New record of the Early Jurassic myriacanthid holocephalan ...

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Myriacanthus paradoxus AGASSIZ, 1836 from Belgium by. Christopher J. Duffin (*) and Dominique Delsate (**). Abstract: A right upper posterior ("palatine") ...
New record of the Early Jurassic myriacanthid holocephalan M yria ca nthus paradoxus AGASSIZ, 1836 from Belgium by

Christopher J. Duffin (*) and Dominique Delsate (**) Abstract: A right upper posterior ("palatine") toothplate from the Grès de Florenville (bucklandi zone, Lower Sinemurian, Early Jurassic) of Clairefontaine (Belgian Lorraine) is described and identified as M yriacanthus paradoxus A G A SS IZ, 1836. This, the first record in Belgium, extends the known palaeogeographical range of the species. K e y words: Chondrichtyes, Holocephali, Myriacanthid, Jurassic, Belgium.

Résumé: Le Grès de Florenville (Zone à b u c k la n d i, Sinémurien inférieur, Jurassique inférieur) de Clairefontaine (Lorraine belge) a livré une plaque dentaire postéro-supérieure droite ("palatine") de Chimère. Elle est ci-décrite et attribuée à M yriacanthus paradoxus A G A S SIZ, 1836. Cette espèce est signalée pour la première fois en Belgique. Son extension paléogéographique connue s'en trouve ainsi élargie. Mots-clefs: Chondrichtyes, Holocephali, Myriacanthid, Jurasique, Belgique.

Kurzfassung: Eine rechtse oberposteriore ("palatine") Zahnplatte von dem Grès de Florenville (B ucklandi-Z one, Unteres Sinemurium, Unter-Jurassicum) von Clairefontaine (belgische Lothringen) wird beschrieben und bestimmt als M yriacanthus paradoxus A G A S SIZ, 1836. Dieser erste Fund in Belgien vergrößert die paläontologische Reichweite dieser Art. Schlüsselwörter: Chondrichtyes, Holocephali, Myriacanthid, Jurassicum, Belgiën. (*) Dr. C. D U FFIN , 146 Church H ill Road, Sutton, Surrey SM3 8NF, England. (**) Dr. D. D ELS A T E , 5 Rue du Quartier, 6792 Battincourt, Belgium.

In tro d u c tio n The myriacanthoids are an extinct group of holocephalans ranging from the Late Triassic (Rhaetian) to the Late Jurassic (Tithonian). They are most commonly represented by isolated toothplates, dorsal fin spines and frontal clasper spines, although some articulated specimens are known from the Low er Lias (Sinemurian) of Lyme Regis, Dorset, England (W O O D W A R D , 1891), Osteno in Lombardy, Italy (D UFFIN , 1992; D U F F IN & P ATTER SO N , in press), the Posidonienschiefer (Toarcian) of Holzmaden, Germany (FRAAS, 1910; DUFFIN , 1983), and the Plattenkalk of Solnhofen, Germ any (ZITTEL, 1887). Holocephalan specimens are relatively rare components of most Jurassic vertebrate faunas, and the geographical and stratigraphical ranges of most taxa seem to be very limited. This is almost certainly due to the scarcity of material. M yria canth us is the type genus of the family, and M . paradoxus is the type species of the genus by monotypy. It is currently known only from the "Lower Lias" of Lyme Regis, and the Westbury Beds (Penarth G roup (Rhaetian, Late Triassic) of A ust Cliff, Avon (D U FFIN , 1994). A n upper anterior ("vomerine") tooth plate from the Hettangian of France (T E R Q U E M , 1855) may pertain to this species, but anterior upper tooth plates are not well known in myriacanthids. Indeed, the upper anterior tooth plates of M . paradoxus from Lyme Regis and Halonodon w arneri D U FFIN , 1984 from the Belgian Sinemurian are virtually indistinguishable. The purpose of the present paper is to extend the known palaeogeographical range of M yria canth us paradoxus into southern Belgium.

G e o lo g ic a l b a c k g r o u n d The Lorraine (southern Belgium and Grand D uchy of Luxembourg) consists of a sequence of cuestas of Early Mesozoic clastic sedimentary rocks. Three cuestas form the Belgian Lorraine; the Sinemurian, Pliensbachian and Bajocian cuestas.

T h e m a in f a d e s o f th e L o w e r L ias in S o u th e rn B elg iu m c o n sists o f th e stro n g ly d ia c h ro n o u s c a la c a re n ite s o f th e G rès d e L u x e m b o u rg (see D U F F IN & DELSATE, 1993 fo r a re v ie w of th e stra tig ra p h y ). T h e n o rth e rn fla n k o f th e S in e m u ria n c u e sta e x p o se d in th e C la ire fo n ta in e a re a sh o w s tw o s p rin g lev els; th e m a jo r o f th e s e tw o is fo rm e d b y th e M a rn e s d e S tra sse n , w h ile te m p o ra r y s p rin g s a lso a rise fro m th e M a rn e s H o n d e la n g e (L o th a rin g ia n ). T he w a te rs fed b y th e s p rin g s u n ite to fo rm th e C la ire fo n ta in e R iv er w h ic h e ro d e s th e b a se o f th e M a rn e s d e S tra sse n a t a ro u n d 338m a n d c u ts in to th e u n d e rly in g sa n d s to n e s. M a n y sm a ll q u a rr ie s a re s ite d o n th e s te e p w o o d e d slo p e s o f th e riv e r valley, e x p lo itin g th e C a lc a ire G ré se u x d e F lo re n v ille fo r local b u ild in g s to n e (M O N T E Y N E , 1958).

T h e s tra tig ra p h y o f th e a re a h a s b e e n e lu c id a te d th r o u g h th e w o rk o f M O N T E Y N E (1958), M A U B E U G E (1966) a n d M E R G E N (1985), a n d is s u m m a ris e d in F ig u re 1. T h e sm a ll q u a rrie s m e n tio n e d a b o v e e x p o se th e fo llo w in g u n its (a s c e n d in g th e se q u en c e) : (i) S a b le s d e M e tz e rt : a d e m in e ra lise d facies o f th e H e tta n g ia n p a r t o f th e G rès d e L u x e m b o u rg y ie ld in g o ccasio n al

Cardinia. (ii) C a lc a ire G ré s e u x d e F lo r e n v ille : th e lo cal E arly S in e m u ria n p a r t o f th e G rè s d e L u x e m b o u rg . It c o n sists o f a 30m to 40m th ick c o m p lex o f s a n d s to n e u n its y ie ld in g Coroniceras bucklandi, Ostrea irregularis, Cardinia copides, C. crassissima, Chlamys textorius, Oxytoma sp ., Pseudomelania clathrata, Isastraea condeana a n d Pentacrinus tuberculatus, m o stly fro m lu m a c h e lle h o riz o n s. (iii) M a r n e s d e S tr a s s e n : b lu e -g re y m a rls w ith c a lc a re o u s h o riz o n s. F o ssils in c lu d e Arnioceras semicostatum, Prototeuthis acutus, Chlamys textorius, Spiriferina walcotti a n d Liogryphaea arcuata. A ro u n d C la ire fo n ta in e , th is fo rm a tio n is a ro u n d 60cm th ic k a n d re p re s e n ts th e S w a b ia n facies o f th e C a lc a ire à G ry p h é e s. It is d a te d a s U p p e r S in e m u ria n (se n su stncto)(semicostatum a n d turneri z o n e s) in th e B elg ian L o rra in e , b u t as L o w e r S in e m u ria n (bucklandi z o n e) in th e L u x e m b o u rg L o rra in e , d u e to a ra d ic a l facies c h an g e. T he B elg ian G rès d e F lo ren v ille p a ss e s la te ra lly in to th e L u x e m b o u rg M a rn e s d e S tra sse n (M A U B E U G E , 1966) b e tw e e n S te in fo rt (G ra n d D u c h y of L u x e m b o u rg ), a n e ig h b o u rin g v illa g e to C la ire fo n ta in e , a n d th e w e s te rn sid e o f L u x e m b o u rg city (a b o u t 13km e a st of C la irefo n ta in e ).

The only holocephalan taxa recorded to date from the Belgian Jurassic are Halonodon w a rne ri D U FFIN , 1984, and Chimaeropsis foussi CASIER , 1959. A second species of Halonodon, H. luxembourgensis D U F FIN & D ELS A T E , 1993, has been described from the Hettangian of Luxembourg.

S y stem atic P alaeon tology

Class Chondrichthyes H U X L E Y , 1880 Subclass Subterbranchialia Z A N G E R L , 1979 Superorder Holocephali B O N A P A R T E , 1832 Order Chimaeriformes (BERG, 1940) sensu P ATTER SO N , 1965 Suborder Myriacanthoidei, PATTER SO N , 1965 Family Myriacanthidae S M ITH W O O D W A R D , 1889

Genus M yria canth us A G A S S IZ , 1837 Type species : M yria canth us paradoxus A G A SS IZ, 1837; Low er Lias (Early Jurassic) of Lyme Regis, Dorset, England. M yria canth us paradoxus A G A SS IZ, 1837 (Plate 1; Textfigure 3a)

1822 "External defensive organ" - D E L A B E C H E , 1, 44, pi. 5 figs. 1-2. A G A SSIZ; A G A SSIZ, 3, pi. 6. 1836 M yria canth us paradoxus A G A SSIZ, 3, 38. 1837 M yria canth us paradoxus ; A G A SSIZ; A G A SSIZ, 3, 39. 1837 M yriacanthus retrorsus A G A SSIZ, 3, pi. 8a figs. 14,15. 1838 M yriacanthus retrorsus ; 1855 Chimaera (Ischyodon) johnsoni A G A S S IZ ; T E R Q U E M , 241, pi. 14 fig. 1. E G ER T O N ; E G E R T O N , 233, pi. 8. 1872 Prognathodus guentheri W O O D W A R D , 44, pi. 2 figs. 1-3. 1891 M yriacanthus paradoxus ; W O O D W A R D , 2, pl. 1 figs. 1-5. 1906 M yriacanthus paradoxus ; D E A N , 143, text-figs. 119, 119A, 142. 1906 M yria canth us paradoxus ; PATTER SO N , 128, text-figs. 13-19; pi. 22 fig. 46; pi. 25 fig. 59; 1965 M yria canth us paradoxus ; pi. 26 fig. 60; pi. 28 fig. 67. PATTER SO N , 45, figs. 7A-C. 1992 M yria canth us paradoxus ; D U F FIN & D E L S A T E , text-fig. 5f. 1993 M yria canth us paradoxus ; D U FFIN , 12, figs. 8a-b. 1994 M yriacanthus paradoxus ;

D ia g n o s is : see P A TTER SO N (1965: 136) H o lo ty p e : B M N H P 6095, a dorsal fin spine (AG ASSIZ, 1836 pi. 6 figs. 1-2) from the Lower Lias (?Sinemurian, Early Jurassic) of Lyme Regis, Dorset, England. B e lg ia n s p e c im e n : IRSNB P 6333, a virtually complete right upper posterior ("palatine") toothplate. L o c a lity : old (disused) sandstone quarry in the village of Clairefontaine, Com m une of A rlon, 500m north of the N4 road (Arlon to Luxembourg). Topographic maps 1/25000 : 68/7-8 and 69/5-6. Text-Figure 2. H o riz o n : Grès de Florenville A g e : bucklandi zone, Low er Sinemurian, Early Jurassic. L ith o lo g y : bioclastic limestone. The specimen is associated on a small block with Cardinia sp. and the external mould of a spire with carina of Coroniceras aff. rotiforme. C o lle c to r : M r Jacques L A M U R Y (Thiaumont).

D e s c rip tio n : The specimen is an almost complete right upper posterior ("palatine") toothplate preserved on a small block of bioclastic limestone (Plate 1 Figure a). The plate is preserved in occlusal view and the mesial extremity is missing. The overall shape is roughly triangular with a slightly curved symphyseal margin. The labial margin is almost complete and measures 48mm in length, while the lingual margin is 21mm long.

The mesial part of the dental plate is occupied by a deep oval antemortem wear facet measuring 19 mm long and 10mm across. The remainder of the occlusal surface is covered by a tritoral pad of hypermineralised tissue often called "pleromin". No diagonal ridges transect the occlusal surface, although a short (13mm long) convex ridge intervenes between the wear facet and the labial margin mesially.

Textfigure 3. Outline drawings of the upper posterior tooth plates of M . paradoxus A G A SSIZ, 1836 and Agkistracanthus mitgelensis D U FFIN & FU R RER, 1981, all in occlusal view, a: IRSNB P 6333; b: Agkistracanthus mitgelensis from the Cotham Member (Lilstock Formation, Penarth Group, Rhaetian) of St. Audries Bay, somerset England. B M N H P 61526; c: Agkistracanthus sp. from the Kössen Beds (Rhaetian) of the Central Austroalpine Sivettra Nape at Alpihorn, Kanton Graubunden. P IM U Z A/1870.

D is c u s s io n

The absence of diagonal ridges distinguishes this specimen from the upper posterior tooth plates of Acanthorhina jaekeli FR A A S , 1910 (Toarcian of Holzmaden) and Metopacanthus granulatus (AGASSIZ, 1837)(Sinemurian of Lyme Regis). The latter species has hypermineralised tissue restricted to the central diagonal ridge of upper posterior teeth, in contrast to the condition in IRSNB P 6333. The only two further myriacanthid genera in which the upper posterior toothplates are known are Agkistracanthus and M yriacanthus. M yria canth us was originally based upon an isolated dorsal fin spine. The discovery of a specimen with associated dorsal fin spine and dentition allowed W O O D W A R D (1906) to diagnose theM . paradoxus more fully. One of the most complete dentitions of M . paradoxus is preserved in B M N H P 477 (Plate 1 Figure b; Text-Figure 4XA G ASSIZ, 1843: 344, plate xlc fig. 22; W O O D W A R D , 1891: 46, plate 2 fig. 3; P ATTER SO N , 1992:47), which has recently been virtually completely freed from the surrounding matrix. This specimen is particularly useful since the upper and lower dentition are preserved in occlusal view (Plate 1 Figure a; Text-Figure 4). The palatine teeth of Agkistracanthus mitgelensis D U F FIN & FU RR ER , 1981 and Agkistracanthus sp. (Rhaetian and Hettangian of Switzerland; Rhaetian of England) possess a mesial wear facet on the occlusal surface (D U FFIN & FU R RER, 1981, plate 2 fig. 3a; D U FFIN , 1994 fig. 5), but D U F FIN (1994: 10) was incorrect in stating that such a feature was exclusive to that species. The upper posterior dental plate of M yria canth us paradoxus also has a mesial wear facet (Text-Figure 4). The long axis of the wear facet in Agkistracanthus is much more lingually situated than

in M. paradoxus , le a v in g a w id e s trip of h y p e rm in e ra lis e d tis s u e la b ia lly (c o m p a re T ex t-F ig u res 3a, b a n d c). F u r th e r m o r e , th e lo n g a x is o f th e w e a r fa c e t is d e c lin e d lin g u a lly fro m th e lo n g a x is o f th e to o th p la te in Agkistracanthus , b u t th e tw o ax e s a re su b p a ra lle l in Myriacanthus a n d IRSN B P 6333. T h e o u tlin e o f th e u p p e r p o s te rio r d e n ta l p la te s in th e tw o g e n e ra a ls o differ. Agkistracanthus h a s th e fo rm o f a n e lo n g a te te a r-d ro p , w h ile Myriacanthus a n d IRSN B P 6333 a re b o th m u c h m o re tr ia n g u la r in o u tlin e . T h u s, b y c o m p a ris o n w ith B M N H P 477, IRSN B P 6333 d e sc rib e d a b o v e m u s t b e lo n g to Myriacanthus paradoxus, a n d as su c h , is th e first re c o rd o f th is sp e c ies in B elgium .

10 m m \

T extfigure 4. C a m e ra lu c id a d ra w in g o f B M N H P 477 (E G ER T O N C o ll.),a rtic u la te d to o th p la te s o f M. paradoxus fro m th e L o w e r L ias o f L ym e R egis.

C o n c lu s io n s A m y ria c a n th id rig h t u p p e r p o s te rio r to o th p la te is d e sc rib e d fro m th e L o w e r S in e m u ria n o f th e B elg ian L o rra in e a s Myriacanthus paradoxus A G A SSIZ. T h is is th e first c o n fid e n t re co rd of th e sp e cie s o u ts id e o f B ritain.

A c k n o w le d g m e n ts We a re v e ry g ra te fu l to J. LAM URY (T h ia u m o n t) fo r a llo w in g u s to s tu d y th e sp e c im e n , a n d fo r d o n a tin g it to th e IRSNB. Dr. P. FOREY k in d ly g a v e access to th e c o lle c tio n s of th e B M N H in o rd e r to s tu d y c o m p a ra tiv e m a te ria l from L ym e R egis. D rs. P. M A U B E U G E , P. M E R G E N a n d R. M O N T E Y N E p ro v id e d in fo rm a tio n o n th e local geology. T he m a n u s c rip t w a s critic a lly a p p ra is e d b y Dr. B. STAH L a n d Mr. D. W ARD.

B E C H E , H.T. de la (1822) : Remarks on the Geology of the South Coast of England, from Bridport Harbour, Dorset, to Babbacombe Bay, Devon. Transactions o f the Geological Society o f London, (2)1: 40-47. London. BERG, L.S. (1940): Classification of fishes, both recent and fossil. Travaux de l'In s titu t de Zoologie. Académie des Sciences U.R.S.S., 5(2): 1-517,190 figs. B O N A P A R T E , C.L.J.L. (1832) : Selachorum tabula analytica. N u o vi A n n a li delle Scienze N a tu ra li, (1)2: 195-214. Bologna. D E A N , B. (1906) : Chimaeroid fishes and their development. Publications o f the Carnegie In s titu tio n , 32, 194pp., llp ls . Washington. D U FFIN , C.J. (1983a): Holocephalans in the Staatliches Museum fur Naturkunde in Stuttgart. 1. Myriacanthoids and Squalorajoids. S tuttg arter Beiträge z u r Naturkunde. B, 97,1-41, 7 figs., 5 pis. Stuttgart. D U FFIN , C.J. (1984): A n ew myriacanthid holocephalan from the Sinemurian (Lower Jurassic) of Belgium. Zoological Society o f the Linnean Society, 82(1): 55-71,4 figs. London. D U FFIN , C.J. (1992): A myriacanthid holocephalan (Chondrichthyes) from the Sinemurian (Lower Jurassic) of Osteno (Lombardy, Italy). A t t i della Societa Ita lia na d i Scienze N a tu ra li e del M useu Civico d i Storia N aturale d i M ila n o , 132(23), (1991): 293-308,10 figs. Milano. D U FFIN , C.J. (1994): Myriacanthid holocephalans (Chondrichthyes) from the British Late Triassic. Neues Jahrbuch f ü r Geologie und Paläontologie Abhandlungen, 192(1): 1-16. Stuttgart. D U FFIN , C.J. & D ELS A T E , D. (1993a): A n e w myriacanthid Holocephalan (Chondrichthyes) from the Early Jurassic of Luxembourg. Neues Jahrbuch f ü r Geologie und Paläontologie Monatshefte, 1993(11): 669-680. Stuttgart. D U FFIN , C.J. & P ATTER SO N , C. (in press): The Jurassic fishes of Osteno. Palaeocronache. Milano. E G E R T O N , P. D E M .G . (1872) : O n Prognathodus guentheri E G E R T O N , a new genus of fossil fish from the Lias of Lyme Regis. Q u a rte rly Journal o f the Geological Society o f London, 28: 233-238, pi. 8. London. FR A A S , E. (1910) : Chimäridenreste aus dem oberen Lias von Holzmaden. Jahresheft des Vereins fü r Vaterländische N aturkunde in W ürttemberg , 66: 55-63, lp l. Stuttgart. G A R M A N , S. (1901) : Genera and families of the Chimaeroids. Proceedings o f the New England Zoological Club, 2: 7577. Boston. G O D E F R O IT , P. (1994) : Les Reptiles m arins du Jurassique inférieur en Lorraine belgoluxembourgeoise. Unpublished Ph.D. thesis, Faculty of Science, Catholic University of Louvain, Belgium. M A U B E U G E , P.L. (1966) : Le Problème du Grès de Luxembourg. H istoire N aturelle du Pays de Luxembourg. Géologie. Musée d'Histoire Naturelle, Luxembourg. M E R G E N , P. (1984) : Géologie et Hydrogéologie du Lias Inférie ur et M oyen en Lorraine belge. Thesis, University of Brussels.

M O N T E Y N E , R. (1958) : Recherches sur le Lias In fé rie u r du Sud de la Belgique. T h esis, U n iv e rs ity o f B ru ssels. PA TTERSO N , C. (1965) : T h e p h y lo g e n y of th e c h im a e ro id s. Philosophical Transactions o f the Royal Society o f London, B249: 101-219. L o n d o n . PA TTERSO N , C. (1992) : In te rp re ta tio n of th e to o th p la te s of c h im a e ro id fishes. Zoological Journal o f the Linnean Society, 106: 33-61,11 figs. L o n d o n . TER Q U E M , O . (1855) : P a lé o n to lo g ie d e l'é ta g e in fé rie u r d e la fo rm a tio n lia siq u e d e la p ro v in c e d e L u x e m b o u rg d 'H e tta n g e . Mémoires de la Société Géologique de France, (2)5: 219-343. P aris. W O O D W A R D , A.S. (1889) : O n th e M y ria c a n th id a e - a n e x tin c t fam ily o f c h im a e ro id fish es. A n n a ls a n d Magazine of N a tu ra l H isto ry, (6)4: 275-280. L o n d o n . W O O D W A R D , A.S. (1891 ) : Catalogue o f the Fossil Fishes in the B ritish M useum (N a tu ra l H isto ry), II. L o n d o n : B ritish M u s e u m (N a tu ra l H isto ry ). Z A N G E R L , R. (1979): N e w C h o n d ric h th y e s fro m th e M a z o n C re e k F a u n a (P e n n s y lv a n ia n ) o f Illinois, p p . 449-500. In : N IT E C K I, M .H . (ed.), Mazon Creek Fossils. A c a d e m y P re ss : N e w York. ZITTEL, K.A. v o n (1887): Handbuch der Paläontologie.I .A btheilung Paläozoologie,3 .Vertebrata(Pisces, Am phibiaReptilia.Aves). xii + 900 p p ., 719 figs. O ld e n b o u rg : M ü n c h e n & L eipzig.

Explanation of Plate 1 Plate 1. F ig u re a, IRSNB P 6333, a rig h t u p p e r p o s te rio r (" p a la tin e " ) to o th p la te of M yriacanthus paradoxus A G A SSIZ from th e G rès d e F lo ren v ille (bucklandi zo n e , L o w e r S in e m u ria n , E arly Ju rassic) o f C la ire fo n ta in e (B elgian L o rrain e) in o cclu sal v ie w (x 1.56); F ig u re b, B M N H P477, a rtic u la te d to o th p la te s o f M . paradoxus fro m th e L o w e r L ias of L ym e R egis, D o rset. T h e p h o to g r a p h w a s ta k e n p a r t w a y th r o u g h c h e m ic a l d e v e lo p m e n t of th e d e n titio n fro m th e

matrix.