Eichstaettisaurus gouldi, Evans & Raia & Barbera, 2004
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publication ID |
https://doi.org/ 10.5281/zenodo.13521483 |
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persistent identifier |
https://treatment.plazi.org/id/F51B9762-FF93-FFCD-FFC1-0D8634F9FAE3 |
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treatment provided by |
Felipe |
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scientific name |
Eichstaettisaurus gouldi |
| status |
sp. nov. |
Eichstaettisaurus gouldi sp. nov.
Figs. 2–5 View Fig View Fig View Fig View Fig .
Etymology: For Stephen J. Gould who died in 2002, in recognition of his contributions to evolutionary biology.
Holotype: MPN 19457 , a partial skeleton preserved in ventral view.
Type locality, horizon, and age: La Cavere outcrop, Pietraroia, Mount Matese, southern Italy. Upper Plattenkalk horizon. I.G.M. [Italian Military Geographic Institute] map sheet 162, III SW−Cusano Mutri ( Fig. 1 View Fig ) N4577431, E2482228. Lower Cretaceous, Albian age.
Diagnosis.—Species of Eichstaettisaurus differing from the type species as follows: lacking any trace of a median suture on either frontal or parietal; interorbital width of the frontal only 20 per cent of frontoparietal suture width; frontoparietal suture with the parietal slightly embayed by median convexity of frontal; frontal slightly wider than parietal at the frontoparietal suture, with posterolateral tip of frontal apparently emarginated from behind by postfrontal.
Remarks.—Although the narrower frontal could be an artefact of immaturity, the complete fusion of both the frontal and parietal, with no trace of the midline sutures, suggests a pattern of skull development differing from that of E. schroederi .
Description of holotype specimen MPN 19457.—The holotype specimen of E. gouldi comprises a small (snout−vent length ca. 56 mm) associated skeleton, preserved in ventral aspect, and including the skull, some parts of the axial skeleton, and parts of the fore and hind limbs and their girdles ( Fig. 2A View Fig ). The skeleton is gracile with thin skull roofing bones. This is suggestive of immaturity, as are the poorly ossified carpus and tarsus. The parietal is shattered in MPN 9457, but its anterior and anterolateral borders, and those of the frontal, are complete and they suggest that the skull sutures were already closed ( Figs. 2B View Fig , 3A View Fig ). The specimen was therefore well past hatching but probably not yet adult. The body proportions overall are closely similar to those of E. schroederi .
Skull ( Figs. 2 View Fig , 3 View Fig ).—The skull is exposed in ventral view with the lower jaws in articulation ( Figs. 2B View Fig , 3A, B View Fig ). Judging by its condition, the skull was probably preserved in this position, with the dorsal surface embedded and little distorted, but with subsequent compression tending to separate the lateral and ventrolateral parts of the skull about the interpterygoid vacuity. The mandibles moved with the maxillae, separating posteriorly but remaining in slight contact at their tips. The orbits are large, rounded and, allowing for compression, somewhat dorsally placed.
The most clearly preserved bone is the long frontal. It is narrow anteriorly, constricts sharply between the orbits, and then widens markedly at the frontoparietal suture (interorbital width roughly 20 per cent of the frontoparietal suture width) ( Fig. 3A View Fig ). The bone is unpaired and has strong cristae cranii (= subolfactory crests or descending flanges) anteriorly and between the orbits, although these do not meet ventromedially. Anterior to the frontal is a damaged mass that probably represents the nasals, suggesting these were quite broad. The frontoparietal suture is well−preserved ( Fig. 3A, B View Fig ) and has a distinctive shape. It is relatively simple, lacking either interdigitations or overlap surfaces. The central part of the frontal embays the parietal slightly, but then straightens bilaterally, before extending into the lateral processes. This gives the suture a very shallow W−shape. The posterolateral tips of the frontals protrude just beyond the parietal, and their posterior margins are slightly embayed. This suggests the postfrontal may have abutted the back of the frontal, rather than clasping its lateral edge. The parietal plate is damaged but the anterior and anterolateral margins are clearly defined. The anterior margin is intact across the midline and there is no evidence of a midline suture. The posterior part of the bone is too badly damaged to determine the shape of the postparietal processes, but they cannot have been long. The central section of the parietal plate is a mass of thin broken fragments. There is no trace of any localised thickening that might indicate the presence of ventrolateral crests, but the central section of the bone seems to enclose curved margins pertaining to a parietal foramen ( Fig. 3A View Fig ).
The overlying lower jaws obscure much of the lateral wall of the skull. The maxillae were short, overlapping the jugals but not extending beyond the midpoint of the orbit. They are separated anteriorly by paired premaxillae, each containing six or seven tooth positions. The maxilla had more than 30 tooth positions, but a precise count is not possible. Most of the teeth are either lost or broken, but the few preserved are small and slender, with a relatively shallow pleurodont implantation (as shown by the weak grooves on the maxilla in Fig. 3A View Fig ).
The shape of the postfrontal, or postorbitofrontal, can be inferred only from the embayment on the frontal. The only representative of the postorbital series clearly preserved is the jugal, exposed on both sides as a strong, curved arch of bone between the posterior end of the maxilla and the posterior orbital margin. It had no posterior spur or process. At the right maxillary−jugal junction, the thin, tapering posterior process of the maxilla underlies the jugal, and a thin splint of bone running along the medial aspect of the maxilla suggests the jugal extended forward to the antorbital margin. The posterodorsal ramus of the jugal obviously contributed to a complete postorbital bar but the lower jaw obscures its dorsal extremity, and therefore its relation to the postorbital and squamosal. On the right side of the skull, between the back of the jaw and the quadrate ramus of the pterygoid, there is a curved bar of bone (in two parts, Fig. 3A View Fig ) that may be a squamosal, or possibly hyoid. The quadrates are not exposed.
The mandibles also obscure the palatal elements, leaving only the pterygoids partly exposed. These are represented by a pair of well−ossified bars running roughly parallel to the margins of the parietal and then, on the left side, curving anterolaterally. The interpterygoid vacuity appears very broad, but allowance must be made for both immaturity and postmortem compression. Adjacent to the posterior tip of the left mandible, there is a rod−like structure, expanded posteriorly, that may be either the epipterygoid or, from its position, the first hyoid ceratobranchial ( Fig. 3A View Fig ).
Both lower jaws are in association, the left ramus being almost complete. The dentary is comparatively slender throughout, but becomes particularly so towards the weak symphysis. No teeth are visible. The lateral surface is marked with a series of eight small neurovascular foramina. The rear of the dentary is deeply bifurcate, with long dorsal and ventral rami of roughly equal length. The anterior tip of the large surangular is correspondingly tapered. A small mass of bone along the dorsal edge of the right mandible at this point may be the coronoid ( Fig. 3A View Fig ), while a thin ventral splint visible on the opposite mandible probably represents the angular ( Fig. 3A View Fig ).
Axial skeleton ( Figs. 2A, B View Fig , 3A View Fig ).—Elements of the cervical, dorsal, sacral and anterior caudal vertebral column are visible ( Fig. 2A View Fig ), but the preservation is poor. The cervical count is estimated at six or seven, but dorsal number is unknown. The first recognisable vertebra lies immediately behind the head and is probably the axis ( Fig. 3A View Fig ). Its centrum is simple, cylindrical, and lacks any trace of a posterior condyle. Between it and the next vertebra is a robust intercentrum (see arrows, Fig. 2B View Fig ). The next centrum is shorter and apparently keeled. Again it seems to be separated from the next vertebra by an intercentrum. The sacrum is obscured by overlying elements of the pelvis. Behind it, there is a short series of at least six anterior caudal vertebrae bearing strong transverse processes. In most cases, the distal ends of the processes are damaged, but the second caudal has a process with a distinct posterior angulation. The caudal centra are broad, cylindrical, and again apparently amphicoelous. None preserves a trace of a fracture plane (autotomy septum), but this is not surprising. The fracture plane typically develops in a more distal position along the tail, and may explain the short caudal series in this specimen.
Pectoral girdle and forelimb ( Figs. 2A View Fig , 4B View Fig ).—The forelimbs are partially preserved on each side and are short in relation to the axial skeleton. They are represented by slender right and left humeri, parts of the right radius and ulna, and parts of each manus. The proximal ends of the humeri lie against irregular bone and cartilage masses pertaining to the pectoral girdle, but these provide no anatomical detail. The right manus preserves parts of at least three long slender digits (probably the central three). Traces of the carpus are visible between the remnants of the epipodials, suggesting that it may have been only partially ossified. An accurate phalangeal count is not possible, but the longest digit (four) seems to have had five components (presumably a metacarpal and four phalanges). The individual phalanges are relatively long, with slender shafts and more expanded rounded extremities. Only two of the ungual phalanges are reasonably complete ( Fig. 4B View Fig ). The ungual is short and rather deep with a strongly concave proximal surface (meeting the small rounded head of the penultimate phalanx), a welldeveloped flexor tubercle, and a sharply tapering tip.
Pelvic girdle and hind limb ( Figs. 2A, C View Fig , 4A View Fig 1 –A View Fig 3 View Fig ).—The pelvic girdle is poorly preserved, but the ventral elements enclose a large thyroid fenestra. The pubes taper anteriorly and have strongly concave medial margins. The ischia are represented only by bone masses, and the ilia are obscured. Again, the hind limbs are short in relation to the snout−vent length (SVL, estimated in a fossil as the distance between the tip of the premaxillae and the posterior edge of the second caudal, the approximate position of the cloaca in living taxa). The femora are slender with little expansion of the articular ends and only a slight sigmoid curvature; the tibia and fibula are considerably shorter (roughly 50 per cent of femoral length). The tibia is widest proximally, narrowing markedly at midshaft. The right foot is only partially preserved, but there is enough to demonstrate its dimensions ( Figs. 2C View Fig , 4A View Fig ). As a whole, the foot is of similar length to the femur ( Fig. 2A View Fig ), and therefore much longer than the crus. The second and third metatarsals are incomplete and rather thin; the fifth is short and was apparently hooked, a conclusion supported by the divergent position of the fifth digit. This digit is also comparatively long. The foot thus lacks the strong asymmetry seen in many fast running modern lizards where the fourth digit is markedly longer than the third or fifth. On first inspection, the unguals of digits three and four look highly unusual ( Figs. 2C View Fig , 4A View Fig 1 View Fig ). The distal end of each penultimate phalanx is small and rounded, but it seems to meet a flared, ring−like, expansion, as though the lizard had rounded tips to the digits ( Fig. 4A View Fig 1 View Fig ). However, this is an artefact of preservation. Superimposing a scaled image of the hand claws onto the pedal digital tips shows that the ring−like effect results from a combination of breakage and distortion ( Fig. 4A View Fig 2 View Fig , A 3 View Fig ). In fact, the pedal unguals resemble those of the manus, with a strongly concave proximal margin for the penultimate phalanx, a short deep proximal blade, a pointed distal tip, and a strong ventral tubercle for the attachment of digital flexors. There is also a suggestion of a small proximodorsal tubercle for extensor muscle attachment. Overall, the appearance is that of a claw capable of being strongly flexed.
Description of the Eichstaettisaurus skull within MPN A 01/82 ( Fig. 5 View Fig ).—A second skull of Eichstaettisaurus has been identified within the body cavity of another Pietraroia reptile specimen, MPN A01/82 (see below). The associated, but disarticulated, skull remains ( Fig. 5 View Fig ) are attributable to E. gouldi on the basis of several distinctive features: the form of the single frontal (marked interorbital constriction, but note that the posterior sutural edge is broken); the general morphology of the dentary (tapering symphysial region, generally shallow profile, deeply bifurcate posterior margin); a surangular of similar depth; and a slender ventral angular. The proportions of the dentary and postdentary bones also correspond.
The frontal is preserved in ventral view and lies just behind the anterior edge of the block (inverted in Fig. 5 View Fig to aid interpretation). It is flanked by the left mandible, and then by the left maxilla. Both are exposed in lateral view. The maxilla has a deep facial process with a rounded profile, and a shallower orbital process. Curving behind the maxilla (anatomically) is an arc of bone bearing a smooth orbital margin. This is presumably the jugal, displaced and rotated from its articulation with the orbital process of the maxilla. Immediately in front of the frontal are several flat bone fragments that may pertain to the anterior part of the frontal and the nasals. The right mandible lies along the right edge of the vertebral mass of the predator but is largely obscured ( Fig. 5 View Fig ).
Both the left dentary and maxilla bear teeth. In most positions, the roots of the teeth can be seen through the thin bone of the alveolar margins, showing that they were pleurodont, but with relatively shallow attachment surfaces. Towards the rear of the jaws, several tooth crowns are exposed. They are small, pointed and slightly spatulate, suggesting a degree of labiolingual compression at the tips.
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