Calyptocephalella canqueli Schaeffer, 1949
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publication ID |
https://doi.org/ 10.4202/app.2009.0093 |
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persistent identifier |
https://treatment.plazi.org/id/BA288784-FF94-FFA4-FCB4-B11A38FB3B15 |
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treatment provided by |
Felipe |
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scientific name |
Calyptocephalella canqueli Schaeffer, 1949 |
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Calyptocephalella canqueli Schaeffer, 1949 View in CoL
Figs. 2–6 View Fig View Fig View Fig View Fig View Fig .
Material.—FCEN−PV 14084 and AMNH 3401, well−preserved fossil tadpoles.
Description.—The specimens ( Fig. 2 View Fig ) are largely articulated and exposed in dorsal view. Most cranial and postcranial elements are preserved as actual bones, but some are preserved as moulds. The approximate lengths of the specimens, measured from the anterior tip of frontoparietals to the posterior margin of the ilia, are 4.3 cm (FCEN−PV14084) and 3.3 cm (AMNH 3401). Even though AMNH 3401 is relatively shorter, it belongs to a later developmental stage than FCEN−PV14084, according to its higher degree of ossification—particularly in the axial and appendicular regions of the skeleton.
FCEN−PV 14084: The only visible skull bones are the frontoparietals and, probably, the parasphenoid ( Fig. 2A View Fig ). The frontoparietals are extensive and likely covered most of the braincase of the living tadpole. The dorsal surface of these elements is sculptured with shallow pits which are more abundant in the posterior half of the bone ( Fig. 3A View Fig ). Their anterior ends are pointed and together form the Vshaped margins of a frontoparietal fontanelle, which extends along one half of the length of the frontoparietals. Posterior to the fontanelle, the medial margins of these bones are parallel to the saggital line, but it is not clear whether these margins were in contact along the midline. The posterior half of each frontoparietal projects laterally, partially covering the dorsal surface of the auditory capsules. Ventrally, each frontoparietal bears a deep lamina perpendicularis, which in life covered the dorsolateral portion of the braincase and the anterodorsal wall of the otic capsule. A bone that underlies the frontoparietals is identified as the parasphenoid owing to its relative position and laminar nature; the poor preservation of this bone does not provide more details.
Six presacral vertebrae are recognized ( Fig. 2A View Fig ), although they show an unequal degree of development and ossification. Presacral vertebra (PV) I is represented by the articular portion of the right half of the neural arch and by its centrum, which at this stage and from a dorsal view is composed of two crescent−shaped ossifications still unfused medially (some cartilage seems to be preserved, filling the space between the ossifications). The following three vertebrae (PV II–IV) are represented by the pedicles of the neural arches, the bases of the prezygapophyses, and the transverse processes. The transverse processes of PV II are robust and mostly laterally directed. PV III bears the longest and most robust transverse processes (length:width, 3:1); they are perpendicular to the notochordal axis and have a constant width throughout their length. The processes of PV IV are more slender and taper distally. The PV V shows only the right transverse process, which is short and blunt. No other transverse process is visible. The centrum of PV V is also preserved, evidenced by two semioval ossifications not fused medially from a dorsal aspect. The PV VI is fragmentary; posterior to this vertebra there are small pieces of bone that cannot be attributed to any specific vertebra. The postsacral region is represented by what seems to be one neural arch and a well−ossified, robust hypochord ( Fig. 4A View Fig ). The hypochord is as long as four presacral vertebrae and is oval in cross section.
The pectoral girdle is divided into two halves which, along with their corresponding forelimbs, are placed on either side of the axial skeleton, as it is evidenced from the preserved left half. The pectoral girdle is represented by the right and left cleithra and the left scapula ( Fig. 5A View Fig ). The cleithrum is a wide and relatively thick lamina with straight anterior and concave posterior margins, shorter proximally than distally. Across the cleithrum there is a low keel that extends from the medial to the distal end. The scapula is poorly developed and poorly preserved; its proximal end is slightly longer than the distal one. The forelimb is represented by the left humerus, the radioulna and three metacarpals. The humeral diaphysis is well ossified, while the rather rounded proximal end shows a granulose texture that suggests its cartilaginous condition. The radius and ulna are already fused, although a shallow sulcus between them hints at a recent fusion. This compound element is approximately as long as the humerus, with which it articulates. Metacarpals are cylindrical elements.
The articulated pelvic girdle and hind limbs are displaced from the axial axis to the left side. The pelvic girdle ( Fig. 6A View Fig ) is represented by the shaft of the ilium, presumably the only ossified element of the girdle by this stage. The iliac shafts, which are oval in cross section, are poorly developed and slightly shorter than the hypochord. Posterior and ventral to these elements, the femur, tibia, fibula, and proximal tarsals are preserved. All of them are poorly developed, although their diaphyses are already ossified. The femur is a little shorter than the ilium. The tibia and fibula are still two separate elements of a length approximately similar to that of the femur. The proximal tarsals are very short (about 1/3 the doi:10.4202/app.2009.0093
length of the fibula) and their epiphyses are wider than their diaphyses, as in adults. Posteriorly, four cartilaginous metatarsals and two proximal phalanges have left their impressions on the sediment.
AMNH 3401: The frontoparietals are similar, both in shape and ornamentation, to those of FCEN−PV 14084. However, these bones are more expanded laterally to form well−developed supraorbital flanges ( Fig. 2B View Fig ). There are two triradiated bones overlapping the posterior end of frontoparietals interpreted as the exoccipitals, exposed in posterior view. No foramina are visible. The axial skeleton consists of eleven pairs of neural arches and a hypochord. The laminae of the neural arches are not imbricated, but they are well developed and ossified, especially those of the anterior four presacral vertebrae. However, none of the neural arches is ossified at the midline; thus each is preserved as two separate halves. All presacrals have ossified pre− and postzygapophyses, although their mutual articulation obscures their morphology. PV II–V bear transverse processes similar to those of FCEN−PV 14084; the transverse processes of the PV VI are short—approximately one third the length of those of the anterior presacrals. No other transverse process is evident. Posterior to the last distinct neural arch (IX), three pieces of bone are interpreted to constitute two postsacral neural arches ( Fig. 4B View Fig ), which would ultimately form the anterodorsal portion of the urostyle. Neural Arch X is broken into two pieces. It is a tall element that forms posteriorly the anterior margin of the foramen intervertebralis. Neural Arch XI is triangular, its dorsal margin taller anteriorly than caudally. The anterior margin forms the posterior border of the foramen intervertebralis. Even though these neural arches are well developed, it is not clear whether they are already fused to each other, although they certainly are not fused to the hypochord, and thus no urostyle is yet formed in this specimen. The hypochord ( Fig. 4B View Fig ) is robust and relatively as long as that of FCEN−PV 14084.
The contralateral halves of the shoulder girdle are located on both sides of the skull ( Fig. 2B View Fig ), indicating that they were still occupying almost a single plane. The cleithrum ( Fig. 5B View Fig ) is relatively longer than that of FCEN−PV 14084. Its proximal end is blunt and the distal end is pointed; thus, the anterior margin is shorter than the posterior one. A keel projects mediolaterally across the dorsal surface of this bone. The scapula ( Fig. 5B View Fig ) is stocky and subtriangular, being wider laterally than medially and having a straight anterior margin. The shaft is about 1.5 times broader than long and the surface of this element bears slight transversal ridges. The preserved right coracoid ( Fig. 5B View Fig ) is represented by the ossified diaphysis. The clavicle ( Fig. 5B View Fig ) is moderately curved with a rounded medial end. Its lateral end possesses a blunt facet that ultimately would have articulated with the scapula. The forelimbs are represented by short humeri, presumably with cartilaginous condyles, and radioulnae (the radius and ulna are clearly fused to one another; Fig. 2B View Fig ).
The only preserved bony elements of the pelvic girdle are the illia oriented transverse to the vertebral column ( Fig. 2B View Fig ). The corpus of the ilium ( Fig. 6B View Fig ) is already ossified but its preservation in medial view prevents the description of any morphological feature other than its triangular shape. The slightly curved iliac shafts are as long as five vertebrae. They bear a low iliac crest over the dorsal margin at the centre of the shaft. The femora are preserved parallel to the ilia and are almost the same length of the latter. The tibia and fibula are already fused forming the tibiofibula, although its dual origin is still evident. The tibiofibula is as long as the femur. Elongated proximal tarsals, representing approximately one half of the tibiofibular length, and four metatarsals are also preserved.
Stratigraphic and geographic range.—Sarmiento Group, Deseadan (Oligocene); Scarritt Pocket, Chubut, Argentina.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.