Pterodactyloidea Plieninger, 1901

Fastnacht, Michael, 2005, The first dsungaripterid pterosaur from the Kimmeridgian of Germany and the biomechanics of pterosaur long bones, Acta Palaeontologica Polonica 50 (2), pp. 273-288 : 275-277

Suborder Pterodactyloidea Plieninger, 1901 Family Dsungaripteridae Young, 1964

Locality: Langenberg Quarry, Oker near Goslar, Lower Saxony, Germany.

Horizon and age: Lower Kimmeridgian mudstones (Werner Fricke personal communication, Goslar, Germany 2004).

Material.—DFMMh/FV 500, 10 thoracic vertebrae, complete pelvis and sacrum, left and right femur,?part of right tibia.

Description.—The specimen was prepared mechanically, revealing most of the dorsal and lateral surfaces of the bones with the rest of the specimen still embedded in the matrix ( Fig. 2 ). The bones are uncrushed and preserved three−dimensionally. The vertebrae, sacrum, and pelvis are fully articulated. The right femur is articulated in its acetabulum, whereas the left femur is slightly displaced out of its acetabulum, but still is in contact with it. The possible remains of the right tibia are situated 37 cm posterior to the right femur and orientated in an anterolateral−posteromedial direction.

Presacral vertebrae.—There are nine presacral vertebrae preserved, still in full articulation with each other and with the sacrum ( Fig. 2 ). The left transverse process of the most anterior, tenth presacral vertebra is visible at the erosional edge where the specimen is broken off. The total length of the presacral vertebral column is 45 mm with each vertebra measuring about 5 mm in length and 12 to 14 mm in width across the transverse process. The length−height ratio of the vertebrae is 1:1, with the spinous process measuring about 50% of the total height. The spinous processes are rectangular in lateral view. The posteriorly elongated dorsal crista of the penultimate presacral vertebra is fused with the anteriorly elongated dorsal crista of the last presacral vertebra forming the supraneural plate. The spinous process and the postzygapophyses of the last presacral vertebra are fused with the first sacral vertebra, but here a suture still is visible. The transverse processes of the last six vertebrae are slender (roughly 1:2 ratio of width to length) and rectangular. The transverse processes of the anterior three vertebrae (including the isolated left transverse process) are bent posteriorly and are more obtuse (1:1 ratio of width to length). Due to the nature of preservation, the articulation of pre− and postzygapophyses are not clearly visible.

Sacral vertebrae.—The sacrum comprises five completely fused sacral vertebrae ( Figs. 2 , 3 ). The size of the vertebrae decreases posteriorly, from 20 mm, 18 mm, 14 mm, 10 mm, to 8 mm in width across the transverse processes. The height of the vertebrae cannot be determined, because the ventral part of the vertebral column is still embedded in the matrix. The supraneural plate of the fused spinous processes is slightly thickened laterally. Irregular longitudinal striations are visible on the surface of this expansion. The transverse processes of the vertebrae, especially of the first sacral vertebra face posterolaterally and are fused with a distinctive suture to the ilium. They are distally expanded in anterior−posterior direction and fused with each other, thus enclosing the spaces between the processes. Like the vertebrae, these intersacral foramina also decrease in size from anterior to posterior.

Pelvic girdle.—The elements of the pelvic girdle are completely preserved with the exception of the ventral parts of the right pubis which are missing ( Figs. 2 , 3 , 8A ). The bones are co−ossified, so that sutures between individual bones are barely detectable. Although the ventral side of the pelvic girdle is still embedded in matrix, it can be assumed from the visible parts and the diverging angle relative to each other, that the pelvis is ventrally open and not fused ( Fig. 4 ). There is no evidence of distortion or disarticulation on the dorsal side of the pelvis or at the fused articulation with the sacral vertebra. Nor are there any signs of any dorsomedially projecting processes of the pelvic bones which continue into the matrix. Unfortunately, no further preparation is possible at this side to clarify this unambiguously.

Ilium.—The ilium is relatively long (47 mm) with the preacetublar processus measuring about 3/5 of the total length and extending anteriorly to the level of the articulation between the sixth and seventh preserved presacral vertebrae. The process is curved anteromedially and expanded laterally with the greatest width at the level of the second last presacral vertebra. The ilium forms the dorsal border of the acetabulum, enclosing the upper half of this excavation. A prominent postacetabular process is developed posterodorsal to the acetabulum and rises above the level of the preacetabular process. This process is orientated more or less horizontally and is slightly concave in dorsal view. The ventral margin of the process is upwardly concave and lies just at the level of the dorsal margin of the acetabulum. The right and left processes are roughly parallel. In about half of the height of the process, a horizontally orientated depression which is deepest anteriorly is visible at about mid−height of the process.

Pubis.—The pubis is rectangular in lateral view, and taller than long. It forms the anteroventral quarter of the border of the acetabulum. On the left side of the pelvis, the anterior margin of the pubis is bent laterally. Whether this is the natural morphology of the pubis or if the bone was deformed post−mortem cannot be determined, because the anterior margin of the right pubis is mostly embedded in matrix. The anterodorsal process of the pubis extends to the level of the suture between the ilium and ischium.

The suture between the pubis and ischium is barely visible. Together, the bones surround the obturator foramen, which has a diameter of about 3 mm. The pubis and ischium are connected by a 3 mm long suture ventral to the obturator foramen.

Ischium.—The ischium is plate−like with two processes. The main process is orientated almost vertically and extends posteriorly to the level of the posterior end of the postacetabular process. At its end, the process is about 6.5 mm in height and 12 mm long. The second process extends posteroventrally from the posteroventral border of the obturator foramen. It is about 6 mm long and about 3 mm high.

The ischium forms the posteroventral quarter of the bor− der of the acetabulum. Both the ischium and pubis enclose the obturator foramen (see description of pubis).

Acetabulum.—The acetabulum extends from the level of the anterior margin of the transverse process of the third sacral vertebra to the level of the anterior margin of the transverse process of the fifth sacral vertebra. The cross−section is circular with a diameter of about 6 mm. The degree of perforation cannot be observed, because most of the acetabulum is filled by matrix. The dorsal border of the acetabulum is formed by the ilium, the anteroventral quarter by the pubis and the posteroventral quarter by the ischium.

Femur.—Both femora are slender and distinctly curved in anterior direction and also exhibit a pronounced inward bowing ( Figs. 5 , 6 ). The neck of the femur is orientated dorsomedially with an angle of 130 degree relative to the diaphysis. It bears a distinctive head with a basal diameter of about 5 mm. A ridge separates the smooth−surfaced head from the neck, giving it a somewhat mushroom−like shape. The greater trochanter is degreater trochanter the femur narrows in the anterior−posterior direction, thus giving the diaphysis an elliptical cross−section. At the distal end, the femur is expanded laterally and medially so that the width of the epiphysis is about twice that of the diaphysis. Two condyles are visible, separated by a medial groove. This groove merges proximally in a medial triangular depression on the posterior surface of the femur. The depression flattens proximally and has about the same length as the width of the distal epiphysis.

veloped ventrolateral to the head and neck. It measures about half of the diameter of the femur at this level. A deep fossa can be seen on the dorsolateral side of the trochanter. Distal to the Possible tibia.—The fragment of a long bone is situated about 36 mm posterior to the right femur ( Fig. 7A ). Its long axis is orientated in an anterolateral−posteromedial direction. The fragment is broken perpendicular to its long axis, thus revealing an elliptical cross−section with a central cavity ( Fig. 7B ). The thickness of the cortex (= bone wall) measures roughly one quarter of its total diameter for the major axis and one third for the minor axis. From the dorsal view a longitudinal groove is visible.

By comparison with other pterosaurs and because of its position and size, this isolated bone most likely represents part of the right tibia.

Figures

Fig. 2. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500. A. Dorsal view of specimen. B. Interpretative drawing. Scale bar 100 mm.

Fig. 3. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500. A. Left lateral view of pelvis. B. Interpretative drawing. Scale bar 10 mm.

Fig. 8. Comparative reconstructions of pterosaurian pelves. A. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500. B. Pterodactylus sp. C. Ornithocheirus sp. D. “Queensland pterosaur”. E. Germanodactylus sp. F. Dsungaripterus weii. All drawn to the same size.

Fig. 4. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500, posterior view of pelvis. For anatomical explanations see text and Fig. 2. Scale bar 10 mm.

Fig. 5. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500, dorsal view of right femur.For anatomical explanations see text and Fig. 2. Scale bar 10 mm.

Fig. 6. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500, dorsal view of left femur.For anatomical explanations see text and Fig. 2. Scale bar 10 mm.

Fig. 7. Dsungaripteridae gen. et sp. indet., DFMMh/FV 500. A. Fragment of?tibia. B. Cross−section of?tibia. Scale bars 10 mm. Note exceptionally thick cortex and consequent constricted lumen in the diaphysis.