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The cranial anatomy of the Early Jurassic turtle Kayentachelys aprix

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Sterli J., Joyce W. G.
Acta Palaeontologica Polonica
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2007
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tom 52
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nr 4
The fossil turtle Kayentachelys aprix is known from Early Jurassic sediments of the Kayenta Formation, Arizona, USA. The detailed description of this taxon’s cranium offered in this paper demonstrates that this turtle presents a mixture of primitive and derived character states. Among others, the presence of an interpterygoid vacuity, a basipterygoid process, a prootic that is exposed in ventral view, and a foramen posterius canalis carotici interni that is formed entirely by the basisphenoid are generally considered primitive for turtles. On the other hand, the presence of an undivided apertura narium, a well developed cavum tympani, an incipient cavum postoticum, and an unpaired vomer are considered to be derived. Kayentachelys aprix has previously been hypothesized to be the oldest stem cryptodiran turtle because of the presence of a flat, vertical plate on the processus pterygoideus externus, and the presence of a processus trochlearis oticum. However, the presence of these characters cannot be confirmed in the available specimens. Other putative stemcryptodiran characters, such as the prefrontal−vomer contact and the presence of an epipterygoid, are herein corroborated as being symplesiomorphies, because they generally appear to be present in basal turtles.
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Cranial anatomy of the iguanodontoid ornithopod Jinzhousaurus yangi from the Lower Cretaceous Yixian Formation of China

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Barrett P. M., Butler R. J., Xiao-Lin W., Xing X.
Acta Palaeontologica Polonica
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2009
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tom 54
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nr 1
35-48
The Yixian Formation (Lower Cretaceous) of Liaoning Province, China, is justifiably famous for its exceptionally preserved fauna, which includes a remarkable diversity of non−avian dinosaurs. Here, we provide the first detailed description of the cranial skeleton of the iguanodontian ornithopod Jinzhousaurus yangi. Many previously unrecorded features have been recognised, permitting a new and more robust diagnosis for this taxon, which is based on a suite of autapomorphic features. Jinzhousaurus and an unnamed sauropod represent the largest, but some of the least abundant, animals in the Jehol Biota, a situation that contrasts with many other Lower Cretaceous faunas in which large dinosaurs are common faunal components. This rarity may be due to either palaeoenvironmental constraints or taphonomic bias, although it is not possible to choose between these alternatives on the basis of current data.
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Cranial anatomy and phylogenetic position of the titanosaurian sauropod Bonitasaura salgadoi

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Gallina P., Apesteguia S.
Acta Palaeontologica Polonica
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2011
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tom 56
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nr 1
Knowledge of titanosaurian cranial anatomy has improved substantially in the last decade because several skulls have come to light or were restudied. The discovery of Bonitasaura salgadoi, a partial titanosaurian skeleton including cranial bones, permitted the definitive recognition of square jaws in a titanosaurian sauropod as well as a peculiar skull morphology that increases the morphological diversity of the group. Here we present a full description and illustration of the skull material of B. salgadoi. Among cranial bones, the lacrimal, quadrate, and dentary exhibit apomorphic differences from those of other titanosaurians. Conversely, the frontal and parietal are more conservative. A phylogenetic analysis recovers B. salgadoi as a member of the Titanosauria, related to mid−sized to large titanosauroids from the Turonian–Campanian of South America, in contrast to a previous hypothesis that suggested a nemegtosaurid affinity. The skull reconstruction presented here shows that the skull of B. salgadoi is anteroposteriorly short and dorsoventrally high, contrasting with the elongate skull of Rapetosaurus krausei.
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Osteology of the sauropod embryos from the Upper Cretaceous of Patagonia

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Salgado L., Coria R. A., Chiappe L. M.
Acta Palaeontologica Polonica
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2005
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tom 50
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nr 1
Exceptionally well−preserved embryonic skulls of Upper Cretaceous (Campanian Anacleto Formation) sauropods from Auca Mahuevo (Neuquén Province, Argentina) provide important insights into the ontogeny and evolution of titanosaurian neosauropods. The most important cranial modifications occurring during titanosaurian ontogeny appear to be centered on the infraorbital and narial regions, which exhibit a substantial degree of “mosaic” evolution. On one hand, the Auca Mahuevo embryos show a large jugal that forms part of the lower margin of the skull and unretracted external nares, as indicated by the position and orientation of the lacrimals as well as the anterior extension of the frontals. Both of these features are ancestral for neosauropods, being present in prosauropods. On the other hand, the embryonic skull exhibits a large ventral notch, tentatively interpreted as homologous to the neosauropod preantorbital fenestra, that opens ventral to the jugal and between the maxilla and the quadratojugal, and a temporal region that closely resembles the adult neosauropod condition. This mosaic of character states indicates that different regions of the skull of titanosaurian neosauropods acquired their characteristic morphology at substantially different rates during their ontogenetic development.
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The cranial osteology of Spermophilus richardsonii [Sabine, 1822] [Richardson's ground squirrel] [Mammalia: Rodentia: Sciuridae]

100%
Russell A. P., Pereschitz R. M., Powell G. L.
Annales Zoologici
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2001
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tom 51
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nr 1
Much is known of the ecology and behaviour of Spermophilus richardsonii (Sabine, 1822) (Richardson's Ground Squirrel), but little has been discussed of its anatomy. Here we document details of its cranial anatomy, based upon 95 specimens from a single locality, focusing primarily on previously undescribed features. This documentation provides the essential information for studying intra- and interpopulational variation in cranial characteristics in both quantitative and qualitative contexts. Skulls of S. richardsonii examined were generally uniform in structure, and no obvious sexual differences were observed.
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