Pterodactylus antiquus Soemmerring, 1812

Augustin, Felix J., Kampouridis, Panagiotis, Hartung, Josephina, Albersdoerfer, Raimund & Matzke, Andreas T., 2022, The geologically oldest specimen of Pterodactylus: a new exquisitely preserved skeleton from the Upper Jurassic (Kimmeridgian) Plattenkalk deposits of Painten (Bavaria, Germany), Fossil Record 25 (2), pp. 331-343 : 331

Pterodactylus antiquus Soemmerring, 1812

Figs 2 , 3 , 4 , 5

Holotype.

BSP AS.I.739, an almost complete skeleton including the skull.

Amended diagnosis.

Modified after Bennett (2013a): Upper Jurassic pterodactyloid with a slender and elongated rostrum; the dorsal margin of the skull straight to only slightly concave upward; nasoantorbital fenestra length ⁓20-25% of skull length in large individuals; number of teeth proportional to skull length with up to ⁓25 teeth per jaw side in large individuals; teeth low conical; teeth largest anteriorly and decreasing in size posteriorly; tooth row length ⁓75% of jaw length; upper tooth row extending posterior to the anterior margin of the nasoantorbital fenestra; a low sagittal bony crest dorsal to the nasoantorbital fenestra and orbit in large individuals, which apparently lacks the striations seen in Ctenochasma , Germanodactylus , and Gnathosaurus ; a soft tissue crest extending dorsally from the bony crest in large individuals; an occipital lappet of soft tissues extending posteriorly from the occipital region; cervical vertebrae 3-7 elongate and neck relatively longer than in Cycnorhamphus , Ctenochasma , and Aurorazhdarcho (shared with " P. " Ardeadactylus longicollum ); in small specimens, WP2 is 93-96% of WP1 length, in large ones ⁓91%; in modified Nopcsa curves, WP1-4 lengths typically exhibit a convex upward curve (shared with Germanodactylus ); in the pes, MtII is longer than MtI or equal to MtI in length; the proximal phalanges of digit I-III show progressive reduction in length whereas those of digits I and IV are subequal (shared with Germanodactylus ).

Referred material.

DMA-JP-2014/004, a nearly complete and articulated skeleton including the complete skull.

Locality.

Rygol Quarry near Painten, Niederbayern, Bavaria, Germany.

Stratum.

Torleite Formation, Beckeri zone, Ulmense subzone, upper Kimmeridgian, Upper Jurassic.

Taxonomic remarks.

For many decades after its discovery, Pterodactylus has been essentially a wastebasket taxon and dozens of species have been assigned to the genus, many of which later turned out to represent rather distantly related taxa. In 1970, Wellnhofer, in his classic monograph on the pterodactyloids from the Solnhofen Limestones, provided a thorough revision of the genus and listed a total of six species: P. antiquus , P. kochi , P. longicollum , P. suevicus , P. micronyx and P. elegans ( Wellnhofer 1970). Subsequently, four of these species have been assigned to their own genera, a decision followed by most researchers without much controversy, with P. suevicus having been assigned to Cycnorhamphus (= Gallodactylus ) (e.g. Fabre 1976; Wellnhofer 1978; Bennett 1996a, 2013b; Unwin 2003), P. elegans to Ctenochasma (e.g. Bennett 1996b, 2007; Unwin 2003; Jouve 2004), P. micronyx to Aurorazhdarcho ( Bennett 1996b, 2013a, Hone et al. 2013), and P. longicollum to Ardeadactylus ( Bennett 2013a; Vidovic and Martill 2018). In contrast to this, the taxonomic status of Pterodactylus kochi has caused considerable debate recently and it is now usually regarded either as a junior synonym of P. antiquus or as belonging to a distinct genus. After the revision of the genus, Mateer (1976) was the first to suggest that P. kochi and P. antiquus are extremely similar and that the former therefore represents a junior synonym of the latter (although it should be noted that a synonymy of the two species has originally been proposed already by Zittel, 1883). Later, Bennett (1996b) conducted statistical analyses of Pterodactylus and other pterodactyloids from the Solnhofen Limestone, likewise concluding that the specimens assigned to P. kochi likely represent immature individuals of P. antiquus . This view has been also expressed by several other subsequent studies ( Jouve 2004; Bennett 2013b, 2018).

Despite the synonymization of P. kochi with P. antiquus , several later studies have treated the two species as separate taxa (e.g. Frey and Martill 1998; Kellner 2003; Unwin 2003). Recently, Vidovic and Martill (2014) found the holotype of P. scolopaciceps , which has been synonymized with P. kochi by Zittel (1883) and was listed as such by Wellnhofer (1970), to differ considerably from other Pterodactylus specimens and thus assigned it to the new genus Aerodactylus . In addition, they assigned a number of other specimens to Aerodactylus scolopaciceps that previously were referred to P. kochi ( Vidovic and Martill 2014). Subsequently, Vidovic and Martill (2018) re-studied several specimens assigned to Pterodactylus and found the holotype of P. kochi and two referred specimens to differ in several respects from P. antiquus . Therefore, they proposed that P. kochi actually belongs to a separate genus, Diopecephalus , which was originally coined by Harry Govier Seeley in the second half of the 19th century ( Vidovic and Martill 2014, 2018). Thus far, a consensus on this topic has not been reached. Regarding the taxonomy of Pterodactylus , we here tentatively follow Mateer (1976), Bennett (1996b, 2013b), and Jouve (2004) and consequently regard P. kochi as representing a junior synonym of P. antiquus , because we find it difficult to differentiate the two taxa based on the proposed diagnoses for the time being.

Comparative description

The specimen consists of a complete, articulated and extremely well-preserved skeleton lying on its right side (Fig. 2 ). Only a very small portion of the left mandible as well as of the left and right tibia is missing. Otherwise, the skeleton is nearly perfectly preserved with every bone present and in its roughly correct anatomical position. The mandible is slightly detached from the skull and is preserved in ventral view. The hyoid bones are present and, like the mandible, are slightly dislocated ventrally, being preserved between the left and right mandibular rami. The wings are folded with the right wing lying partly under the left one and partly under the body skeleton. The hind limbs extend laterally and both are visible in posterolateral view.

For the comparison below, we largely relied on the classical monograph of Wellnhofer (1970), in which he described every Pterodactylus specimen known at the time and additionally provided the most comprehensive overview of the genus including five specimens of P. antiquus and 23 specimens of P. ' Pterodactylus kochi '. Wellnhofer (1970) also provided detailed measurements for all of these Pterodactylus specimens, which formed the basis for the quantitative comparison presented below (for details, see Wellnhofer 1970: chapter 10). Note that we here use the corrected measurements for TM 10341 by Bennett (2013a) that differ considerably from those listed by Wellnhofer (1970). In order to make the comparison as clear as possible, and because there has been considerable debate on the taxonomy of Pterodactylus (see above), we here refer to individual specimens instead of referring simply to P. antiquus or P. kochi . Moreover, we provide both the specimen number used in the Wellnhofer (1970) monograph (i.e. his 'Exemplar Nr.') and the official repository number. Notably, specimen JME 29.III.1950 (Exemplar Nr. 9), which was originally referred to P. kochi by Wellnhofer (1970), has been reassigned to Germanodactylus cristatus by Bennett (2006), and we herein follow this referral. When referring to Pterodactylus in the comparison below, we include both P. antiquus and P. kochi , as we tentatively accept the synonymy of the two as outlined above. For an overview of the measurements of the skeleton and individual bones as well as some selected dimensions, see Table 1 .

Cranial skeleton

The skull of DMA-JP-2014/004 is complete and exposed in left lateral view (Fig. 3 ). It has a total length of approximately 48 mm, and thus lies within the lower range previously observed in Pterodactylus with reported skull lengths ranging between 23 mm in the smallest specimen (BSPG 1967 I 276, Exemplar Nr. 6) and 149 mm in the largest specimen preserving a complete skull (BMMS 7, without Exemplar Nr.) ( Wellnhofer 1970; Bennett 2013a). Like in other specimens of Pterodactylus , the orbit is circular in outline and has a diameter of slightly more than 10 mm. The orbit is thus relatively large compared to overall skull length (ca. 20%), likely reflecting the young ontogenetic age of the specimen. Wellnhofer (1970) provided SOL-indices (= Schädel-Orbita-Längen-Index, German for skull-orbit-length index) for the pterodactyloids from the Solnhofen Archipelago, which range from 30 in the smallest individual of Pterodactylus (BSPG 1967 I 276, Exemplar Nr. 6; skull length of 23 mm) to 15 in the largest (BSPG 1883 XVI 1, Exemplar Nr. 28; skull length of 113.5). With an SOL-index of 20 and a skull length of 48 mm, the new specimen from Painten matches the observed relationship between SOL-index and skull length for pterodactyloids very well (see Wellnhofer 1970: fig. 17) and falls within the range defined as the transitional ontogenetic stage (between juvenile and adult).

The sclerotic ring is preserved within the dorsal half of the orbit and even the individual sclerotic elements can be discerned, although an exact number of sclerotic elements cannot be provided due to the small size and imperfect preservation. The sclerotic ring is ellipsoidal in shape being slightly longer than high, although it seems to be diagenetically somewhat compressed dorsoventrally. Judging from other specimens preserving the sclerotic ring like BSPG 1968 I 95 (Exemplar Nr. 2) and SMNS 81775 (without Exemplar Nr.), the sclerotic ring normally has a circular outline and occupies almost the entire orbit ( Wellnhofer 1970; Bennett 2006: fig. 6). The nasoantorbital fenestra has an anteroposterior length of 16 mm, occupying around one third of the skull length, which is similar to other Pterodactylus specimens including the holotype of P. antiquus (BSPG AS I 739, Exemplar Nr. 4) ( Wellnhofer 1970). In very young individuals, the ratio between nasoantorbital length and skull length is slightly smaller, around one fifth to one fourth (e.g. BSPG 1967 I 276, Exemplar Nr. 6) ( Wellnhofer 1970). The parietal region of the skull posterior to the orbit is rounded. The dorsal margin of the skull is relatively straight and slightly concave. The ventral margin of the skull and the palatal region are completely straight.

The mandible is complete and preserved in ventral view, although it is slightly distorted in a way that the left lateral aspect is partly visible. It has a total length of 38 mm, while the symphysis is 14 mm long, thus occupying slightly more than one third (approximately 37%) of the length of the mandible. In general, it seems as if the symphysis becomes proportionately slightly larger (relative to mandible length) during ontogeny, with the ratio ranging between 37% in small individuals (BSPG 1967 I 276, Exemplar Nr. 6; skull length of 23 mm) and 43% in large individuals (BSPG AS I 739, Exemplar Nr. 4; skull length of 108 mm) ( Wellnhofer 1970). The distance between the left and right mandibular ramus at the level of the joint is 7 mm, although this value should be treated with caution due to the slight distortion of the lower jaw. The suture between the mandibular rami is well discernible, being completely straight and extending anteroposteriorly. The paired hyoid bones are located between the posterior parts of the lower jaw and have an elongated, slightly bowed morphology, and thus resemble those of the very small specimen BSPG 1967 I 276 (Exemplar Nr. 6) ( Wellnhofer 1970: fig. 5).

The tooth crowns are overall low and conical, just as in all other specimens of Pterodactylus . There are 14 teeth preserved in the left upper jaw, extending from the jaw tip up until the anterior third of the nasoantorbital fenestra. The size of the teeth progressively decreases posteriorly - again a feature present in several other Pterodactylus specimens including the type specimens of both P. antiquus (BSPG AS I 739, Exemplar Nr. 4), and of P. kochi (BSPG AS XIX 3, Exemplar Nr. 23) ( Wellnhofer 1970: fig. 3, pl. 1-2). In the left lower jaw, 14 teeth are present that gradually become smaller posteriorly and extend for 17 mm measured from the tip of the jaw (roughly 45% of the total mandible length). As was demonstrated by Wellnhofer (1970) as well as later by Jouve (2004) and Bennett (2013a), the tooth count in Pterodactylus changes in proportion with the length of the skull and thus the ontogenetic age of the specimen. The number of teeth in the upper jaw ranges between 12 in small individuals (BSPG 1967 I 276, Exemplar Nr. 6; skull length of 23 mm) and 18 in large individuals (BSPG AS I 739, Exemplar Nr. 4; skull length of 108 mm) ( Wellnhofer 1970).

Axial skeleton

The neck of DMA-JP-2014/004 (Fig. 4a ) comprises seven cervical vertebrae (but see Bennett 2004, 2013a) and has a length of approximately 28 mm, which compares well with other Pterodactylus specimens of a similar size such as (the slightly smaller) TM 10341 (Exemplar Nr. 1) that has a neck length of 25.9 mm and a skull length of 44.5 mm ( Bennett 2013a). The dorsal series comprises 15 vertebrae, while the number of sacral vertebrae is difficult to assess due to the slightly displaced ilium (Fig. 4a ). The combined length of the dorsal and sacral region (= PCRW-length of Wellnhofer 1970 and Bennett 2013a) is 33 mm and thus similar in size but proportionately slightly smaller compared to that of the similarly-sized specimen TM 10341 (Exemplar Nr. 1), in which the dorsal and sacral vertebral column have a combined length of 33.3 mm ( Bennett 2013a). The tail of the new specimen from Painten is partially covered by the ilium, and therefore its exact length and the number of caudal vertebrae cannot be reliably determined. The ribs are still attached to their respective vertebrae, are very thin and slightly curved. However, they are partly concealed by the overlying forelimb elements. The overlapping gastralia are present in the abdominal area of the specimen, anteroventrally of the pelvis.

Appendicular skeleton

The forelimbs are complete and mostly articulated, although the right wing is partly underlying the body skeleton (Fig. 4b ). The measurements were thus taken from the left forelimb. The scapula and the coracoid are preserved next to each other, the former having a length of 13 mm and the latter of 11 mm, although the coracoid is not fully visible in the left or the right side. The left humerus, which is slightly dislocated from the glenoid, has a length of 18 mm. Radius and ulna are lying next to each other, being completely parallel and more or less equal in length. Both are considerably longer than the humerus with a length of 25 mm. As discussed by Wellnhofer (1970), the wrist of Pterodactylus consists of two proximal carpals and four distal carpals. In the new specimen from Painten, the two proximal carpals contact the distal joints of radius and ulna, while the four distal carpals are preserved as small, blocky elements between the proximal carpals and the metacarpals. The four metacarpals are subequal in length and preserved parallel to each other, but metacarpals I-III are much smaller and partly covered by metacarpal IV. The wing metacarpal (i.e. metacarpal IV) is similar in size to, albeit slightly shorter than, the humerus with a length of 16 mm. The pulley-like distal joint of the wing metacarpal is well visible in dorsal view. The phalanges of the wing finger are elongated and rod-like and decrease in size distally, with lengths of 22.5 mm (wing phalanx 1), 21.5 mm (wing phalanx 2), 19.5 mm (wing phalanx 3) and 17 mm (wing phalanx 4). The distal-most phalanx of the left wing finger is slightly dislocated from the third one. The right wing is completely articulated but largely hidden under the body skeleton. The other fingers are articulated with their respective metacarpals and are completely preserved. The phalangeal formula of the hand is 2-3-4-4-0, as is typical for pterosaurs. The proportions of the wing of the Painten specimen are very similar to those reported from other specimens of Pterodactylus , with the humerus being around a quarter to a third shorter than the radius, the wing metacarpal being similar in size to (albeit slightly smaller than) the humerus, and the wing phalanges becoming progressively but slowly shorter (for a comparison of the forelimb proportions in Pterodactylus , see also below).

The pelvis comprises the articulated ilium, which is firmly attached to the sacral vertebrae, the pubis and the ischium (Fig. 5 ). The hind limbs are both well visible, being stretched out laterally (Fig. 5 ). The femora are articulated with the pelvis, the slightly demarcated femoral head still being connected to the acetabulum. The femur has a length of 18.5 mm and thus is slightly shorter than the tibia, which has a length of 23.5 mm, a condition also seen in all other Pterodactylus specimens ( Wellnhofer 1970; Bennett 2013a). The fibula is very thin, tightly attached to the tibia, and only extending for the proximal half of the tibia. The tarsals are tightly interlocked and articulated in the right hind limb, whereas in the left hind limb, the tarsals are somewhat disarticulated. Of the five tarsals (two proximal and three distal ones) typically present in Pterodactylus ( Wellnhofer 1970), at least four (two proximal and two distal ones) are visible in the specimen from Painten. The feet are again well preserved and articulated, comprising all five metacarpals and all five digits. Among the metatarsals, metatarsal II is the longest, metatarsal I and III are subequal in length and slightly shorter than metatarsal II. Metatarsal IV is shorter than metatarsal I and II, and metatarsal V is considerably shorter than the other metatarsals, being only a small splint-like bone. The first four digits bear small claws, whereas the fifth digit consists only of a single short phalanx. The phalangeal formula is 2-3-3-3-1. As demonstrated by Wellnhofer (1970), the phalangeal formula of Pterodactylus is dependent on the ontogenetic age of the animal, varying between 2-3-3-3-1 in juveniles and 2-3-4-4-1 in adults. Therefore, the phalangeal formula of the specimen from Painten again indicates an individual of juvenile to subadult age.

Skeletal proportions and Nopcsa curves

The length of the skull, neck, combined dorsal and sacral vertebral column (=PCRW-length of Wellnhofer 1970 and Bennett 2013a), humerus, radius, wing metacarpal, wing phalanx 1-4, femur and tibia were plotted in order to produce a modified Nopcsa curve (see Bennett 2013a). In this diagram, we also plotted the respective lengths of all other Pterodactylus specimens (measurements taken from Wellnhofer 1970 as well as Bennett 2013a for specimen TM 10341 and Frey and Tischlinger 2000 for an uncatalogued specimen stored in a private collection). The resulting Nopcsa diagram (Fig. 6 ) is essentially an updated version of the one figured by Bennett (2013a: fig. 9). In general, the specimen from Painten, DMA-JP-2014/004, is remarkably similar to the other Pterodactylus specimens regarding its skeletal proportions. The skull is the longest element in all specimens, while the neck is significantly shorter. In the large majority of specimens, including DMA-JP-2014/004, the combined length of the dorsal and sacral vertebral column (=PCRW-length) is greater than that of the neck, with some notable exceptions such as the holotype of P. antiquus (BSPG AS I 739, Exemplar Nr. 4), in which the PCRW-length is smaller than, or equal to, the length of the neck. Notably, all of these exceptions are relatively large specimens with skull lengths of more than 80 mm. All specimens smaller than that (i.e. having skull lengths below 80 mm) have a neck shorter than their combined dorsal and sacral vertebral column.

In all specimens referred to Pterodactylus , the humerus is much shorter than the PCRW-length and the radius is longer than the humerus (Fig. 6 ). The metacarpal of the wing finger is again considerably shorter than the radius and has a similar size as the humerus in all specimens aside from SM R4074, in which the wing finger metacarpal is comparatively very long, having almost the same length as the radius. In all specimens except SM R4074 (which seems to have an unusually long fourth metacarpal), the first wing finger phalanx is much longer than the wing finger metacarpal. In all specimens of Pterodactylus , phalanges 1-4 of the wing finger are progressively shorter, which, in the diagram (Fig. 6 ), results in a slightly convex and gentle downward curve. The femur is significantly longer than the wing phalanx 4 but shorter than the tibia. In summary, the outline of the Nopcsa curve of the specimen from Painten is nearly identical to that of similarly sized Pterodactylus specimens, thus indicating remarkably similar skeletal proportions and placing DMA-JP-2014/004 unequivocally within the genus Pterodactylus .

Figures

Figure 2. Pterodactylus antiquus, DMA-JP- 2014 / 004, from the Upper Jurassic (Kimmeridgian) Torleite Formation of Painten; overview photograph.

Figure 3. Pterodactylus antiquus, DMA-JP- 2014 / 004, from the Upper Jurassic (Kimmeridgian) Torleite Formation of Painten; detail photograph of the skull.

Figure 4. Pterodactylus antiquus, DMA-JP- 2014 / 004, from the Upper Jurassic (Kimmeridgian) Torleite Formation of Painten; detail photograph of the axial skeleton (a), as well as the forelimbs (b).

Figure 5. Pterodactylus antiquus, DMA-JP- 2014 / 004, from the Upper Jurassic (Kimmeridgian) Torleite Formation of Painten; detail photograph of the hind limbs.

Figure 6. Modified Nopcsa curves of the skeletal proportions of Pterodactylus antiquus (including P. kochi). The measurements were taken from Wellnhofer (1970) as well as from Frey and Tischlinger (2000). Note that we used the corrected values of TM 10341 (Exemplar Nr. 1) provided by Bennett (2013 a) that differ considerably from those listed by Wellnhofer (1970). Specimen JME 29. III. 1950 (Exemplar Nr. 9) was excluded because it was shown by Bennett (2006) to belong to Germanodactylus cristatus. The heavy black line represents the curve for the new specimen from Painten described herein (DMA-JP- 2014 / 004). The line with the third-largest skull represents the holotype of P. antiquus (BSPG AS I 739, Exemplar Nr. 4; skull length of 108 mm), and the line directly below that of the Painten specimen (DMA-JP- 2014 / 004) represents TM 10341 (Exemplar Nr. 1; skull length of 44.5 mm). Abbreviations: mcIV, metacarpal IV (i. e. the wing finger metacarpal); PCRW, combined length of the dorsal and sacral vertebral column (= PCRW-length of Wellnhofer 1970 and Bennett 2013 a; praecaudale Rumpfwirbelsaeule); r, radius; s, skull; t, tibia; wp 1 - 4, wing finger phalanx 1 - 4.