The earliest known Salamanders (Amphibia, Caudata):A record from the Middle Jurassic of England

THE EARLIEST KNOWN SALAMANDERS (AMPHIBIA, CAUDATA) " A RECORD FROM THE MIDDLE JURASSIC OF ENGLAND

by SUSAN E. EVANS*, ANDREW R. MILNER** & FRANCES MUSSETT***

ABSTRACT

R~,SUMI~

Marmorerpeton gen. nov. represented by M. kermacki sp. nov. and M. freemani sp. nov., is the earliest known genus of fossil salamander from the Upper Bathonian, Middle Jurassic of Kirtlington, Oxfordshire, England. Marmorerpeton is more primitive than any other known salamander in the absence of intravertebral spinal nerve foramina in the atlantal centrum, but in other features it resembles members of the family Scapherpetontidae, neotenous salamanders otherwise known from the Upper Cretaceous and Palaeocene. The Kirtlington herpetofauna is a unique freshwater assemblage of Middle Jurassic small amphibians and reptiles, several of which represent the earliest known occurrences of their respective groups.

Marmorerpeton gen. nov., repr6sent6 par M. kermacki sp. nov. et M. freemani sp. nov., provenant du Bathonien sup6rieur, Jurassique moyen de Kirtlington, Oxfordshire, Angleterre, est le plus ancien genre de caudate fossile. I1 est plus primitif que les autres caudates connus ~t cause de l'absence des foramens intravert6braux dans le centrum atlantal, mais il ressemble par d'autres caract~res aux membres de la famille des Scapherpetontidae, caudates n6ot6niques du Cr6tac6 sup6rieur et du Pal6oc~ne. L'herp6tofaune de Irdrtlington constitue un ensemble unique d'amphibiens et de reptiles dulqaquicoles du Jurassique moyen, certains de ses 616ments repr6sentent les premiers sp6cimens connus de leurs groupes respectifs.

KEY-WORDS : AMPHIBIA,CAUDATA,MORPHOLOGY,SYSTEMATICS,JURASSIC,ENGLAND. MOTS-CL~LS: AMPHIBIA, CAUDATA, MORPHOLOGIE,SYSTI~MATIQUE,JURASSIQUE,ANGLETERRE.

* Department of Anatomyand DevelopmentalBiology,UniversityCollegeLondon,WindeyerBuilding, ClevelandStreet, LondonWIP 6DB, UK. Department of Biology,BirkbeekCollege,MaletStreet, LondonWC1E7HX, UK. *** Department of Biology,UniversityCollegeLondon,MedawarBuilding,GowerStreet, LondonWC1E6BT, UtC * *

Geobios, n Q21, fasc. 5

p. 539-552, 9 fig.

Lyon, octobre 1988

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INTRODUCTION The pre-Cretaceous fossil record of the amphibian order Caudata is extremely poor, consisting of only two certain Upper Jurassic records. These are Karaums, represented by a single well-preserved skeleton from the Karabastau Formation of Kazakhstan (Ivakhnenko 1978) and Comonecturoides represented by a femur and two vertebrae from the Morrison Formation of Wyoming (Hecht & Estes 1960 ; Estes 1981). Other pre-Cretaceous fossils described as salamanders have proved to be of uncertain systematic position. The small poorly preserved Triassums from the Upper Triassic of Uzbekistan was described as the earliest salamander (Ivakhnenko 1978) but is indeterminate and possibly a larval temnospondyl amphibian (Estcs 1981). The genus Albanelpeton is represented by an atlantal centrum from the Bajocian (early Middle Jurassic) of Aveyron, France (Seiffert 1969) and much undescribed material from the Upper Jurassic of Portugal (Estes 1981) but its status as a salamander has recently been questioned. Fox & Naylor (1982) have proposed thatAlbanerpeton represents a distinct, fourth order of lissamphibians. Other workers continue to argue that Albanerpeton is a salamander (Estes & Sanchiz 1982) and it appears that the available morphological information about Albanerpeton is insufficient to permit its relationships to be determined (Milner 1988). T h e specimens reported here represent the first unequivocal fossil salamanders to be recorded from pre-Upper Jurassic rocks and hence the earliest known fossil salamanders. They all derive from the microvertebrate assemblage in the Kirtlington Mammal Bed at Kirtlington in Oxfordshire. The techniques for the collection and preparation of much of this material were described by Kermack et alii (1987). It consists of numerous isolated bones of medium-size salamanders, mostly about 30 cm in total length,

although one humerus appears to have belonged to an individual at least 40 cm long. Many of the bones resemble those of members of the Scapherpetontidae (Auffenberg & Goin 1959 ; Estes 1965, 1969, 1981 ; Naylor 1983), an extinct family of neotenous salamanders. However some features of the atlantal construction suggest that this material belongs to a more primitive grade of salamander than any previously described. With respect to characters of major systematic significance, there is only one morphological type of any given salamander bone in this size category, and unity of this material at a generic level is the simplest assumption. However, some bones (the atlantes, premaxillaries and maxillaries) occur in two distinct subtypes and this has necessitated the creation of two species. These are diagnosed from the atlas vertebrae and exoccipitals, no other certain species-level association being possible. The distinct subtypes of premaxillary and maxillary are described separately and are identified by initial letters (A-D) but there is little morphological basis for associating them with the type atlantes or each other, and so they are simply identified as Marmorerpeton sp.indet.. Most of the remaining material (such as the trunk vertebrae) occurs in only one recognizable form and is thus also indeterminate within the genus. The specimens described and figured here were collected either by Professor K.A. Kermack and colleagues or by Mr E.F. Freeman and have all been donated to the Department of Palaeontology, British Museum (Natural History) (BMNH). Mr. Freeman is undertaking quantitative and associational ecological work with his collections and the specimens collected by him retain a catalogue number (prefixed by EF) in relation to this work.

LOCALITY AND HORIZON This material was collected from various parts of the Old Cement Works Quarry, near Kirtlington in Oxfordshire (Freeman 1976, 1979 ; Kermack et alii 1987). It is derived from the IGrtlington Mammal Bed near the base of the Forest Marble which is of Upper Bathonian (Middle Jurassic) age (approximately 170 Ma, Harland et alii 1982) A fnll account of the strati-

graphy is given by Freeman (1979). The palaeoenvironment appears to have been a shallow non-stagnant body of fresh water, with occasional influxes of poorly sorted sediment (Freeman 1979). The Mammal Bed has produced a rich microvertebrate fauna of which only some-~mammals have been described to date (Freeman 1976, 1979 ; Kermack et alii 1987).

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SYSTEMATICS AND DESCRIPTION Class Amphibia Order CAUDATA Family Incertae Sedis

material was obtained. HOLOTYPE :

Genus Marmorerpeton nov. DERIVATION OF NAME : Generic name from the Greek marmoros = marble, after the Forest Marble ; herpeton = a creeping animal.

TYPE-SPECIES :

British Museum (Natural H~istory) Department of Palaeontology R.11361, a large atlantal centrum (figs 1a-e). REFERRED MATERIAL :

BMNH R.11362, a second atlas ; R.11363 (EF 77 : 5 : 1 : 6), an exoccipital (figs 2 a-c), together with numerous atlantes of similar configuration to the holotype and an additional three exoccipitals.

Marmorerpeton kermacki nov.

b DIAGNOSIS :

A genus of neotenous salamander showing general resemblance to members of the Scapherpetontidae but with the following characteristics of the atlantal centrum : atlantal centrum primitively without intravertebral spinal nerve foramina (figs lb, le, 3b, 3e) and unusually elongate, the length equalling the width; ventral face of atlas flattened and pitted (figs la, 3a) ; lateral face of atlas bearing several deep pits but no foramina (figs le, 3e) ; interglenoid tubercle small and perforated anteriorly ; centrum notochordal and without calcified rings on the cotyles (figs lc, ld, 3c, 3d).

c

d

The following diagnostic characters occur in attributed elements : ventral face of trunk centrum without medial keel or paired fossae, but a medial depression generally present (fig. 8f) ; premaxillary with narrow posterior shelf for articulation with vomer (figs 5a, c) ; prominent mandibular symphysis circular in cross-section (fig. 7c) ; humerus lacking a crista dorsalis (fig. 9a).

Marrnorerpeton kermacki sp. nov.

DERIVATION OF NAME :

After Professor K.A. Kermack who organized the collection of the samples from which much of this

Fig. 1 - Marmorerpeton kermacki nov. gen. nov. sp. BMNH tll1361, holotype atlantal centrum : a) ventral, b) dorsal, e) anterior, d) posterior and e) left lateral aspects ; from the Upper Bathonian o[K.irtlington, Oxfordshire ; scale = I ram. Holotype, centrum de l'atlas : a) face ventrale, b) face dorsale, c) face ant~rieure, d) face post6rieure, ~e) face latdrale gauche ; Bathonien sup6rieur de Kirtlington, Oxfordshire ; ~chelle = I ram.

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LOCALITY :

DIAGNOSIS :

Old Cement Works Quarry, Kirtlington, Oxfordshire, England.

HORIZON : Kirtlington Mammal Bed, near base of the Forest Marble, Upper Bathonian, Middle Jurassic; approximate age 170 million years.

a

b

Species of Marmorerpeton in which the anterior cotyles of the atlas centrum are roughly circular, with a dorsomedial indentation. The anterior cotyle height is over 80% of its width in large vertebrae. The posterior width of the vertebra is between 50% and 57% of the anterior width. The interglenoid tubercle is slightly elongate and in most specimens the lower lip protrudes relative to the upper lip. There are three lateral pits, two round and one elongate, but no lateral ridge.

c

Fig. 2 - Marmorerpeton kermackinov. gen. nov.sp. BMNHR.11363,left exoccipital: a) posterior aspect ; b) left lateral aspect ; e) dorsomedial aspect ; abbreviation: x = vagalforamen; from the Upper Bathonianof Kirtlington,Oxfordshire; scale = 1 ram. Exoccipital gauche : a) face post6rieure ; b) face latdrale gauche ; c) face dorsom6diale ; abr6viation : x = foramen vagal. Bathonien supgrieurde Kirtlington,Oxfordshire; 6chelle = 1 mm.

Marmorerpetonfreemani sp. nov. DERIVATION OF NAME : After Mr E.F. Freeman who first recognized the significance of this locality and who collected the holotype specimen.

HOLOTYPE :

DIAGNOSIS : Species of Marmorerpeton in which the anterior cotyles of the atlas centrum are dorsoventrally flattened ovoids with no indentations. The anterior cotyle height is 63-65 % of its width in the large type vertebra. The posterior width of the vertebra is 37 % of its anterior width. The interglenoid tubercle is shorter than in M. kermacki and the lips do not protrude. There are three elongate lateral pits and a lateral ridge.

British Museum (Natural History) Department of Palaeontology R.11364 (EF 75 : 6 : 1 : 18), a large atlantal centrum (figs 3a-e).

Marmorerpeton sp. undet. LOCALITY :

REFERRED MATERIAL:

Old Cement Works Quarry, Kirtlington, Oxfordshire, England.

BMNH R.11365, type A premaxillary (figs 5a, b) ; R.11366, R.11367, type B premaxillaries (figs 5c-e) ; R.11368 (EF 76 : 1 : 11 : 1), R.11369, type C maxillaries (figs 6a-c) ; R.11370 (EF 77 : 5 : 1 : 5), a type D maxillary (fig. 6d, e) ; R.11371, a left vomer (fig. 7c) ; R.11372, an incomplete small vomer ; R.11373, R.11374, dentaries (figs. 7a, b) ; R.11375, a neural spine (figs 8a-b) ; R.11376, R.11377, trunk vertebrae (figs. 8c-h) ; R. 11378, a caudal centrum (fig. 8i);

HORIZON : Kirtlington Mammal Bed, near base of the Forest Marble, Upper Bathonian, Middle Jurassic ; approximate age 170 million years.

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a

b

R.11379 (EF 77 : 1 : 1 : 1), a large right humerus (figs 9a, b ) , R.11380, a small humerus. Over 100 further uncatalogued specimens including trunk vertebrae, jaw and vomer fragments. There are other postcranial elements such as scapulocoracolds and ilia which may also belong here but for which the attribution is uncertain (see below).

c

d LOCALITY:

Old Cement Works Quarry, Kirtlington, Oxfordshire, England. e HORIZON :

Kirtlington Mammal Bed, near base of the Forest Marble, Upper Bathonian, Middle Jurassic ; approximate age 170 million years.

Fig. 3 - Marmorerpeton freemani nov. gen. nov. sp. BMNH R.11364, holotype atlantal centrum : a) ventral, b) dorsal, c) anterior, d) posterior and e) left lateral aspects ; from the U p p e r Bathonian of Kirtlington, Oxfordshire ; scale 1 mm.

DESCRIPTION:

Most of this material belongs to salamanders of 25 - 30 cm length. The numbers of trunk and caudal vertebrae are unknown but each vertebra was up to 5 mm

Holotype, centrum de l'atlas : a) face ventrale, b) face dorsale, c) face antrrieure, d) face postrrieure, e) face latdrale gauche ; Bathonien supdrieur de Kirtlington, Oxfordshire ; 6chelle = 1 mm.

a

b

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A Fig. 4 - Bivariate plots of selected dimensions of Marmorerpeton atlantes from Kirtlington. a) relationship of height (H) to width (W) of anterior cotyles of atlantes. M. kerrnacki : + = left, • = right ; M. freemani : = left,(~) = right, b) relationship of anterior width (A) to posterior width (B) of atlantes. • = M. kermacki ; ( ~ ) = M. freemani.

[3

W

®

W

A

Analyse bivarire de dimensions choisies des atlas de Marmorerpeton de Kirtlington. a) rapport entre la hauteur (H) et la largeur (W) des cotyles antrrieurs des atlas. M. kermacki : + = gauche, • = droit ; M. freemani : = gauche,(~) = droit, b) rapport entre la largeur afftrrieure (A) et la largeur postrrieure (B) des atlas. • = M. kernmcki ; ( ~ ) = M. freemani.

++1 O

o •

H

[3

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a

b

Fig. 5 - Marmorerpetonsp. under,a) BMNHtll1365, left premaxillarytypeA (internalaspect) ; b) BMNH R.11365, leftpremaxillarytypeA (external aspect) ; c) BMNH R.11366, right premaxillarytype B (internal aspect) ; d) BMNH R.11366, right premaxillarytype B (external aspect) ; e) BMNH R.1!367,smallright premaxiUarytype B (externalaspec0 ; from the Upper Bathonianof Kirtlington, Oxfordshire ; scale = 1 ram. a) Pr6maxillairegauche typeA (faceinterne) ; b) Pr6maxillairegauchetypeA (faceexterne) ; c) Pr6maxillairedroit typeB (faceinterne) ; d) Pr6maxillairedroit type B (face externe) ; e) Petit pr6maxillairedroit typeB (face externe). Bathoniensup6rieur de Kirtlington, Oxfordshire ; 6chelle = 1 ram.

long and comparison with modern caudates, many of which have about 50 vertebrae, suggests the above length. One humerus (R.11379), when scaled against modern salamandrid material appears to represent a larger individual of at least 40 cm total length. The following description of the atlantal centrum applies to both species of Marrnorerpeton. The atlantal centrum is without intravertebral spinal nerve foramina (figs lb,e ; 3b,e), the apparent foramina on the atlas visible in fig. le are closed pits and grooves. This configuration of a lateral pit or groove above two pits or anteroposterior grooves characterizes all the atlantal centra of both species of this genus. A similar arrangement occurs behind the spinal foramen in the scapherpetontid Piceoerpeton (Naylor 1983). The detailed configuration appears to differ between the

two species of Marmorerpeton and is a diagnostic character at the species level. The intravertebral foramina are prominent structures in the typical caudate atlas centrum and their absence here is certain. This is a primitive characteristic found in no other caudate, living or fossil. The atlantal centrum is unusually elongate, the length equalling the width (figs la, 3a). It appears to be relatively longer than that of any other known caudate and only some scapherpetontid atlantes approach this shape (e.g. Lisserpeton in Estes 1965, fig. 2). The atlantal centrum possesses a distinct interglenoid tubercle with a central notochordal pit (figs lc, 3c). The anterior cotyles extend onto the sides of the medial tubercle as condylar facets. The posterior cotyle (figs ld, 3d) is deeply conical and the ventral surface of the atlantal centrum is evenly heavily pitted (figs la, 3a). These are both scapherpetontid characteristics.

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Y

,-4

Fig. 6 - Marmorerpeton sp. undet, a) BMNH R.11368, right maxillary type C.(internal aspect) ; b) BMNH R.11368, right maxillary type C (external aspect) ; c) BMNH R.11369, fight maxillary type C (posterior region in external aspect) ; d) BMNH R.11370, left maxillary type D (internal aspect) ; e) BMNH R.11370, left maxillary type D (external aspect) ; from the Upper Bathonian of Kirtlington, Oxfordshire ; scale = 1 mm. a) Maxillaire droit type C (face interne) ; b) Maxillaire droit type C (face externe); c) Maxillaire droit type C (rggion postgrieure en face externe) ; d) Maxillaire gauche type D (face interne) ; e) Maxillaire gauche type D (face externe). Bathonien sup6fieur de Kirtlington, Oxfordshire ; 6chelle = I mm.

Although all atlantal centra share the above characteristics which separate them from those of all other caudates, living or fossil, they can also be segregated into two types based primarily on the shape of the anterior cotyle. In most specimens, the cotyles appear to be almost circular with a dorsomedial indentation but in one large atlas, R.11364, the cotyles are dorsoventrally flattened. The possibility that this was ontogenetic or individual variation was considered and two bivariate plots of different atlas dimensions were constructed using all available material. The first plot of individual cotyle height against width is depicted in fig. 4a. The second plot of anterior width against posterior width of the atlas is depicted in fig. 4b. In fig. 4a, it may be seen that most of the anterior cotyles form a closely defined series, but that two

are quite distinctly separate and these are the left and right cotyles of R.11364. Likewise in ilK. 4b, the only specimen which falls outside the main sequence is R.11364. These proportional differences and the anterior cotyle shapes form a major component of the species diagnoses given above. The two types of vertebra also differ in the pit and groove configuration on the side of the centrttm, most specimens showing two pits and one elongate groove while R.11364 has three elongate grooves. Finally the interglenoid tubercle of R.11364 is relatively shorter than in the other atlantes with less pronounced tips. Although R.11364 is a large atlantal centrum, these differences are not simply ontogenetic as there are a few other large atlantal centra which resemble the smaller ones. Consequently the commoner type of atlantal centrum (14 specimens)

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b

a ~,~4"..*at

~ i ~iL~'i ?~ ~i .

..

..

Fig. 7 - Marmorerpeton sp. undet, a,b) BMNH R.11373, anterior left dentary (medial aspect and symphysis) ; c) BMNH R.11371, left vomer (palatal aspect) ; from the Upper Bathonian of Kirtlington, Oxfordshire ; scale = 1 mm. a,b) Partie ant6rieure du dentaire gauche (vue m6diale et symphysaire) ; c) Vomer gauche (vue palatine). Bathonien supdrieur de Kirtlington, Oxfordshire ; 6chelle = 1 mm.

has formed the basis of one species, M. kermacki, while R.11364 forms the basis of the second species, M. freemani. Four incomplete exoccipitals have been recognized in this material, one of which, R.11363, is described and illustrated here (figs 2a-c). In all specimens, the shape of the occipital condyle is roughly circular with a slight ventromedial extension (fig. 2a) and thus corresponds to the atlantal cotyles of M. kermacki. Consequently the exoccipitals may be confidently assigned to that species. They vary in size over the same range as the atlantes of M. kermacki and the bone is pitted in a similar manner. Parts of the anterior regions of the exoccipitals are invariably broken, R.11363 bears an incomplete occipital arch and the vagus foramen is exposed as a notch and groove on the distal side of the exoccipital (fig. 2b).

There are numerous premaxillaries, aii of which belong to forms in which they are paired structures. All possess a short, wide pars facialis ( = dorsal process) which diverges from the midline indicating the presence of an internasal fontanelle. There is space for 7-8 large teeth, although none have well preserved teeth present. The premaxiUaries can be partitioned into two morphological subtypes here identified as type A (27 specimens) and type B (3 specimens). Much of the following description centres on the pars facialis of each premaxillary type as this region bears most of the distinguishing features. Premaxillaries in which the pars facialis is damaged or broken off are difficult to place. A left premaxillary, R.11365, is the basis of the description of type A. At least 8 teeth were present. The external surface of the premaxillary is convex and is smooth in small specimens but possesses some dermal ornament over the pars facialis of large specimens (fig. 5b). The pars facialis is very broad in relation to its height. Its dorsal edge is smoothly rounded or possesses a slight lateral spine. The internal surface of the pars facialis is deeply concave and at its dorsal edge, it has a broad facet for contact with the nasal (fig. 5a). The pars palatina or palatine flange is narrow although in some small specimens it broadens slightly medially. This contrasts with the situation in Lisserpeton in which the pars palatina is very broad (Estes 1965, fig. 4). The medial edge of the pars facialis meets the alveolar region at a right angle and is sufficiently inset from the medial edge of the alveolar region that there must have been an internasal fontanelle between the partes faciales (figs 5a, b). There is also a pocket depression on the internal face of this junction. The lateral border of the pars facialis bears a rounded notch where it meets the alveolar region, probably for a branch of the trigeminal nerve (C.N.V) (figs 5a, b). A large right premaxillary, R.11366 (figs 5c, d), and a small right premaxillary, R.11367 (fig. 5e), form the basis of the description of type B. At least 7 teeth were present. The external surface is smooth and almost flat with one or two foramina present (figs 5d, e). The pars facialis is narrower than in A and is taller than wide. The medial edge of the pars facialis slopes gently back from the alveolar region and there is a posteriorly directed terminal point. Again the divergence of the partes faciales anteriorly indicates the presence of an internasal fontaneUe. There is a narrow facet on the internal side of the apical region, probably for a narrow contact with the nasal (fig. 5c). The rest of the

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8

g

h

t 7"

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Fig. 8 - Marmorerpeton sp. undet, a) BMNH R.11375, neural spine (dorsal aspect) ; b) BMNH ILl1375, neural spine (left lateral aspect) ; c) BMNH R.11376, trunk vertebra (anterior aspect) ; d) BMNH R.11376, trunk vertebra (left lateral aspect) ; e) BMNH R.11376, trunk vertebra (dorsal aspect) ; 0 BMNH ILl1376, trunk vertebra (ventral aspect) ; g) BMNH 1Ll1377, trunk centrum (left lateral aspect) ; h) BMNH R.11377, trunk centrum (ventral aspect) ; i) BMNH tll1378, caudal centrum (ventral aspect) ; from the Upper Bathonian of Kirtlington, Oxfordshire ; scales = I mm. a) Neur6pine (vue dorsale), b) Neur~pine (face lat6rale gauche) ; c) Vert6bre dorsale (face ant~deure) ; d) Vert6bre dorsale (face lat6rale gauche) ; e) Vert6bre dorsale (face dorsale) ; f) Vert6bre dorsale (face ventrale) ; g) Centrum dorsal (face lat6rale gauche) ; h) Centrum dorsal (face ventrale) ; i) Centrum caudal (face ventrale) ; Bathonien sup~rieur de Kirtlington, Oxfordshire ; 6chelles = 1 mm.

internal face of the pars palatina is slightly concave. There is no pocket depression near the anterior junction of the pars facialis and the alveolar region. The pars palatina is a narrow shelf in the small specimen (R.11367) where it is completely preserved. There are no complete maxillaries but several large fragments are present. The teeth are too poorly preserved in any of them to be of systematic use, but the tooth bases are similar in size to those in the premaxillaries. The maxillaries can be partitioned into two morphological subtypes here identified as type C (5 specimens) and type D (1 specimen). Two right maxillaries R.11368 and R.11369 (fig. 6a-c) show most of the osteological features of type C. The pars facialis

or dorsal process is narrowly triangular and has a few dermal ornament pits near its apex on the external side (fig. 6b). On the upper edges of its external face, the pars facialis has two narrow facets (fig. 6b). By analogy with C r y p t o b r a n c h u s , the facet on the anterior edge is for the nasal, while that on the posterior edge is for the prefrontal and/or the frontal. R.11369 shows that at the base of the posterior edge of the pars facialis is a deep notch which may be for the lacrimal foramen (fig. 6c). The absence of facets here suggests the possibility that there may have been no lacrimal ossification. On the internal face there is a deep oval foramen at the junction of the alveolar region and the pars facialis for the maxillary division of nerve V (fig. 6a~. The palatal ridge at the base of the pars facialis is

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shallow. When seen end-on, the pars facialis is incurved medially, curving smoothly into the alveolar region, suggesting that one species of Marmorerpeton had a wide flat snout like Cryptobranchus. R.11370 (fig. 6d-e) is the only certain type D maxillary. It is a left maxillary broken immediately behind the pars facialis which has lost its posterior edge. The pars facialis appears to be longer and broader than in type C and with a posteriorly directed terminal point and no dermal ornament except for a shallow groove which runs roughly parallel to the anterodorsal edge (fig. 6e). Where the anterior edge of the pars facialis meets the alveolar region there is a short step or notch. The external face of the alveolar region is smooth but bears small foramina for sensory nerves. On its internal face, the pars facialis bears a deep medial pocket facet, either for a prefrontal or nasal, but there is no foramen in this region (fig. 6d). There is also a double groove below the pocket facet anteriorly, which corresponds to the notch at the anterior base of the pars facialis (fig. 6d). When seen end-on, the pars facialis is relatively upright and joins the alveolar region at a sharp angle. In the absence of well-preserved teeth on these specimens, we have been unable to identify any morphological criteria that would permit us to associate premaxillaries and maxillaries. It may be noted that A and C are relatively more abundant than B and D (27 + 5 : 3 + 1) and it is tempting to associate them on this basis. However, a large sample (300 +) of alba'nerpetontid vertebrae in the Kirtlington assemblage comprises roughly equal numbers of atlas and trunk vertebrae ! This suggests that, for this assemblage, it may be unwise to associate bones into species purely on the basis of relative numbers. The vomer bears teeth in a curved row near its anterior edge, paralleling the marginal dentition. R.11371 (fig. 7c) bears about 7 teeth but is broken medially and the palatal plate is incomplete. R.11372 is a smaller, less well preserved vomer but bears a more complete row of 9 teeth. A tooth-row paralleling the marginal dentition is the larval-type configuration in caudates and is retained to a large size only in neotenous caudates such as the eryptobranchids and scapherpetontids. No certain characters could be found to distinguish the dentaries into more than one subtype. All appear to have the same type of sculpture, the same type of tooth and the same shape of intermandibular

symphysis. The dentary is relatively deep with large bicuspid teeth which are only weakly pedicellate (fig. 7a). Such weak pedicely is found in several neotenous caudates including the scapherpetontids. Study of fragments representing various parts of the dentary suggests an estimate of 25 - 35 teeth in a dentary ramus. The external face of the dentary bears a horizontal groove at the level of tooth bases. Such grooves are known in several batrachosauroidids and scapherpetontids. One characteristic of the dentary distinguishes Marmorerpeton from Lisserpeton, namely a prominent mandibular symphysis which is circular in cross-section (fig. 7b). The mandibular symphysis bears concentric growth-zones as described in the scapherpetontid Piceoerpeton by Naylor & Krause (198I), and similar growth-zones can be observed throughout the marginal tooth-bearing bones. There is an open Meckel's canal dosing near the anterior end of the dentary (fig. 7a). This feature shows some variation in this material. In 19 specimens there are 3-5 dentary teeth over the dosed region of the Meckelian groove as in fig. 7a. In 6 specimens there are 7-8 teeth over this region. This may be generally, though not precisely, size-linked with the progressive closure of the Meckellan groove occuring with growth and the relative reduction in tooth-size in large salamanders. The same phenomenon appears to occur in Piceoerpeton as figured by Naylor & Krause (1981, fig. 3). The trunk vertebrae lack spinal nerve foramina (figs 8d, g), a primitive character found in several caudate families. The trunk centra resemble those of some batrachosauroidids in that they are deeply amphicoelous with almost circular cotyles and prominent notochordal perforations (fig. 8a). The anterior cotyles lack ring-like calcifications. The ventral face of the trunk centrum bears no medial keel or paired fossac (fig. 8f), but there may be a medial depression (fig. 8h). The medial depression is even more pronounced on the caudal centra (fig. 8i). The rib-bearers are distinctly bicipital, the upper rib-bearer emerging above the level of the top of the centrum. Some neural spines (fig. 8a, b) are prominent elongate backwardly -directed structures. These are believed to characterize the families Batrachosauroididae and Scapherpetontidae. The neural spine tips are finished in cartilage (fig. 8a), a scapherpetontid characteristic. The distribution of such neural spines along the trunk is unknown as no form bearing them is known from articulated material. Trunk vertebra R.11376 (fig. 8c-t) has an apparently complete neural spine which is short and low, and there may be varia-

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a

tion in neural spine height along the trunk as in salamandrids (Estes 1982, p.192).

d C C d'-

.--C

V

Fig. 9 - Marmorerpeton sp. undet, a) BMNHR.11379,fragmentsof large left humerus (anterior aspect) ; b) BMNH R.11379, large left humerus (proximalaspect). Salamandra maculata, c) outline of humerus for comparison with fig. 9a ; d) proximal end of humerus for comparison with fig. 9b ; abbreviations : cd = crista dorsalis, car = crista ventralis ; from the Upper Bathonian of Kirtlington, Oxfordshire; scale = 1 cm. Marmorerpeton sp. a) Fragments d'un grand humerus gauche (face antdrieure) ; b) Grand humerus gauche (extrdmit6 proximale). Salamandra maculata c) Silhouette d'un humeruspour eomparaison avec la fig. 9a ; d) ExtrEmit6proximaled'un humerus pour comparaison avec la fig. 9b ; abrEviations : cd = crista dorsalis, cv = crista ventralis. Bathonien supErieur de Kirtlington,Oxfordshire; 6chelle = 1 cm

A large humerus (R.11379) is represented by its two ends (fig. 9a). Although found as separate fragments, they derive from a single 18 kg sample of matrix and are assumed to be the remains of a single bone, particularly as no other salamander humerus of comparable size has been found at this site. Unfortunately the shaft was not recovered. Scaled against the humeri of modern salamanders, it appears to have belonged to an indMdual of about 40 cm total length. Growth-rings can be seen in the broken sections of the bone. Both proximal and distal ends are expanded and the shaft appears to have been slender. At the proximal end is an epiphyseal surface for the "ball" of the humerus head (fig. 9b). The dorsal side of the proximal region lacks a crista dorsalis for insertion of the m. latissimus dorsi. This feature is variable in modern salamanders, being prominent in hynobiids, plethodontids and salamandrids (fig. 9c) but weakly developed or absent in other families (Estes & Sancliiz 1982). Although the absence of a crista dorsalis is not diagnostic for neotenous caudates, it is certainly consistent with that condition. The ventral side of the proximal region bears a crista ventralis for the m. dorsalis scapulae but does this not extend beyond the proximal end of the bone. In end view (fig. 9b), the proximal end of the humerus of Marmorerpeton closely resembles that of the modern Salamandra (fig. 9d). The distal end of the bone is more expanded than in Scapherpeton and bears a ventral depression. The areas for the radial and ulnar epiphyses are only slightly differentiated. There are no crests or tubercles for the fore-arm flexors and extensors. It may be noted here that there are also several scapulocoracoids and ilia of suitable size and shape to be referred to Marmorerpeton sp.. The ilia conform to the description of that in Scapherpeton given by Estes (1981). Unfortunately the configurations of Albanerpeton scapulocoracoids and ilia are at present unknown and Albanerpeton is more abundant than Marmorelpeton in the Kirtlington fauna. There is, however, a difference in size range, the largest Albanerpeton being similar in size to the smaller Marmorerpeton specimens. These elements are sufficiently large that they probably belong to Marmorerpeton but because they might possibly belong to Albanerpeton, their description is deferred, pending the possibility of more precise attribution.

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S Y S T E M A T I C POSITION :

This material may be characterized as a fossil caudate because of the atlas vertebra with the anterior cotyles extending onto the medial tubercle, and the trunk vertebrae with bicipital rib-bearers. These are both characteristic caudate features (Estes 1981). The weakly pedicellate teeth, the vomerine dentition paralleling the marginal dentition in such a comparatively large salamander and the humerus lacking a crista dorsalis combine to suggest that it was a neotenous form, regardless of its systematic position. The absence of intravertebral spinal nerve foramina in the atlantal centrum is a primitive character found in no other living or fossil caudate (Edwards 1976), and suggests that Marmorerpeton is the most primitive caudate, as well as the earliest. The absence of such foramina in the trunk centra is a primitive feature found in several caudate families (Edwards 1976). All the more specific resemblances are with members of two extinct families of neotenous salamanders, the Batrachosauroididae and the Scapherpetontidae. The elongate, backwardly-directed neural spines and the groove on the external face of the dentary occur in members of both families and the amphicoelous trunk centra with circular cotyles and prominent notochordal perforations have previously 0nly been described in some batrachosanroidids. There are however, many more resemblances to the scapherpetontids. The pits andgrooves on the sides and the ventral surface of the atlas ; the conical posterior cotyle of the atlas ; the neural spine-tips of the trunk vertebrae finished in cartilage and the broad vomer with gently curved vomerine tooth-row are all scapherpetontid features. The dentition most closely resembles that of the scapherpetontid Lisserpeton in the shape and size of the teeth, but other features of uncertain phylogenetic polarity serve to distinguish Marrnorerpeton from Lisserpeton. These include the elongate atlantal centrum ; the medial depression on the ventral surface of the trunk centrum instead of a keel ; the narrow shelf on the premaxillary ; and the circular cross-section to the mandibular symphysis. Because of character reversals

produced by neoteny, the evolutionary polarity of many of these osteological characters is unknown. Hence the above listed resemblances to the scapherpetontids may be phenetic rather than cladistic, particularly as the Scapherpetontidae is a poorly defined family (Estes 1981, p. 49) in which the association of atlantes with other elements is problematic (Naylor 1983, p. 51). In summary, Marmorerpeton resembles members of the family Scapherpetontidae in several characters of uncertain polarity, but in one character of relatively certain polarity (absence of intravertebral foramina in the atlas) it is more primitive than any known salamander, living or fossil (Edwards 1976). For this reason we feel it is premature to assign Marmorerpeton to the Scaplierpetontidae but simply categorize it as Familylncertae Sedis within the Caudata. The alternative systematic positions suggested by these characteristics both have interesting implications. (1) If Marmorerpeton is a scapherpetontid, and the scapherpetontid characters could be shown to represent uniquely derived conditions, then the family Scapherpetontidae, hitherto known from Upper Cretaceous and early Cenozoic assemblages, must have originated in the Middle Jurassic or earlier, and this may prove to be true of other salamander families as well. This hypothesis would also imply the convergent development of the spinal nerve foramen in the atlantal centrum within scapherpetontid and in non-scapherpetontid salamanders. (2) If alternatively, Marrnorerpeton is argued to be the most primitive known salamander based on this character, then the resemblance of Marmorerpeton to the scapherpetontids may be convergence associated with neoteny. It is possible that early neotenous salamanders such as Marmorerpeton, the scapherpetontids and batrachosauroidids are phenetically similar, not through immediate relationship but through common possession of primitive larval caudate characters convergently retained to a large size through neoteny. The scapherpetontids have proved difficult to define (Estes 1981), are unusually variable in features such as atlantal centrum construction (Naylor 1983) and may represent a polyphyletic assemblage of neotenous primitive salamanders.

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THE KIRTLINGTON HERPETOFAUNA

Marmorerpeton kermacki and M. freemani are associated with a large assemblage of small amphibians and reptiles in the Kirtlington fauna. The amphibians include a third, smaller salamander of uncertain relationships, a frog of the family Discoglossidae and abundant material referrable to the enigmatic amphibian family Albanerpetontidae. The reptiles include small turtles, small crocodiles and a small champsosaur. The significance of this material is not only that the salamanders, the discoglossid and the champsosaur are the earliest examples of their respective taxa (the albanerpetontid is slightly younger than the Aveyron specimen), but that they occur together as a freshwater assemblage. This is the first extensive assemblage of Middle Jurassic freshwater microvertebrates to be described and it bears a significant resemblance to later Mesozoic freshwater assemblages

rather than earlier ones. Even though the salamanders cannot be certainly referred to later families, elements of this salamander - discoglossid - albanerpetontid - turtle - crocodile - champsosaur association can be recognized in the Upper Jurassic at Guimarota, the Lower Cretaceous at Una and in late Cretaceous assemblages of the Judith River (= Oldman) and Lance Formations of North America. This suggests that such freshwater tetrapod assemblages in the northern continents were established by the Middle Jurassic and thereafter evolutionarily relatively stable until the early Tertiary. Champsosaurs last appear in the fossil record in the late Palaeocene, scapherpetontid salamanders in the early Eocene and albanerpetontids in the Miocene. Other elements persist in the northern continents up to the present.

CONCLUSIONS The discovery of Marmorerpeton kermackt, M. freemani and the third Kirtlington salamander demons-

Marmorerpeton is unclear, it may be the sister-taxon to

trates that indisputable members of the Caudata (i.e. not albanerpetontids) were present in the Middle Jurassic and that some of them were neotenous. Marmorerpeton is more primitive than any other known candate in the absence of intravertebral spinal nerve foramiua in the atlantal centrum and demonstrates that this caudate characteristic was acquired subsequent to

all other caudates or it may be a primitive scapherpetontid. We do not have sufficient knowledge of the polarity of characters in early salamanders to resolve this matter. The Kirtlington assemblage demonstrates that the Upper Jurassic-Eocene freshwater herpetofauna of the northern continents was already established by the Middle Jurassic.

the bicipital rib-bearers. The systematic position of

Acknowledgements

Our thanks go to Professor Kenneth A. Kermack who organized the collection and preparation of most of this material, and to Mr Eric F. Freeman who first recognized the potential of this locality, and who

generously made significant specimens available to us for study. We should also like to thank Dr A. de Ricq16s for considerably improving the French R6sum6 and figure captions.

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REFERENCES

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FREEMAN E.F. (1979) - A Middle Jurassic mammal bed from Oxfordshire. Palaeontology, London, 22 : 135-166. HARLAND W. B., COX A. V., LLEWELLYN P. G., PICKTON C. A. G., SMITH A.G. & WALTERS R. (1982) - A geologic time scale. Cambridge Uni-

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ESTES R. (1965) - A new fossil salamander from Montana and Wyoming. Copeia, New Haven, 1965, (1) :90-95.

HECHT M. & E.sq~ R. (1960) - Fossil amphibians from Quarry Nine. Postilla, New Haven, 46 : 119.

ESTES R. (1969) - The Batrachosauroididae and Scapherpetontidae, late Cretaceous and early Cenozoic salamanders. Copeia, New Haven, 1969, (2) :225-234.

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MILNER A.R. (1988) - The relationships and origin of 1Mng amphibians. In "The Phylogeny and Classification of the Tetrapods, Vol. 1 : Amphibians, Reptiles, Birds", BENTON M.J. ed., Systematics Association Special Volume 35A : 59102. Clarendon Press, Oxford.

ESTES R. & SANCHIZ B. (1982) - Early Cretaceous lower vertebrates from Galve (Teruel), Spain. Z Vert. Paleont., Norman, 2 : 21-39. FOX R.C. & NAYLOR B. G. (1982) - A reconsideration of the relationships of the fossil amphibian Albanerpeton. Can. J. Earth Sci., Ottawa, 19 : i18-128. FREEMAN E.F. (1976) - Mammal teeth from the Forest Marble (Middle Jurassic) of Oxfordshire~ England. Science, Washington, 194 : 1053-1055.

NAYLOR B. G. (1983) - New salamander (Amphibia : Caudata) atlantes from the Upper Cretaceous of North America. Z Paleont., Tulsa, 57 : 48-52. NAYLOR B.G. & KRAUSE D.W. (1981) - Piceoerpeton, a giant early Tertiary salamander from western North America. Z Paleont., Tulsa, 55 : 507-523. SEIFFERT J. (1969) - Urodelen-atlas aus dem obersten Bajocien von SE-Aveyron (Sudfrankreich). Palaeont. Z., Stuttgart, 43 : 32-36.

Manuscrit d6pos6 le 21.03.1988 Manuscrit d6fmitif re~u le 20.06.1988