Citation: Holgado B, Dalla Vecchia FM, Fortuny J, Bernardini F, Tuniz C (2015) A Reappraisal of the Purported Gastric Pellet with Pterosaurian Bones from the Upper Triassic of Italy. PLoS ONE 10(11): e0141275.
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The skeletal elements exposed on the surface are described and discussed according to an anatomical order (first skull, then axial, and finally appendicular elements; forelimb elements before hind limb elements; limb elements are described according to their position from proximal to distal) following the identification as pterosaurian bones according to [1], notwithstanding it is potentially or actually wrong. The reasons of the referral of each element to a pterosaurian skeletal element by Dalla Vecchia et al. [1] are reported first; then, the element is described in detail, discussing the resemblance of bones or structures to the bones of pterosaurs or other taxa, if the case. In order to avoid confusion in the description, the elements were indicated with lower case letters of the alphabet (from a to s; see Fig 2A). Subsequently, each element is compared with the bones of basal pterosaurs to which it was referred by Dalla Vecchia et al. [1] in order to establish whether the referral is reliable or not. Finally, alternatives to the original attribution [1] are reported, if they are possible. The sample of Middle-Late Triassic reptiles utilized for comparison includes some lepidosauromorphs (kuehneosaurid and sphenodontians), thalattosaurians (Endennasaurus), Pachystropheus, trilophosaurs, rhynchosaurs, Longisquama, Mecistotrachelos, Sharovipteryx, drepanosauromorphs, protorosaurians, basal archosauriforms, phytosaurs, ornithosuchids, aetosaurians, poposauroids, rauisuchids, basal crocodylomorpha, Scleromochlus, early pterosaurs, basal dinosauromorphs, basal dinosauriformes, and basal dinosaurs.
The pellet with the elements as interpreted by Dalla Vecchia et al. [1] and analyzed in the text (A); the elements according our interpretation (B). In A, purported cranial elements are in yellow colour, axial elements are in pink, and appendicular elements in blue; letters mark the elements as they were identified by Dalla Vecchia et al. [1] following the order of description in the text: palatines (a1, a2), pterygoid (b), cervical vertebrae (c and d), cervical rib (e), dorsal vertebrae (f1-f5), dorsal rib (g), caudal vertebrae (h1-h2), hemapophysis (i), gastralia (j), ulna (k1-k2), radio (l1-l2), wing metacarpal (m), wing phalanx 1 (n), wing phalanx 2 (o), wing phalanx 3 (p), wing phalanx 4 (q), femur (r), metapodial (s). A further element, which was not mentioned by Dalla Vecchia et al. [1], is marked with x. The drawing is based on Figure 3 of Dalla Vecchia et al. [1], redrawn and modified. Anatomical abbreviations are explained in the text. The scale bar equals 10 mm.
The skeletal elements were not actually described by Dalla Vecchia et al. [1], who just tried to match them with those of non-pterodactyloid pterosaurs, in particular Preondactylus buffarini and the other Triassic taxa known in 1988 when the paper was written (i.e., Eudimorphodon ranzii and Peteinosaurus zambellii).
The elements of the pellet identified by Dalla Vecchia et al. [1] are listed here according such identification, they are described, and then compared to those of pterosaurs in order to check whether the original referral [1] is plausible or not. If a resemblance to elements of other reptiles is apparent, it is also mentioned.
The gastric pellet is lens-like, 52 mm long, 33 mm wide, and 3.2 mm of maximum thickness. The distribution of the bones within the pellet is chaotic, although there are preferential orientations for long bone remains. The identifiable elements are mainly partial vertebrae and portions of long bone shaft that are clumped in a background of smaller bone fragments (Figs 1 and 2). As it was observed by Dalla Vecchia et al. [1], there is no evidence of a background of amorphous organic matter surrounding the bones.
Two small bones of grossly similar morphology placed along the margin of the right lower corner of the pellet are identified as palatines in Figure 3 of Dalla Vecchia et al. [1], but they are not mentioned in the text. Their margins are smooth, thus they are plausibly not affected by breakage, i.e. they are not just misshapen bone fragments. The nearly completely exposed one (Fig 3) is 6.5 mm long, its maximum width is 2.2 mm and its maximum thickness is 0.5 mm. It is roughly triangular, narrow and elongated, with a blunt apical extremity; there is probably a notch at its wider extremity (left in Fig 3).
As for the purported palatines, a small bone is identified as a pterygoid in Figure 3 of Dalla Vecchia et al. [1], but it is not mentioned in the text. It is a thin, slender, and pointed fragment of bone cropping out from the lower right corner of the pellet. The exposed portion is 8 mm long.
The two elements referred as cervical vertebrae in Figure 3 of Dalla Vecchia et al. [1] and in the text (page 123) are only partly preserved; they are strongly crushed, and probably broken. They occur close to each other and to the purported caudal vertebra (h1), which is better preserved and exposed. Their morphology is quite difficult to interpret.
This element is mentioned only in Fig 3 of Dalla Vecchia et al. [1]. It is an elongate group (7 mm long) of strap-like and overlapping small bones placed close to the purported cervical vertebrae (elements c and d). It was probably referred to a cervical rib by Dalla Vecchia et al. [1] just because it is close to the purported cervical vertebrae. It is apparently made of a folded lamina of bone and it is not definitely filiform, or a bundle of filiform structures. The cervical ribs of Triassic pterosaurs have long filiform shafts that form bundles along the ventrolateral sides of the cervical segment of the vertebral column [22]. Those filiform shafts cannot be recognized in the purported cervical rib/s of MFSN 1891.
Five elements were identified as dorsal vertebrae by Dalla Vecchia et al. ([1]: Figure 3), presumably based on their morphology. They are located along the marginal part of the pellet. The better preserved and exposed is the one labeled f1 in Fig 2A; the others will be described in clockwise order moving around the pellet.
The following vertebra (f4) is also a centrum crushed against other bones (Fig 6C). Dalla Vecchia et al. [1] did not notice a close partial neural arch in possible dorsal view with two paired zygapophyses similar to that present in element f3, possibly the postzygapophyses. It is unclear whether they belong to a further vertebra, whose centrum is mostly covered by the arch, or to the one indicated by Dalla Vecchia et al. [1].
A dorsal rib is mentioned only in Figure 3 of Dalla Vecchia et al. [1]. It is a small bone mostly covered by the paired long bones k2-l2 in the upper right corner of the pellet. The proximal part appears to be that of a dicephalous rib with a distinct but short tuberculum and a long capitulum (see below). A short ridge runs along the proximodorsal margin of the shaft. The shaft is covered by the two long bones and crops out from l2, but the distal portion is not preserved. The shaft appears to be markedly arched. Its referral as a dorsal rib is plausible.
Dalla Vecchia et al. [1] mention this element only in Figure 3 of. It is a small, Y-shaped bone that is partially covered by element d (Figs 4A, 4B and 9). It has elongated and scarcely divergent pedicels (18) that are expanded at the proximal extremity. The third branch of the Y is the spine, which is relatively long and narrow, both transversally and caudocranially; its covered distal end can be observed in the microCT virtual rendering or dataset. The total length of the bone is 8.5 mm; the spine is 4.9 mm long, but its unexpanded distal extremity seems to be broken, so it was probably longer. The identification of element i as a hemapophysis is evidently correct, having the plesiomorphic morphology for this element in reptiles [49].
Only one gastral element is identified in Figure 3 of Dalla Vecchia et al. [1] but they are more abundant, mainly in the right half of the pellet (Fig 2B). They are small and filiform bones, sometimes clearly ending with a sharp point. Pterosaurs have gastralia, as do many other diapsids [48].
The couple k1-l1 crosses the pellet longitudinally. The practically complete k1 (Fig 10A) is 39.5 mm long according to the interpretation by Dalla Vecchia et al. [1], with a straight shaft that seems to arch slightly only distally where it ends with a condyle. The proximal part is slightly broader than the mid-shaft and is deeply collapsed in the middle; the proximal extremity ends against the purported cervical rib, and is probably broken. The surface of the mid-distal part of the shaft shows thin and long longitudinal ridges. The distal portion of the shaft is covered by other bones; according to Dalla Vecchia et al. [1], the distal extremity of the ulna (i.e., the condyle) seems to be in continuity with the shaft, but this cannot be ascertained, not even with the microCT data. The condyle (Fig 10B) is relatively small, rounded and slightly asymmetrically developed caudally; a groove seems to run along its cranial margin and a small foramen pierces its exposed side.
The purported radius (l1) lies alongside k1 proximally, but diverges slightly distally (Fig 10A). Its 'proximal' extremity is clearly broken and the 'proximal' segment of its shaft is totally collapsed, suggesting, as for the element k1, that it was hollow inside. Here, an elongate fragment of bone sticks out, which was referred to the 'radius' by Dalla Vecchia et al. [1], but it has blunt margins and a pitted surface and probably belongs to another element. Apart this 'proximal' segment contacting k1, the extent of the diaphysis of l1 is unclear, because there seems to be at least three segments of long bone shaft parallel to each other: the elements r and l1 and one indicated with the acronym ilb in Fig 10C; the latter overlaps l1 distally and tapers to a blunt extremity only 0.5 mm wide (Fig 10C). A further, distinct and long fragment crops out distally and is also marked with the abbreviation ilb in Fig 10C. The extremities of l1 appear to be broken; as preserved, the bone in about 36 mm long. 2ff7e9595c