Bernissartiidae Dollo, 1883

Sweetman, Steven C., Pedreira-Segade, Ulysse & Vidovic, Steven U., 2015, A new bernissartiid crocodyliform from the Lower Cretaceous Wessex Formation (Wealden Group, Barremian) of the Isle of Wight, southern England, Acta Palaeontologica Polonica 60 (2), pp. 257-268 : 259-265

Family Bernissartiidae Dollo, 1883

Type genus: Bernissartia Dollo, 1883 ; Barremian fissure fill at the Sainte-Barbe coal mine, Bernissart, Belgium.

Genera included: Bernissartia Dollo, 1883 ; Koumpiodontosuchus gen. nov.

Diagnosis (based on cranial characters).—Small crocodyliforms with estimated total length ca. 600–660 mm, differing from all others by possession of heterodont, tribodont dentition with low crowned, bulbous, mesiodistally elongate, single cusped posterior teeth lacking mesial and distal carinae; brevirostrine skull with preorbital/cranial length ratio ca. 0.55; orbits with an anterolaterally projecting notch bounded by the lachrymals; horizontally orientated premaxillae with slight expansion anterior to the undivided, anterodorsally placed naris; presence of a lateral notch at the contact between the premaxilla and maxilla; posterior dentary teeth that occlude medial to the maxillary teeth; enlarged third and fourth dentary teeth that occlude inside the lateral edge of the rostrum in a depression, rather than lateral to the rostrum as in extant crocodilians; robust postorbital bars; frontals with no interorbital transverse ridge; absence of external mandibular fossae; frontals between the orbits narrower than their anterior and posterior ends; exoccipitals in the paroccipital process with a curved outline above the quadrates; jugal with convex dorsal margin below the orbit; wide separation of the posterior margin of the orbits from the anterior margins of the supratemporal fenestrae; absence of antorbital fenestrae; profuse dorsal ornamentation of the quadratojugal; anteroposteriorly elongate, elliptical choana lacking a medi- an septum; lack of preorbital foramen; mandibular dentition with two adjacently placed caniniform teeth; presence of lacrimo-nasal suture; orbits larger than supratemporal fenestrae; infratemporal fenestrae triangular in outline, quadratojugal spine present; long posterolateral projections of the squamosals pointed; and frontals slightly concave between the orbits giving rise to a low supraorbital rim medially.

Remarks.—In the following differential diagnosis, comparisons are made with Norell and Clark’s (1990) description of Bernissartia fagesii . This is based on their examination of the lectotype IRSNB R46. Their interpretation differs in some respects from earlier interpretations of the type material and of a specimen from the Barremian of Spain referred to B. fagesii by Buscalioni and Sanz (1990). Furthermore, Andrade et al. (2011) provide a list of character states scored for 418 cranial characters based on their examination of IRSNB R46. Their interpretation of some characters is also at variance with those of other authors, although in most cases this results from their substantially more complex assessment.

Genus Koumpiodontosuchus nov.

Etymology: From Greek κουμπί, button, οδοντωτός, toothed, in reference to the characteristic button-shaped posterior teeth, ancient Greek σοΰχος, for the Egyptian crocodile-headed god Sobek.

Type species: Koumpiodontosuchus aprosdokiti sp. nov.; monotypic; see below.

Diagnosis.—As for species; see below.

Stratigraphic and geographic range.—As for the type species; see below.

Koumpiodontosuchus aprosdokiti sp. nov.

Fig. 3 .

Etymology: From Greek απροσδόκητη, unexpected, in reference to the unexpected fortuity of recovery of the rostral part of the specimen and the unexpected conclusions with regard to its taxonomic status.

Holotype: Combined specimens IWCMS 2012.203 and 204, the posterior and rostral parts, respectively, of a substantially complete, isolated skull comprising the cranium and mandibles in occlusion with it.

Type locality: The foreshore near the village of Yaverland on the south-east coast of the Isle of Wight, UK; British National Grid Reference SZ 615851.

Type horizon: Wessex Formation, Lower Cretaceous, Barremian, exact horizon uncertain but from one of the plant debris beds occurring between beds 26 and 38 ( Radley 1994).

Diagnosis.—Small, brevirostrine crocodyliform, estimated total length ca. 660 mm and preorbital/cranial length ratio ca. 0.54, with heterodont, tribodont dentition unique to the only other known member of the family, but differing from it in dental formula: third and fourth mandibular teeth caniniform and placed in alveoli lacking an interalveolar septum; five globose posterior maxillary teeth. Anteroposteriorly elongate choana with no median septum, entirely bounded by the pterygoids but in an extreme anterior position. Premaxillary median suture with nasals not extending to the posterior border of the naris. Splenial participating in the mandibular symphysis for a little more than one fifth of its anteroposterior length. Orbits with an anterolateral notch.

Differential diagnosis.—Differs from Bernissartia fagesii in: nasals that do not extend anteriorly to form part of the posterior margin of the naris; premaxillae with a long median suture which bifurcates posteriorly at contact with the nasals; rostrum less laterally expanded anteriorly; long lacrimo-jugal suture; jugal height in the infratemporal region “stepped” with respect to the anterior part; posterior part of the jugal long and terminating in a sharp apophysis; splenial participates in the mandibular symphysis for approximately one fifth of its length; mandibular symphysis proportionately longer than that of B. fagesii ; anterior frontal process in dorsal contact with the nasals quadrangular and wide; frontals comprise a substantial part of the anterior margin of the supratemporal fenestrae; lachrymals much longer than broad; pterygoids fused posteriorly, with a median suture anteriorly and entirely enclosing the choana; postorbitals rather small and smaller than the squamosals; palatines more anteriorly expanded; dental formula; and lateral outline of the skull seen in dorsal view as described below.

Description.— Skull: Skull length measured from a line joining the posterior extremities of the parietals to the tip of the rostrum is ca. 112 mm. The exact length cannot be determined in view of the fracture between the anterior and posterior parts and erosion of the anterior margins of the premaxillae but would have been slightly greater. This compares with a similarly measured length of ca. 111 mm for Bernissartia fagesii taken from the photograph provided by Buffetaut (1975: pl. 1). The preorbital/cranial length ratio is ca. 0.54. In dorsal aspect ( Fig. 3A ) the lateral margins are gently convex from the posterior end to approximately one quarter of the distance anteriorly from the posterior margin of the rostrum. The latter tapers anteriorly with a slight lateral expansion in the region of the fourth and fifth maxillary teeth. A notch occurs at the anterolateral junction between the maxillae and premaxillae, which are laterally expanded anteriorly and surround the anterodorsally placed, undivided naris.

Orbits, supratemporal and infratemporal fenestrae: Orbits are large and on the left side most of the orbital margin is preserved. Unusually, but in common with Bernissartia fagesii , there is a pronounced anterolateral notch in the orbit. This was considered by Norell and Clark (1990) to be an artefact of crushing of the skull of the lectotype but is also seen in an apparently juvenile specimen, also assigned to B. fagesii by Buscalioni and Sanz (1990), from the Barremian of Spain. This serves to confirm that the notch is a synapomorphy of the Bernissartiidae . The supratemporal fenestrae are small, occupying about one third of the dorsal area occupied by the orbits and are oval in dorsal outline with their long axes anteroposteriorly orientated. The infratemporal fenestrae are triangular in outline, tapering posteriorly. Most of the external surfaces of bones comprising the cranium are profusely sculpted with pits whereas the dentary (here and below, see Fig. 3 ) is sculpted with grooves.

Premaxilla: The premaxillae are horizontally orientated and surround the subcircular naris which opens anterodorsally. The premaxillae are separated anteriorly by an anteroposteriorly elongate median suture which bifurcates posteriorly at contact with the nasals. In dorsal view the bones are paddle-shaped being expanded laterally anterior to the notch accommodating caniniform teeth of the lower dentition. The premaxillae participate for a little more than half of the anteroposterior width of the notch. Each premaxilla accommodates four acuminate teeth. Except at their anterolateral margins the premaxillae cannot be seen in ventral view because they are obscured by the symphyseal part of the mandibles.

Maxilla: The maxillae comprise most of the rostrum and both their dorsal and lateral surfaces are evenly sculpted with sub-circular pits of somewhat variable diameter. There is a pronounced lateral convexity over the fourth and fifth maxillary teeth. Each maxilla accommodates 19 teeth but on the left side, where the dentition is not obscured by matrix, the alveoli at the fifth and seventh loci are vacant. However, traces of the lateral margins of an apparently partially resorbed root can be seen in the seventh alveolus. The posteriormost five teeth (at loci 15–19) are bulbous. That at locus 14 is acuminate but still somewhat globose. On the left side the apex of the first of the globose teeth (at the 15 th locus) appears unworn but the two teeth posterior to it are worn apically and bear horizontal facets. Ornamentation of posterior teeth is similar to that described for B. fagesii in comprising numerous fine apicobasally orientated ridges which do not bifurcate and which become very faint towards the base of the crown. The 17 th tooth on both sides of the dentition also has an apicobasally orientated labial groove which would render the teeth kidney shaped in occlusal view, as previously reported for isolated teeth from the Isle of Wight referred to Bernissartia sp. indet. and to Bernissartia sp. , cf. Bernissartia and Bernissartiidae indet. from elsewhere in Europe and southern Scandinavia ( Buffetaut and Ford 1979; Schwarz-Wings et al. 2009 and references therein). Antorbital fenestrae are absent.

In ventral view the maxillae are separated by a median suture which extends posteriorly as far as the 8 th –9 th maxillary teeth. The suture between the maxillae and palatines is broadly U-shaped, projecting anteriorly. On either side of the median suture each maxilla is somewhat ventrally convex. On the left side, where a portion of the mandible is missing from IWCMS 2012.204, the maxilla bears an anteroposteriorly-orientated groove immediately labial to the maxillary teeth to accommodate those of the dentary. Where visible, the maxillae do not participate in the anterior margin of the suborbital fenestrae. However, some anterior or anterolateral participation is suggested for areas obscured by the mandibles.

Nasal: The suture separating the nasals from the lachrymals, maxillae and premaxillae is sigmoidal ( Fig. 3A 2 ). The nasals are separated from each other by a median suture, and anteriorly meet to form a sharply pointed apophysis that separates the premaxillae. They do not extend to the naris but posteriorly they contact the lachrymals in a well-defined suture. In contrast, that separating the nasals from the prefrontals is indistinct and has not been ascertained with certainty.

Lachrymal: The lachrymals are anteroposteriorly longer than mediolaterally wide and posteriorly comprise the anterolateral margin of the orbit.

Prefrontal: The prefrontals are anterolaterally-posteromedially wide, being approximately twice as wide as they are anteromedially-posterolaterally long, they form a large part of the anteromedial border of the orbits.

Frontal: The frontals are fused posteriorly but are separat- ed by a median suture anteriorly. They are medially constrict- ed and narrow between the orbits as reported for B. fagesii . In this region they are also somewhat ventrally concave, the raised lateral edges forming low supraorbital rims around the medial margins of the orbits. Posteriorly they are somewhat laterally expanded and on the undamaged left side can be seen to form approximately half of the anterior margin of the supratemporal fenestra. Medially the suture between the frontals and the parietals is transverse but laterally it is somewhat posteriorly deflected as it approaches the supratemporal fenestra as seen on the undamaged left side. Anteriorly the frontals are separated from the nasals by a mediolaterallyorientated suture.

Parietal: The parietals are completely fused and comprise a ventrally concave platform posterior and medial to the supratemporal fenestrae, of which they form most of their medial margins. The parietals are parallel-sided laterally along their contact with the squamosals and posteriorly form a posteriorly convex process above the supraoccipital. This has a laterally narrow and shallow median excavation unlike the deeper and wider excavation seen in the same position in B. fagesii , which renders the posterior margin of its parietals bilobate. Small posterodorsal articular processes are developed at the lateral extremities of the bones possibly for articulation with nuchal osteoderms. In occipital view, the suture between supraoccipital and parietals is placed at the ventral extremity of the dorsal process of the parietals, but close to the suture with the squamosals.

Squamosal: In contrast to the parietals, the squamosals are somewhat dorsally convex. They extend and narrow posterolaterally becoming pointed at their extreme posterior ends. They are gently convex laterally above the quadrates and the dorsal margins of the infratemporal fenestrae. Anteromedially as seen on the left side, the squamosal forms a large part of the posterior and lateral margin of the supratemporal fenestra. The squamosal is separated from the postorbital by a suture, the lateral extremity of which is somewhat more anteriorly placed than the medial extremity. On the occipital surface of the squamosals foramina occur posteriorly at their junction with the parietals. The suture between the squamosals and exoccipitals descends from the lateral margin of the foramen on each side to lie on the dorsal surface of the exoccipital at its posterolateral extremity. While dorsal convexity of the squamosals is indicative of immaturity in some crocodyliforms, for the reasons stated above it is not considered to represent immaturity of the individual described here.

Postorbital: As seen on the left side, the suture between the postorbital and frontal is sinuous and anteroposteriorly orientated. Posteromedially the bone forms the anterolateral margin of the supratemporal fenestra. Anterolaterally the bone is broken and it is not therefore possible to ascertain the shape of its external margin. The unornamented postorbital bar is massive being comprised of elements of the postorbital and the jugal. Medial to the suture between those bones it is substantially raised anterodorsally and it is vertical or very slightly anteriorly inclined in lateral view. In anterior view the anterodorsal margin of the postorbital bar is somewhat medially inclined.

Jugal: The jugal is anteroposteriorly long and terminates posteriorly in a sharp apophysis. In lateral view the bone broadens progressively anterior to this. Below the anterior margin of the infratemporal fenestra, at its contact with the posterior extremity of the maxilla, the jugal is three times deeper than it is anteriorly below the lateral margin of the orbits and is triangular in lateral view, the vertex being ventrally directed. Either side of this the ventral margins are dorsally convex. The anterior suture with the lachrymal is long and that with the maxilla occupies half its anteroposterior length. The jugal is entirely sculpted laterally with sub-circular pits, in contrast to the lateral surface of the maxilla underlying it, which is sculpted with larger, somewhat shallower, anteroposteriorly elongated pits

Quadratojugal: Laterodorsally the quadratojugal is ornamented with pits, but dorsomedially these are absent. A long, anteriorly projecting spine extends into the infratemporal fenestra, but this does not participate in its medial margin, which comprises the lateral margin of the postorbital and the squamosal. On the right side, the internal surface of the quadratojugal is exposed to reveal the suture with the quadrate, which lies parallel to the lateral margin of the quadratojugal spine.

Quadrate: The unornamented dorsal surface of the quadrate is visible on the right side. Anteriorly it is pierced by two foramina. The larger of these is located lateral and somewhat anterior to the other. Both foramina lie in a depression, the anterolateral margin of which is bounded by the suture between the quadratojugal and the quadrate. The depression represents the lateral floor of the middle ear cavity. Medially the cranioquadrate canal opens broadly anterolaterally comprising a dorsolaterally-ventromedially inclined opening between the exoccipital and the quadrate.

Palatine: Posterior to the suture with the maxillae the palatines are separated by an anteroposteriorly complete median suture. Anteriorly the bones are laterally expanded particularly in the areas anterior to the anterior extremities of the suborbital fenestrae. Posterior to this they are very slightly medially concave towards the mid-point of the suborbital fenestrae but broaden slightly at the posterior ends as they approach the pterygoids. The area of contact with the underlying anterior margins of the pterygoids (see below) is somewhat posterodorsally inclined to create in combination a broad V-shape posterior process ( Fig. 3C 2 ) which becomes very thin posteriorly. In addition, each of the palatine bones has a small posteriorly projecting spinal process at its posterolateral extremity, which overlaps the anteroventrolateral extremities of the pterygoids.

Pterygoid: The pterygoids are very wide and comprise the entire posterior margin of visible parts of the suborbital fenestrae. They also appear to completely surround the choana (internal naris) the anterior margin of which lies ca. 2.3 mm posterior to the anterior margins of the bones. Anterior to the anterior margin of the internal naris the pterygoids are separated along a median suture but they are fused posterior to its posterior margin. Anteriorly, as indicated above, the pterygoids appear to lie dorsal to the posterior margins of the palatines in an overlapping relationship rather than meeting them in vermiform sutures as normally observed. This relationship and placement of the choana within the pterygoids is unique and raises questions concerning our interpretation. However, very careful examination in all available orientations failed to reveal any trace of sutures posterior to the anterior margin of the choana, particularly on the left side where there are few fractures and there is little crushing. This together with matched, posteriorly projecting lateral spinal processes at what are perceived to be the posterolateral margins of the palatines supports this interpretation. In the broad areas posterior to the posterior margins of the suborbital fenestrae the pterygoids are dorsally convex forming a domed roof to the posterior part of the palate.

Choana: The choana or internal naris lacks a dividing septum and comprises a single opening. It is elliptical in outline but broader anteriorly than posteriorly with an anteroposterior length of ca. 16 mm and a maximum width of ca. 7 mm.

Ectopterygoid: The ectopterygoids are largely obscured by the mandibles but their medial suture with the pterygoids is posteromedially convex. Their ventral surfaces are confluent with those of the pterygoids, ventromedially declined and contribute to doming of the palate in this region.

Supraoccipital: In occipital view the supraoccipital is triangular in outline, its vertex directed ventrally. It does not extend to the dorsal margin of the foramen magnum which is bounded dorsally and laterally by the exoccipitals. Ventrally, a posteriorly projecting midline ridge is present but the dorsal part is broken away.

Exoccipital: The occipital surfaces of the exoccipitals are penetrated by a large number of minute, randomly distributed foramina.A vertically orientated suture separates the left and right exoccipital bones and meets the supraoccipital a short distance below the ventral extremity of the distal supraoccipital ridge. As seen on the right side, the exoccipital forms a large part of the lateral margin of the foramen magnum. As also seen on the right side, laterally it forms the posterodorsal surface of the cranioquadrate passage and contacts the squamosal posterior to the posterior margin of the quadrate. On the left side the suture between the exoccipital and quadrate is obscured and on the right side the suture line could not be determined ventrally. A large foramen is present lateral to the lateral extremity of the occipital condyle possibly for accommodation of the carotid artery. Dorsal to this there are two further closely associated foramina. Medial to these and close to the lateral margin of the foramen magnum there is another substantial foramen, the internal opening of which cannot be seen. In ventral view there is a line of denticulation extending from the medial extremity of the cranioquadrate canal to the lateral border of this foramen. A number of minute foramina are also present in the same area and as in other crocodyliforms these foramina are assumed to lie within the exoccipital rather than the quadrate.

Quadrate: Only the dorsal part of the quadrate is visible on the right side and it is entirely obscured on the left. As described above the suture between the quadrate and exoccipital cannot be determined with certainty and the bones may be almost entirely fused.

Basioccipital: In contrast to the suture between the quadrate and the exoccipital, the suture delineating the basioccipital is well-defined extending in ventral view from the dorsolateral margin of the occipital condyle anterolaterally. Commencing approximately one quarter of the distance to the ventral extremity of the basioccipital a strongly laterally compressed, posteriorly projecting keel is present which may have extended to the ventral extremity of the bone. However, the base of the crest was broken away prior to final burial and fossilization. Lateral to the keel, the bone is excavated to produce well-defined, dorsolaterally orientated concavities. A number of randomly distributed, minute foramina are present. Ventrally the basioccipital contacts the pterygoids where it extends as a V-shaped process on the palatal surface. The basisphenoid is not visible, being obscured by the basioccipital-pterygoid contact.

Occipital condyle: The occipital condyle is dorsoventrally flattened and elliptical in occipital view. The posterior surface is concave comprising two laterally placed condyles separated by a shallow anteriorly U-shaped valley.

Foramen magnum: The left side of the foramen magnum is obscured by matrix and an adhering indeterminate fragment of bone. However, its outline can be determined from the unobscured right side. It is triangular with a shallow dorsally convex dorsal surface and strongly concave ventral surface bounded laterally by shallow ventrolaterally convex surfaces. The dorsal and lateral margins are bounded exclusively by the exoccipitals. The basioccipital appears to form a small part of the extreme ventral margin of the foramen magnum and a suture between it and the exoccipital can be seen on the ventral surface of the foramen on its right side.

Dentary: Only the anterior part of the mandibular dentition is visible, the posterior part being obscured both by matrix and the maxilla, which occludes labial to it. Posterior to the acuminate anterior teeth described below, dentary teeth are placed lingual to, between, and closely adjacent to those of the maxilla in an imbricate relationship. This can be seen on the left side where part of the mandible is missing. However, very few of the large number of isolated, low-crowned, Wessex Formation bernissartiid teeth examined show lateral facets attributable to contact between teeth in the upper and lower dentitions (SCS personal observation). Teeth in the anterior part of the mandibular dentition are mostly broken, but those occurring posteriorly as far as that lying between the 9 th and 10 th maxillary teeth are evidently acuminate. The two closely juxtaposed dentary teeth occupying alveoli lacking a dividing septum and which occlude into the notch occurring at the lateral junction between the premaxilla and maxilla are enlarged and caniniform. The anteriormost dentary teeth are procumbent and their apices extend anterodorsally beyond the labial extremity of the premaxillary teeth. Morphology of the more posterior teeth cannot currently be determined as the lingual surfaces are covered by matrix which it was considered undesirable to remove. The ventral margin of the dentary is straight in lateral view. Posterior to the posterior margin of the mandibular symphysis the dentary is sculpted with anteroposteriorly elongate pits and grooves and anterior to this the surface bears many deep pits of small diameter at the base of which small foramina can be seen in many. The dorsolateral surface bears an anteroposteriorly extensive groove into which the maxillary teeth occlude. The bone tapers anteriorly from its posterior end, but is laterally expanded as it approaches the posterior margin of the mandibular symphysis. In the mid part of the symphysial region the bone is laterally expanded giving the anterior part a paddle-shaped profile. Posteroventrally as seen in lateral view, the dentary contacts the angular as a posteriorly extending apophysis and as a blunter posteriorly projecting apophysis with less regular outline dorsolaterally. The latter extends as a thin sheet of bone over both the angular and surangular.

Splenial:As seen in the transverse sections revealed at the break between the anterior and posterior parts of the skull, the splenial does not participate in mandibular alveoli. The bone is lateromedially narrow and of uniform thickness except at its extreme anterior and posterior ends where it becomes extremely thin and acuminate in ventral view. Anteriorly, the splenial participates in ca. 22% of the anteroposterior length of the mandibular symphysis (for 5 mm of the 23 mm of its total length).

Angular: A large part of the posterior part of the angular is missing on the right side and the posteroventral part is missing on the left side. Direct comparison with the shape of the ventral border of the angular of B. fagesii cannot therefore be made. The bone is, however, robust with an anteroventral surface ornamentation similar to that observed on the dentary. Posteriorly this ornamentation is lacking. The suture between the angular and surangular is dorsoventrally declined.

Surangular: Anteriorly the surangular becomes very thin, terminating in an anteriorly projecting, posteriorly V-shaped apophysis which overlies the dentary. Lateral ornamentation comprises a number of pits more closely resembling those seen on the dorsal surface of the skull (e.g., those on the squamosal) than those on other parts of the mandible.

Articular: The articular is entirely broken away on the right side but a fragment bounded by the posterior margin (as preserved) of the surangular can be seen in occipital view.

Indeterminate fragments: A number of osteoderm fragments are present on the left side in the area adjacent to the basioccipital and exoccipital. These are of a size consistent with assignment to the specimen under discussion, their surface ornament is similar to that described for Bernissartia but none preserve diagnostic features. A bone fragment of uncertain affinities adheres to the left lateral margin of the foramen magnum.

Stratigraphic and geographic range.— Known with certainty only from the upper part of the Wealden Group Wessex Formation (late Barremian) at the type locality. However, isolated teeth identical to those seen in the holotype specimen occur throughout the Wealden Group (Barremian–early Aptian) of the Isle of Wight ( Buffetaut and Ford 1979) and have been recovered from Lower Cretaceous strata elsewhere in southern Britain .

Figures

Fig. 3. Bernissartiid crocodyliform Koumpiodontosuchus aprosdokiti gen. et sp. nov. from the Barremian Wessex Formation of the Isle of Wight, UK. Holotype specimen IWCMS 2012.203–204, in dorsal (A), occipital (B), ventral (C), and left lateral (D) views. Photographs (A –D), schematic repre1 1 sentations to show anatomical features including sutures between bones (A 2 –D 2). “?” in B 2 denotes an indeterminate bone fragment adhering to the left lateral margin of the foramen magnum.

Fig. 2. Schematic lithological log of the upper part of the Wessex Formation exposed in the cliff and on the foreshore in the vicinity of Yaverland on the south east coast of the Isle of Wight. Modified from Radley (1994) with additional data.