F I R S T R E C O R D O F A N U P P E R T R I A S S I C C E R A T O D O N T I D

( D I P N O I , C E R A T O D O N T I F O R M E S ) IN T H A I L A N D A N D ITS

P A L E O G E O G R A P H I C A L S I G N I F I C A N C E

by

MICHEL MARTIN* and RUCHA INGAVAT**

Abstract R6sum6

The first discovered Norian continental vertebrate locality of Thailand has yielded one minute toothplate of a ceratodontid. This remain belongs probably to Ceratodus cf. szechuanensis. C. szechuanensis YOUNG was previously recorded from the Upper Triassic of China, which would provide evidence for a land connection between Thailand and China as early as the late Triassic.

La premi6re faune norienne de Vert6br6s confinen- taux d6couverte en Tha'flande comprend une petite plaque dentaire de C6ratodontid6 qui appartient vrai- semblablement ~t Ceratodus cf. szechuanensis. C. sze- chuanensis YOUNG ~tait d~j~t connu dans le Trias sup6rieur chinois, ce qui pourrait montrer que la Thaflande et la Chine 6talent d6j~ en contact au Trias sup6rieur.

KEY-WORDS : CERATODONTID, TRIASSIC, SOUTH-EAST ASIA, CHINA, BIOMETRY.

MOTS-CL]~S : C~RATODONTIDI~S, TRIAS, ASIE DU SUD-EST, CHINE, BIOMI~TRIE,

Introduction

During the last Thai-French expedition to north- eastern Thailand (November and December 1980) one of us (Martin) found evidence of vertebrate remains

in an outcrop which had previously yielded estheriids and plants. Thereafter we have collected, a very rich vertebrate assemblage in this locality (1).

Geology

This locality lies near Chulabhorn Dam (formerly Nam Phrom Dam), between Khon Khaen and Phit- sanuloke, on the Khorat plateau and near its western edge, in north-eastern Thailand. The fossiliferous

layers (black shales and limestones) belong to the Huai Hin Lat Formation (2) and on the basis of in- vertebrate remains they have been referred to the Norian from the estheriids (3) and from the plants

* Laboratoire de G6ologie, Facult6 des Sciences, 33 rue Louis Pasteur, 84000 Avignon, France.

** Geological Survey Division, Department of Mineral Resources, Rama VI Road, Bangkok 4, Thailand.

G6obios, n ° 15, fasc. 1 p. 111-114, 1 fig., 1 tabl. Lyon, f6vrier 1982

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(4). The vertebrate assemblage includes scales of semionotid and palaeonisciform fishes, scales of coe- lacanthids, the back part of a large stegocephalian skull referred to Cyclotosaurus and jaw remains refer-

rable to phytosaurs (1). During the preparation of the hind part of the Cyclotosaurus skull, one small tooth- plate of Ceratodus was discovered. This toothplate will be studied herein.

Paleontological description

Subclass Dipnoi MOLLER, 1844 Order Ceratodontiformes BERG, 1940

Family CERATODONTIDAE GILL, 1872 Genus Ceratodus AGASSIZ, 1838

Ceratodus cf. szeehuanensis YOUNG, 1942

Material : a single toothplate TF 1440-4 belonging to the collection of the Department of Mineral Resour- ces, Bangkok.

This minute left upper toothplate bears 5 sharp rid- ges which radiate from the tip of the inner angle. The first ridge is the shortest and the first notch is a little broader than the second one. The inner angle reaches 95 ° (fig. lc). The pterygopalatine process arises from the entopterygoid above the second ridge (fig. 1 a,b).

The presence of the phytosaurs strengthens the attribution (already made on the basis of the inverte- brate remains) of the locality to the Norian. So, we must compare this ceratodontid toothplate to other small (probably juvenile) toothplates found in Upper Triassic levels. Since the geographical position of Thailand in the Triassic is in query we shall have to deal with remains discovered almost in every part of the world.

Minute and small toothplates of ceratodontids are recorded in Europe, with C. kaupi AGASSIZ, C. phii- iipsi AGASSIZ, C. multicristatus VOROBJEVA and C. concinnus PLIENINGER, in Siberia with C. multicrista- tus, C. recticristatus VOROBJEVA, C. donensis VOROBJEVA & MINIKH and Asiatoceratodus sharovi VOROBJEVA, in north America, with C. dorotheae CASE and C. crosbiensis WARTHIN, in north Africa with Arganodus atlantis MARTIN and C. arganensis MARTIN, in south Africa, with C. capensis WOOD- WARD and C. ornatus BROOM (5,6, 7), in India and in Madagascar with C. hislopianus OLDHAM and C. virapa OLDHAM (new determination of the Malagasy forms given by one of us (8) and in China, with C. szechuanensis YOUNG (9 , 10). The holotype of C. youngi LIU & YEH (9) is a large worn plate of C. sze- chuanensis (11) and one of us (Martin) identifies the holotype of C. shenmuensis LIu & ~EH (10) with C. szechuanensis. These chinese toothplates are yielded by Upper Triassic and/or Lower Liassic beds (9 , 10). On account of the morphology, this toothplate

from Thailand could be closely related to C. concin- nus, C. phillipsi, C. donensis or C. szechuanensis (fig. 7 a,b,c ; 6 a,b ; 5 ; 3, a,b). The other species are not similar to this remain : C. kaupi has crushing ridges (5), C. multicristatus, C. recticristatus, A. atlantis, C. arganensis, C. dorotheae and perhaps C. crosbiensis possess toothplates which bear 7 ridges (7). C. capen- sis is known only by the holotype which is broken and cannot provide a good basis for such comparison (7). The plates of C. ornatus are stouter and shorter than the Thai plate TF 1440-4 (fig. 4). The species from India and Madagascar cannot be closely related to the Thai toothplate because of their obtuse inner angle (120 ° at least). The study of C. concinnus has shown that it is possible to determine such minute toothplate on the basis of biometry (5). Since we are dealing with a single toothplate the study method of E.I. Vorobjeva and M.G. Minikh (12) will be used (fig. 2). C. szechuanensi~ data have been taken from Liu's and Yeh's measure- ments and from measurements made on Liu's and Yeh's plates (9 , 10),

This Thai specimen does not fit C. concinnus on account of g 2, BC1/BCp, C1C2/C1Cp, C1C2/BCp and C. phillipsi according to ~/1, C1C2/BC1. On the basis of C1C2/BC1 and C2C3/C2Cp the plate TF 1440-4 is different from C. donensis.

On the other hand this toothplate is more similar biometrically to C. szechuanensis (data got from 3 specimens) except that the index BC1/BCp could be different but we are dealing with 3 toothplates instead of about 50 for C. concinnus and C. phillipsi. If we compare the results obtained from Chinese and Thai specimens together, they differ at least from C. con- cinnus by the greater value of the index BC1/BCp, they differ from C. phillipsi at least in the angle g 1 and almost every index is larger in C. donensis (maxi- mal value at least).

On account of biometrical results this ceratodontid from Thailand is probably closely related to C. sze- chuanensis and this plate will be referred to Ceratodus cf. szechuanensis. Since only a few Chinese specimens are known and since we have discovered only one toothplate in Thailand there remains some doubt about the determination, we must be cautions because the morphological and biometrical range of variabi- lity is almost unknown in C. szechuanensis.

61 jPr

I C

- 1 1 3 -

Cp

3a 3b 4

6a 6b 7b

5

Fig. 1 -

Fig. 2 -

Fig. 3 -

Fig. 4 -

Fig. 5 -

Fig. 6 -

Fig. 7 -

Ceratodus cf. szechuanensis Y O U N G (TF 1440-4). l a : face dorsale ; lb : face labiale ; lc : face occiusale (s.,g.), x 3.

l a : dorsal face ; lb : labial face ; le : occlusal face (ut.,1.), x 3.

Mesures d 'apr6s E.J .Vorobjeva & M.G. Minikh (12).

Measurements f rom E.J. Vorobjeva & M.G. Minikh (12).

Ceratodus szechuanensis Y O U N G . 3a : plaque dentaire sup6rieure gauche, x 2 [d'apr6s S.L. Liu & H.K. Yeh (t0)] ; 3b : plaque dentaire inf~rieure gauche, x 2 [d'apr~s S.L. Liu & H.K. Yeh (9)].

3a : left upper toothplate, x 2 [from S.L. Liu & H.K. Yeh (10)] ; 3b : left lower toothplate, x 2 [from S.L. Liu & H.K. Yeh (9)].

Ceratodus ornatus B R O O M (BM. P l l 271, s.,d.), x 4.

(BM. P l l 271, ut. ,r .) , x 4.

Ceratodus donensis V O R O B J E V A & M I N I K H [holotype d 'apr~s E.I. Vorobjeva & M.G. Minikh (12)]. (i.,d.), × 2.

[holotype f rom E.I. Vorobjeva & M.G. MJnikh (12)]. (lt.,r.), x 2.

Ceratodus phillipsi A G A S S I Z . 6a : RAS 157c (s., g.), x 2 ; 6b : SMNS 50 930 (s.,g.), x 2.

6a : RAS 157c (ut.,1.), x 2 ; 6b : SMNS 50 930 (ut.,1.), x 2.

Ceratodus concinnus P L I E N I N G E R . 7a : SMNS 51 111 (s.,g.), x 2 ; 7b : SMNS 51 109 (i.,g.), x 1 ; 7c : SMNS 51 121 (s.,d.), x 1. 7a ; SMNS 51 111 (ut.,1.), x 2 ; 7b : SMNS 51 109 (It.,1.), x 1 ; 7c : SMNS 51 121 (ut. ,r .) , x 1.

Ahr6viations. s : sup6rieur, i : inf6rieur, d : droit, g : gauche, pr : processus pterygopalatin.

BM : British Museum, SMNS : Staatliches Museum ftir Na turkunde Stuttgart . La plaque RAS 157c appart ient ~ la collection Coupatez et Wouters , 29, av. Dailly, Bruxelles.

Abbreviations. ut : upper toothplate, It : lower toothplate, 1 : left, r : right, pr : pterygopalatine process. The toothplate RAS 157c belongs to Coupatez ' s and Woute r ' s collection, 29, av. Dailly, Brussels.

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~2 DCI CICp CIC2 CIC2 ClC2 C2C3 I 2 3 ~ BCp BCp BCI CICp BCp C2Cp

i03" 76" 46" 23 e 95 85 ii0 49 38 43 50 1

+ + + + + + + + +6 +6 + - 9 -6 -6 -6 -7 -II -II -7 - - -7

i01* 90" 54" 29 ° 99 62 115 60 31 36 41 2

+ +7 + +6 +5 ~ + + + +7 + - 6 - -7 - - -10 -12 -7 -5 - -5

113" 37 e 107 90 102 68 61 3a

78" 20 e 82 65 80 53 55 3b

95* 80 e 55" 25" i00 61 107 52 30 32 44 4

I05" ~r0* 56" 27 e I00 83 112 53 40 44 55 5a

95" 70" 40" 20" 80 70 i00 44 32 36 44 5b

TabL 1 - 1 : C. concinnus (mean) ; 2 : C. phi l l ips i (mean) ; 3 : C. donensis(12), 3a : maximum, 3b : mini- mum ; 4 : C. cf. szechuanensis ; 5 : C. szechuanensis, 5a : maximum, 5b : minimum.

Paleobiogeographica i s ignif icance

Accord ing to M.E . Ridd (13) the contac t between China and south-eas tern Asia was established in the late Triassic. The freshwater cera todont ids f r o m China and Tha i land seem rather closely related, on

accoun t o f close morpholog ica l similarity and good h i ,me t r i ca l fit. This relat ionship could be evidence o f terrestrial connect ions between China and S.E. Asia dur ing the Late Triassic.

Conc lus ions

The Chinese species C. s zechuanens i s or a closely related species is p robab ly present in Thai land dur ing the Nor ian , which would show that land connect ions

were already established between these two regions dur ing the late Triassic.

Acknowledgements i

We thank our colleagues who took part with us in the Thai-French palaeontological expedition of 1980 : E. Buffe-

taut (Paris), L. Ginsburg (Paris), P. Janvier (Paris), N. Sat- tayarak (Bangkok) and V. Suteetorn (Bangkok).

References

(1) BUFFETAUT E., GINSBURG L., INGAVAT R., JAN- VIER P., MARTIN M. & SUTEETORN V. - Terra cognita, Paris, special issue, 1981, p. 116.

(2) CHONGLAKMANI C. & SATTAYARAK N. - Proc. 3rd Reg. Conf. Geol. Min. Res. SE Asia (P. Nutayala edit.), Bangkok, 1978, p. 739-762.

(3) KOBAYASHI T. - Geol. Palaeont. SE Asia, Tokyo, 16, 1975, p. 57-90. (4) KON'NO E. & ASAMA K. - Geol. Palaeont. SEAsia , Tokyo, 12, 1973, p. 149-171.

(5) MARTIN M. - Stuttgarter Beitr. Naturkde, Stuttgart, B, 56, 1980, 15 p.

(6) MARTIN M. - C.R. 105 e congr. Soc. savantes, Caen, 1980, Paris, science III, p. 47-59.

(7) MARTIN M. - Stuttgarter Beitr. Naturkde, Stuttgart, B, 69, 1981, 28 p.

(8) MARTIN M. - Bull. Soc. g~oL Fr., Paris, 1981. (in press). (9) LIUS L. & YEH H.K. - Vert. Palasiatica, Peking, 1 (4), 1957, p. 310-311.

(10) LIU S.L. & YEH H.K. - Vert. Palasiatica, Peking, 4 (1), 1960, p. 14-16.

(11) VOROBJEVA E.I. - Paleont. J. (Transl.), Washing- ton, 4, 1967, p. 102-111.

(12) VOROBJEVA E.I. & MINIKH M.G. - Paleont. J. (Transl.), Washington, 2, 1968, p. 76-87.

(13) RIDD M.E. - J. Geol. Soc. London, 137, 1980, p. 635-640.