pothesis „rilophos—urus w—s ™omp—red to — v—riety of restri—l —nd semiE—qu—ti™ —r™hos—uromorphs in €—rrish

—pproxim—tely ™ontempor—neous —r™hos—uromorphs @IWVTD figsF QEIIAD trunkD m—nus —nd pes lengths were

me—sured to o˜t—in — sense of their proportions in — th—t —lso ˜r—™ket „rilophos—urus phylogeneti™—llyF

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er QWW

pigF P E €lot showing the ˜ody proporE

tions of „rilophos—urus —nd

known terrestri—l —r™hos—uroE

morphsF w—nusGpes length w—s

determined —s the dist—n™e from

the longest digit to where the

™—rpomet—™—rpusGt—rsomet—t—rE

sus meets the uln— —nd r—diusG

ti˜i— —nd fi˜ul—D respe™tivelyF

„he trunk w—s the dist—n™e from

the —nterior portion of the skull

to the —™et—˜ulumF ell d—t—

dr—wn from pu˜lished figures

in €—rrish @IWVTA —nd qregory

@IWRSAF „he —˜err—nt position

of the €seudhesperosu™hus d—t—

point in the pesGtrunk r—tio ™olE

umn is due to the me—suring

proto™ols usedD —nd does not reE

fle™t the —mount of the pes —™tuE

—lly inter—™ting with the groundF

„his is —pp—rent when ™onsiderE

ing th—t „rilophos—urus h—s pl—nE

tigr—de m—nus —nd pes where—s

€seudhesperosu™hus h—s — digitiE

gr—de m—nus —nd pesF ƒee „—˜le

P for r—w d—t—F

wide v—riety of —r™hos—uromorphsF por these me—sureE elong—ted met—™—rpus —nd met—t—rsusD whi™h skew the

ments the lengths of the m—nus —nd pes were deterE m—nusGtrunk —nd pesGtrunk r—tiosF „he results for

mined ˜y the lengthD in l—ter—l viewD from the longest €seudhesperosu™hus should not ˜e ™onsidered indi™—tive

digit to where the met—™—rpusGmet—t—rsus meets the r—E of the size of the m—nus —nd pesD whi™h —™tu—lly interE

dius —nd uln—Gti˜i— —nd fi˜ul—D respe™tivelyF „he trunk —™ted with the groundD espe™i—lly ™onsidering th—t

lengths were determined ˜y me—suring from the —nteE €seudhesperosu™hus h—s — digitigr—de m—nus —nd pesD

rior prem—xill— to the l—st s—™r—l verte˜r—e —s re™onE where—s „rilophos—urus h—s — pl—ntigr—de m—nus —nd

stru™ted in the v—rious illustr—tionsF sing the full ˜ody pes @qregory IWRSY €—rrish IWVTAF

re™onstru™tion of „rilophos—urus in qregory9s @IWRSD plF „hese m—jor differen™es in ˜ody proportions reE

QQA osteologyD — t—˜le @„—˜F PA —nd ™orresponding gr—ph fute the null hypothesis previously put forw—rdF ƒpe™iE

@pigF PA w—s gener—ted ™omp—ring the m—nusGtrunk fi™—llyD it is o˜vious th—t „rilophos—urus h—s ™ompletely

length r—tio —nd the pesGtrunk length r—tioF „his r—tio different —ppendi™ul—r proportions th—n —ny ™ontemE

is more me—ningful th—n either the m—nusGtot—l length por—neousD or even ™losely rel—tedD terrestri—l or semiE

or pesGtot—l length r—tios ˜e™—use the long t—il of „riloE —qu—ti™ —r™hos—uromorphF

phos—urus offsets the lengths of the l—rge m—nus —nd pes „he l—rge m—nus —nd pes of „rilophos—urus w—s

@pigF IeAF elsoD full ˜ody lengths were not in™luded likely used to help ˜ridge g—ps while m—neuvering in

˜e™—use of the su˜je™tive n—ture of most —r™hos—uroE treesD —s in v—rious —r˜ore—l igu—nids like sgu—n— igu—n—F

morph t—il lengths due to in™omplete ™—ud—l seriesF ƒu™h g—p ˜ridging is often —sso™i—ted with — rigid trunk

„rilophos—urus h—s m—nus —nd pes proportions @ƒF ‚enestoD persF ™ommFAD whi™h qregory @IWRSA noted

th—t —re ex™eedingly l—rge for its trunk size @pigF PAF in „rilophos—urusD in —ddition to elong—ted lim˜proporE

„he m—nusGtrunk r—tio of „rilophos—urus is dou˜le th—t tions @rilde˜r—nd IWURY g—rtmill IWVSAF „rilophos—urus

of most —r™hos—uromorphs me—suredD the —r™hos—uriE differs from most —r˜ore—l —nim—ls in th—t its elong—ted

form iup—rkeri— —nd the sphenosu™hid €seudhesperosuE lim˜proportions —re due to elong—tion of the m—nus

™hus ˜eing ex™eptionsD ˜ut even these two t—x— yield —nd pesD spe™ifi™—lly the ph—l—ngesF „his is —typi™—l ˜eE

r—tios su˜st—nti—lly lower th—n „rilophos—urusF „rilophoE ™—use —n —r˜ore—l —nim—l whose m—nus —nd pes is elonE

s—urus h—s the se™ond l—rgest pesGtrunk r—tioD ˜ehind g—ted usu—lly h—s elong—ted met—™—rp—ls —nd met—t—rs—lsF

€seudhesperosu™husF „he r—tios for ˜oth €seudhesperoE e m—jority of lim˜r—tio studies @iFeFD widdleton 8

su™hus —nd „rilophos—urus —re ™onsider—˜ly higher th—n q—tesy PHHHA use r—tios ex™luding ph—l—nge—l proporE

those of the other —r™hos—uromorphsF st should ˜e tionsF „husD when in™orpor—ting „rilophos—urus d—t—

noted th—t while €seudhesperosu™hus h—s — l—rge into su™h studies inevit—˜ly it groups with terrestri—lD

m—nusGtrunk —nd pesGtrunk r—tioD this is ˜e™—use of its not —r˜ore—lD —nim—lsF ƒu™h me—surement regimes —re

RHH ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF

@gh—tterjee IWURAF „rilophos—urus h—s ™—ud—l verte˜r—e ignoring v—lu—˜le d—t—D espe™i—lly in light of re™ent stuE

th—t differ ™onsider—˜ly from those of rhyn™hos—ursF dies interpreting ™ert—in theropodsD su™h —s wi™ror—ptor

„he ™—ud—l ™entr— —re ™ylindri™—l —nd ˜e™ome more zh—oi—nus @ˆu et —lF PHHHA —nd ipidendros—urus ningE

elong—ted ˜oth rel—tively —nd —˜solutely posteriorly ™henensis @h—ng et —lF PHHPAD —s —r˜ore—l ˜—sed purely

—long the ™—ud—l seriesF on ph—l—nge—l —nd ungu—l proportionsF

„rilophos—urus —lso possesses distin™tive ™hevronsF

exi—l skeletonF „he verte˜r—l ™olumn of „rilophE et the —nterior end of the ™—ud—l seriesD „rilophos—urus9

os—urus h—s fe—tures th—t distinguish it —mong —r™hos—urE ™hevrons —re —pproxim—tely —s t—ll —s the verte˜r—e they

omorphsF „here —re even ™onsider—˜le differen™es ˜eE origin—te fromF „here is — morphologi™—l ™h—nge of the

tween it —nd the ™losely rel—ted rhyn™hos—ursF „his is ™hevrons from the —nterior to posterior end of the ™—uE

—pp—rent not only in the num˜er of verte˜r—e ˜ut —lso in d—l seriesF „he ™hevrons r—nge from typi™—l †Esh—pedD

their morphologyF posteroventr—lly dire™ted ™hevrons —nteriorly to ™hevE

„he rel—tively short ne™k —nd ex™eedingly long t—il rons th—t h—ve —n un™ommon h—t™het sh—pe in l—ter—l

—re the most distinguishing fe—tures of the —xi—l skeleton view —nd ventr—l exp—nsions th—t p—r—llel the ™ylindri™—l

of „rilophos—urusF „rilophos—urus h—s U ™ervi™—lD IU dorE ™—ud—l series posteriorlyF

s—lD P s—™r—l —nd —pproxim—tely RH ™—ud—l verte˜r—e xumerous ext—nt —r˜ore—l spe™ies h—ve t—ils th—t

@qregory IWRSA @pigF IeAF qener—lly —r™hos—uromorphs —re prehensile —nd —re used to —id in ™lim˜ingF „he ™—ud—l

h—ve IH or more —mphi™oelous ™ervi™—l verte˜r—eD verte˜r—e —nd ™hevrons of „rilophos—urus indi™—te th—t

where—s „rilophos—urus h—s only U opistho™oelous ™erE its t—il w—s not prehensileD —lthough it ™ould h—ve ˜een

vi™—l verte˜r—eF „he distin™tiveness of „rilophos—urus is used to —id in ˜—l—n™ing —nd ˜r—™ing itself —g—inst the

evident even when ™omp—red to ™losely rel—ted ™l—des su˜str—teF elthough ™ylindri™—l —nd elong—te ™entr— —re

su™h —s rhyn™hos—ursD the only other —r™hos—uromorphs often seen in the prehensile t—ils of ext—nt —nim—lsD the

with simil—r ™ervi™—l ™ountsF „he rhyn™hos—urs ryperE elong—te zyg—pophyses of „rilophos—urus pre™lude its

od—pedon @fenton IWVQA —nd €—r—d—pedon @gh—tterjee t—il from ˜eing prehensileF „husD the ™—ud—l verte˜r—e

IWURA ˜oth h—ve V ™ervi™—lsD IT dors—ls @—lthough ryE h—ve preE —nd postE zyg—pophyses th—t interlo™k tightly

perd—pedon m—y h—ve IUAD —nd P s—™r—l verte˜r—eF „he with one —nother —long the ™—ud—l seriesF ƒu™h — rigid

m—jor differen™e in verte˜r—l stru™ture —nd num˜er is stru™ture of the t—il would h—ve limited its movement

th—t the rhyn™hos—urs h—ve ˜etween PS —nd QH ™—ud—lsD ˜oth dors—lly —nd l—ter—llyF elsoD the ™hevrons of „riloE

where—s „rilophos—urus h—s —pproxim—tely RH ™—ud—lsD phos—urus h—ve wedgeEsh—ped dors—l f—™ets th—t insert

resulting in — extremely long t—pered t—ilF sndeedD the ˜etween the ™entr—D limiting flexure of the t—il ventr—llyF

t—il is so long th—t it —™™ounts for more th—n h—lf the ƒimil—r h—t™hetEsh—ped ™hevrons —re —lso present in p—E

length of the —nim—lF roweverD the length of the t—il of ™hypleuros—urs @ƒ—nders IWWVA —nd the phytos—ur wyE

„rilophos—urus is somewh—t open for interpret—tion —s striosu™hus @qozzi 8 ‚enesto PHHQAY in these —qu—ti™

qregory @IWRSA re™onstru™ted the t—il using PH verte˜r—e —nim—ls the ™hevrons in™re—se the stiffness of the t—il to

found either —rti™ul—ted or —sso™i—ted with the —rti™uE —llow for — stronger swimming strokeF „husD the t—il w—s

l—ted skeleton he used —s the prim—ry m—teri—l for his stiff —nd un—˜le to move very f—r in —ny dire™tionF ƒu™h

osteologyF „his t—il re™onstru™tion ™ont—ins QQ verte˜r—e restri™tion of t—il movement would not —llow for —ny

—nd due to the elong—tion of the most posterior ™—ud—l gr—sping or ™urlingF ‡ith no gr—sping or ™urlingD the t—il

verte˜r—e he postul—ted the t—il ™ont—ined —pproxim—tely ™ould not offer —ny type of prehensile movementF rowE

RH verte˜r—eF „rilophos—urus h—s t—il proportions th—t everD the unique h—t™hetEsh—ped ™hevrons on the posterE

—re ™omp—r—˜le to those of the s™—nsori—l sgu—n— igu—n— ior h—lf of the ™—ud—l series of verte˜r—e ™ould h—ve ™onE

in over—ll proportions —nd likely used it in — simil—r ™eiv—˜ly ˜een used to in™re—se the fri™tion of the t—il

m—nnerD for ˜—l—n™eF sing — long t—il for ˜—l—n™ing is —g—inst the su˜str—te —nd —dded further rigidityD whi™h

— ™ommon fe—ture —mong —r˜ore—l —nim—ls —nd ™ontr—sts would h—ve —ided in ˜r—™ing „rilophos—urus while ™lim˜E

with the rel—tively short —nd m—ssive t—ils of fossori—l ingF ixt—nt —r˜ore—l reptiles use the ˜ulk of their elonE

diggers @goom˜s IWVQAF g—ted t—ils to m—int—in their ˜—l—n™e while ™lim˜ingD „riE

„he morphology of the ™—ud—l verte˜r—e —lso difE lophos—urus likely used its t—il in — simil—r m—nnerF

fers ™onsider—˜ly ˜etween the rhyn™hos—urs —nd „riloE

phos—urusF „he ™—ud—ls of ryperd—pedon h—ve ™entr— €e™tor—l girdleF „he pe™tor—l girdle of „rilophE

th—t —re rhom˜oid in l—ter—l viewD with l—rge ™hevrons os—urus shows some modifi™—tion from th—t of most

th—t —re twi™e the height of the verte˜r—e from whi™h —r™hos—uromorphsD —s would ˜e expe™ted of —n —r˜ore—l

they origin—te @fenton IWVQAF €—r—d—pedon huxleyi h—s —nim—lF

™—ud—ls with ™entr— th—t —re highly ™ompressed —nteroE „he s™—pul—e of „rilophos—urus —re ™onsider—˜ly

posteriorlyD so mu™h so th—t the neur—l spines extend ˜ro—der dors—lly ™omp—red to other —r™hos—uromorphs

further —nteriorly —nd posteriorly then do the ™entr— @‚omer IWSTAF purther ™—rtil—ginous exp—nsion of the

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er RHI

pigF Q E veft humerus of „rilophos—urus j—™o˜si @xwwxr €EQWWQTA l—™king the deltope™tor—l ™rest @eEtD wExA in e —nd fD —nterior viewY g

—nd hD dist—l viewY i —nd pD proxim—l viewY q —nd rD posterior viewY s —nd tD dors—l viewY w —nd xD ventr—l viewF e left humer—l he—d

of „F j—™o˜si @xwwxr €E QWWQUA in u —nd vD dors—l viewY y —nd €D ventr—l viewY  —nd ‚D —nterior viewY ƒ —nd „D proxim—l viewF

xote the size of the deltope™tor—l ™rest —nd length of the entepi™ondyleF e˜˜revi—tionsX dp™ E deltope™tor—l ™restD e™t ± e™tepi™ondyleD

ent ± entepi™ondyleD h±he—dD r™ ± r—di—l ™ondyleD u™ E uln—r ™ondyleF

RHP ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF

„he unique —nterior exp—nsion of the proxim—l s™—pul—r ˜l—de is indi™—ted ˜y the irregul—r sh—pe of the

humer—l he—d in „rilophos—urus is not seen to the s—me ˜l—des9 dors—l surf—™e @qregory IWRSAD giving „rilophoE

extent in other —r™hos—uromorphs or ext—nt —r˜ore—l s—urus even l—rger —nd more ro˜ust s™—pul—e th—n sugE

reptilesD ˜ut —ppe—rs ™losest in morphology to th—t of gested ˜y the preserved ˜oneF ƒu™h s™—pul—r exp—nsions

the igu—nid sgu—n— igu—n—F roweverD it provided „riloE would h—ve —llowed for — l—rger —re— for the origin of

phos—urus with —n —re— for the —tt—™hment of mus™ul—E the s™—pul—r deltoidD whi™h inserts into the highly modE

ture th—t would —id in ™lim˜ingF ƒu™h exp—nsions ™reE ified proxim—l humerusD dis™ussed ˜elowF „he dors—l

—ted — l—rge —re— for the insertion of the supr—™or—™oiE m—rgin of the ™or—™oid is shelfElike —nd extends f—rther

deus mus™leF „his mus™le is used to prevent the trunk posteriorly th—n the tip of the dors—l s™—pul—r ˜l—deF xo

from s—gging @‚omer IWRWAF e l—rge supr—™or—™oideus other —r™hos—uromorphs exhi˜it this ™onditionF „he gleE

mus™le would h—ve —llowed „rilophos—urus to ˜e —˜le to noid foss— —rti™ul—tes with the humerus on three sides

™ontrol the dorsoEventr—l position of its trunk rel—tive @—nteriorlyD posteriorlyD —nd ventr—llyAD suggesting — very

to its lim˜sF „his level of ™ontrol would h—ve —llowed strong ™onne™tion ˜etween these two elementsF sn ™onE

„rilophos—urus to keep its ˜ody ™lose to —ny surf—™e it tr—stD other —r™hos—uromorphs h—ve — glenoid foss— th—t

™hose to ™lim˜D whi™h is ne™ess—ry to prevent toppling ˜ounds their humeri on only two sides @—nteriorly —nd

while ™lim˜ing @g—rtmill IWVSAF ventr—llyAF

„he deltope™tor—l ™rest of „rilophos—urus @pigF Q „he pe™tor—l girdle of „rilophos—urus h—s numerE

uEvD yE„A is very l—rge for — nonEdinos—uri—n —r™hoE ous l—rge —re—s for the origins of mu™h of the forelim˜

s—uromorphF st —ppe—rs tri—ngul—r in —nterior view —nd mus™ul—tureF „he l—rge ™or—™oid h—s — signifi™—nt —re—

is very simil—r to the deltope™tor—l ™rest of sgu—n— igu—E for the origin of the pe™tor—lisD whi™hD ™oupled with —

n—F ƒu™h — prominent deltope™tor—l ™rest suggests — l—rge l—rge insertion —re— on the deltope™tor—l ™restD dis™ussed

insertion for the pe™tor—lis mus™leF sndi™—tions of — l—rge ˜elowD would h—ve given „rilophos—urus — very strong

pe™tor—lis suggest „rilophos—urus ™ould pull its —rm forelim˜mus™ul—tureD useful in m—int—ining ˜—l—n™e—nd

˜—™kw—rd —nd downw—rd with gre—t for™e during lo™oE footing while ™lim˜ingF e prominent tu˜er™le —nterior

motion @‚omer IWRWAF to the glenoid indi™—tes — l—rge —re— for the origin of the

„he dist—l he—d of the humerus of „rilophos—urus tri™eps @qregory IWRSAD whi™h would —tt—™h dist—lly to

is —lso highly distin™tive @pigF Q gEhD sEtD wExAD with the l—rge ole™r—non of the uln— —nd serve to extend the

the l—rge entepi™ondyle ˜eing the key fe—tureF „he enE fore—rm @‚omer IWRWAF e mus™ul—r fore—rm would h—ve

tepi™ondyle of „rilophos—urus is shelfElike —nd h—s no helped „rilophos—urus to exert — l—rge —mount of for™e

entepi™ondyl—r for—men penetr—ting itD in ™ontr—st to in order to move —long —nd gr—sp su˜str—tesF

€seudop—l—tusD hesm—tosu™husD —nd €ostosu™husD —ll of

rumerusF „he humerus of „rilophos—urus @pigF QA whi™h h—ve prominent for—min—F ‡hile proportion—tely

is highly spe™i—lized —nd h—s proxim—l —nd dist—l he—ds sm—llerD the entepi™ondyle of sgu—n— igu—n— is —lso proE

with sever—l ™h—r—™teristi™s th—t —re unique —mong —r™hE minent —nd l—™ks — for—menF „rilophos—urus h—s — proE

os—uromorphsF „hese in™lude fe—tures of ˜oth the proxE minent tri—ngul—r e™tepi™ondyle @pigF Q sD tAD where—s no

im—l —nd dist—l ends of the humerusF prominent e™tepi™ondyle is dis™ern—˜le on —ny of the

„he proxim—l he—d of the humerus @pigF Q gEhD —r™hos—uromorphs ex—minedF roweverD — ™omp—r—˜le

uEvD yE€A of „rilophos—urus is one of the most unique e™tepi™ondyle is found on the humerus of sgu—n— igu—E

—spe™ts of its —n—tomyF st fe—tures —n —nterior exp—nsion n—F en exp—nsion of the dist—l humerusD posteroventr—l

th—t is m—t™hed only in the rhyn™hos—ur ysti™h—lki— to the r—di—l ™ondyle @pigF Q gD hAD is unique to „riloE

elder—e —nd the —etos—ur hesm—tosu™hus h—plo™erusD phos—urus —nd in™re—ses the size of the dist—l humerus

™—using o™™—sion—l ™onfusion —s to the t—xonomi™ —sE ™onsider—˜lyD ™overing — third of the dist—l humer—l —re—F

signment of isol—ted humeri @vong 8 wurry IWWSAF sn „his exp—nsion of the dist—l humerus —lso h—s sigE

™ontr—stD most —r™hos—uromorph humeri h—ve —n —nteE nifi™—n™e for the extensor mus™les of the fore—rmF „he

riorly line—r proxim—l he—d with — medioEventr—lly deE exp—nsionD —nterior to the uln—r ™ondyleD shows — l—rge

fle™ted deltope™tor—l ™restD giving the proxim—l he—d —n —mount of rugosityD whi™h is more pronoun™ed venE

—lmost te—rdrop sh—pe in dorsoEl—ter—l viewF „rilophoE tr—lly then dors—lly @pigF Q gEhAF „his rugosity indi™—tes

s—urus h—s — distin™tive proxim—l he—d th—t —nteriorly th—t the dist—l humer—l exp—nsions served —s — l—rge —re—

™omes to — pointD more so th—n hesm—tosu™husD giving for the origin of the extensor mus™les of the fore—rm —nd

it — tetr—r—di—te he—d in dorsoventr—l view @pigF Q sEvAF m—nusF „he —n™oneusD extensor ™—rpi r—di—lisD extensor

foth —nterior —nd posterior ends of the humer—l he—d digitorum ™ommunisD —nd extensor ™—rpi uln—ris —ll oriE

—re exp—nded ventr—llyD giving the he—d — symmetri™—lD gin—te from this prominent exp—nsion @‚omer IWRWAF

inverted Esh—pe in proxim—l view @pigF Q ƒE„AF „his sn „rilophos—urusD the flexor mus™lesD —s well —s

—lso ™ontr—sts with most —r™hos—uromorphsD whi™h h—ve the extensor mus™lesD h—d strong —tt—™hments on the

—symmetri™—l humer—l he—ds in proxim—l viewF humerusD spe™ifi™—lly on the entepi™ondyleF pun™tionE

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er RHQ

w—nusF yne of the prim—ry gr—sping tools of —ny

—r˜ore—l —nim—l is its m—nusF „rilophos—urus h—s — m—nus

stru™ture th—t is ™ompletely different from th—t of —ny

other —r™hos—uromorph @pigF IfAD espe™i—lly in reg—rd to

the orient—tion of the digitsF ƒu™h —n —˜err—nt digit

stru™ture is only seen in ™ert—in glidingD l—™ertid reptiles

@gol˜ert IWUHY iv—ns 8 r—u˜old IWVUAF ƒkelet—l fe—E

tures —sso™i—ted with the mus™ul—ture supporting these

digits indi™—te th—t „rilophos—urus in life would h—ve

˜een —˜le to exert — strong gr—sp on — su˜str—teF

„he orient—tion of the digits in the m—nus of —r™hE

os—uromorphs is extremely ™onsistentD „rilophos—urus

˜eing one of the few ex™eptionsF „he st—nd—rd —r™hE

os—uromorph m—nus h—s its first through fourth digits

su˜p—r—llel —nd h—s — divergentD l—ter—lly proje™tingD fifth

digitF „he orient—tion of the digits of „rilophos—urus is

in dire™t opposition to this st—nd—rd model ± its first

digit proje™ts medi—llyD —nd the se™ond through fifth

digits —re su˜p—r—llel @pigF IfAF

sn er™hos—uromorph—D there is no m—nus stru™E

ture —n—logous to th—t of „rilophos—urusY only the glidE

ing l—™ertid reptiles goeluros—ur—vus —nd s™—ros—urus

sh—re — simil—r orient—tion of digits @gol˜ert IWUHY iv—ns

8 r—u˜old IWVUAF „hese gliding l—™ertids —re thought to

h—ve used their m—nus —nd pes to ™lim˜trees in order to

g—in l—un™hing points from whi™h to glide @gol˜ert

IWUHY iv—ns 8 r—u˜old IWVUAD whi™h is ˜eh—vior seen

in —ll gliding spe™ies @rilde˜r—nd IWURAF s™—ros—urus —nd

„rilophos—urus ˜oth possess — divergentD medi—lly dire™E

tedD first digit of the m—nusF ‡hile the ™omplete m—nus

pigF R E gomp—rison ˜etween the ™l—ws of „rilophos—urusD drep—nE

of s™—ros—urus is not preservedD gol˜ert @IWUHA ˜—sed his

os—ursD —nd other ™lim˜ing m—mm—ls —nd ˜irdsF „he ˜l—™k

interpret—tion of — divergent first digit of the m—nus of

—rrow indi™—tes the pro™ess for the insertion of the flexor

s™—ros—urus on —n offset first met—™—rp—lF „he m—nus —nd mus™lesF „rilophos—urus ˜uettneri ™l—w modified from

qregory @IWRSAD —ll other ™l—ws from ‚enesto 8 €—g—noni pes of goeluros—ur—vus h—ve longD slenderD ™ylindri™—l

@IWWSAF digits ™—pped with l—ter—lly ™ompressed ™l—ws with proE

minent flexor insertions @iv—ns 8 r—u˜old IWVUAD —s

does „rilophos—urus @pigF IfAF

—llyD the entepi™ondyle serves —s one of the prim—ry

‚e™onstru™ting the mus™ul—ture of the m—nus —nd

—tt—™hment sites for the mus™les of the fore—rmF „he

pes is diffi™ultF „his is due to the p—lm—r —poneurosis shelfElike entepi™ondyle indi™—tes — l—rge surf—™e —re—

—nd pl—nt—r —poneurosisD whi™h le—ve no indi™—tions of

for the origin of the flexor mus™les of the fore—rmD the

the origin of the flexor mus™les of the m—nus —nd pesF

epitro™hleo—n™oneusD flexorsD —nd pron—tor profundusF

‡h—t ™—n ˜e inferred is the presen™e of l—rge flexors due

„he length of the entepi™ondyle is up to PH7 of the

to the l—rge su˜ungu—l pro™ess present on the ™l—ws of

length of the humerus in „rilophos—urusY in ™omp—riE

˜oth the m—nus —nd pes of „rilophos—urus @pigF RAF „oE

sonD hesm—tosu™husD €ostosu™husD —nd €seudop—l—tus

gether with l—rge flexor mus™les ™ome siz—˜le extensor

h—ve entepi™ondyles th—t —re IQ7D IT7D —nd IT7 of

mus™les inserting into the digitsF v—rge extensorsD speE

their over—ll humer—l lengthF „he l—rger entepi™ondyleD

™ifi™—lly the extensor digitorum ™ommunis —nd the exE

™omp—red to other —r™hos—uromorphsD indi™—tes th—t

tensor ™—rpi uln—risD —re suggested ˜y — l—rge origin—tion

the mus™les of the fore—rm of „rilophos—urus —re very site of these mus™les on the —nterior exp—nsion of the

l—rge for —n —nim—l its sizeD resulting in — powerful dist—l humerusD dis™ussed —˜oveF

fore—rmF e l—rge entepi™ondyle is ™h—r—™teristi™ of „he unique orient—tion of the digits of „rilophoE

m—ny —r˜ore—l —nim—ls @goom˜s IWVQAF ƒu™h flexors s—urusD together with the strong extensors —nd flexors of

would h—ve in™re—sed the power with whi™h the m—nus the m—nus of „rilophos—urusD would —llow for — solid

™ould ™ontr—™t its digitsD thus influen™ing the grip of grip dire™ted tow—rd the —re— ˜ene—th the ˜odyD due to

the m—nusF the medi—lly dire™ted first digitF

RHR ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF

pigF S E ‚ight femur @photos reversedA of „rilophos—urus j—™o˜si @xwwxr €EQWWIUA in e —nd fD —nterior viewY g —nd hD posterior viewY i

—nd pD dors—l viewY q —nd rD ventr—l viewY s —nd t proxim—l viewY u —nd vD dist—l viewF xote the extension of the intern—l tro™h—nter

down the femor—l sh—ft —nd the sm—ll dist—n™e ˜etween the proxim—l intern—l tro™h—nter —nd the proxim—l femor—l he—dF e˜˜revi—E

tionsX ™tf E ™ristoti˜iofi˜ur—lisD f™ ± fi˜ul—r ™ondyleDgtE gre—ter tro™h—nterD it ± intern—l tro™h—nterD t™ ± ti˜i—l ™ondyleF

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er RHS

pigF T E eD hi—gr—m of geometri™ me—surements of ™l—w ™urv—tureF e perpendi™ul—r @ghA is dr—wn to ˜ise™t the ™hord @efA of the inner —r™D

Á Á Á whi™h is itself ˜ise™ted —t the point ˆF €erpendi™ul—rs —re dr—wn @ii —nd ii9A to ˜ise™t the ™hords eˆ —nd ˆfF „hese perpendi™ul—rsD

Á Á A of the ™ir™le of whi™h the —r™ is — p—rtF „he r—dii —re then dr—wn to e—™h end of the —r™ @ei —nd when extendedD meet —t the ™enter @i

Á AF „he —ngle @‰A ˜etween these r—dii @re—d dire™tly from protr—™torA is — me—sure of the degrees of the —r™ @—fter pedu™™i— IWWQAF fD fi

gh—rt showing the ™l—w ™urv—tures of diverse ˜irds with three distin™t ™l—w typesF i—™h ™olumn is — single spe™iesF „rilophos—urus ™le—rly f—lls outside of the interv—l ™ont—ining ground dwelling ˜irds @modified from pedu™™i— IWWQAF

RHT ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF

pemurF vike the humerusD the femur of „rilophoE gits of the pes of „rilophos—urus h—ve — strong medi—l

s—urus @pigF SA is unique —mong —r™hos—uromorphsF „he ™urv—tureD where—s the fifth digit is strongly ™urved l—tE

defining ™h—r—™ter of the femur of „rilophos—urus is the er—lly @pigF IgAF elsoD unique —mong the —r™hos—uroE

extensive intern—l tro™h—nterF ƒu™h tro™h—nter dimenE morphsD the m—nus —nd pes of „rilophos—urus m—y h—ve

sionsD together with the over—ll sh—pe of the femurD ˜e—r penultim—te ph—l—nges th—t —re longer th—n proxim—l

— striking resem˜l—n™e to the femur of er—eos™elisF ph—l—ngesF „his ™h—r—™ter is found only in —r˜ore—l ˜irds

„he femur of „rilophos—urus h—s — proxim—l he—d @ropson PHHIA —nd pteros—urs @ nwin IWWT—D˜AF „he

th—t is te—rdropEsh—ped in proxim—l view @pigF S sEtAD orient—tion of the digits —nd rel—tive digit—l lengths —re

while other —r™hos—uromorphs h—ve proxim—l he—ds th—t —ll simil—r to the —r˜ore—l sgu—n— igu—n—F

—re l—ter—lly exp—nded in proxim—l viewF „he slight sigE emong —r™hos—uromorphsD „rilophos—urus h—s —

moid—l flexure —t the proxim—l —nd dist—l ends of the unique —nkleF „he —str—g—lus —nd ™—l™—neum ™ont—™t

femur of „rilophos—urus @pigF S iErA ™ontr—sts with e—™h other o˜liquely with no interlo™king ™ont—™t —s

the mu™h more ex—gger—ted flexure in €seudop—l—tusD in other —r™hos—uromorphs @€—rrish IWVTY ƒereno

in whi™h the entire sh—ft of the femur is sigmoid—lD IWWIAF „he l—rge perfor—ting for—men —nd the l—™k of

where—s the femor— of €ostosu™husD irythrosu™husD hroE —n interlo™king —str—g—lus —nd ™—l™—neum is reminis™ent

mi™osu™hus —re mu™h more line—rF „—ng—s—urusD of the eosu™hi—n ‰oungin—D the nothos—ur

„he prominent intern—l tro™h—nter @pigF S eEhD —nd to — lesser extent the protoros—ur €rotoros—urus

qEtA extends from ne—r the proxim—l he—d —nd runs @‚omer IWSTAF „he l—ter—llyEproje™ting ™—l™—ne—l tu˜er

ne—rly — third of the length of the entire femurF ix™ept found in phytos—urs —nd proterosu™hids is —lso present

for size this tro™h—nter strongly resem˜les th—t of the in „rilophos—urusD —lthough in „rilophos—urus the tu˜er

˜—s—l reptile er—eos™elis @‡illiston IWIRY qregory IWRSA is exp—nded ˜oth l—ter—lly —nd dors—llyD giving it — mu™h

—nd th—t of sgu—n— igu—n—F ‡e ™omp—re the intern—l more ˜l—deElike —ppe—r—n™e th—n in either phytos—urs or

tro™h—nter of „rilophos—urus to the —r™hos—uri—n fourth proterosu™hidsF „he ™om˜in—tion of the perfor—ting

tro™h—nter ˜—sed on qregory 8 g—mp @IWIVA ‘˜ut see for—men —nd l—ter—lly proje™ting ™—l™—ne—l tu˜er pl—™es

€—rrish @IWVQA for —n —ltern—tive interpret—tion of femorE „rilophos—urus in the primitive t—rs—l group —mong

—l homology“F sn gener—lD —r™hos—uromorph femor— on —r™hos—uromorphs @€—rrish IWVTAF

the whole h—ve proportion—tely mu™h sm—ller intern—l e diffi™ulty f—™ed ˜y —ny —r˜ore—l —nim—l is —

tro™h—nters @—lso ™—lled fourth tro™h—ntersA th—t —re little ™ontrolled he—d first des™entF er˜ore—l reptiles h—ve —

more th—n sm—ll tri—ngul—r proje™tionsD gener—lly — primitive lo™omotor posture th—t —llows supin—tion of

fourth of the w—y down the femurF the hind lim˜D en—˜ling the foot to grip —nd the —nim—l

„he femur of „rilophos—urus shows ™h—r—™teristi™s to —™hieve — ™ontrolled he—d first des™ent @g—rtmillD

indi™—ting it w—s used for qui™k —nd powerful moveE IWVSAF xot only did the primitive posture of „rilophoE

mentF „he intern—l tro™h—nter is the insertion of the s—urus —llow it to supin—te its footD ˜ut it —ppe—rs to h—ve

™—udifemor—lisD —n import—nt femor—l retr—™torF ƒu™h — h—d — very ™—rtil—ginousD —nd therefore flexi˜leD —nkleF

l—rge —nd extensive pro™ess would indi™—te — very l—rge „his flexi˜ility w—s enh—n™ed ˜y the l—™k of — fi˜ul—r

™—udifemor—lisD giving „rilophos—urus powerful hind f—™etD so there w—s little to no fi˜ul—rE™—l™—ne—l ™ont—™t

lim˜movement —s mentioned —˜oveF„he intern—l troE @qregory IWRSAF

™h—nter is lo™—ted more proxim—lly in „rilophos—urus

ngu—lsF „he orient—tion of the ungu—lsD or th—n in ne—rly —ll other —r™hos—uromorphsD ex™ept for

™l—wsD on the digits of „rilophos—urus does not —ppe—r er—eos™elisF pun™tion—llyD the intern—l tro™h—nterD ˜eing

to resem˜le th—t of other primitive —r™hos—uromorphsF ™lose to the proxim—l femor—l he—dD —llows for the r—pid

wost primitive —r™hos—uromorphs h—ve ™l—ws th—t —re retr—™tion of the femurD vi— the ™—udifemor—lis @€—rrish

˜ro—d —nd th—t proje™t str—ight out of the ph—l—nges IWVTAD thus —llowing for r—pid movement of the femurD

without —ny signifi™—nt ™urv—tureF „he ™l—ws of „riloE —nd thus the entire hind lim˜F

phos—urus @pigF TeA —reD —s qregory @IWRSD pF QIPA deE

€esF „he pes of „rilophos—urus @pigF IgAD like the s™ri˜ed themD 4l—rge strongly ™ompressed l—ter—llyD longD

m—nusD is distin™t from th—t of other —r™hos—uromorphsF re™urvedD ‘—nd“ sh—rp pointedF4 „he ™l—ws of the pes of

es dis™ussed e—rlierD the pes is rel—tively l—rgeD repreE „rilophos—urus —lso do not proje™t str—ight out of the

senting —n enormous per™ent—ge of the trunk length of ph—l—ngesY they —re inste—d dire™ted slightly medi—lly

„rilophos—urus @pigF IeAF ‡hile ret—ining the ph—l—nge—l or l—ter—lly @pigF I gAF „he first —nd fourth ph—l—nges

formul— of primitive —r™hos—uromorphsD „rilophos—urus of the pes h—ve ™l—ws th—t —re oriented inw—rdsD the first

h—s — pes with — distin™t orient—tion of digitsF „he typiE ph—l—nx oriented l—ter—lly —nd the fourth ph—l—nx mediE

™—l —r™hos—uromorph ™ondition is to h—ve digits dire™ted —llyD tow—rds the se™ond —nd third ph—l—ngesD indi™—ting

—nteriorlyD in™luding — fifth digit th—t is offset due to the th—t they would —llow for ˜etter gr—sping of — ™entr—l

vEsh—ped fifth met—t—rs—lF sn ™ontr—stD the first four diE pointF ƒu™h —n —rr—ngement of the ph—l—nges is not seen

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er RHU

in other primitive —r™hos—uromorphs —nd would seeE ˜e —˜le to interlo™k with its supporting surf—™e to genE

mingly ˜e of little v—lue —mong groundEdwelling —niE er—te — nonverti™—l ™ont—™t surf—™e @g—rtmill IWVSAY inE

m—lsF terlo™king would —lso in™re—se the —mount of fri™tionD

—nother key ™omponent in ™lim˜ing @rilde˜r—nd IWURAF

ƒu™h interlo™king ™ould e—sily ˜e —™™omplished ˜y the

xwwxr ƒpe™imen gl—w gurv—ture

sh—rp ™l—ws of „rilophos—urusD drep—nos—ursD —nd other @degreeA xum˜er

—r˜ore—l —nim—lsF „he strong flexors inserting to the €ERHIIU IIIFS

ventr—l pro™ess of the ™l—ws would —llow —r˜ore—l —niE €ERHIIV IHTFS

m—ls to use their own ˜ody weight to prevent slipping €ERHIIW ISSFS

in —ny dire™tion @rilde˜r—nd IWURAF

€ERHIPH IPHFS

e l—rge m—nus —nd pes with spe™i—lized ™l—ws is

€ERHIPI IPRFS

not only indi™—tive of —r˜ore—l —nim—ls ˜ut —lso of fosE

€ERHIPP IRIFS

sori—lD digging —nim—lsF ‡hile some might postul—te —

€ERHIPQ IIRFS

fossori—l mode of living for „rilophos—urus ˜—sed on

€ERHIPR IIUFH

these f—™torsD the morphology of the ™l—ws does not

€ERHIPS IIWFH

support su™h —n interpret—tionF „rilophos—urus does

€ERHIPT IIRFH

not possess —ny spe™i—lized ™l—ws like hrep—nos—urusD

€ERHIPU IQPFH whi™hD prior to the work of ‚enesto @PHHHAD w—s interE

€ERHIPV IRTFUS preted —s fossori—l @€inn— IWVHD IWVRD IWVTAF „his interE

€ERHIPW IRVFS pret—tion h—d hrep—nos—urus using the single disproporE

tion—tely l—rge ™l—w on the m—nus —s — digging impleE €ERHIQH IITFS

mentF „he ™l—ws of „rilophos—urus —lso —re l—ter—lly €ERHIQI IPRFS

™ompressedF es noted ˜y qregory @IWRSAD — fossori—l €ERHIQP IQUFS

—nim—l would h—ve ˜ro—d ™l—ws th—t would m—ximize

€ERHIQQ IRIFH

the surf—™e —re— the ™l—ws ™ont—™ted with e—™h strokeF

€ERHIQR IQIFS

v—ter—lly ™ompressed ™l—ws would ™ont—™t the le—st surE

€ERHIQS IQTFH

f—™e —re— per strokeF ƒ™r—t™h digging like th—t of the

€ERHIQT IIVFS

—nte—ter gy™lopes ™ould ˜e suggested for „rilophos—urus

€ERHIQU ISHFUS

˜ut is unlikely due to the modifi™—tions of ˜oth the hind

€ERHIQV IPVFH

—nd forelim˜s in the l—tterD where—s s™r—t™h diggers opE

€ERHIQW ISTFS

er—te prim—rily with only their front lim˜sF „husD the

€ERHIRH IRPFH ™l—w morphology of „rilophos—urus indi™—tes it would

€ERHIRI IQRFS h—ve ˜een — poor diggerF

„o further test the utility of the ™l—ws for terresE

„—˜F Q E gl—w ™urv—ture of sele™ted xwwxr „rilophos—urus speE

tri—l or —r˜ore—l use we undertook — qu—ntit—tive —n—lyE ™imensF

sis modified from pedu™™i— @IWWQA —s des™ri˜ed in the

methods —nd m—teri—ls se™tion —˜oveF „he ™l—w ™urv—E „he ™l—ws of the m—nus —nd pes of „rilophos—urus

ture of „rilophos—urus r—nges from IHTFSë to ISSFSë @pigF resem˜le the ™l—ws of weg—l—n™os—urus @g—lz—v—r— et —lF

TfD „—˜le QAF „he d—t— extend over ˜oth the per™hing IWVHY ‚enesto IWWRD PHHHY ‚enesto 8 €—g—noni IWWSA

—nd ™lim˜ing ™l—w ™urv—ture interv—ls est—˜lished for @pigF TAF „he ™l—ws of „rilophos—urus —re hooked to —

ext—nt ˜irds ˜y pedu™™i— @IWWQA —nd do not overl—p with signifi™—nt degreeD sh—rpD —nd —s n—rrow —s those of

the ground dwelling ˜irds @pigF TfAF „he „rilophos—urus ™lim˜ing —nim—ls —nd weg—l—n™os—urus @‚enesto IWWRD

™l—ws we used were not —rti™ul—ted —nd ™ould not ˜e PHHHA @pigF TY „—˜le QAF „rilophos—urus —lso sh—res with

—ssigned to — digit @or even lim˜A with ™ert—intyF rowE weg—l—n™os—urusD ˜irdsD —nd ™lim˜ing m—mm—ls — simiE

everD we distinguished two ™l—w morphotypes ˜—sed on l—r insertion point —long the ventr—l pro™ess of the ™l—w

™l—w ™urv—ture d—t—D one th—t fell in the per™hing interv—l for the flexor mus™le @‚enesto 8 €—g—noni IWWSA @pigF

—nd the other th—t fell in the ™lim˜ing interv—lF „his is TAF es ‚enesto 8 €—g—noni @IWWS pF WTA pointed out

seen —lso in er™h—eopteryxD —nd w—s used ˜y pedu™™i— 4longD sh—rpD —nd n—rrow hooked ™l—wsD provided with

@IWWQA to support the —r˜ore—l interpret—tion of er™h—eE ventr—l pro™ess for the insertion of flexor mus™lesD —re

opteryxF yur results —re ™omp—r—˜le to pedu™™i—9s @IWWQA ™h—r—™ters th—t ™—n ˜e found in ™lim˜ing —nim—lsF4 ƒu™h

study ˜y virtue of the f—™t th—t —ll verte˜r—te ™l—ws —re — su˜ungu—l pro™ess is — ™h—r—™teristi™ found throughout

simil—r enough to —llow for ™omp—risons ˜etween speE —r˜ore—l —nim—ls @goom˜s IWVQAF

™ies @—ni PHHHAF „he d—t— support the hypothesis th—t gl—ws like those of „rilophos—urus —re key fe—E

„rilophos—urus w—s —r˜ore—lD —nd our prelimin—ry ™l—w tures used to gener—te — verti™—l for™e to ™lim˜F „o genE

™urv—ture me—surements of groundEdwelling reptiles deE er—te su™h — for™e „rilophos—urus would h—ve needed to

RHV ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF „F F xote the ™lose simil—rity ˜etween the „rilophos—urus j—™o˜si F sFigu—n— —nd j—™o˜si pigF U E e t—˜le ™omp—ring the proxim—l humeriD posterior femor—D —nd ™l—ws of terrestri—lD semi—r˜ore—lD —nd —r˜ore—l v—r—nidsD igu—nidsD —nd

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er RHW

monstr—te — lesser degree of ™urv—ture ˜y ™omp—risonF —g—inst gr—vity —nd up su˜str—tesF „he ™l—ws of the pes

would interlo™k with the su˜str—te —nd provide the fri™E „his follows wertens @IWRPAD who noted th—t —mong

tion needed to support „rilophos—urusF eny —ddition—l v—r—nid spe™ies those whi™h —re —r˜ore—l h—ve ™l—ws

with in™re—sed ™urv—tureF ƒu™h — ™omp—rison ˜etween weight ˜—l—n™ing or distri˜ution needed to prevent topE

pling would ˜e —™™omplished ˜y the long t—ilD simil—r to the ™l—ws of diverse —r˜ore—l —nim—ls is not without

—n sgu—n—F pre™edentF ‚enesto 8 €—g—noni @IWWSA ™omp—red v—rE

w—ny simil—rities exist ˜etween the lim˜s of „riE ious drep—nos—ur ™l—ws with those of —r˜ore—l ˜irds

lophos—urus —nd the —r˜ore—l sgu—n— igu—n—F „he l—rge —nd m—mm—ls to further su˜st—nti—te the ide— th—t the

deltope™tor—l ™restD entepi™ondyleD —nd e™tepi™ondyle of drep—nos—urs weg—l—n™os—urus —nd hrep—nos—urus

the humerus —re sh—red ˜y ˜oth gener— @pigF QAF elsoD were —r˜ore—lF

˜oth h—ve very l—rge intern—l tro™h—ntersD suggesting

simil—r mus™ul—ture —nd powerful hindlim˜movement

@pigF SAF gomp—risons with ext—nt terrestri—l —nd —r˜ore—l reptiles

„rilophos—urus w—s —˜le to utilize its method of

‡hen ™omp—red to terrestri—lD semi—r˜ore—lD —nd ™lim˜ing on v—rious l—rge trees th—t were distri˜uted

—r˜ore—l reptilesD the morphology of „rilophos—urus is throughout wh—t is tod—y the southwestern nited

most simil—r to th—t of —r˜ore—l reptilesF pigure U ™omE ƒt—tes during the v—te „ri—ssi™F „wo l—rge v—rieties of

p—res the proxim—l humeriD posterior femor—D —nd ™l—ws trees from the v—te „ri—ssi™D er—u™—rioxylon —rizoni™um

of „rilophos—urus with — v—riety of v—r—nids —nd igu—E —nd ƒ™hilderi— —d—m—ni™—D ˜oth grew to di—meters th—t

nids th—t r—nge from terrestri—l to —r˜ore—lF would e—sily —™™ommod—te —n —dult „rilophos—urusF

„he posterior proxim—l humer—l he—d is l—rger in er—u™—rioxylon —rizoni™um re—™hed — m—ximum di—E

more —r˜ore—l —nim—ls —nd opens to form — wider —r™h meter of IFUP meters —nd ƒ™hilderi— —dm—ni™— re—™hed

in proxim—l viewF „he posterior femur of the terrestri—l — m—ximum di—meter of HFW meters @esh 8 gre˜er PHHHY

—nd semi—r˜ore—l reptiles h—s either t—ll or extensive gre˜er 8 esh PHHRAF

intern—l tro™h—ntersD ˜ut not ˜othY only „rilophos—urus ƒwinging —mong ˜r—n™hesD —s in prim—tesD reE

—nd sgu—n— igu—n— sh—re t—ll —nd extensive intern—l troE quires long —rmsD — mo˜ile s™—pul—D —nd — high degree

™h—ntersF „he ™urv—ture of the ™l—ws of these terrestri—l of movement of the humerus rel—tive to the pe™tor—l

reptiles is f—irly low with — sm—ll not™h on the dist—l end girdle @rild˜r—nd IWURAF ‡hile „rilophos—urus does

with — sh—rp ™l—wF wore —r˜ore—l reptiles h—ve mu™h h—ve long forelim˜s it is due to the length of the m—nusD

more ™urved ™l—ws th—t —re more re™urvedF sn —ll three not the extended humerusD r—diusD —nd uln— seen in

—re—s of ™omp—rison „rilophos—urus groups with —r˜orE swinging prim—tesF „he tight —sso™i—tions of the ˜ones

e—lD not terrestri—l or semi—r˜ore—l reptilesF of the pe™tor—l girdle of „rilophos—urus would not —llow

—ny movement of the s™—pul—D thus m—king it impossi˜le

wode of life for swingingF e high degree of humer—l mo˜ility is imE

„he pro˜lem of m—neuvering in —n —ngled to verE possi˜le for „rilophos—urus ˜—sed on the glenoid foss—

ti™—l environment must ˜e solved ˜y —ll —r˜ore—l —niE ˜ounding the humer—l he—d on three sidesF „husD the

m—lsF †—rious solutions —re seen —™ross numerous t—x—F osteology of „rilophos—urus strongly ™ontr—sts with th—t

„he osteologi™—l ™h—r—™teristi™s of „rilophos—urus indiE of —n —r˜ore—l swingerF

™—te th—t it solved this pro˜lem in — m—nner like th—t of sn order to le—p from one ˜r—n™h or one tree to

sgu—n— igu—n—F the nextD — spe™i—lized verte˜r—l stru™ture is neededF

‡e propose th—t „rilophos—urus moved up —ngled ve—ping —nim—ls h—ve —n in™re—sed num˜er of pres—™r—l

su˜str—tes qui™kly —nd with ™onsider—˜le powerD using dors—l verte˜r—e whose ™entr— —re elong—ted ™omp—red

˜oth its forelim˜s —nd hindlim˜s for propulsionF „he to rel—ted nonEle—ping spe™ies @rilde˜r—nd IWURAF „he

forelim˜s with the l—rge pe™tor—lis —nd extensive foreE dors—l verte˜r—l series of „rilophos—urus h—s no elong—E

lim˜mus™ul—ture helped to propel „rilophos—urus —long tion of —ny ™entr— —nd h—s — num˜er of verte˜r—e ™omE

su˜str—tesF „he orient—tion of the digits of the m—nusD p—r—˜le to other —r™hos—uromorphsF „husD „rilophoE

with its medi—lly dire™ted first digitD —nd the sh—rply s—urus h—s —n —xi—l skeleton th—t m—kes it impossi˜le

™urved ™l—ws of the m—nusD would give „rilophos—urus for it to le—pF

— solid gripD helping to ret—in its footing on su˜str—tes e unique m—nus —nd pes ™—n give —n —nim—l —

—nd —id in propulsionF novel w—y to move —long su˜str—tesF „he m—nus of „riE

„he hindlim˜s served —s the other prim—ry proE lophos—urusD while unique —mong —r™hos—uromorphsD

pulsive for™eD ˜—sed on the osteology —nd mus™ul—ture does not sh—re key ™h—r—™teristi™s with some other

of the femurF „he qui™kD powerful retr—™tion of the feE highly spe™i—lized ™lim˜ing m—mm—ls —nd reptilesF ƒu™h

™lim˜ing m—mm—ls —nd reptiles h—ve ™lefts in their murD vi— the ™—udifemor—lisD with the medi—llyEdire™ted

m—nus —nd pes th—t —llow their digits to oppose e—™h digits of the pesD w—s used to propel „rilophos—urus

RIH ƒpielm—nn tF eFD re™kert eF fF 8 vu™—s ƒF qF

—nd —r˜ore—l reptiles „rilophos—urus —ppe—rs morpholoE otherD —s in ™h—meleonsF „here is no eviden™e for su™h —

™left in the m—nus or pes of „rilophos—urus or in ext—nt gi™—lly most simil—r to —r˜ore—l reptilesF e model for its

igu—nids like sgu—n— igu—n—F ‡hile „rilophos—urus did movement —long the trunks of l—rge trees is ˜—sed on the

h—ve — unique orient—tion of digitsD th—t —ppe—rs rel—E osteology of the —nim—l —nd suggests th—t like living

tively wellEsuited for —n —r˜ore—l h—˜it—tD its m—nus sgu—n— igu—n—D it used ˜oth its forelim˜s —nd hindlim˜s

—nd pes do not h—ve opposing digits —s in some other for propulsion —nd its t—il for ˜—l—n™eF

™lim˜ing m—mm—ls —nd reptilesF

e™knowledgmentsF fo˜u—hle of widl—ndD „ex—sD don—ted his

gon™lusion extensive ™olle™tions of „rilophos—urus spe™imens to the xwwxrD

m—king this study possi˜leF v—ur— e˜r—™zinsk—s helped to ™oordin—te „he ˜ody proportions of „rilophos—urus distinE

the lo—n of the v—rious herpetologi™—l spe™imens from the wi™hig—n guish it —mong —r™hos—uromorphsD espe™i—lly the rel—E

ƒt—te niversity wuseumF tF „F qierm—kowski f—™ilit—ted viewing of tive size of the m—nus —nd pes ™omp—red to the trunkF

the wuseum of ƒouthwestern fiology spe™imensF u—te eigler —nd

„he fun™tion—l morphology of the pe™tor—l girdleD foreE

†in™ent vF worg—n re—d e—rly dr—fts of this m—nus™ript —nd m—de helpE

lim˜sD pelvi™ girdleD hind lim˜s —nd ungu—ls indi™—te th—t

ful ™ommentsF v—rry ‚ineh—rt provided input on our st—tisti™—l methE

„rilophos—urus possesses numerous ™h—r—™teristi™s th—t odsF ƒilvio ‚enesto —nd t—mes p—rlow offered insightful reviewsF „he

suggest it w—s —r˜ore—lD —n ide— left unexplored for h—rtmouth ƒenior pellowship €rogr—m provided one of us @teƒA fundE

ing in order to ™omplete this studyF ne—rly TH ye—rsF ‡hen ™omp—red to ext—nt terrestri—l

‚ipi‚ixgiƒ

esh ƒF‚F 8 gre˜er qF„F @PHHHA E „he v—te „ri—ssi™ er—u™—rE gol˜ert iF rF @IWUHA E „he „ri—ssi™ gliding reptile s™—roE

s—urusF fullF emF wuseum x—tF ristFD IRQX VUEIRPD ioxylon —rizoni™um trees of the €etrified porest x—E

xew ‰orkF tion—l €—rkD erizon—D ƒeF €—l—eontologyD RQX ISEPVD

goom˜s wFgF @IWVQA E v—rge m—mm—li—n ™l—wed her˜ivoresX g—m˜ridgeF

— ™omp—r—tive studyF „r—nsF emF €hilF ƒo™FD UQ @UAX IE fenton wFtF @IWVQA E „he „ri—ssi™ reptile ryperod—pedon

WTD €hil—delphi—F from ilginX pun™tion—l morphology —nd rel—tionE

gre˜er qF „F 8 esh ƒF ‚F @PHHRA E „he v—te „ri—ssi™ ƒ™hilE shipsF €hilF „r—nsF ‚F ƒo™F vondonD fD QHPX THSEUIVD

deri— —d—m—ni™— —nd ‡oodworthi— —rizoni™— trees of vondonF

the €etrified porest x—tion—l €—rkD erizon—D ƒeF fenton wFtF @IWWHA E „he spe™ies of ‚hyn™hos—urusD—

€—l—eontologyD RUX PIEQVD g—m˜ridgeF rhyn™hos—ur @‚eptili—D hi—psid—A from the widdle

grush €F tF @IWVRA E e l—te pper „ri—ssi™ sphenosu™hid

„ri—ssi™ of ingl—ndF €hilF „r—nsF ‚F ƒo™F vondonDfD

™ro™odili—n from ‡—lesF €—l—eontologyD PUX IQIEISUD

QPVX PIQEQHTD vondonF

g—m˜ridgeF fenton wFtF 8 ‡—lker eFhF @PHHPA E irpetosu™husD — ™ro™oE

hem—r ‚F iF 8 folt tF ‚F @IWVIA E hentition—l org—niz—tion

dileElike ˜—s—l —r™hos—ur from the v—te „ri—ssi™ of ilE

—nd fun™tion in — „ri—ssi™ reptileF tF €—leontFD SS @SAX

ginD ƒ™otl—ndF oolF tF vinne—n ƒo™FD IQTX PSERUD vonE

WTUEWVRD v—wren™eF

donF

ilder ‚F vF @IWUVA E €—leontology —nd p—leoe™ology of the

g—lz—v—r— wFD wus™io ‚F 8 ‡ildD ‚F @IWVHA E weg—l—n™oE

ho™kum qroupD pper „ri—ssi™D row—rd gountyD

s—urus preonensis nF gF nF spFD — new reptile from the

„ex—sF wFƒF thesisD niversity of „ex—s —t eustinD PHS

xori—n of priuliF qort—ni—D PX SWETRD dineF

pF

g—rtmill wF @IWVSA E glim˜ingF snX rilde˜r—nd wFD fr—m˜le

iv—ns ƒF iF 8 r—u˜old rF @IWVUA E e review of the pper

hF wFD viem uF pF 8 ‡—ke hF fF @edsFA E pun™tion—l

€ermi—n gener— goeluros—ur—vusD ‡eigeltis—urus —nd

†erte˜r—te worphologyF r—rv—rd niversity €ressD

qr—™ilis—urus @‚eptili—X hi—psid—AF oolF tF vinne—n

UQEVVD g—m˜ridgeF

ƒo™FD WHX PUSEQHQD vondonF

g—se iF gF @IWPVA E sndi™—tions of — ™otylos—ur —nd of —

iwer ‚F pF @IWTSA E „he —n—tomy of the the™odont reptile

new form of fish from the „ri—ssi™ ˜eds of „ex—sD

iup—rkeri— ™—pensis froomF €hilF „r—nsF ‚F ƒo™F vonE

with rem—rks on the ƒhin—rump gonglomer—teF nivF donD PRVX QUWERQSD vondonF

wi™hig—n gontrF wuseum €—leontFD QX IEIRD enn erE pedu™™i— eF @IWWQA E ividen™e from ™l—w geometry indi™—tE

˜orF ing —r˜ore—l h—˜its of er™h—eopteryxF ƒ™ien™eD PSWX

gh—tterjee ƒF @IWURA E e rhyn™hos—ur from the pper „ri—sE UWHEUWQD ‡—shingtonD hFgF

si™ w—leri porm—tion of sndi—F €hilF „r—nsF ‚F ƒo™F qower hF tF @IWWTA E „he t—rsus of erythrosu™hid —r™hos—ursD

vondonD fD PTUX PHWEPTID vondonF —nd impli™—tions for e—rly di—psid phylogenyF oolF tF

gh—tterjee ƒF @IWVSA E €ostosu™husD — new the™odonti—n repE vinne—n ƒo™FD IITXFQRUEQUSD vondonF

tile from the „ri—ssi™ of „ex—s —nd the origin of „yrE qower hF tF @PHHQA E ysteology of the e—rly —r™hos—uri—n

—nnos—ursF €hilF „r—nsF ‚F ƒo™F vondonD fD QHWX QWSE reptile irythrosu™hus —fri™—nus froomF ennF ƒouth

efri™—n wuseumD IIH @IAX IEVVD g—pe „ownF RTHD vondonF

„he v—te „ri—ssi™ —r™hos—uromorph „rilophos—urus —s —n —r˜ore—l ™lim˜er RII

wexi™o wuseum x—tF ristF ƒ™ien™e fullFD PRX TQETTD qozzi iF 8 ‚enesto ƒF @PHHQA E e ™omplete spe™imen of

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i—n @v—te „ri—ssi™A of vom˜—rdy @xorthern st—lyAF ‚ivF wer™k trF tF ‡F @IWWSA E „he ™r—ni—l —n—tomy of „rilophoE

stF €—leontF ƒtr—tFD IHWX RUSERWVD wil—noF s—urus ˜uettneri —s reve—led ˜y high resolution ™omE

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tive my™ology —nd osteologyF xoF sssF fullF emF wuE e˜h—ndlungen ƒen™ken˜ergF x—turfF qesFD IEQ @RTSAD

seum x—tF ristFD QVX RRUESTQD xew ‰orkF IEQWWD ƒtuttg—rtF

re™kert eFfF @PHHRA E v—te „ri—ssi™ mi™roverte˜r—tes from widdleton uFwF 8 q—tesy ƒFwF @PHHHA E „heropod forelim˜

the lower ghinle qroup @ytis™h—lki—nEed—m—ni—nX design —nd evolutionF oolF tF vinne—n ƒo™FD IPVX IRWE

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x—tF ristF ƒ™ien™e fullFD PUD IUH pFD el˜uquerqueF wurry €F eF @IWVTA E †erte˜r—te p—leontology of the ho™kE

re™kert eFfFD vu™—s ƒFqFD u—hle ‚F 8 eigler uF iF @PHHIA E um qroupF snX uF €—di—n @edFA E „he feginning of the

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