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From the Mccoy Brook Formation (Lower Jurassic) of Nova Scotia

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From the Mccoy Brook Formation (Lower Jurassic) of Nova Scotia 328 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 14, NO. 3, 1994 and cyclostratigraphyof the associated lacustrine sed- ed cranial and mandibular bones, and associated imentary rocks, indicate an earliest Jurassic (Hettan- articulatedphalanges of three digits of the rightmanus. gian) age for the tetrapod-bearingbasal strata of the Hypodigm--In addition to the holotype, we exam- McCoy Brook Formation (Olsen et al., 1987, 1989). ined the following specimens duringthe course of this Bones referableto a small sphenodontianlepidosaur study:NSM 988GF2.1, incomplete left dentary;NSM are particularlyabundant in two types of facies. Lake- 988GF4.1, complete left dentary; NSM 988GF3.1, margin and fluvial sandstones have produced the best 988GF32.1, 988GF33.1, incomplete left maxillae; material,including two incomplete skulls and a partial NSM 988GF34. 1, nearlycomplete rightmaxilla; NSM postcranial skeleton. Paleotalus deposits comprising 990GF90. 1, nearly complete left maxilla; MCZ 9105, angular clast-supportedbasalt breccias with a matrix dorsoventrallycrushed, incomplete skull with almost of sandstone or mudstone have yielded dissociated but complete mandible in occlusion; MCZ 9106, well-pre- well-preservedsphenodontian bones. served partial postcranial skeleton including left hu- First-handcomparisons with other Late Triassicand merus and ulna, articulated left hind-limb and pes, Jurassicrhynchocephalian lepidosaurs indicate that the articulateddistal portions of the right tibia and fibula Nova Scotianmaterial represents a new sphenodontian and rightpes, both ilia, and articulatedpartial vertebral referableto Clevosaurus.Olsen et al. (1987) reported column from the posterior dorsal to the distal caudal the presenceof two differenttaxa of Sphenodontiafrom region;MCZ 9110, scatteredpalatal bones; MCZ9112, the McCoy Brook Formation at Wasson Bluff, but the incomplete left maxilla; MCZ 9113, incomplete left original identification of cf. Pelecymala sp. was based dentary and attached coronoid; MCZ 9114, complete on what, after additional preparation,proved to be a right maxilla. fragmentarypalatine referableto the new clevosaur. In Horizon and Locality -With the exception of NSM this paper,we describethe excellentlypreserved cranial 988GF2.1 and NSM 988GF34.1 (which were found at and postcranial remains of this new sphenodontian site F), all specimens discussed in this study were col- from the McCoy Brook Formation. This form is of lected from sites K and K' (as designated by Schlische special interest because of its bearing on problems of and Olsen in Olsen et al., 1989:fig. 11.6). The bones early Mesozoic paleobiogeography. occur in the basal portion of the McCoy Brook For- Following Benton (1985:147), we give preference to mation (Lower Jurassic: Hettangian) of the Fundy the name Sphenodontia Williston, 1925 (and hence Group (Newark Supergroup) at Wasson Bluff, near the vernacular term "sphenodontian") over Spheno- Parrsboro, Cumberland County, Nova Scotia. The dontida Estes, 1983 (and its vernacular derivative geographic coordinates for these exposures are latitude "sphenodontidan"). Furthermore, we use Rhyncho- 45*23'40" N and longitude 64'14'00" to 30"W. cephalia sensu Gauthieret al. (1988) to referto a more Diagnosis--Most closely related to C. mcgilli but inclusive clade comprisingGephyrosaurus Evans, 1980 differingfrom that taxon in the presenceof but a single (LowerJurassic, England) and Sphenodontia.All spec- premaxillary"incisor" tooth in adults, the presenceof imens used in this study will be deposited in the Nova three, ratherthan five, additional teeth in the maxilla Scotia Museum, Halifax (denoted by the acronym (character of uncertain polarity), the (plesiomorphic) NSM) and the Museum of ComparativeZoology, Har- absenceof the hourglass-shapedconstriction of the pa- vard University (denoted by the acronymMCZ). Some rietals,and the (plesiomorphic)absence of an L-shaped of the NSM specimens will be exhibited in the Fundy suborbitalfenestra. Geological Museum (Parrsboro,Nova Scotia). DESCRIPTION General Remarks SYSTEMATICPALEONTOLOGY All known of Clevosaurus bairdi are small. 1866 specimens LEPIDOSAURIAHaeckel, NSM 988GF1.1 and MCZ 9105 both have an esti- RHYNCHOCEPHALIAGiinther, 1867 sensu the Gauthier et 1988 mated length of the skull roof (measured along al., of about 1.9 cm. of various SPHENODONTIA 1925 midline) Regardless pres- Williston, ervational differences between these two specimens, CLEVOSAURUSSwinton, 1939 the skull ofMCZ 9105 appears more gracile in its build CLEVOSAURUSBAIRDI, sp. nov. than that of NSM 988GF1.1. Etymology -Named for Donald Baird, in recogni- Skull tion of his many important contributions to the pa- leontological exploration of Newark Supergroup strata The two incomplete skulls NSM 988GF1.1 (Figs. 1, in Nova Scotia, and in appreciation of his unfailing 2) and MCZ 9105 (Figs. 3, 4) complement each other encouragement and support of our research over the in terms of preserved structural detail and thus permit years. a comprehensive survey of the cranial structure in Cle- Holotype--NSM 988GFl.1, an excellently pre- vosaurus bairdi (Fig. 5). Small-scale fracturing renders served but slightly crushed partial skull with both den- the tracing of some sutures on MCZ 9105 difficult. taries in occlusion, several associated but disarticulat- In NSM 988GFl.1, each premaxilla (pm) bears a 334 JOURNAL OF VERTEBRATE PALEONTOLOGY, VOL. 14, NO. 3, 1994 possibly marking part of the course of V. pterygoidea, Just behind the glenoid facet, a small foramen (ch.t) is present on the posterodorsal surface of the ecto- on the medial portion of the retroarticular process pterygoid. probably transmitted the chorda tympani nerve. The triradiate pterygoid has an anterolaterally di- rected transverse process, a fairly broad, anteriorly di- Dentition rected palatal process, and a thin, mediolaterally flat- tened quadrate process (Fig. 2A, q.f.pt). It does not As in Clevosaurus hudsoni (Fraser, 1986, 1988) and enter into the margin of the suborbital fenestra. other sphenodontian lepidosaurs (Harrison, 1901; The epipterygoid is rod-like dorsally but becomes Robinson, 1976), the acrodont marginal dentition of flattened and expanded ventrally where it contacts the C. bairdi exhibits pronounced regional differentiation. medial surface of the quadrate process of the pterygoid Early in ontogeny, the anterior teeth of both the den- dorsal to the basipterygoid joint (NSM 988GF1.1). tary and maxilla are completely worn away (Fig. 6B), in these the bones form Mandible and, regions, jaw sharp bony ridges that functionally replace the teeth. The stout symphysis projects distinctly downward. The premaxillary dentition is known only in the ma- Behind it, the ventral margin of the robust dentary (d) ture specimen NSM 988GF1.1, where each premaxilla is convex in side view and rounded up to the level of holds a single large "incisor" tooth with a blunt chisel the coronoid process, where it becomes sharp. In some edge. specimens (e.g., MCZ 9105), fine longitudinal stria- Anteriorly, the fragment of a small maxilla MCZ tions extend anteroposteriorly along the ventral margin 9112 bears three small teeth between which smaller of the dentary. Medially, the dentary bears an open denticles are developed; these teeth appear to represent groove for Meckel's cartilage along its entire length. the hatchling dentition (sensu Robinson, 1976). In MCZ There is definitely no splenial (NSM 988GF1.1). The 9112 there is an anterior additional tooth with a low, mediolaterally flattened tooth-bearing ramus of the somewhat elongate crown with an oval base; in larger dentary is distinctly curved inward anteriorly toward specimens, there are several teeth of this type (Fig. 6A). the symphyseal facet. Its lateral surface bears a prom- Behind this anterior series of additional teeth, there inent "lip" of secondary bone (s.b) just below the teeth. are up to three large, flanged teeth. Each flanged tooth Up to three mental foramina, presumably for cuta- consists of an anterior cusp and a blade-like, obliquely neous branches of the inferior alveolar nerve, are sit- posterolingually directed flange ("talon" of Cocude- uated below this lip. The prominent coronoid process Michel, 1963), which slightly overlaps the tooth behind of the dentary is positioned lateral to the posterior end it lingually. The tooth crown is covered by thick, darkly of the tooth row and forms the lateral portion of the colored enamel with distinct vertical wrinkling. In MCZ coronoid eminence of the mandible. A shallow de- 9105, the three flanged additional teeth in the maxilla pression, which presumably reflects the extent of the are well worn and are followed behind by two small pars superficialis of M. adductor mandibulae externus, conical teeth. In NSM 988GF1.1, wear has nearly is developed anteriorly on the lateral aspect of the cor- obliterated the upper teeth. onoid portion of the dentary. Posterior to the coronoid The anterior teeth are heavily worn (NSM 988GF2. 1) eminence, the dentary continues as a tall, thin, and or completely obliterated (e.g., MCZ 9113) on all den- somewhat tapering lamina that overlaps the surangular taries found to date. In side view, the additional teeth portion of the articular complex. A small mandibular have more or less triangular, anteroposteriorly some- foramen (f.i.n), presumably for passage of a cutaneous what elongate crowns with blunt apices. In NSM branch of the inferior alveolar nerve, is enclosed by 988GF4.1, the crown of a replacement tooth is visible
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