ON CERTAIN PORTIONS OF THE SKELETON OF PROTOSTEGA GIGAS, HAY 1895

These consist of a large portionof the plastronofa large individual whose remains were entombed in the Cretaceous deposits of Butte Creek, to-gether amounts to 1.2 metres, including the

FIELD COLUMBIAN MUSEUM PUBLICATION 7.

CHICAGO, U. S A.

November

ON CERTAIN PORTIONS OF THE SKELETON OF

PROTOS-TEGA GIGAS COPE. O P. HAY

The Dermochelyoid turtle, Protostega gigas, was first described

more fullydescribed and illustrated the structure of this remarkable

reptile.

a number of vertebrae, ten ribs, some marginal bones, certain tionsoftheskull, somelimbbones,and somelargeplates. Of thelat-

ofoneor two others These plateshe considered asbelongingtothe

Baur(Biolog.Centralblatt, vol.9, p 190). This authorpointed outthat

the plates were components of the plastron, an opinionthat findsabundant confirmationin the materials here to bedescribed These

consist of a large portionof the plastronofa large individual whose

remains were entombed in the Cretaceous deposits of Butte Creek,

to-gether amounts to 1.2 metres, including the estimated length of a

two bones are united bysuture, which maybe seenimmediately in

front ofthe fractureproduced inexcavating thefossil. Therelation

between the two bones isaveryshort one, in comparison with that

of Thalassochelys

58 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i.

extreme width of the hypoplastron issomewhat lessthan that of the

bone is thickest just behindand somewhatmesiadof the excavation

hypoplastron isnot so thick, but stillquite thickandsolid. Theresponding bones in Professor Cope's possession werenotmore thanhalf an inch in thickness, at the most This condition was in all

Thalasso-chelys, in which again the plastron is more developed than inChelonia As usual in all the recent marine turtles, this angle ex-

end of the epiplastron. Neither ofthe epiplastra wassecured InThalassochelysthe anterior endsofthe epiplastra extendin front of a

limbs to those for thehindlimbs This, in the Protostega plastron

extend behind the excavations for the hinderlimbs asfaras do the

epiplastra from the anterior excavations Ifthese proportions hold

good for Protostega, the wholelengthof the plastron would amount

to at least 2.4metres

As shown by the figure, the hinder end of the hypoplastron is

prolongedbackwardand somewhat inwardasalong process Mesiad

of Chelonia and Thalassochelys, a longer process Aportionofthis

somewhat toward the middlelineofthe body, as wellas backward

Between the two processeshasbeenreceived the forkedend ofthe

the xiphiplastron. This chamfering of the bone continuesbeyond

withthe xiphiplastron. Thewhole structureishere extremely

simi-lar to that seenin Chelonia and

Nov. 1,1895. SKELETON Protostega gigas HAY. 59Had the breadth of the body of Protostega possessed the same

ratio to the lengththat wefind existing in Thalassochelys,thelowerside

ofthe animal would have been about 2.2metreswide Thepositions

location ofthe axis ofstrongestdevelopmentofthetwoplastralbones

This isshown too bymeasuring outward from the excavation for the

of the digitations ofthe plastralbones must havelacked asmuch as

30 cm of reaching the marginalbones Thiswill leave a space ofabout120cm fromthe bottomoftheexcavationforonearmtothatfor

the other When we cometo comparethe distance fromthe hinderto

(Mem. Ac. dei Lincei, 1884, 3 ser., vol. 18), withthe distance of

measure-ments have almost exactly thesame ratio that I have given them inProtostega

about 43 cm in width; and opposite theunion of the hyo-and

hypo-plastron, about 90cm Thisis somewhatsmaller, however, than the

fontanelle found in Protosphargis, and much smaller than that of

Dermochelys

butwhen we cometo compare the twoplastra, wefind abundant

dif-ferences That of Protosphargisis considerablyless developed thanthat of Protostega Notwithstanding this, there wason the front of

for-ward and inward toconnect with the epiplastron. In Protostega the

corresponding angle of the hyoplastron is broad, rounded off, and

digitated In Protosphargis again there isabroad notch in the

Pro-tosphargis isin one respect notwhollyaccurate The epiplastra

Accompanyingthe plastral boneshere described isanotherbone

which must he regarded asthe nuchal Considerable portionsof itarewanting ateachlateralextremity;andthetipofthe processwhichprojects backward toward the first dorsal neural arch is also broken

The of thebone outward on each

60 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. t.

side ofthe middle line lessthan 18 cm Ifthe lengthofthebone had

the sameratio to the remainder of the carapaceof Protostega that we

find in Chelonia, it should extendlaterallyabout40 cm Thatit had

anterio-posteriorextent of the bone were equal to that of Chclonia, itwouldbe about30 cm at the narrowest part; but it isonly 6 cm In-

median, backwardly projecting process and the anterior thickened

borderofthenuchalof Chelonia The reduction in the

anterio-pos-terior direction reallyappears tohave gonefurtherthanin

been removed, so that it, as well as the other borders, are jagged

and thin. In Protostegait is the hinderborderofthe bone which has

been removed

somewhat bevelled, so as to look downward and forward Onthe

upper surface, near the anteriorborderon each side, isabroad

body of the nuchal probably reached the firstneural It mustthen

on the under surface ofthe nuchal notuberclefor articulation with

the last cervical vertebra

plates, such-as is found in Dermochelys, the remains here described

afford no light. No evidence of its presence has been furnishedby any of the specimens of Protostega so farproduced It isneverthe-

lesstooearly to assure ourselve that there was no such a structure,

whichwas being tumbled about bythe waves and dragged byvorous lizards.

Protostega The vertebras, like the remainder of the skeleton, had

relation-ships to the vertebral axis were thusrendered obscure

thought that some of these vertebrasbelonged to the dorsal region.Otherswere regarded asappertaining to the neck.

axis, ina specimen of Chelonia with carapace 790mm. longis 35 mm.

Nov.2i,i895 SKELETON OF Protostega gigas HAY.

cer-vical would have a length ofabout no mm Thelongest vertebrain

sur-face It is quite improbable therefore that it belongedto the

as beingso small,the conclusion wasreachedthat eithertheexpanded

proximal ends interfered with each otherin themiddleline or the

ribsmust havebeenarticulated to diapophyses Since,however,the

and would have been proportionally wide, while the widest rib

be-lieving that any rib touched eitherits fellowor its neighbors The

to 275 mm., and the next twoor threewerenot much shorter In

conclude thatthere were wide spacesbetween the ribseven nearthe

asadvanced a stage of reduction as theyhavein Dermoehelys Their

of Protosphargis

of theskull the sameas that foundin Thalassochelys, I canmake the

whole length of the skull, including the supraoccipital spine, only

about 1 8 inches, or 45 cm Thedistance fromthe snoutto the dyle wouldbeclose to 13 inches,or 32cm Professor Cope's specimen,

con-judging fromthe size ofthe plastralbonesin his possession,was not

measuredto the condyle, we shall notmake ittoo great

62 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL.

skull onplatesX and XI ofthe workcitedrendersit highlyprobable

postfrontal; while the figureonplate XI, said torepresent thefrontal, really portrays the maxillary, prefrontal, vomer, and pala-

post-tine. In such case, the length ofthe skull would be abouta fourth

greater, or 40 cm

ofabout 31 to 24. Hence the length ofthe carapaceofmyspecimen

musthave been close to 3.i metres Theneck ofourliving marineturtles projectsbeyond the front of the carapace a distance equal to

atleast one-sixthofthe length ofthe carapace Hence, we are safe

there-fore forthe length ofthis turtlethe following figures:

Carapace 3.10

62 Finn ;Y, VOL i.

'

the ,iry, prefron

post-skullwouldbe al <urth Ionia has aratio to the :

24 V >fthecarapaceofmy

been close to3.1 metres .< of our living marine

;.s beyond the frontof the carapace a distance equal to

At least on?-&uth of the length ofthe carapace Hence, we are safe

there-fore for the length of thisturtle tl iigures:

Skull ofCervus ? Female

Fig i. View from above.

side.

ZOOLOGY,

Skull of Cervussteerii. Male.

side.

'

Skull of Cervus steerii. Female.

Fig i. Viewfromabove.

side.

Skull of Tragulus nigricans. Male.

Fig i. View from above.

side.

Skull ofPteropusauri-nuchalis. Male.

Fig i. View from above.

Skull of Pteropuslucifer. Male.

Fig i. View from above.

2 " "

side.

ZOOLOGY,