Anoualerpeton priscus, Gardner & Evans & Sigogneau-Russell, 2003

Gardner, James D., Evans, Susan E. & Sigogneau-Russell, Denise, 2003, New albanerpetontid amphibians from the Early Cretaceous of Morocco and Middle Jurassic of England, Acta Palaeontologica Polonica 48 (2), pp. 301-319 : 309-313

Anoualerpeton priscus sp. nov.

Figs. 3 , 4 .

Albanerpeton Estes and Hoffstetter ; Evans and Milner 1994: 306.

Celtedens megacephalus (Costa); McGowan 1996: 233, figs. 1–9, 11–13; McGowan 1998b: 116; McGowan 2002: 3.

Celtedens cf. C. megacephalus (Costa); McGowan and Ensom 1997: 117.

Celtedens cf. megacephalus (Costa); McGowan 1998a: fig. 1G.

Celtedens ibericus McGowan and Evans ; McGowan 1998a: fig. 4.

Genus and species indeterminate; Gardner 2000a: 67, fig. 4.

Kirtlington albanerpetontid; Gardner 2000a: 68; Gardner 2002: 14.

Kirtlington species; Gardner 2002: 12.

Etymology: Priscus, Latin “ancient”, referring to this being the oldest known, diagnosable albanerpetontid species.

Holotype: BMNH R.16336 (original number UCK 14 ), incomplete left premaxilla lacking dorsal end of pars dorsalis, lateral end of pars dentalis, and most of pars palatinum, with preserved tooth row containing nine broken tooth bases and empty tooth slots, one of which preserves an in situ replacement crown ( Fig. 3A ).

Holotype locality, horizon, and age: Kirtlington Cement Quarry, Oxfordshire, south−central England ( Evans and Milner 1994: fig. 18.1); “Kirtlington Mammal Bed” sensu Freeman (1979), basal part of Forest Marble Formation. The lower part of the Forest Marble Formation is dated as Middle Jurassic (middle late Bathonian) based on correlation withthe Oppelia aspidoides ammonitezone(seeMetcalfetal.1992:fig. 2).TheKirtlingtonMammalBedisinterpretedashavingbeendeposited under non−marine conditions in a swampy coastal region ( Evans and Milner 1994). See Freeman (1979) and Evans and Milner (1994) for additional information.

Referred specimens.—All catalogued and uncatalogued specimens are in the collection of the BMNH. Specimens previously listed by McGowan (1996) each bore informal UCK catalogue numbers, which are indicated below in brackets following the permanent BMNH catalogue number. Premaxillae (n = 24) BMNH R.14157, R.16337 (UCK 15), R.16353 (UCK 17), and 21 uncatalogued; maxillae (n = 33): BMNH R.16338 (UCK 10), R.16339, R.16357 (UCK 05), R.16364, R.16365, and 28 uncatalogued; dentaries (n = 97): BMNH R.16340, R.16343 (UCK 01), R.16344 (UCK 03), R.16354 (UCK 06), R.16355 (UCK 02), R.16356 (UCK 08), R.16477, and 90 uncatalogued; frontals (n = 19): BMNH R.14158–14160, R.16342 (UCK 26), R.16345 (UCK 27), R.16351 (UCK 25), R.16352 (UCK 24), and 12 uncatalogued; parietals (n = 5): BMNH R.16346 (UCK 23) and four uncatalogued; quadrates (n = 17): BMNH R.16358 (UCK 33), R.16359 (UCK 34), and 15 uncatalogued; atlantes (n = 6): BMNH R.16341, R.16348 (UCK 18), R.16349 (UCK 21), R.16350 (UCK 20), and two uncatalogued; axes (n = 2) BMNH R.16347 (UCK 22) and one uncatalogued; trunk vertebrae (n = 14): BMNH R.16360 (UCK 28), R.16361 (UCK 29), R.16362 (UCK 31), and 11 uncatalogued; caudal vertebra (n = 1): BMNH R.16363 (UCK 32); and indeterminate pieces of dentition and unsorted material.

Distribution.—Known only from the holotype locality.

Diagnosis.—Species of Anoualerpeton differing from Early Cretaceous congener described above as follows: suprapalatal pit located more laterally in pars dorsalis of premaxilla, essentially within margin for external narial opening and in line with sixth or seventh tooth position from medial end of tooth row; dorsal opening of palatal foramen in premaxilla medial to base of suprapalatal pit; internasal process on frontals relatively more elongate (midline length about 1.2 times width across base) and blunt distally; anterolateral processes on frontals an indistinct shoulder, with distal end blunt; and ventrolateral crests on large frontals triangular in transverse view, with ventral face flat to shallowly concave.

Description.—The collection from Kirtlington contains substantial numbers of isolated jaws, frontals, parietals, quadrates, and vertebrae, none of which is complete. Examples of these elements previously were reported and figured by McGowan (1996) and, where known, generally resemble those of Anoualerpeton unicus . For these reasons, our descriptions below focus on taxonomically significant and otherwise notable features of the jaws, frontals, and atlas.

Premaxilla ( McGowan 1996: fig. 1; Gardner 2000a: fig. 4d; here: Fig. 3A–C ).—The most nearly complete specimens are the holotype BMNH R.16366 ( Fig. 3A ), BMNH R.16337 ( Fig. 3B ), and BMNH R.14157 ( Fig. 3C ); collectively these three specimens document much of the structure of the premaxilla. All premaxillae are isolated and none shows evidence of medial fusion. As no specimen at hand preserves the dorsal part of the pars dorsalis, nothing can be said about the relative proportions of the pars dorsalis, the pattern of contact dorsally with the nasal, or the nature of the dorsal boss. The pars dorsalis on the holotype preserves the base of the lateral notch for contact with the lacrimal. The suprapalatal pit resembles that in Anoualerpeton unicus in being similarly small and oval in outline, in lying above the level of the pars palatinum, and in opening laterolingually, but differs in being positioned farther laterally across the pars dorsalis, virtually within the external narial margin and in line with the sixth or seventh tooth position from the medial end of the row. The palatal foramen is relatively small, but in contrast to An. unicus the dorsal opening of this foramen lies medial to the base of the suprapalatal pit. The palatal foramen is free of sediment in BMNH R.14157 and a thread pushed into the dorsal opening ( Fig. 3C 2) demonstrates that the canal descends ventromedially through the pars palatinum ( Fig. 3C 1 ). The pars palatinum is lingually broad as in other albanerpetontids, with a prominent vomerine process medially and broad maxillary process laterally. The lingual face of both processes is indented by a shallow facet for contact with a palatal bone, presumably the vomer. The lingual edge of the maxillary process dorsally bears a low ridge that, in life, held the lingual edge of the premaxillary dorsal process on the maxilla when the two jaws were articulated.

Maxilla ( McGowan 1996: fig. 2; here: Fig. 3D ).—The two most nearly complete specimens, BMNH R.16338 and R.16339, are from the left side and anatomically overlap for about a dozen tooth positions behind the posterior edge of the internal narial margin. The more nearly complete specimen, BMNH R.16338 ( Fig. 3D ), preserves most of about the anterior four−fifths of the bone, but lacks the leading edge of the premaxillary dorsal process and a large triangular piece from the pars dentalis below the nasal process. This specimen has been broken in two; the more posterior part was figured by McGowan (1996: fig. 2). Judging by the profile of the ventral edge of the bone immediately in front of and behind the missing section of the pars dentalis, the occlusal edge was ventrally convex in the missing region. This interpretation is supported by the convex dorsal edge on the referred dentaries (see below). BMNH R.16339 (unfigured) is broken anteriorly across the posterior limit of the internal narial margin and preserves about the posterior half of the bone with the last 16 tooth positions. Maxillae from Kirtlington resemble those of Anoualerpeton unicus as follows: labial ornament absent; similarly elongate premaxillary lateral process; anterior end of tooth row lies anterior to level of leading edge of nasal process; and, evidently, occlusal edge of pars dentalis ventrally convex in outline.

Dentary ( McGowan 1996: figs. 7, 8; here: Fig. 3E–H ).—The available dentaries are fragmentary and no specimen preserves more than about one−half of the bone. One of the most informative specimens is BMNH R.16344, which is the anterior end of a left dentary that preserves the first 11 tooth positions. Figured in labial view by McGowan (1996: fig. 8d) and here in lingual view ( Fig. 3E ), BMNH R.16344 shows that dentaries of Anoualerpeton priscus resemble those of An. unicus in having the occlusal edge of the anterior part of the bone strongly convex in labial or lingual outline. The other specimens figured here preserve more posterior areas of the dentary ( Fig. 3F–H ). As in most other albanerpetontids, including An. unicus , the labial face of the bone is unornamented and there is no dorsal process immediately behind the tooth row. In other respects, dentaries of An. priscus are typical for albanerpetontids.

Teeth ( Figs. 3A 1, B, D 1 , D 2, E–H, 4A–E ).—Intact teeth resemble those of other albanerpetontids and, particularly, Anoualerpeton unicus in arrangement, attachment, and structure. Although no jaw preserves an intact tooth row, tooth counts on the upper and lower jaws are probably similar to those in other albanerpetontids. Teeth on the dentary and, evidently, the maxilla are heterodont in size anteriorly, to about the same extent as in An. unicus . On the dentary BMNH R.16344 ( Fig. 3E ) the teeth adjacent to the apex of the dental parapet are larger than the more anterior teeth and, presumably, the more posterior ones as well. Although the maxilla BMNH R.16338 is missing the critical region of the pars dentalis below the nasal process, judging by adjacent teeth and tooth slots, the teeth along the missing part of the tooth row were also enlarged. The form of the tooth crowns varies to an even greater extent than in An. unicus . Crowns range in labial or lingual outline from chisel−shaped ( Fig. 4A ), to wedge−shaped ( Fig. 4B, C ), to pointed ( Fig. 4D ). Differences in crown form are due to variation in the following attributes: length of central cuspule relative to mesial and distal cuspules (e.g., central cuspule moderately longer than mesial and distal cuspules on chisel−shaped crowns versus central cuspule markedly longer on pointed crowns); relative expression of distal and mesial cuspules (e.g., mesial and distal cuspules typically more strongly developed on chisel− and wedge−shaped crowns versus comparatively less well developed on pointed crowns); and mesio−distal width of crown relative to pedicel width (e.g., crown typically broader than pedicel in teeth with chisel− and wedge−shaped crowns versus crown typically narrower than pedicel in teeth with pointed crowns). As in An. unicus , tooth crowns tend to be more pointed or wedge−shaped along the anterior part of the maxilla and dentary, and more chisel−shaped posteriorly ( Fig. 4E ).

Frontals ( McGowan 1996: figs. 3, 4; Gardner 2000a: fig. 4A–C; here: Fig. 4F–I ).—Frontals are solidly fused medially, with occasional specimens retaining a faint median line of fusion ventrally. The two most nearly complete and informative specimens anatomically overlap one another in the area of the posterior slots for receipt of the prefrontals: BMNH R.14158 ( Fig. 4F ) is about the anterior one−third of a pair of large frontals, whereas BMNH R.16342 ( Fig. 4G ) is about the posterior two−thirds of a slightly smaller pair of frontals. Frontals of Anoualerpeton priscus resemble those of An. unicus in overall structure and proportions, but differ in the form of the internasal and anterolateral processes and the ventrolateral crest. BMNH R.14158 shows that the internasal process is relatively more elongate (midline length about 1.2 times width across base) and rounded distally and that the anterolateral processes are less pronounced and more rounded distally. BMNH R.14159 ( Fig. 4H ) and R.14160 ( Fig. 4I ) are less nearly complete examples of small and large frontals, respectively; these specimens show that with growth the ventrolateral crest changed from convex to more nearly triangular in transverse profile and the ventral face of the crest became shallowly concave dorsally. Some specimens at hand for An. priscus come from individuals slightly two−thirds of tooth row. H. BMNH R.16340, right dentary, anteriorly and posteriorly incomplete ramus preserving about posterior two−thirds of tooth row and anterior part of area for attachment of postdentary bones. Osteological abbreviations: dpf, dorsal opening of palatal foramen; lf, lateral foramen; mp, maxillary process on pars palatinum; rc, in situ replacement crown; sp, suprapalatal pit; syp, symphyseal process; vp, vomerine process on pars palatinum; vpf, ventral opening of palatal foramen;?f, unknown foramen. Specimens at different scales.

larger than those represented for An. unicus and give an estimated snout–pelvic length of about 50 mm for the former species.

Other elements ( McGowan 1996: figs. 5, 6, 9, 11–13).— Other albanerpetontid elements from Kirtlington include parietals, quadrates, and vertebrae. In general these elements are similar to those described elsewhere for albanerpetontids, with one notable exception. Each of the six atlantal centra from Kirtlington bears a transverse groove on either side of the centrum, above and behind the anterior cotyle; in life, this groove carried the first spinal nerve. Although the walls of the arch are broken behind the groove in all specimens, the smooth dorsal surface along the anterior rim of the groove indicates that the groove was open dorsally and that no bony bridge extended dorsoposteriorly over the groove to create an enclosed foramen. Atlantes are not known for Anoualerpeton unicus , but an open groove for the first spinal nerve also has been noted in undescribed, basal Cretaceous atlantes of Celtedens sp. from Purbeck, England (S.E. Evans, unpublished observation). In all other albanerpetontid atlantes for which the path of the spinal nerve has been documented, the spinal foramen is completely enclosed within the base of the wall of the neural arch. These latter specimens are from the Cretaceous of North America and Miocene of France, and most can be attributed with confidence to Albanerpeton ( Estes and Hoffstetter 1976; Fox and Naylor 1982; Gardner 1999a –c, 2000b). The above observations suggest that the form of the spinal foramen in the atlas may vary at the generic level among albanerpetontids.

Remarks.—Association of albanerpetontid skull and postcranial elements from Kirtlington within one species is justified because there are no significant morphological differences among homologous elements recovered from the site ( McGowan 1996; Gardner 2000a). The only exception involves the degree of dorsal ornament on the frontals. Most frontals exhibit the usual albanerpetontid pattern of polygonal pits enclosed by low ridges. BMNH R.14158 is notable because the dorsal surface is virtually smooth (cf., Fig. 4F 1 versus G 1); this condition does not appear to be due to postmortem abrasion or erosion. Similar variation has been documented in some other albanerpetontid species for which adequate series of frontals are available (e.g., Albanerpeton nexuosus ; Gardner 2000b: fig. 6A, C). Although the source of variation in frontal ornament is uncertain, it does not appear to be taxonomically significant ( Gardner 2000b). Specimens from Kirtlington show considerable size variation, with the largest two or three times the size of the smallest, but morphological differences among homologous specimens (e.g., form of ventrolateral crest on frontals; cf., Fig. 4G 2, H 2, I) are within the expected range of individual and ontogenetic variation within a single species.

Three localities in the Forest Marble Formation collectively have yielded the second oldest occurrences of albanerpetontids from anywhere in the world. Besides the Kirtlington Cement Quarry, fragmentary albanerpetontid elements have been reported from the formation at Tarlton Clay Pit in Gloucestershire and at Watton in Dorset, both in England ( Evans and Milner 1994: table 18.2). Specimens from the last two localities are too incomplete to be identified to species or genus. Evans and Milner (1994: table 18.2) questionably listed albanerpetontids at the slightly older (early Bathonian) Hornsleasow Quarry, in the Chipping Norton Limestone Formation of Gloucestershire, but no mention of albanerpetontids appeared in subsequent, more detailed accounts of the locality and its assemblage ( Metcalf et al. 1992; Metcalf and Walker 1994). An undescribed axis has since been identified that confirms the presence of albanerpetontids at Hornsleasow Quarry (S.E. Evans, unpublished observation). The only reliable record of similar antiquity for the Albanerpetontidae is an atlantal centrum ( Seiffert 1969; Estes and Hoffstetter 1976) from the Gardies locality, southern France. Gardies originally was considered to be late Bajocian in age ( Seiffert 1969), but more recent work has revised the age estimate upwards to early Bathonian ( Kriwet et al. 1997 and references therein). Nessov (1988) reported an albanerpetontid frontal from the upper Middle Jurassic (Callovian) of Kirghizia, but this record is unproven ( Gardner and Averianov 1998). Elsewhere in the Jurassic, albanerpetontids are known by isolated and largely undescribed elements, including frontals that have been referred to Celtedens ( McGowan 1998a, 2002; however, see Wiechmann 2000), from two Upper Jurassic (Kimmeridgian) localities in Portugal —Guimarota ( Estes 1981; McGowan 1998a; Wiechmann 2000) and Porto Pinheiro ( Estes 1981).

Figures

Fig. 3. Jaws of Anoualerpeton priscus sp. nov.; Middle Jurassic (late Bathonian), Kirtlington, England. A–C. Premaxillae. A. BMNH R.16336, holotype, left premaxilla, lacking dorsal part of pars dorsalis, lateral part of pars dentalis, and most of pars palatinum and preserving no intact teeth, in lingual (A1) and laterolingual (A2) views. B. BMNH R.16337, right premaxilla, lacking dorsal part of pars dorsalis and medial pars of pars palatinum and pars dentalis, in labial (B1) and lingual (B2) views. C. BMNH R.14157, right premaxilla, lacking dorsal part of pars dorsalis, ventral part of pars dentalis, and lateral end of maxillary process and preserving no intact teeth, in lingual (C1) and dorsal (C2) views, both with hair extending obliquely through palatal foramen, and in occlusal (C3) view. D. BMNH R.16338, left maxilla, missing part of pars dentalis below nasal process and about posterior one−fifth of bone, in labial (D1), lingual (D2), and dorsal (D3) views. E–H. Dentaries, all in lingual view. E. BMNH R.16344, left dentary, posteriorly incomplete ramus preserving about anterior one−quarter of bone. F. BMNH R.16354, right dentary, anteriorly and posteriorly incomplete ramus preserving posterior part of tooth row and anterior part of area for attachment of postdentary bones; G, BMNH R.16356, left dentary, anteriorly and posteriorly incomplete ramus preserving about posterior

Fig. 4. Teeth and frontals of Anoualerpeton priscus sp. nov.; Middle Jurassic (late Bathonian), Kirtlington, England. A–E. Close ups of teeth, all in lingual view. A. BMNH R.16365, right maxilla, crown of tooth at second locus from broken anterior end of bone or, when tooth row was complete, about one−fifth of distance posteriorly along row. B. BMNH R.16356, left dentary, crowns of adjacent teeth at fourth (B1) and fifth (B2) loci from broken anterior end of bone or, when tooth row was complete, about three−fifths of distance posteriorly along row. C. BMNH R.16477, right dentary, crown of tooth at eighth locus from broken anterior end of bone or, when tooth row was complete, about one−half of distance posteriorly along row. D. BMNH R.16357, right maxilla, crowns of teeth at seventh (D1) and ninth (D2) loci from broken anterior end of bone or, when tooth row was complete, about one−third of distance posteriorly along row. E. BMNH R.16340, right dentary, row of five teeth and one empty tooth slot, extending from second to seventh loci from broken anterior end of bone or, when tooth row was complete, about three−fifths of distance posteriorly along row. F–I. Frontals. F. BMNH R.14158, anterior one−third of fused frontals, broken posteriorly between slots for receipt of prefrontals, in dorsal (F1) and right lateral (F2) views. G. BMNH R.16342, posterior two−thirds of fused frontals, broken anteriorly between slots for receipt of prefrontals and missing posterior end of ventrolateral crests on both sides, in dorsal (G1) and ventral (G2) views. H. BMNH R.14159, posterior part of small, fused frontals, broken anteriorly between slot for receipt of prefrontals on right side and midway along orbital margin on left side and missing left posterior corner, in dorsal (H1) and ventral (H2) views. I. BMNH R.14160, fragment of large, left frontal, preserving orbital margin, in ventral view. Osteological abbreviations: ap, anterolateral process; as, anterior slot; gr, groove; lfu, line of fusion; ps, posterior slot; vlc, ventrolateral crest. Specimens at different scales.

Fig. 1. Upper jaws and frontals of Anoualerpeton unicus sp. nov., type species; Lower Cretaceous (Berriasian), Anoual, Morocco. A, B. Premaxillae. A. MNHN.MCM 187, holotype, right premaxilla, lacking pars palatinum, in labial (A1) and lingual (A2) views. B. MNHN.MCM 188, left premaxilla, lacking dorsolateral part of pars dorsalis and vomerine and maxillary processes on pars palatinum, in labial (B1) and lingual (B2) views. C. MNHN.MCM 189, left maxilla, lacking about posterior one−fifth of bone, in labial (C1), lingual (C2), and dorsal (C3) views. D, E. Fused frontals. D. MNHN.MCM 190, nearly complete frontals, lacking distal end of left anterolateral process and posterior end of ventrolateral crests on both sides, entire specimen in dorsal (D1) and ventral (D2) views and closeup of anterior part in right lateral view (D3). E. MNHN.MCM 191, less nearly complete frontals, missing distal tip of internasal process, posterior end of left ventrolateral crest, and right posterolateral corner of bone and showing damage to median portion sustained during photography (cf., Fig. 2K), in dorsal view. White areas are broken surfaces and cross hatches are sand grains. Specimens at different scales.