Rhamphorhynchinae, Nopcsa, 1928
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https://doi.org/ 10.4202/app.00805.2020 |
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https://treatment.plazi.org/id/0C4187EA-4019-FFAC-FCAD-FC54FC7CFE82 |
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Felipe |
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Rhamphorhynchinae |
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Rhamphorhynchinae gen. et sp. indet.
Figs. 2‒6 View Fig View Fig View Fig View Fig View Fig .
Material.― MUHNCAL.20165, a complete left humerus; two fragments of a diaphysis of a wing phalanx and a possible dorsal vertebra belonging to a single, medium sized pterosaur individual from Cerritos Bayos , west Calama , Antofagasta Region, Chile; Cerro Campamento Formation , poorly preserved, too. The preserved height is ~8.2 mm. Apparently, its articular contour has a semicircular shape, whereas its dorsal margin was concave, given by the ventral contour of the neural canal. The general morphology of the vertebra resembles that of a dorsal vertebra, but due its the incompleteness cannot be conclusively ascertained .
Humerus: An almost complete left humerus is preserved. It is three-dimensionally preserved and is exposed in posterior view ( Fig. 3 View Fig ). The humerus is 71 mm long, and the mediolateral width of the diaphysis at its midpoint is 7.7 mm, with a length/width ratio of 9.2. The humerus is assigned to a pterosaur based on the posterior inclination of the caput humeri, the presence of a well-expanded anterior deltopectoral crest, and relatively thin cortical bone ( Wellnhofer 1978, 1991; Buffetaut et al. 2015). The deltopectoral crest is located at the proximal end of the humerus. The deltopectoral crest is almost complete, dorsoventrally narrow, and well extended anteriorly. It is elongated and projects approximately perpendicular from the humeral shaft. As in several non-pterodactyloid pterosaurs and in some basal pterodactyloids, the proximal and distal margins of the deltopectoral crest lie almost on the same level as the medial crest ( Wellnhofer 1978: fig. 1b–d; Unwin and Martill 2017). Furthermore, the deltopectoral crest is proximodistally constricted at its base and expanded anteriorly, in a hatchet-shaped form. At its anterior end, the deltopectoral crest is partially fractured. This portion joins with a carbonate layer present in the rock, making it difficult to determine the exact morphology of the anterior edge of the deltopectoral crest. However, it is observed that the proximodistal edge curves distally, which gives the deltopectoral crest an ax-like shape.
Thehatchetortongue-shapedformofthedeltopectoralcrest and its proximal location are features considered diagnostic of Rhamphorhynchidae by Kellner (2003) and Unwin (2003). This morphology is present in several rhamphorhynchids ( Fig. 4 View Fig ), such as species of Rhamphorhynchus (Wellnhofer 1975a, 1978; O’Sullivan and Martill 2015), Dorygnathus ( Padian 2008b) , Nesodactylus ( Colbert 1969) , Qinglongopterus ( Lü et al. 2012) , and Bellubrunnus ( Hone et al. 2012) . The shape of the deltopectoral crest MUHNCAL.20165 especially resembles that present in the genera Rhamphorhynchus and Nesodactylus , in which the hatchet-shaped deltopectoral crest is especially evident ( Colbert 1969: fig. 8; Wellnhofer 1975a: fig. 11; Fig. 4E, R View Fig ). However, the deltopectoral crest of MUHNCAL.20165 is more elongated anteroposteriorly than in Nesodactylus hesperius ( Fig. 4 View Fig ). The morphology of the deltopectoral crest of MUHNCAL.20165 is quite different of species of Campylognathoides , in which the deltopectoral crest is short, approximately triangular in shape and its proximal end is proximally curved (see O’Sullivan et al. 2013: fig. 5h, i). The proximal portion of the humerus is dorsoventrally expanded and has two well-marked depressions, limited proximally by the posterior edge of the humeral head, and separated by a medial crest. The caput humeri is partially eroded, and it is flexed posteriorly, as apparently in all pterosaurs ( Wellnhofer 1978; Unwin 2003). The proximal portion of the caput humeri has a saddle-shaped articular surface, as is common in pterosaur humeri ( Rauhut et al. 2017). Thus, the articular end is concave mediolaterally, and convex anteroposteriorly. The humeral head is slightly displaced posteriorly with respect to the diaphysis axis, a feature apparently present in all pterosaurs ( Wellnhofer 1978; Unwin 2003; Unwin and Martill 2017). Its articular surface is partially eroded, although there are two bulges separated by a short groove. The dorsal crest of the humeral head is triangular and well projected proximodorsally, as in species of Rhamphorhynchus Wellnhofer 1975a ) and Nesodactylus ( Colbert 1969) . The depressions located below the humeral head extend distally until the beginning of the diaphysis. The lateral depression is wider and more excavated than the medial.
Since the humerus is exposed in posterior view, it is not possible to corroborate the presence of pneumatopores piercing the anterior surface of the proximal end of this bone. The absence of pneumatopores has been described in basal pterosaurs ( Claessens et al. 2009), such as Rhamphorhynchus muensteri Goldfuss, 1831 ( Bonde and Christiansen 2003). Likely, the absence of pneumatic pores in the humerus is a common character among non-pterodactyloids: in Pterodactyloidea, the humeri usually have pneumatopores ( Bonde and Christiansen 2003; Claessens et al. 2009; Elgin and Hone 2013; Unwin and Martill 2017). The medial crest (also called ulnar crest) is almost squared with its more medially expanded edge slightly rounded and its distal edge forming an obtuse angle with the diaphysis. This structure corresponds to the area in which the subcoracoscapularis muscle was fixed ( Colbert 1969). The medial crest is shorter than in species of Rhamphorhynchus (Wellnhofer 1975a, 1978), Dorygnathus ( Padian 2008a) , and Nesodactylus ( Colbert 1969) . The medial crest of MUHNCAL.20165 differs from that of species of Nesodactylus in that it is more extended proximo-distally and its posterior end does not form such an acute angle ( Fig. 4 View Fig ). The medial crest of MUHNCAL.20165 also differs from that of Nesodactylus hesperius Colbert , 196; in the latter species the medial extension of the crest is much larger than in MUHNCAL.20165 (see Colbert 1969: fig. 8).
The diaphysis of MUHNCAL.20165 is robust and straight in posterior view but is more gracile than that in the humeri of rhamphorhynchids such as Rhamphorhynchus muensteri (Wellnhofer 1975a, 1978; Fig. 4D, E View Fig ) and Rhamphorhynchus etchesi O’Sullivan and Martill, 2015 ( O’Sullivan and Martill 2015; Fig. 4P View Fig ). In dorsal and ventral views, the diaphysis of MUHNCAL.20165 is anteriorly curved, as in non-pterodactyloid pterosaurs, although the degree of curvature and extent are variable ( Unwin and Martill 2017). The curvature of the shaft of the humerus of MUHNCAL.20165 is well marked ( Figs. 3 View Fig , 4 View Fig ), as in rhamphorhynchids such as species of Rhamphorhynchus (Wellnhofer 1975a, 1978), Dorygnathus ( Wellnhofer 1978; Padian 2008b), and Nesodactylus ( Colbert 1969) , and as in some unidentified rhamphorynchid species from the Taynton Limestone Formation, Stonefield, Oxfordshire, UK ( O’Sullivan and Martill 2018). The three-dimensional preservation of the humerus of MUHNCAL.20165 suggests that no relevant taphonomic distortion occurred, which indicates that the anteriorly curved shaft constitutes a distinctive feature of this taxon. In Pterodactyloidea, the shaft of the humerus tends to be straighter ( Unwin and Martill 2017). The distal end is quite eroded, which makes it difficult to observe many of its features. Because the humerus is preserved in posterior view, it is not possible to observe the capitulum or the trochlea.
The distal epiphysis is lateromedially expanded, similar to the humerus of Rhamphorhynchus muensteri (Wellnhofer 1975a, 1978; Fig. 4D View Fig ), of Dorygnathus banthensis Theodori, 1830 (PSB 759a, see Theodori 1852; Padian and Wild 1992; Fig. 4H View Fig ), and a distal fragment of a humerus of an unidentified rhamphorynchid species from Oxford Clay Formation, England (NHMUK PV R 1995 illustrated in O’ Sullivan 2018: fig. 4). The ectepicondyle is located more proximally than the entepicondyle. The ectepicondyle is dorsally protruding and triangular in shape, whereas the entepicondyle does not protrude ventrally. The ventral half of the distal epiphysis of MUHNCAL.20165 is more distally extended than the dorsal half, whereas in the species of Rhamphorhynchus both portions of the distal epiphysis are approximately at the same level (Wellnhofer 1975a, 1978; Fig. 4D View Fig ).
Wing phalanx: The diaphysis of a wing phalanx is preserved in two fragments ( Fig. 4 View Fig ). The close association of the phalanx with the left humerus suggests that both elements could correspond to the same wing, however, the incomplete preservation of the phalanx fragments makes it difficult to ascertain. The pterosaurs generally have four phalanges in the wing finger which vary in length, morphology of the epiphyses and thickness ( Wellnhofer 1991; Unwin 2006).
The wing phalanx of MUHNCAL.20165 is robust, as in Rhamphorhynchus muensteri (see Wellnhofer 1975a: fig. 15). The total length of the wing phalanx (corresponding to the sum of both fragments) is 161.7 mm (85.6 and 76.1 mm, respectively). The preserved length of the wing phalanx of MUHNCAL.20165 is greater than the length of the first wing phalanx of Sericipterus wucaiwanensis Andres, Clark, and Xing, 2010 , corresponding to 127.4 mm ( Andres et al. 2010). The preserved length of the wing phalanx of MUHNCAL.20165 is less than that of wing phalanges I–III of Rhamphorhynchus etchesi , corresponding to 171, 175, and 163 mm, respectively ( O’Sullivan and Martill 2015). However, it is possible that the complete wing phalanx of MUHNCAL.20165 was similar or even longer than that of at least one of the first three wing phalanges of R. etchesi . In addition, the preserved length of the wing phalanx of MUHNCAL.20165 is less than that of one of the longest wing phalanx described in Rhamphorhynchus muensteri , which measures about 180 mm (see Bennett 1995: fig. 1). However, as in the case of R. etchesi , it is not possible to determine with certainty whether the length of the complete phalanx of MUHNCAL.20165 was indeed less than the length of the longest wing phalanges of R. muensteri . The maximum anteroposterior width of the phalanx is 9.1 mm, and the maximum dorsoventral height is 8.3 mm. The ratio between the anteroposterior width of the mid-point of the diaphysis of the humerus and that of the wing phalanx is 0.85. This value is slightly less than in Jianchangopterus zhaoianus Lü and Bo, 2011 (which is the widest wing phalanx of this pterosaur) corresponding to 0.96 ( Lü and Bo 2011). The preserved length of the phalanx in relation to the preserved length of the humerus does not support correspondence to one of the two most distal phalanges (III and IV) since these tend to be much more gracile and shorter (especially the terminal phalanx) in relation to the humerus than the two more proximal ones, as is described in Qinglongopterus guoi Lü, Unwin, Zhou, Gao, and Shen, 2012 ( Lü et al. 2012). In one specimen of R. muensteri, Hone et al. (2015) mention that the wing phalanges I and II are slightly longer than the phalanges III and IV, but the latter two are more gracile. Thus, the preserved shaft probably corresponds to the first or second wing phalanx. Unfortunately, none of these fragments preserve proximal or distal ends, making it difficult to assess the complete morphology and the whole phalanx length, and therefore, precluding accurate comparisons with other pterosaurs.
In the wing phalanx of MUHNCAL.20165, there is a longitudinal furrow which is flanked by two asymmetric crests, of which the dorsal one is more prominent than the ventral one ( Fig. 5 View Fig ). The presence of this furrow is considered a diagnostic feature of Rhamphorhynchinae ( Unwin 2003) . This trait was described in the rhamphorhynchines Nesodactylus hesperius of the Oxfordian of Cuba ( Colbert 1969: fig. 10, modified from Gross 1937), R. muensteri from the Tithonian of Germany ( Colbert 1969: fig. 10, modified from Gross 1937; see Wellnhofer 1978: fig. 13) and R. etchesi from the Tithonian of England ( O’Sullivan and Martill 2015: figs. 4, 9). In R. muensteri and R. etchesi , the fourth wing phalanges present the furrow on its caudal surface, which covers practically all of its extension. In addition, this furrow can be clearly seen in the first wing phalanx of an indeterminate Rhamphorhynchinae from the Oxford Clay Formation (NHMUK PV R 4759, O’Sullivan 2018: fig. 5).
The cross-section is similar to that of R. muensteri and N. hesperius , as illustrated in Colbert (1969: fig. 10) and this work ( Fig. 5 View Fig ). Its area is variable along the diaphysis, and we interpreted the larger area as the most proximal portion of the phalanx. As in the first wing phalanx of N. hesperius Colbert 1969 : fig. 10) and R. muensteri ( Gross 1937) , the anterior surface of the wing phalanx of MUHNCAL.20165 is partially sharp in what we interpret as the distal portion of the phalanx, becoming more rounded in what we interpret as the proximal portion, as in the first wing phalanx section of R. muensteri illustrated in Gross (1937).
The only pterosaur outside of Rhamphorhynchinae in which the presence of a longitudinal furrow in a wing phalanx has been described is in the dimorphodontid Caelestiventus hanseni Britt, Dalla Vecchia, Chure, Engelmann, Whiting, and Scheetz, 2018 , of the Upper Triassic from North America Britt et al. 2018). This furrow was described in the terminal phalanx of this pterosaur (the only preserved postcranial element of this species). However, it is not known whether the proximal phalanges of C. hanseni had a longitudinal furrow. Furthermore, the age at which this species (and the Dimorphodontidae family) lived together along with other anatomical differences between the humeri of dimorphodontids and rhamphorhynchids do not support the inclusion of MUHNCAL. 20165 in Dimorphodontidae (see discussion on this issue).
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