Ornithocheiridae Seeley, 1870

Elgin, Ross A. & Frey, Eberhard, 2012, A nearly complete ornithocheirid pterosaur from the Aptian (Early Cretaceous) Crato Formation of NE Brazil, Acta Palaeontologica Polonica 57 (1), pp. 101-110 : 103-106

Family Ornithocheiridae Seeley, 1870

Genus and species indet.

Description.—The cervical column is represented by four vertebrae, identified as cervicals 5–8 (C5–8) ( Figs. 2 , 3 ). The morphology of these vertebrae is typical for ornithocheiroid taxa ( Table 1), in that the cervical vertebrae are 2–2.7 times as long as they are wide, they have a wide neural canal and widely diverging pre− and postzygapophyses, and the prezygapophyses are located lateral to the postzygapophyses ( Bennett 2001). The neural spines of C5–6 are broken and no comment can be made on their relative height. Caudal to the 6 th cervical vertebrae the remaining cervicals have been displaced from their natural position and are now visible in their craniolateral (C7) and cranial (C8) aspects. The neural spine of the 7 th cervical is tall and thin with respect to the vertebral body while the most caudally located cervical vertebrae (i.e., C8–9) preserve large robust ribs that remained in situ, suggesting that these had fused to the transverse processes. Although the 9 th cervical itself is not visible, being overlain by the 8 th, its presence is confirmed by a single large rib situated caudal to that of the 8 th cervical ( Fig. 3C ). The capitulum and tuberculum are widely spaced, by approximately 16 mm, and the shaft is narrow, decreasing rapidly to 6 mm by the mid corpus. The rib of the 9 th cervical is complete and terminates in a robust, slightly convex surface after a length of 89 mm.

The centra of the thoracic vertebrae are missing, buried and/or badly damaged such that the description of these elements is restricted to the neural spines, three of which are partially fused and form a supraneural plate. Thin suture lines separating the individual neural spines are visible ( Fig. 2 ). The neural spine of the first visible thoracic vertebra lies separate from the supraneural plate, although it is uncertain whether this is due to damage or displacement of the skeleton, or whether the neural spine simply did not form part of this structure. A large oval depression with a raised rim occuhttp://dx.doi.org/10.4202/app.2010.0079

pies the lateral flank of the third visible thoracic vertebra, forming the articulation for the medial articular surface of the scapula. Caudal to the notarial vertebrae the vertebral column is kinked and the more caudal thoracic vertebrae are badly damaged, indistinct and partly overlain by the left femur. These are also seen in lateral aspect and they have a maximum height of 19 mm from the base of the centrum to the top of the neural spine.

Nothing can be said about the sacral vertebrae, which are obscured from view by the overlying pelvic girdle. At least six gastralia have separated from the main body of the fossil and were displaced to overlie the distal portion of the right ulna following the disintegration of the dorsal column. These gastralia are preserved as three opposing sets and are associated with a limited amount of mineralised tissue. Eleven caudal vertebrae lie loose from the axial column and are scattered between the notarial vertebrae and the right scapulocoracoid. These are identical in appearance to those of C. piscator ( Kellner and Tomida 2000) , being long and narrow, typically between 2 and 4 times as long as they are wide. Where visible, the neural spines are positioned cranially and protrude past the cranial margin of the vertebrae, indicating that these bones belong to the middle portion of the tail. The terminal−most caudal vertebrae remain in articulation and are mediolaterally compressed to a greater degree than the other caudals. These are conical in form and do not expand at their articular surfaces ( Fig. 2 ).

The right scapulocoracoid is preserved in cranial view. No suture line between the two elements is visible, indicating that the structure was fully fused. The glenoid body measures 23 mm across its widest part and the scapula is shorter than the coracoid, the condition typical of ornithocheiroids ( Frey et al. 2003c; Kellner 2003; Unwin 2003). The scapula is offset against the glenoid body at an angle of 121 ° and the dorsal rim of the articular surface is visible as a flat, slightly convex surface that would have braced against the sub−oval facet of the notarium. The coracoid is about half as thick as the scapula in the mid−shaft region and forms an angle of 60 ° against the scapula. The proximal portion of the coracoid, where it would have articulated with the sternum is obscured by overlying sediment. The vertical distance between the dorsal surface of the scapula articular surface and the sternocoracoid articulation is estimated to have been no greater than 100 mm.

The individual bones of the forearm are mostly preserved in either near articulation or bent beyond bone lock. Both humeri are visible in dorsal aspect and preserve a short, warped, sub−triangular deltopectoral crest that is approximately one third of the total humeral length. The caudal tuberosity is short, and no pneumatic foramina are observed where it converges with the shaft of the humerus, although the compacta of these surfaces is slightly damaged. On the distal portion of the left humerus, along the craniodorsal margin of the shaft, a pronounced flange, 15% the humeral length, may be the insertion for the flexor muscles of the carpus ( Bennett 2003). Towards the distal margin of the humerus, the humeral shaft expands to about twice its width at the elbow joint, preserving an almost straight dorsal margin perpendicular to the long axis of the shaft. The epiphyseal gap is partially open.

The left ulna lies at an angle of 72 ° to the humerus while the right makes an angle of 53 °. Both have become slightly disarticulated from their natural positions. Both ulnae are about six times longer than they are wide and preserve no obvious muscle scars. While the right radius lies in situ along the right ulna the left radius has separated from the ulna and preserves a mid shaft width of 10–13 mm.

The carpals have fused to form two distinct syncarpal blocks but these have disarticulated from one another and are badly damaged so that no anatomical details can be observed.

The fourth metacarpals have been displaced by approximately 180 ° and lie sub−parallel to the ulnae; the distal roller joints are located near the proximal ends of the ulnae. Both wing metacarpals are also preserved in ventral view, with the ventral part of the roller joint measuring 16 mm across at its widest point, and they retain a natural articulation with the first phalanges of the wing finger. At least two additional metacarpals, presumably belonging to the left wing, are also preserved. Both are long and narrow and at least one would have made contact with the distal syncarpal during life.

The digits of the left manus are well preserved, and although the individual phalanges have disarticulated from each other they have not been displaced any great distance. The distal bones retain a contact with their respective unguals. The phalanges are about half as wide as the proximal margins of the unguals and slightly curved, with expanded proximal and distal margins at the articular facets to accommodate the neighbouring elements. The unguals are slightly curved with longitudinally concave ventral faces, forming a sulcus that extends almost the entire length of the bone. The phalanges of the right manus are mainly obscured and only two partial phalanges and one ungual are visible.

Only the first phalanges of the wing fingers are preserved and lie in natural articulation with the fourth metacarpals, making angles of 89 ° and 68 ° against the long axis of the left and right metacarpals respectively. The extensor tendon process has fused to the proximal face of the first phalanx and a large pneumatic foramen is present on the caudoventral surface of the right phalanx, adjacent to the proximal articulation. At its distal terminus the cranial margin of the first wing finger phalanx gradually merges with the gently convex distal articulation. Caudally this articulation facet forms a sharp caudally directed process that is formed by the steeply convex caudodistal margin of the shaft. This creates an expanded surface for the second wing phalanx that would have directed the distal phalanges caudally.

The individual elements of the pelvis have fully fused to form two complete pelvic plates, although these are in a poor condition. The compacta is damaged and the bone itself is crushed over several underlying elements. The left ischiopubic plate is observed in lateral view while the right is seen in caudolateral aspect, the acetabulum dominating the lateral faces of each and the obturator foramen being fully enclosed within the pubis. The cranial and caudal margins of the left pubis are shallowly concave, being almost symmetrical about the long axis of the bone. The bone is narrowest about its mid point before expanding towards its ventral margin, however, the ventral margin of the pubis is broken and its original shape cannot be determined. While the long axis of the pubis is directed ventrally, that of the ischium is directed caudoventrally at an angle of 46 ° against the pubis. As with the pubis, it is narrowest about its mid point and expands towards its ventral margin. Approximately half the caudal portion of the left ischium has been broken and lost from the

http://dx.doi.org/10.4202/app.2010.0079

specimen while the right has been distorted and is directed through the bedding plane of the slab. The preacetabular process of the ilium is long and thin but its cranial portion is either overlain by the ulna (left) or broken (right). The postacetabular process of the right pelvic plate partially overlies that of the left, which in turn has been crushed over the remains of the sacral vertebrae. The postacetabular process expands caudodorsally for approximately one quarter of its total length due to the curvature of the dorsal margin of the bone. Caudal to this expansion, the dorsal and ventral margins are directed caudoventrally, creating a caudoventrally directed process more or less uniform in width.

The femora lie adjacent to the pelvis and preserve a long, narrow femoral collum femoris, approximately 17 mm long, and a moderately bowed, laterally curving shaft. The femoral head is offset against the shaft at an angle of 20 °. Although both tibias have disarticulated from their respective femurs, they have not been displaced much. The tibia is long and slender, becoming increasingly narrow towards its distal articulation. Neither fibula is preserved. The distal articulation of the left tibia is broken and missing but the right is complete and terminates as a flat surface, 7.5 mm in width, indicating that the calcaneum and astragalus had not fused with this bone to create a tibiotarsus ( Fig. 4 ). Two tarsals, the astragalus and a distal tarsal, lie level with the distal margin of the tibia but off to one side. The astragalus is weakly crescentic in shape and is observed in medial aspect. A large foramen pierces the craniomedial portion of the bone. Although its caudomedial face is damaged, the preserved remains suggest that the medial surface was convex, projecting medially as described by Kellner (2004). The dorsal margin of the astragalus is concave to form the articulation with the distal surface of the tibia, while the ventral margin is strongly convex. The distal tarsal is as large as the astragalus itself, with a generally smooth convex surface and lies in contact with three of the four metatarsals.

The right metatarsals are very long and thin, the longest reaching a length of 58 mm with a mid−shaft diameter of only 1 mm. The length of these bones ranges from 54–58 mm, but at least one of the first four metatarsals is noticeably shorter with a length of only 45 mm. The fifth metatarsal is clearly distinct from the others, and is about one fourth to one fifth the length of metatarsals I–IV and has a sub−triangular outline with slightly convex medial and lateral margins.

The pedal phalanges are delicate and show only slight curvature. Their proximal and distal margins are slightly expanded at the interphalangeal articulations and in all cases the unguals maintain a natural articulation with the penultimate phalanx. The unguals themselves are equal in width to the preceding phalanges and are only slightly curved.

Figures

Fig. 2. New ornithocheirid pterosaur specimen (SMNK PAL 3854) from the Nova Olinda Formation, Crato Basin, Brazil.Photograph detailing the cervical, notarial thoracic and terminal caudal vertebrae.

Fig. 3. New ornithocheirid pterosaur specimen (SMNK PAL 3854) from the Nova Olinda Formation, Crato Basin, Brazil. A. 5th cervical vertebrae. B. 6th and 7th cervical vertebrae. C. 8th and 9th cervical ribs. Photographs (A, B, C) and explanatory drawings (A, B, C). Black shading highlights gaps/foram1 1 1 2 2 2 ina with the bone and the collapsed neurocentral canal.

Fig. 4. The foot and pedal function of the new ornithocheirid pterosaur from the Nova Olinda Formation, Crato Basin, Brazil. A. SMNK PAL 3854. Line tracing of the ankle region (A1) and reconstructions of the ornithocheiroid pes, based on the described specimen (A2). B. The azhdarchoid pes, based on SMNK PAL 3900. Both reconstructions are scaled to a common humeral length.