A COMPARISON OF THE PALATES OF PERMIAN AND TRIASSIC DICYNODONTS By A. R. I. Cruickshank ABSTRACT Whils cmparing he skulls f sme Triassic dicyndns wih Permian members f he family, i was ned ha he inerperygid space in he frmer is cnsisenly smaller han in he laer (Cruickshank 1965: 1967). In analysing his difference furher, he palaes f a series f Permian and Triassic dicyndns were examined, eiher direcly r frm published diagrams. Frm graphs drawn using he varius measuremens aken frm he palaes, he gelgical age f he specimens can be deduced as can heir esimaed lenghs, if fragmenary. THE DICYNODONT PALATE-GENERAL MEASUREMENTS I is pssible divide he dicyndn palae in fur main regins, here erme d " mu h", ". merna I nares ""., merperygol d" space an d "b ram-case " (fig. 1). The lenghs f hese regins, measured n he mid-line f he palae were pled n w series f graphs (figs. 2-6). The able f measuremens can be seen in Cruickshank (1962). Frm figure 2 i can be seen ha when he lenghs f he inernal nares and he inerperygid spaces are cmpared, hen in general, he inerperygid space f he Permian frms is greaer han 6% f he lengh f is inernal nares, whereas he value fr he Triassic frms is always less han 6%. I is cnsidered ha his is significan because dicyndns are he dminan fssil grup in he erresrial depsis f "Gndwanaland" and hey hus migh be used as sraigraphic markers where he mre cmmnly used macrfssils are missing. Oher measuremens were als pled see if here were her similar relainships beween he pars f he palae and hese are described belw. The lengh f he "muh" when pled agains he al lengh f he specimen shws in general a linear relainship beween he w parameers and n disincin beween Permian and Triassic frms is seen. The "muh" being abu 3% f he al lengh f he specimen, excep in he case f hse ver 4 mm, where he value drps belw his (fig. 3a). Where he lengh f he "muh" is expressed as a percenage f he al median basal lengh f he skull, n disincin can be drawn beween Permian and Triassic frms nce mre (fig. 3b). In general his cnclusin hlds gd fr all he graphs where he pars f he palae are expressed as percenages f he whle skull lengh. Hwever wih increased knwledge f he dicyndns and using prper saisical echniques, perhaps sme pins f ineres may emerge frm hese graphs (figs. 3b, 4b, 5b, 6b). 23
When he lengh f he "inernal nares" is pled agains al median basal lengh f he skull, a endency can be seen fr he Permian and Triassic frms separae u (fig. 4a). The lenghs f he "inernal nares" f he Triassic dicyndns ranges beween 2-23% f he whle, whereas hse f he Permian dicyndns range beween 13-15/ f he whle. Hwever, n cnclusins can be drawn frm his graph fr skulls f less han 15 mm verall lengh. A measure which migh be f value is cmpare he lengh f he inerperygid space wih he whle skull (fig. Sa). The inerperygid space f Permian dicyndns in he -15 nml range is always mre han 12% f he whle skull lengh. Even abve 3 mm verall lengh he inerperygid space is never less han 8% f he whle. On he her hand he majriy f Triassic dicyndns seem have an inerperygid space less han 8/ f he whle lengh f he skull, and nly ne has a value greaer han 12%. The lengh f he "braincase" (fig. 6a) seems bear a linear relainship he res f he skull in much he same way as he muh des, excep ha here seems be less deviain frm he sraigh line. This measure may be f use in esimaing he verall lengh f fragmenary specimens. DISCUSSION This ype f analysis is bes dne wih many mre specimens han were available in his insance. Thus n aemp has been made apply her han he ms empirical f inerpreains he graphs. In addiin, n accun has been aken here f he Upper Permian genus Cisecephallls. This genus has n inerperygid space, he area being filled wih a par f he parasphenid rsrum (Keyser, in press). Thus n place culd be fund fr i in his r similar analyses. Hwever Cisecephalus is already a ms impran zne-fssil f he Suh African Karr beds, even if i is aberran in he palaal regin. Cruickshank (J 967, p. 21) has already discussed he evluinary mechanisms which may have caused he niceable difference beween he lengh f he inerperygid spaces in Permian and Triassic dicyndns. As far as his paper is cncerned i shuld be ned (fig. 2) ha here seems be a crrelain beween he hrizns f he specimens measured and heir psiin n ha graph. Fr insance a grup f hree larger dicyndns (Dapcephalus leniceps (Owen» sraddles he 6% line and wards he lwer end f he size range a number f Lysrsaurus specimens are clse, bu sill n he "Triassic" side f he line. Dapcephalus (Ewer 1961) is a frm characerisic f he upperms Permian in Suh Africa and Lysrsaurus is he zne-fssil f he succeeding beds, which are f Lwer Triassic age. The her frms marked n he graph range hrugh he Lwer Middle Triassic, and end n he far righ wih Sahleckeria (vn Huene 1942) an upper Middle Triassic frm. Thus i seems pssible separae Permian and Triassic dicyndns n he 24
ne palaal characer wih cnfidence, bu wheher hese can be assigned a disinc hrizn wihin he era n hese grunds is uncerain a presen. I wuld like express my hanks Dr F. R. Parringn, F.R.S., f he Universiy Museum f Zlgy, Cambridge fr his help and encuragemen while I was his research suden. Dr K. A. Jysey helped cnsiderably wih he inerpreain f he graphs. Financial assisance was given by he Universiy f Edinburgh and he D.S.I.R. REFERENCES CRUICKSHANK, A. R. I., 1962. Eas African Triassic dicyndns. Ph.D. Thesis. Univ. Camb. CRUICKSHANK, A. R. I., 1965. On a specimen f he anmdn repile Kannemeyeria 1aifrns (Brm) frm he Manda Frmain f Tanzania, Tanganyika. hc. Linn. Sc. Lnd. 176, 149-157. CRUICKSHANK, A. R. I., 1967. A new dicyndn genus frm he Manda Frmain f Tanzania (Tanganyika). J. Zl. Lnd. 153, 163-28. EWER, R. F., 1961. The anamy f he anmdn Dapcephalus leniceps (Owen). Prc. zl. Sc. Lnd. 136, 375-42. HUENE, F. VON, 1942. Die Jssi1en Repi1ien des siidamerikanischen Gndwanalandes an der Zeienwende. Munich: C. H. Beck. KEYSER, A. W. (in press). On he mrphlgy f he anmdn genus Cisecepha1us Owen 1876. 25
EXPLANATION OF TEXT FIGURES Fig. 1. A. Diagrammaic represenain f dicyndn palae shw he regins discussed in his paper. B. Generalised diagram shw he regin arund he inerperygid space in Triassic dicyndns. C. The same fr Permian dicyndns. ECT -Ecperygid; PAL-Palaine; PM X-Premaxilla ; PSP-Parasphenid; PT Perygid; V-Vmer. ip.sp.-inerperygid space; ip. vac.-inerperygid vacuiy; lab.fs.-labial fssa. a-"muh"; b-"inernal nares"; c-" inerperygid space"; d-"braincase". Fig. 2. Fig. 3. Fig. 4. A. B. A. B. Graph shw he relainship beween he inernal nares (b) and he inerperygid space (c). All measuremens in mm. Graph shw he relainship beween he muh (a) and he al (median basal) lengh. All measuremens in mm. Graph shw he relainship beween he muh expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. Graph, shw he relainship beween he inernal nares (b) and he al (median basal) lengh. All measuremens in mm. Graph shw he relainship beween he inernal nares expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. Fig. 5. A. Graph shw he relainship beween he inerperygid space (c) and he al (median basal) lengh. All measuremens in mm. B. Graph shw he relainship beween he inerperygid space expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. Fig. 6. A. Graph shw he relainship beween he braincase (d) and he al (median basal) lengh. All measuremens in mm. B. Graph shw he relainship beween he braincase expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. 26
EXPLANATION OF TEXT FIGURES Fig. 1. A. Diagrammaic represenain f dicyndn palae shw he regins discussed in his paper. B. Generalised diagram shw he regin arund he inerperygid space in Triassic dicyndns. C. The same fr Permian dicyndns. ECT -Ecperygid; PAL-Palaine; PMX-Premaxilla; PSP-Parasphenid; PT Perygid ; V-Vmer. ip.sp.-inerperygid space; ip. vac.-inerperygid vacuiy; labjs.-labial fssa. a-"muh"; b-"inernal nares" ; c-"inerperygid space"; d-"braincase". Fig. 2. Fig. 3. A. B. Graph shw he relainship beween he inernal nares (b) and he inerperygid space (c). All measuremens in mm. Graph shw he relainship beween he muh (a) and he al (median basal) lengh. All measuremens in mm. Graph shw he relainship beween he muh expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. Fig. 4. A. B. Graph. shw he relainship beween he inernal nares (b) and he al (median basal) lengh. All measuremens in mm. Graph shw he relainship beween he inernal nares expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. Fig. 5. A. Graph shw he relainship beween he inerperygid space (c) and he al (median basal) lengh. All measuremens in mm. B. Graph shw he relainship beween he inerperygid space expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. Fig. 6. A. Graph shw he relainship beween he braincase (d) and he al (median basal) lengh. All measuremens in mm. E. Graph shw he relainship beween he braincase expressed as a percenage f he al (median basal) lengh, and he al (median basal) lengh. 26
B c & p v AL - CT PT / ip.vac. 7~AL '-(j I r- PT ip.sp Fig. 1 ~ 5 Permian Triassic 4 3 ~ 1 i A 6Y' Fig. 2 4 6 8.b. 27
21 18 Permian a Triassic i. /~ I./. Fig.3a 3 % 6....,j ;......... Fig.3b 28
21 18 23% 27 b 15 12 9 Permian Triassic 6 3 Fig.4a 78 4 bxloo al 3 2 Q;) T... ~ : :)... Fig.4b 29
5 Permian 4 Triassic 12~ ~'k 3 ~ 2. "* :; 1 p' Fig. Sa 4 3 c x/oo al 2 I Fig. Sb 3
3 27 24 21 18 d 15 Permian Triassic 12 9. 6 Fig.6a.. 3 \" 8 $ 4 d xloo al 3 2... * GO.. a- Fig.6b alle!2gh 31