Anoualerpeton unicus, Gardner & Evans & Sigogneau-Russell, 2003
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publication ID |
https://doi.org/ 10.5281/zenodo.13345778 |
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persistent identifier |
https://treatment.plazi.org/id/221B87D5-B31E-1B04-9D62-FB27BB11FDC3 |
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treatment provided by |
Felipe |
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scientific name |
Anoualerpeton unicus |
| status |
sp. nov. |
Anoualerpeton unicus sp. nov.
Figs. 1 View Fig , 2.
Anoual species; Gardner 2002: 12.
Anoual albanerpetontid; Gardner 2002: 14.
Etymology: Unicus, Latin “alone” or “solitary”, referring to this being the only known albanerpetontid species from Gondwana.
Holotype: MNHN. MCM 187 View Materials , right premaxilla missing most of pars palatinumandlateralmostpartofparsdentalis,withpreservedtoothrow containing three broken teeth and five tooth slots ( Figs. 1A View Fig , 2A).
Holotype locality, horizon, and age: Anoual microvertebrate locality, about 100 km east of the city of Anoual and near a fort called Ksar Met Lili, Talsinnt Province, eastern High Atlas Mountains, east−central Morocco ( Sigogneau−Russell et al. 1998: fig. 1); unnamed non−marine limestone lens, Couches Rouges (“red beds”) sandstone. The fossiliferous lens occurs within marine beds in the upper part of the Couches Rouges sandstone ( Sigogneau−Russell et al. 1990) and is interpreted as having been deposited in a deltaic setting ( Sigogneau−Russell et al. 1998). Nanofossils support an Early Cretaceous age, probably Berriasian, for the lens ( Sigogneau−Russell et al. 1990; Duffin and Sigogneau−Russell 1993). See Sigogneau−Russell et al. (1998) and Evans and Sigogneau−Russell (2001) for additional information.
Referred specimens.—Premaxillae (n = 4): MNHN.MCM 188, 198–200; maxillae (n = 5): MNHN.MCM 13, 189, 201–203; dentaries (n = 34): MNHN.MCM 4, 5, 19–34, 41–48, 192–197, 204, 205; frontals (n = 3): MNHN.MCM 11, 190, 191; parietal (n = 1): MNHN.MCM 12; articular (n = 1): MNHN.MCM 6; humerus (n = 4): MNHN.MCM 7, 14–16; trunk vertebrae (n = 15): MNHN.MCM 8, 9, 35–40, 49–55; and caudal vertebrae (n = 3): MNHN.MCM 10, 17, 18.
Distribution.—Known only from the holotype locality.
Diagnosis.—Species of Anoualerpeton differing from Middle Jurassic congener described below as follows: suprapalatal pit located more medially in pars dorsalis of premaxilla, just medial to margin for external narial opening and in line with fourth or fifth locus from medial end of tooth row; dorsal opening of palatal foramen in premaxilla below or within base of suprapalatal pit; internasal process on frontals relatively shorter (midline length subequal to width across base) and pointed distally; anterolateral processes on frontals pointed distally and distinct from main body of bone; and ventrolateral crests on frontals convex ventrally to bevelled in transverse view.
Description.—None of the 71 catalogued specimens at hand is complete, but the available jaws and frontals document most of the structure of these elements. Because the specimens are small and fragile, in some cases we have left cemented matrix attached to the bone rather than risk irreparable damage by attempting to remove it.
Premaxilla ( Figs. 1A, B View Fig , 2A, B).— The two most nearly complete premaxillae are MNHN. MCM 187 View Materials (holotype) and 188. The holotype ( Figs. 1A View Fig , 2A) is from the right side, is about 1.9 mm high, and retains an intact pars dorsalis, but lacks the more lingual part of the pars palatinum and the lateral end of the pars dentalis. MNHN. MCM 188 View Materials ( Figs. 1B View Fig , 2B) is from the left side, is about 1.7 mm high, and lacks the lateral end of the pars dentalis, dorsolateral part of the pars dorsalis, and the lateral and medial parts of the pars palatinum. The former specimen is more robust than the latter and is from a slightly larger individual. The remaining premaxillae are from comparable−sized individuals, but preserve only the base of the pars dorsalis and varying amounts of the pars palatinum and pars dentalis .
The medial edge of each specimen bears elongate grooves and a flange, indicating that the premaxillae were sutured (i.e., paired) in life with their opposite. MNHN.MCM 187 and 188 show that the pars dorsalis is relatively short and broad, with the ratio of height:width across the suprapalatal pit about 1.4. On MNHN.MCM 187 the dorsal edge of the pars dorsalis bears weak suture marks forcontactwith the nasaland the process is indented laterally above the external narial margin by a narrow, shallow notch for receipt of the lacrimal. In labial aspect about the dorsal one−third of the pars dorsalis on
MNHN.MCM 187 bears a low, indistinct boss that is ornamented with low, relatively broad ridges enclosing shallow, irregular pits. MNHN.MCM 188 preserves the medial edge of an evidently less prominent boss. All specimens show that the remainder of the labial face of the bone is relatively smooth and perforated by small, scattered external nutritive foramina. The lateral corner of the pars dentalis is indented by a smooth facet that, in life, was overlapped labially by a complementary process from the maxilla.
MNHN.MCM 187 and 188 are the most informative specimens for documenting the lingual structure of the pars dorsalis. The suprapalatal pit ( Fig. 1A View Fig 2, B 2) lies in the lateral half of the process, medial to the external narial margin and in line with the fourth or fifth tooth position from the medial end of the tooth row, and well dorsal to the pars palatinum. The pit is oval in outline, relatively small (i.e., occupies about two percent of lingual surface area of pars dorsalis), and opens laterolingually. To either side, the suprapalatal pit is bracketed by an indistinct internal strut. A few tiny, sediment−infilled lateral foramina perforate the pars dorsalis laterally, in the wall for the external narial opening. The remainder of the lingual surface of the pars dorsalis is smooth.
None of the five specimens retains an intact pars palatinum, but judging by preserved sections and broken surfaces the process was a lingually broad, horizontal shelf as in other albanerpetontids. MNHN.MCM 188 medially preserves the base of the lingually projecting vomerine process. MNHN.MCM 187, 188, and 198 are useful for documenting and interpreting the openings associated with the pars palatinum. The first two specimens have two tiny foramina that open dorsally in the junction between the pars palatinum and pars dorsalis, in the vicinity of the suprapalatal pit. The larger and more dorsolabial of these two foramina opens just below the suprapalatal pit in MNHN.MCM 187 ( Fig. 1A View Fig 2), but more dorsally within the ventral margin of the pit in MNHN.MCM 188 ( Fig. 1B View Fig 2). We interpret this foramen as the dorsal opening of the palatal foramen, because in other albanerpetontid taxa, including the Jurassic species described below, the dorsal opening of the palatal foramen is consistently present and closely associated with the ventral margin of the suprapalatal pit ( Gardner 2000a). In life the suprapalatal pit probably housed a gland ( Fox and Naylor 1982) and the palatal foramen may have carried a duct from the gland into the roof of the mouth ( Gardner 2000a). The inferred ventral opening of the palatal foramen lies in the junction between the pars palatinum and pars dentalis in MNHN.MCM 187 ( Fig. 1A View Fig 2) and, although not visible in figures published here, slightly more lingually in the ventral face of the pars palatinum in MNHN.MCM 188; these positions are consistent with the pattern in other albanerpetontids. In both specimens the ventral opening of the palatal foramen is displaced medially relative to the dorsal opening of the foramen. Although the palatal foramen is plugged with matrix in both specimens, the relative positions of the dorsal and ventral openings imply that the canal connecting the two openings extends dorsolaterally–ventromedially through the pars palatinum. This canal is exposed in the broken surface of the pars palatinum on MNHN.MCM 198 (unfigured) and confirms that the canal extended obliquely through the shelf. As for the smaller and more lingual foramen (= “unknown foramen” in Fig. 1A View Fig 2, B 2) that opens in the dorsal surface of the pars palatinum, judging by the condition in other albanerpetontids this foramen likely communicates, via a canal extending obliquely through the pars palatinum, with a similarly small foramen that opens in the lingual face of the pars dentalis, medial to and slightly below the ventral opening of the palatal foramen. The function of this smaller foramen is unknown. The pars dentalis is deep. Tiny foramina pierce the lingual face of the pars dentalis above some tooth positions. Maxilla ( Figs. 1C View Fig , 2C).—The two best preserved maxillae collectively document all but the posteriormost end of the bone. MNHN.MCM 189 ( Figs. 1C View Fig , 2C) and 201 (unfigured) are broken well behind the internal narial margin and preserve about the anterior two−thirds to four−fifths of the bone. The former specimen is from the left side and has the first 17 loci, whereas the latter is from the right side and retains the first 14 loci. MNHN.MCM 189 is about 3.1 mm long and was probably about 4.5 mm long when the bone was intact; MNHN.MCM 201 is from a slightly smaller individual. Available specimens resemble other albanerpetontid maxillae as follows: pars facialis elongate and low, becoming shallower posteriorly; nasal process projects dorsally, triangular in outline, and bevelled posteriorly for articulation with lacrimal; premaxillary dorsal and lateral processes prominent, the former a lingually expanded shelf and the latter an anteriorly projecting flange; pars palatinum a lingually broad shelf, narrowing posteriorly, with lingual edge indented anteriorly by concave internal narial margin, and, more posteriorly, bearing shallow trough dorsolingually for articulation with unknown palatal bone(s); and pars dentalis deep, becoming shallower posteriorly. The labial face of the bone is smooth, except for tiny external nutritive foramina scattered across the more anterior part of the pars facialis. The premaxillary lateral process is relatively long (i.e., length greater than height at base) and blunt distally. Unlike many other albanerpetontid maxillae, including the Jurassic material described below, the dorsal surface of the pars palatinum adjacent to the nasal process lacks a saddle−shaped bony patch for contact with the base of the lacrimal. Also, the ventral surface of the premaxillary dorsal process lacks the transverse ridge that, in life, abutted against the lateral edge of the maxillary process on the premaxilla when the two bones were articulated. The occlusal edge of the pars dentalis is convex ventrally in labial or lingual outline. In MNHN.MCM 189 the pars dentalis is deepest adjacent to about the sixth locus. Tiny foramina are variably present in the lingual face of the pars dentalis above the teeth. The anterior end of the tooth row lies several loci anterior to the level of the leading edge of the nasal process.
Dentary ( Fig. 2D–G).—A catalogued size series of 34 broken dentaries is available. The most nearly complete specimen, MNHN.MCM 204 ( Fig. 2D), is a left dentary that is intact from the symphysis back to the level of the anterior margin of the opening for the Meckelian canal and bears 30 tooth positions with 25 teeth and five tooth slots. The specimen is about 3.6 mm long and would have been about one−third again as long when the bone was complete. In dentaries from Anoual the occlusal edge of the dental parapet is strongly convex dorsally in labial or lingual outline, with the apex labial to the eighth–tenth loci. This condition is most pronounced in larger specimens, such as MNHN.MCM 204 and MNHN.MCM 195 ( Fig. 2D 1 View Fig , E, respectively), but it also occurs in smaller specimens (e.g., MNHN.MCM 4 and 5; unfigured). In other respects, the structure of the dentary is typical for albanerpetontids. In dorsal aspect the bone is broadly curved. The labial face is smooth and a row of up to five or six external nutritive foramina extends along the anterior half of the bone. Below these foramina a low ridge is variably developed; this ridge marks the upper boundary of a shallow scar that extends anteroposteriorly along the lateroventral and ventral surfaces of the bone, for attachment of the intermandibularis musculature. A foramen opens in the underside of the symphysis. The symphyseal face is vertical anteriorly and posteriorly bears one or two symphyseal prongs that, in life, interlocked in a mortise−and−tenon fashion with one or two complementary prongs on the opposite dentary. In lingual aspect the dental parapet is moderately deep. The subdental shelf is moderately broad lingually, shallow, and gutter shaped anteriorly, and becomes deeper and narrower posteriorly. No dentary has the area for attachment of the postdentary bones intact, but several specimens, including MNHN.MCM 192 and 193 ( Fig. 2F, G, respectively), preserve enough of this region to show that the opening for the Meckelian canal extends forward below about the posterior one−quarter to one−third of the tooth row and that the dorsal edge of the bone behind the tooth row was smooth and lacked a dorsal process.
Teeth ( Figs. 1A–C View Fig 2; 2A–I).—Marginal teeth are characteristic for albanerpetontids in being highly pleurodont, non−pedicellate, straight, closely packed, and in having crowns that are labiolingually compressed and bear three mesiodistally−aligned cuspules. The structure of the tooth crowns is more variable than in species of Albanerpeton . Crowns on some teeth in Anoualerpeton unicus are decidedly chisel−like, with the central cuspule relatively low and the occlusal surface of the crown essentially convex in lingual outline; this pattern is typical for Albanerpeton . Some tooth crowns in An. unicus are more wedge−shaped in lingual or labial outline, with the central cuspule considerably longer than the mesial and distal cuspules ( Fig. 2H, I). Similar variation in tooth crown structure also occurs in the Jurassic congener described below and in an indeterminate Early Cretaceous (Berriasian) Celtedens sp. from Purbeck, England ( Evans and McGowan 2002: pl. 1: 9); in these European taxa the central cuspule on some teeth is even more elongate, resultincomplete ramus preserving posterior part of tooth row and anterior part of area for attachment of postdentary bones, in lingual view. H, I. Close ups of tooth crowns, both in lingual view. H. MNHN.MCM 199, right premaxilla, crown of tooth at sixth locus from medial end of tooth row. I. MNHN.MCM 5, right dentary, crown of tooth at eighth locus from anterior end of tooth row. J, K. Fused frontals, both in ventral view. J. MNHN.MCM 190, nearly complete frontals, lacking distal end of left anterolateral process and posterior end of ventrolateral crests on both sides. K. 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, photographed before damage (cf., Fig 1E View Fig ). Specimens at different scales.
ing in a more pointed crown. In jaws from Anoual the premaxillary teeth and the more anterior teeth on the maxilla and dentary tend to have wedge−shaped crowns, whereas teeth farther back tend to have more chisel−shaped crowns. Tooth counts are typical for albanerpetontids. MNHN.MCM 198 is the only premaxilla with an intact tooth row and preserves ten tooth positions. No maxilla or dentary preserves a complete tooth row, but specimens with anatomically overlapping sections of the row yield estimated, maximum counts of, respectively, 25 and 35 tooth positions. Most specimens preserve evidence of tooth replacement in the form of empty replacement slots and several, such as the maxilla MNHN. MCM 189 ( Figs. 1C View Fig 2, 2C: anteriormost tooth), also have a lingual resorption pit in the base of one or more teeth. The dentary MNHN.MCM 34 (unfigured) preserves a non−functional, replacement tooth at the second locus. Teeth on the maxilla and dentary are strongly heterodont in size, with teeth about one−third of the distance along the tooth row from the anterior end being longer than nearby teeth ( Figs. 1C View Fig 2, 2D 2).
Frontals ( Figs. 1D, E View Fig , 2J, K).—The two most nearly complete specimens are figured here: MNHN.MCM 190 ( Figs. 1D View Fig , 2J) and MNHN.MCM 191 ( Figs. 1E View Fig , 2K). The more nearly complete specimen, MNHN.MCM 190, lacks only the distal end of the left anterolateral process and the posterior end of the ventrolateral crests on both sides. The two halves are solidly fused medially. The specimen is 3.7 mm in midline length and 2.4 mm wide across the posterior edge, which yields a relative length (ratio of midline length:posterior width) of about 1.5. The internasal process is acuminate in dorsal or ventral outline and relatively broad, with the midline length subequal to the width across the base. The lateral face of the internasal process bears an elongate groove ( Fig. 1D View Fig 3 View Fig ) for articulation with the medial edge of the nasal. The anterolateral process is distinct from the main body of the bone and is pointed distally. The more anterior slot between the internasal and anterolateral processes for receipt of the posterior end of the nasal and the more posterior slot between the anterolateral process and the orbital margin for receipt of the posterior end of the prefrontal are both deep. The dorsal margin of the latter slot is shallowly excavated medially. The anterior end of the orbital margin, as demarcated by the posterior end of the slot for receipt of the prefrontal, is approximately in line with the anteroposterior midpoint of the bone. MNHN.MCM 190 is vaguely bell−shaped in outline, with the posterior edge nearly two times wider than the distance between the slots for receipt of the prefrontals. Behind the base of the anterolateral process, the lateral edge of the bone first extends posteriorly in a straight line, then curves outwards in a shallow arc at about 25° from the midline. The posterior edge of the bone is transverse and shallowly concave to either side of the midline. Dorsally, the bone is ornamented with shallow, broad polygonal pits enclosed by a network of narrower, low ridges. In ventral view, the ventrolateral crest is relatively narrow—i.e., crest at the anterior limit of the orbital margin is about 0.4 times as wide as the width across the posterior edge of the frontals, between the medial edges of the crest. The ventrolateral crest is somewhat convex ventrally in transverse profile, with the more lateral part along the orbital margin shallowly bevelled and facing ventrolaterally. Posteriorly the medial face of the ventrolateral crest is indented by a facet for receipt of a complementary process from the parietal. Although the ventrolateral crest is broken more posteriorly, this structure probably extended farther back to underlap the parietal, as in other albanerpetontids (e.g., Estes and Hoffstetter 1976: pl. 8: 2).
MNHN.MCM 191 ( Figs. 1E View Fig , 2K) is a larger, but less nearly complete fused pair of frontals. Originally the specimen lacked only the distal ends of the internasal and left anterolateral processes, the posterior end of the left ventrolateral crest, and the right posterolateral corner ( Fig. 2K). The specimen was broken during photography and some bone was lost from the median area ( Fig. 1E View Fig ). The specimen is 4.6 mm long in midline length and was probably 4.8 mm long or slightly longer when complete; the posterior width is estimated at about 3.0 mm. The estimated ratio of midline length:posterior width is 1.6, which compares favorably with
MNHN.MCM 190. Based on the assumption that snout–pelvic length in albanerpetontids is about ten times the midline length of the frontals ( Gardner 1999b), MNHN.MCM 191 suggests a snout–pelvic length of about 50 mm. In addition to being larger, MNHN.MCM 191 differs from MNHN.MCM 190 as follows: bone somewhat more triangular in dorsal or ventral outline; laterodorsal margins of internasal process straighter in dorsal or ventral outline (but with midline length of process remaining subequal to width across the base); lateral edge of bone more nearly concave along its entire length and extending laterally at a lesser angle of about 20° in dorsal or ventral outline; and ventral face of ventrolateral crest more bevelled. In other respects, MNHN.MCM 190 and 191 resemble one another.
Other elements.—An articular, 15 trunk vertebrae, three caudal vertebrae, and four humeri complete the inventory of albanerpetontid material from Anoual. These are typical for albanerpetontids and do not differ appreciably from homologous specimens reported from the Middle Jurassic ( McGowan 1996), Lower Cretaceous ( Estes and Sanchíz 1982; McGowan and Ensom 1997), and Miocene ( Estes and Hoffstetter 1976) of Europe and from the Lower Cretaceous of North America ( Gardner and Averianov 1998; Gardner 1999b).
Remarks.—Association of albanerpetontid specimens from Anoual within one species is supported by three lines of evidence. First, the provenance of the specimens is unique—no other albanerpetontids are known from Gondwana. Second, the specimens were collected from a single horizon at one locality. The fossiliferous lens at Anoual is restricted, with a depth of only about 20 cm and an areal extent of some 200 m 2 ( Sigogneau−Russell et al. 1998). Third, there is no compelling morphological evidence that more than one taxon of albanerpetontid is represented. The maxillae and dentaries have two complementary attributes that justify their association: occlusal margin of jaw convex and teeth strongly heterodont in size anteriorly. Comparisons with other albanerpetontids known by more extensive series of frontals and premaxillae, particularly species of Albanerpeton (see Gardner 2000a, b), suggest that differences among the Anoual premaxillae in relative build and proportions and among frontals in overall shape and in details of the internasal process, lateral edge of the bone, and transverse crest are within the expected limits of intraspecific variation for albanerpetontids.
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