papers of the michigan academy of science, arts, and … · 2014. 11. 2. · p. s. petrolei was...

PAPERS OF THE MICHIGAN ACADEMY OF SCIENCE, ARTS, AND LETTERS VOL. L I , 1 9 6 6 ( 1 9 6 5 MEETING)

T U R T L E S O F T H E G I L L I L A N D F A U N U L E F R O M T H E P L E I S T O C E N E O F K N O X C O U N T Y , T E X A S

R O B E R T E. P R E S T O N

Oberlin College

DURING the years 1956-58 and 1962, W a l t e r W . Dalquest , C l a u d e W . Hibba rd , a n d W i l l i a m G. Mel ton , J r . collected fossil ver tebrates and mollusks from exposures of the Seymour Format ion a long the va l l ey wa l l s of the South W i c h i t a R i v e r in Knox County, T e x a s . Among the ver tebrate r emains is a l a rge tur t le fauna collected by Dalquest . T h e fami ly T r i o n y c h i d a e (aqua t ic ) a n d the fami ly T e s t u d i n i d a e (aqua t ic genus Pseudemys; terrestr ial genera Terrapene, Geochelone and Gopherus) are we l l represented by bony-shell e lements . Discussions of the aqua t i c tur t les a n d ment ion of the terrestr ia l species are conta ined in this report, a long w i t h a discussion of the aqua t i c hab i t a t and the c l imate of the faunule to which they belong.

T h e Seymour Format ion was n a m e d by C u m m i n s (1893, p . 1 8 1 ) . According to S t r ick l in (1961, p . 1 9 ) , the Seymour Format ion " and younger a l l u v i u m immed ia t e ly west of Seymour, T e x a s , a re the l a t e ra l accretions of two streams—the northerly-shift ing Brazos a n d an easterly-shifting former t r ibu ta ry of the Brazos." A measured section is presented by Getz and H i b b a r d ( 1 9 6 5 ) . T w o faunules have been recovered from the formation. T h e Vera faunu le (Getz and H i b b a r d 1965) l ies direct ly benea th deposits of Pear le t te ash and is equ iva len t to the C u d a h y fauna (late Kansan) of Kansas (H ibba rd 1944 and 1958; Paulson 1961) , Ok lahoma (Leonard 1950) , a n d T e x a s (Johnston and Savage 1 9 5 5 ) . T h e Gi l l i l and faunule (H ibba rd a n d Dalquest 1960 and 1962; Mel ton 1964) which contains the tur t les is from the lower three strata, consisting of sand and gravel i n t e rmixed w i th sandy sil t and red clay lenses. T h e faunule recovered from these lower un i t s is I rv ing ton ian in age (Savage 1951, p . 2 8 9 ) . T h e fauna l assemblage of the I rv ing ton ian (post-Blancan and p re -Rancholabrean) is character ized by some

unadvanced m a m m a l i a n species compared wi th the R a n c h o l a b r e a n and by the absence of Bison. H i b b a r d and Dalquest (1962) have

221

Plate I. Pseudemys scripta bisornata carapace and plastron (UMMP 46756) .

Turtles of the Gilliland Faunule 225

FIG. 1. Pseudemys scripta bisornata nuchal (UMMP 46692) . X 2

T A B L E I I

PLASTRON MEASUREMENTS (IN mm) OF GILLILAND Pseudemys

Forelobe Hindlobe UMMP Catalog No. Plastron Length Length X Width Length X Width

46674 130-135 60 X 70 74 X 74 46680 162 75 X 80 91 X 87 46748 — — 126 X 126 46753 162.5 75 X — 89 X 84 46756 152 73 X 73 80 X 80

Discussion— Most of the G i l l i l a n d ma te r i a l referable to Pseudemys was identif ied as such by W a l t e r Auffenberg. T h e bones wi th diagnost ic features—nuchals (preneurals) and p las t ra l bones—all be long to the P. scripta g roup. Descriptions of two fossil P. scripta from T e x a s are summarized by H a y ( 1 9 0 8 ) . T h e G i l l i l a n d speci-

226 Robert E. Preston

mens are ident ica l w i th the form described by Cope from an unknown s t ra t igraphic posit ion in Atascosa County. P. s. petrolei, described ear l i e r by Le idy , possesses features of the nucha l bone and epiplas t ron which do not agree wi th the G i l l i l a n d ma te r i a l bu t which are iden t ica l w i th corresponding features of Recent P. s. scripta, the easternmost subspecies of the g roup . At the present t ime it seems reasonable to r e t a in as subspecific designat ions specific names given by ear l i e r authors to Pleistocene fossils since subspecific stocks could have ar isen du r ing g lac ia l or in te rg lac ia l periods.

On the basis of l imi ted studies of Recent skeletal ma t e r i a l in the Univers i ty of M i c h i g a n M u s e u m of Zoology (a series of 10 P. s. scripta from eastern North Caro l ina , 12 P. s. elegans from northwestern Tennessee , 16 P. s. elegans from Cameron County, T e x a s , and 7 P. s. ornata from var ious local i t ies in Cent ra l Amer ica ) , I have found the fol lowing apparen t c l ine of bony shell characters in the Pseudemys scripta g roup. In the southeastern U . S., the subspecies P. s. scripta has the an te r ior edge of the epiplas t ron rounded off and not serrate; the carapace and nucha l bone modera te ly keeled middorsa l ly ; the nucha l l a m i n a long, narrow, a n d strongly set off by deeply impressed sulci; and the first central l a m i n a nar row anter ior ly re la t ive to the m a x i m u m w i d t h of the nucha l bone.

As the range of the Cent ra l Amer i can subspecies, P. s. ornata, is approached, the m e d i a n ca r ina becomes less pronounced or is absent; the first centra l l a m i n a becomes wider an ter ior ly re la t ive to the m a x i m u m nucha l bone wid th ; and the nucha l l a m i n a becomes shorter, wider , and de l inea ted by shal lower sulci . T h e anter ior edges of the ep ip las t ra are acute and serrate except in P. s. scripta. T h e above-mentioned i ndex of central l a m i n a anter ior w id th is presented in T a b l e III for var ious Recent popula t ions and fossil specimens of Pseudemys scripta. P. scripta nucha ls and ep ip las t ra from the G i l l i l and faunule are s imi la r to those of the subspecies P. s. elegans and P. s. ornata. T h e turt les can be considered ident ica l wi th Recent P. s. elegans except for shell thickness.

Description of the population.—Approximate total lengths were computed from measurements on bones of 49 ind iv idua l s . T h e proport ions used were taken from U M M P 46756 and are close to the average proport ions in Recen t P. s. elegans. T h e average estim a t e d carapace leng th is 187 m m (7.4 in ) w i th a m a x i m u m of 269 m m (10.6 i n ) . . T h e s e va lues are s imi la r to corresponding da ta from Recent popula t ions of P. s. troostii and P. s. elegans bu t fall

FIG. 2. Carapace-length distribution of Gilliland faunule Pseudemys based on estimates from individual bones.


short of the average and m a x i m u m for M e x i c a n and Cent ra l American races (Carr 1 9 5 2 ) . La rge turt les (greater than 225 m m carapace length) are more common in the fossil g roup than they are in Recen t collections. T h i s may be due pure ly to the circumstances of " col lect ing." A series of specimens from Cameron County, T e x a s , has an average carapace leng th of 194 m m .

T A B L E III

RATIO OF WIDTH OF NUCHAL BONE TO ANTERIOR WIDTH OF FIRST CENTRAL LAMINA

FOR FOSSIL AND RECENT SPECIMENS OF Pseudemys scripta ( = TRACHEMYS)

Nuchals Similar to P. s. scripta Nuchals Similar to P. s. elegans

Trachemys sculpta = 2.20 Trachemys bisornata = 1.67 (Hay 1908) (Hay 1908)

Trachemys sculpta = 2.03 Trachemys bisornata = 1.75 (Gilmore 1930) (Hay 1916)

Trachemys euglypha = 2.04 P. s. bisornata = 1.58 ± 0.14 (Hay 1908) (Gilliland Faunule)

Trachemys petrolei = 1.85 P. s. elegans = 1.70 ± 0.28 (Hay 1908) (Texas)

P. s. scripta = 2.02 ± 0.17 P. s. ornata = 1.45 ± 0 . 1 3 (North Carolina) (Central America)


T h e d is t r ibu t ion of carapace lengths in the popu la t ion (Fig. 2) reflects the smal l amoun t of sexua l d imorph i sm character is t ic of the species. Other members of the fami ly d i sp lay this phenomenon to an even grea te r degree. T h e b imoda l d is t r ibut ion is st i l l apparen t when plas t ron parts , none of which fit together, from 29 ind iv idua l s are measured and plot ted. T h i s fact min imizes the possibil i ty that the d is t r ibu t ion is a resul t of dup l i ca t ion in measur ing carapace and plas t ron par ts .

I t is immed ia t e ly evident that the average bony shell thickness of the G i l l i l a n d popula t ion is grea ter than the average for any of the Recent cont inenta l North Amer ican subspecies. Diet and other env i ronmenta l factors are known to influence shell thickness, and it is possible that selection m a y have increased the average shell thickness of a popu la t ion du r ing this par t of the Pleistocene. Only the Pleistocene fossil representat ives of the genus are thick-shelled. T h e phenotypic na tu re of the shell thickness i n the popu la t ion is suggested by the d a t a presented i n Fig. 3, where a conservative i n d e x of shell thickness is plot ted against size a n d compared w i th a series of 16 Recent P. s. elegans from Cameron County , T e x a s . Thickness as a function of size is non l inea r over par t of its r ange in the fossil group, whereas the re la t ion i n the Recen t popu la t ion is more or less l inea r . A series of smal le r specimens from Reelfoot L a k e , Tennessee, a l t hough more va r i ab le in this character , shows the same l inear i ty . Ex t rapo la t ing the graphs for any of these popula t ions ( inc lud ing a smal l series of P. s. scripta from North Carol i n a ) , leads to the conclusion that shell thickness is i n rough ly the same range of va lues for young i n d i v i d u a l s of each subspecies.

Pleistocene distribution.—before m a n y conclusions can be d r a w n rega rd ing the d is t r ibut ion of fossil Pseudemys, firsthand study of the fossil ma te r i a l is requ i red . Add i t iona l col lect ing wi l l , of course, prove necessary and i nva luab l e . For thcoming conclusions wou ld be ex t remely v a l u a b l e as a check on, if not a pa r t i a l basis for, the systematics of Recen t members of the group, which has a lways been a p roblem to herpetologists . For a p r e l im ina ry look at the Pleistocene P. scripta, i t is useful to adopt tenta t ively the characters ment ioned ear l i e r for separat ion of the eastern subspecies, P. s. scripta, from the r e m a i n d e r of the group. H a y (1908) gives a descript ion of P. s. petrolei (Le idy ) based upon a nucha l bone and two epip las t ra from T e x a s ; These bones are very s imi la r to the nucha l and epiplas t ron of Recen t P. s. scripta. T h e anter ior edge of the

Turtles of the Gilliland Faunule 2 2 9

epiplas t ron is not serrate, a n d the first central l a m i n a is nar row re la t ive to the m a x i m u m w i d t h of the nucha l bone ( T a b l e I I I ) . H e also (1916 and 1923) inc ludes P. s. bisornata, previously described by Cope (1878) from T e x a s , w i th ma te r i a l from an unknown horizon in the Vero beds, St. Luc ie County , Flor ida . S t ra tum 3 at this local i ty conta ins h u m a n remains .

T h e present d is t r ibut ion of the subspecies of P. scripta is c lear ly

FIG. 3. Thickness of plastron at symphysis of epiplastra as a function of size (measured by width of epiplastral lip) for Pseudemys scripta bisornata (Gilliland faunule) and P. s. elegans (Cameron Co., T e x a s ) .

the resul t of geographic and c l imat ic condi t ions a l t e rna te ly separa t ing and re jo in ing ancestral popula t ions (Carr 1962, p . 2 7 9 ) . One popula t ion , P. s. troostii, a long the western slopes of the Appalach ians i n Kentucky and Tennessee d isplays in t e rg rad ing characters between P. s. elegans to the west and P. s. scripta on the eastern slope. No geographic over lap of P. s. troostii w i t h e i ther of these subspecies has been demonstra ted, a l t hough C a r r (1952, p . 259) ascribes this mere ly to lack of collect ing. Popula t ions of P. scripta are capab le of ex t remely r a p i d mig ra t ion as has been discovered


from observation of an ar t i f ic ial ly in t roduced popu la t ion in Michi gan and from other suggestive evidence (see Car r 1952, p . 2 5 0 ) . T h e above-mentioned records ind ica te the occurrence of P. s. petrolei in T e x a s (nucha l and epip las t ron s imi la r to Recen t P. s. scripta of the southeastern U . S . ) , and of P. s. bisornata (nuchal s imi la r to Recen t P. s. elegans of the centra l and western U . S.) i n F lor ida . From this a case can be m a d e for: (1) a previous, more extensive d is t r ibu t ion of both Recen t subspecies or the i r Pleistocene counterpar ts at different t imes; (2) the i r subsequent d i sappearance from parts of their respective ranges; and (3) the re invasion by the popula t ions now occupying those par ts of their ranges . For an e x a m p l e : d u r i n g a w a r m a n d / o r dry per iod turt les s imi la r to P. s. scripta may have shifted nor thward a n d turt les s imi la r to P. s. elegans moved eas tward into F lor ida ; and, conversely, du r ing a cool a n d / o r moist per iod s. elegans-like tur t les m a y have moved southward into Mexico and s. scripta-like turt les wes tward in to T e x a s . P. s. petrolei was found in a b i t u m e n horizon i n H a r d i n County , T e x a s (Hay 1908) , i nd ica t ing a moist per iod. On the other h a n d the centra l por t ion of the P. scripta g roup , consisting of the subspecies s. troostii, s. elegans, and s. gaigeae, may be a system of in tergrades between two pre-Pleistocene stocks—one in the southeastern U . S. and the other i n the southwestern U . S. and Mex ico .

Pre-Pleistocene records of Pseudemys scripta—The oldest fossil assigned to the genus is a plastron from the Chadron formation (Oligocene) of South Dakota (Cla rk 1 9 3 7 ) . H a y (1908) discusses

P. s. hilli Cope taken from the Lower Pl iocene deposits of Decatur County , Kansas. Records of Pseudemys from one la te Pl iocene and two H e m p h i l l i a n local i t ies i n Kansas were repor ted by Ga lbrea th ( 1 9 4 8 ) . P. s. delicata (Hay 1916) is based on a p l eu ra l bone from the la te Pl iocene i n F lor ida . T h e P. scripta g roup has been someth ing of a " ca tchal l " for ea r l i e r workers , no tably Hay . Auffenberg (1958) has removed one species, nuchocarinata ( H a y ) , wh ich does

not belong to Pseudemys. T h e disposit ion of some of Hay ' s Pleistocene species awai ts e x a m i n a t i o n of the types.

Habitat.—decent P. s. elegans are p r imar i l y herbivorous as adul t s and thus prefer some aqua t i c vegetat ion. T h e species inhabi t s lakes , coves, and oxbows of la rger r ivers and has been recorded from shal low pra i r i e ponds where the wa te r level may become too low to cover the shell (Car r 1952, p . 2 5 4 ) . T h e subspecies P. s. gaigeae,


occurr ing west of P. s. elegans, is recorded only from rivers bu t is thought to occur in essential ly the same habi ta t s as P. s. elegans.

Terrapene sp.

Par ts of at least two box tur t les are i n the collection. U M M P 46757 consists of the front par t of the carapace (nuchal , first a n d second neura ls , and first two p leura l s and per iphera l s on both s i d e s ) . U M M P 51876 is a fragment of the hyoplastron.

Subfami ly T e s t u d i n i n a e

At least three species are present in the faunule . T h e ma te r i a l w i l l be described by Auffenberg.

Geochelone sp. L a r g e Geochelone

T h e least incomplete specimens are U M M P 34825, 40601, a n d 47098. Measurement of No. 34825 (carapace) indicates a m a x i m u m wid th of about 100 cm (40 i n ) . T h e plas t ron of No. 40601 is approx imate ly 75 cm from the hyo-hypoplast ra l suture to the front, which makes the tur t le about 6 ft long. T h e par ts of No. 47098 are from an a n i m a l 4^ to 6 ft in length.

Geochelone sp. Sma l l Geochelone

(Fig. 4)

T h e carapace ( U M M P 46787) of this species (Fig. 4) is th in compared wi th that of the above species and belongs to Auffenberg's (1963) Turgida l i ne .

Gopherus nr . polyphemus

(Fig. 5)

U M M P 41509 (Fig. 5) is a complete plastron. Several other pa r t i a l plastrons from tur t les 18 in to 2 ft i n length are present. U M M P 41508 from Burne t t R a n c h is the complete an te r ior pa r t of the shell. T h e tur t le was 47 cm wide at the a x i l l a r y notch. According to Auffenberg (oral communica t ion) these specimens


are more s imi l a r to G. polyphemus than to other Recen t species

of the genus .

Habitat.—The h ab i t a t preference of the nonbur rowing g ian t Geochelone is extensively discussed by H i b b a r d ( 1 9 6 0 ) . T h e form could not h ibe rna te and thus demanded a c l imate of very m i l d winters . Recen t examples of Gopherus genera l ly i n h a b i t subt ropica l

FIG. 4 . Small Geochelone right anterior quadrant of carapace ( U M M P 4 6 7 8 7 ) .

areas of the world , a l though three smal l species occur i n the southern U . S. i n semiar id or savanna s i tuat ions. Recen t G. polyphemus i nhab i t s dry, u p l a n d regions in F lor ida and the Gulf coastal p l a i n west to Lou i s i ana . A la rger Recen t species, G. flavo-marginatus, occurs i n north-central Mex ico (Legler 1959) .


F A M I L Y TRIONYCHIDAE

Trionyx spinifer ssp.

(Fig. 6)

U M M P 39371 (hypoplastron) ; No. 40602 (near ly complete except skul l a n d x iph ip l a s t r a ) ; No. 46682 (p leura l bone) ; and

FIG. 5 . Large Gopherus plastron ( U M M P 4 1 5 0 9 )

plas t ron fragments Nos. 46671, 46681, a n d 46706. T h e hypoplas t ron ( U M M P 39371) is somewhat th icker (9 m m ) than the average

for Recent T. spinifer. It represents a tur t le of 30-35 cm ( lea thery)


FIG. 6. Trionyx spinifer carapace, hyoplastra and hypoplastra ( U M M P 40602) .

Discussion.—Hay records Pleistocene Trionyx (= Amyda) from V i r g i n i a ( 1 9 2 3 a ) , from two local i t ies i n F lor ida (1908, 1927) , and from T e x a s ( 1 9 2 4 ) . T h e T e x a s specimen is from deposits a long

carapace length , close to the m a x i m u m for Recent ind iv idua l s . T h e other plastron fragments are from even la rger softshells. U M M P 40602 (Fig. 6) represents a tur t le 12-15 cm long. Inc luded wi th this specimen are l i m b and g i rd le bones.


the Brazos R i v e r at P i t tbr idge . One of the F lor ida specimens is assigned to the species ferox, and the T e x a s specimen is p laced in 1\ emoryi on the basis of geographic locat ion. Ga lbrea th (1948) records Trionyx fragments from Seward and M e a d e counties, Kansas, possibly of Pleistocene age. It is impossible to d is t inguish between T. spinifer and T. ferox on the basis of shell osteology. T. ferox i s a species considered ind igenous to Flor ida , a n d there is no evidence to ind ica te i t has ever had a wider d is t r ibut ion than it has at present. T h e r e is a fourth North Amer ican species of softshell, T. ater, which is weak ly differentiated from T. spinifer, a n d wh ich cannot be d i s t inguished from spinifer osteological ly. T h i s species occurs in clear-water ponds i n Coahu i l a , Mexico , about 500 mi les south of Knox County. It is not l ike ly that i t occurred in the G i l l i l a n d faunule . T h e species spinifer consists of several races showing more or less consistent characters w i t h i n each race according to the d ra inage system each inhabi t s . T h e Recent subspecies found in the Brazos R i v e r d ra inage is T. s. pallidus W e b b ( 1 9 6 2 ) . T h e r e is no publ i shed fossil record of the th i rd species of

softshell, T. muticus. W e b b (1962, p . 474) compares the bony plastrons of T. spinifer and T. muticus. Among other d i s t inguish ing features, the l ine bisect ing the d iv ided outer projection of the hypoplas t ron makes an angle of about 30° w i th the hyo-hypoplastral su ture i n spinifer. T h e same ang le is close to 45° i n muticus.

Habitat.—The Recent T e x a s subspecies T. s. emoryi is sa id by Cope (Carr 1952, p. 425) to be " abundan t in a l l pe rmanent water " in northwestern T e x a s . T h e h igh p la ins race, T. s. hartwegi, is obl iged to be more strictly f luviat i le . In any case, these a n i m a l s r equ i r e a soft bottom, of silt or sand, consistent w i th their feeding habi ts . T h e water must have been sufficiently slow-moving to deposit sand and also to provide an abundance of the inver tebra te fauna (pa r t i cu la r ly crustaceans and annel ids) compris ing the t r ionychid diet .

ASSOCIATED FORMS, C L I M A T E , AND HABITAT

Inc luded in the r ema inde r of the herpetofauna are bones of Alligator sp. T h e envi ronmenta l condit ions r equ i r ed by this a n i m a l are i n accord wi th the p ic ture presented by the che lonian fauna; namely , gene ra l ly w a r m tempera tures a n d the presence of permanent wa te r con ta in ing some vegetat ion (H ibba rd 1960, W o o d b u r n e 1959) . T w o species have been repor ted by Pierce Brodkorb from


the G i l l i l and av i fauna : Caracara pretulosa (Howard) (Brodkorb 1964a) and Agriocharis anza H o w a r d ( H i b b a r d 1960, Brodkorb 1 9 6 4 b ) . T h e la t ter species is re la ted to the Recent ocel la ted turkey, A. ocellata ( C u v i e r ) , of southern Mex ico and Cent ra l Amer ica . Payn te r (1955, p . 84) inc ludes in the hab i ta t s of this turkey " Open deciduous forest, savannas, milpas, and other c lear ings . . . " A. anza is known also from the M i d d l e Pleistocene of Ca l i fo rn ia (Brodkorb 1964a, p. 3 2 4 ) .

T h e Recent North Amer ican caracara , Caracara cheriway (Jac-q u i n ) , ranges from the southern U . S. to Cent ra l Amer ica . It occurs in p ra i r i e s i tuat ions i n F lor ida (Howel l 1932) . Of inc iden ta l interest is Nicholson's (1928) observation that smal l tur t les are the p r inc ipa l food of the caracara i n F lor ida (Howel l 1932, p . 1 8 6 ) . C. pretulosa was o r ig ina l ly described from the Uppe r Pleistocene tar pi ts of Cal i forn ia and occurs i n the M i d d l e Pleistocene of F lor ida (Brodkorb 1964a, p . 2 9 2 ) .

C l a u d e W . H i b b a r d (oral communica t ion) stated that the large numbers of camels and tapirs (browsers and grazers) and also the la rger number s of g lyptodons and horses (grazers) ind ica te a savanna s i tuat ion. T h e abundance of vegetat ion, as wel l as affording posit ive evidence of a grea ter ra in fa l l for the region a t that t ime, precludes a r id i ty as a feature of the c l imate . Other m a m m a l s occurr ing in the faunule are mammoths , mastodons, g round sloths, a g i an t a rmad i l l o (H ibba rd 1960) , peccaries, deer, and two genera of pronghorns ( H i b b a r d and Dalquest 1 9 6 2 ) . Mel ton (1964, p. 129) indica tes the gene ra l ly southern d is t r ibut ion of g lyptodons in North Amer ica and points to their l a rge size and common occurrence in the G i l l i l and faunu le as evidence i n favor of H ibba rd ' s (1960) genera l conclusions r ega rd ing the p reva i l ing c l imate . Getz

and H i b b a r d (1965) discuss extensively the c l imate of the Vera faunule .

T h e preferred hab i ta t s of each of the two a q u a t i c tur t le species have been ment ioned . T a k e n together they represent quieter-flowing port ions of r ivers and streams, or isolated ponds, w i th sand bottoms and some vegetat ion. Since specimens of these forms are abundan t , the absence of other r iver -dwel l ing tur t le species is conspicuous. T h e genera Chelydra and Kinosternon are associated wi th mud-bottom habi ta t s and at least some aqua t i c vegetat ion. T h e r e is no f luviat i le clay in the horizon from which the tur t le fauna was recovered; ins tead the gravel , sand, and sandy sil t bot tom of a modera te ly fast-flowing r iver . T h e genus Graptemys r equ i res


a b u n d a n t vegetat ion. T h e spineless softshell, T. muticus, presently inhab i t s only Mississippi d ra inage . Its absence from the faunu le is not unexpected . T h e lack of any Pseudemys floridana or P. concinna ma te r i a l from this or any other Pleistocene local i ty west of Flor ida , pa r t i cu l a r ly among such a l a rge collection of scripta specimens, suggests that the floridana g roup m a y be a re la t ive latecomer to the T e x a s region. T h e a l l i ga to r snapper (Macroclemys temminckii) could be expected to occur i n this habi ta t . Its present d i s t r ibu t ion inc ludes the Brazos R ive r . Aside from this possibil i ty, however, and provided the absence of other forms ment ioned is due to condit ions of habi ta t , the aqua t i c port ion of the tur t le fauna , a l t hough consisting of only two species, can be considered complete .

ACKNOWLEDGMENTS

I wish to thank C l a u d e W . H i b b a r d of the M u s e u m of Paleontology for gu idance and for the oppor tuni ty to do this work and W i l l i a m G. Mel ton , J r . for his ideas and i nva luab l e inst ruct ion in p repara t ive technique . I a m grateful to Char les F. W a l k e r , George Zug a n d K. K. A d l e r of the M u s e u m of Zoology for the loan of Recen t ma t e r i a l and add i t iona l gu idance i n this study. W a r r e n F. W a l k e r , J r . cont r ibuted helpful cr i t ic ism of the manuscr ip t . Pa r t i cu la r g ra t i tude is due the la te Norman E. Har tweg for communica t ing to me a par t of his great devotion to science. His insp i ra t ion w i l l cont inue to serve me i n future study.

T h e artists were Kather ine Strand, Bonnie Ha l l , and B a r b a r a Gagnon Bi lge . T h e p la te was p repared by Karoly Kutasi .

F inanc ia l support for the field work in 1962 was accorded by the Na t iona l Science Foundat ion , Project G-19458.

L I T E R A T U R E C I T E D

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