n*entilkilt ilil Biok,gr', 1995. l(-l):19: 1995 by CheloninD Research Foundltion Geographic Variation in the Matamata Turtle, Chelus fimbriatus, with Observations on its Shell Morphology and Morphometry MlncBLo R. SANcnnz-Vu,urcnAr, PnrER C.H. PnrrcHARD:, ArrnEro P.rorrLLo-r, aNn Onan J. LINlnBs3 tDepartment of Biological Anthropolog-,- and Anatomy, Duke lJniversin' Medical Cetter. Box 3170, Dtu'hcun, North Carolina277l0 USA IFat 919-684-8034]; 2Florida Audubotr Societ-t, 460 High,n;a,- 436, Suite 200, Casselberry, Florida 32707 USA: iDepartanento de Esttdios Anbientales, llniyersitlad Sinzrin Bolltnt", Caracas ]O80-A, APDO 89OOO l/enerte\a Ansrucr. - A sample of 126 specimens of Chelusftmbriatus was examined for geographic variation and morphology of the shell. A high degree of variation was found in the plastral formula and in the shape and size of the intergular scute. This study suggests that the Amazon population of matamatas is different from the Orinoco population in the following characters: shape ofthe carapace, plastral pigmentation, and coloration on the underside of the neck. Additionatly, a preliminary analysis indicates that the two populations could be separated on the basis of the allometric growth of the carapace in relation to the plastron. Kry Wonus. - Reptilia; Testudinesl Chelidae; Chelus fimbriatus; turtle; geographic variationl allometryl sexual dimorphism; morphology; morphometryl osteology; South America 'Ihe matamata turtle (Chelus fimbricttus) inhabits the scute morpholo..ey. Measured characters (in all cases straight- Amazon, Oyapoque. Essequibo. and Orinoco river systems line) were: maximum carapace len.-uth (CL). cArapace width of northern South America (Iverson. 1986). Despite a mod- at the ler,'el of the sixth marginal scute (CW). and midline erately good generic fossil record (Wood.1976: Bocquentin plastral length (MPL: LSMV of Medem. 1976). Midsearn and Rancy .,l98l; Bocquentin. 1988: BocqLlentin and Santos. length of the inter-eular (lG ). gular (G ). humeral (H),, pectoral 1 989; S6nchez-Villa.-qra. 1992: Sdnchez-Villasra et al.. I 993. lPl. abdominal (AB ). femoral (F). and anal (AN) scutes was alon-e lon-e plastron. Instead 1995) and the -.ereat interest show'n in this species by herpe- measured the axis of the of tologists, naturalists. and turtle hobbyists (see Pritchard and measllrin,_e the gular scute alon-9 one of the contact seams and the inter-eular (as in Lovich and Ernst, Trebbau, 1984, for a review), there are no quantitative between the -gulars studies of its morphology and morphometry. Such studies 1989), it was measured alon-e the long axis of the plastron, as are necessary to understand the individual and geographic in Ernst and Lovich (1986). In the method of Lovich and variability of this turtle and to clarify the systematics of the Ernst ( 1989), the contact between the gulars (when present) fossil species of the genus. is not considered, and a large amount of error is thereby Pritchard and Trebbau ( I 984) reviewed the few pub- introduced, in addition to the error introduced by the highly lished growth data for South American pleurodires. Geo- variable shape and size of the intergular. Variation in the graphic variation has been mentioned in some published plastral formula (PF) for each population was quantified studies of the matam ata, but the limited observations using the "measure of plastral variation" (MPV;Lovich and made have sometimes been based upon very small samples Ernst, 1989) and measures of diversity were calculated using (e.g., Medeil, 1960; Schmidt, 1966). This paper presents the Shannon-Weiner index (H'; Lovich et al.. 1991). We the results of a study of individual and geographic varia- used the Jaccard coefficient as a similarity measure to tion and various aspects of the morphology and mor- compare the plastral formulae of the Am azon and Orinoco phometry of the shell of Chelus fimbriutus. Nomencla- samples (see Lovich et al., l99l). ture of shell elements follows Pritchard and Trebbau Observations made by Medem (1960). Pritchard and ( l e84). Trebbau (1984), and in this work indicate that an analysis of geographic variation should include the tollowin-e qualita- MATERIALS AND METHODS tive characters: intergular shape. color pattern on the ventral side of the neck, presence of dark plastral pi-umentation. and A sample of 126 specimens (123 preserved and 3 living) carapace shape. The shape of the carapace \\'as characterized of Chelus fimbriatus was examined. The sample embraced dichotomously as follows: almost the entire known geographic distribution of the "rectangular," when the distal ed-9es of marginal species (Fig. 1, and list of Specimens Examined). Twenty- scutes 4-8 and the central lon-e axis of the carapace are one additional specimens from a single locality in the Estado parallel; and Cojedes, Venezuela, were examined by PCHP and are used - "oval," when the parallel-sided section of the cara- here only to show intrapopulational variability in intergular pace is restricted to mar-einals 5-7 . le+ CHel-oNtnN CoNSERVATToN AND BroLoGy, Volume I, l{untber 1 - 1995 Figure l. Map of northem South America showing the localities from which specimens were examined. Specimens of uncertain provenance were not included here. A chi-square test was performed to examine the rela- the slopes for the two populations were homogeneous in tionship of the shape of the carapace to the provenance of the each case, ANCOVAs were performed. All variables were specimens (Conover, 1980). Only specimens with CL longer tested and found to be normally distributed. than 145 mm (n - 108) were considered for this analysis, The sex of many skeletal specimens was uncertain, so since hatchlings and small juveniles do not present a com- rigorous analysis of sexual dimorphism was not possible. pletely ossified shell with a well detined shape. Localities Observations were made on the normal range of variation as (except for outliers) were classified as belonging either to well as abnormalities in the shell scutes or bones. Sample the Amazon or to the Orinoco river systems. Such division size for the analyses performed varies since the state of is justified by the observations of Medem ( 1960), Pritchard preservation of the specimens was heterogeneous (some and Trebbau ( 1984), and those in this work. The Amazon consisted of shells without scutes, some were preserved in and Orinoco hydrographic systems do make contact, with liquid so the bony sutures could not be seen, etc.). Addition- the Brazo Casiquiare in Venezuela the most important ally, the complete sample could not be used for the analysis connection between the two (Sioli, 1984). Our sample does of geographic variation, as 38 specimens were of unknown not include specimens from the Casiquiare. locality. Preliminary calculations were performed to test for differences between the Amazon and the Orinoco popula- RESULTS tion in proportions of the shell during growth. Analyses of covariance ANCOVA (Sokal and Rholf, 198 l) were per- Morphology and Morphometry formed using the statistical package BIOM@ (Rholf, 1988). We used midline plastral length, MPL, as the covariate Neural Bones. Chelas is unusual among chelids (as because of its relatively flat configuration, as straight-line is Hltdromedusa) in- havin-e well-developed neural bones carapace length measurements may not reflect hidden growth forming a continuous series. Ther. are unusually thick, masked in its convexity and sculpturing (Ernst and Lovich, dorsally forming a wide. tuberculate keel. \rentrally the 1986; Lovich et al., 1990). The dependent variables were CL neurals provide part of the concar itr on each side of the and CW. so two different sets of tests were performed. Plots midline that, together u'ith contributions tiom the pleurals of the data showed their relationships to be linear, with and the free proximal parr of the nL,S. u-onstitutes the tunnel- logarithmic conversions not necessary. After checking that like Channel that hOUSeS the .r.,,1:,;;r17r.:t_, c/crl-si mUSCleS. SnrucHez-Yl-tAGRA Er AL. Geographic Variation in Chelus 295 - fimbriatus Pleural Bones The pleural bones of Chelus normally number eight pairs (nine on the left side in PCHP 1209 because of a subdivision of the last pleural). Even a single, isolated Chelus pleural bone is immediately identifiable by its unique and highly distinctive sigmoid shape. The first pair of pleurals is anteriorly elongated, as are the first neurals, the nuchal bone, and the neighboring peripherals. There is some tendency towards alternation in width of the proximal and distal ends of subsequent pleurals, with pleural III having a widened proximal end (corresponding to the elongated vertebral III), and pleurals II and IV being distally widened. In one individual (PCHP 1230), represented only by an incomplete set of shell bones, two of the left pleural bones (III and IV) have become completely fused, although all other bony sutures in this relatively small (CL ca.310 mm ) male were unfused. Many of the carapace bones of this specimen showed severe pitting, similar to that illustrated by Zangerl (1969) for the fossil cheloniid Oligochelone rupeliensis, but the erosive disease does not appear to have caused this isolated unilateral bony fusion. In nearly all cases (44 of 48,92Vo),, the eighth pleurals meet behind the last neural, separating the latter from the Figure 2. Intergular shape variation in a single population of Chelusfintbriatus from Estado Cojedes, Venezuela. The drawings single triangular suprapygal. There is no contact between the are not to scale. last pleurals in four specimens (AMNH 591 1, AMNH 70638, PCHP 39 (Fi-u.3). PCHP 1038), in which the last neural The typical condition of seven neurals was found in 38 contacts the suprapygal. out of 4 4 (86To) specimens examined. Five individuals in the Mcrrgirtal Scutes artcl Periplteral Bones. Most of the sample have eight neural bones, either by the transverse specimens shou'ed l2 pairs of mar-ginal scutes- (86 of 90, division of neural I (PCHP 39, FSM 22266) or of neural VII 96%).Onl1' tour specimens (AMNH 70638, MCNM un- (AMNH 59 1 1 , PCHP 1209) or by the insertion of an azy-sous nunrbered.