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A New Skeleton Of The Cryptoclidid Plesiosaur Tatenectes Laramiensis Reveals A Novel Body Shape Among Plesiosaurs, F. Robin O’Keefe, Hallie P. Street, Benjamin C. Wilhelm, Courtney D. Richards, Helen Zhu
A New Skeleton Of The Cryptoclidid Plesiosaur Tatenectes Laramiensis Reveals A Novel Body Shape Among Plesiosaurs, F. Robin O’Keefe, Hallie P. Street, Benjamin C. Wilhelm, Courtney D. Richards, Helen Zhu
F. Robin O’Keefe
Current knowledge of plesiosaurs of clade Cryptoclidia is constrained by a lack of fossils from outside the Oxford Clay deposits of England. Recent fieldwork in the Sundance Formation of the Bighorn Basin, Wyoming, has resulted in the recovery of significant new fossils of cryptoclidid plesiosaurs, including the small-bodied form Tatenectes laramiensis. A new partial skeleton of this taxon is reported here; it is the most complete and best-preserved example of the taxon found to date, comprising a complete dorsal vertebral series, many ribs and gastralia, and a complete pelvic girdle. This skeleton illuminates several unique features of the taxon, including …
Osteology Of The Cryptocleidoid Plesiosaur Tatenectes Laramiensis, With Comments On The Taxonomic Status Of The Cimoliasauridae, F. Robin O’Keefe, Hallie P. Street
Osteology Of The Cryptocleidoid Plesiosaur Tatenectes Laramiensis, With Comments On The Taxonomic Status Of The Cimoliasauridae, F. Robin O’Keefe, Hallie P. Street
F. Robin O’Keefe
Recent field work in the Bighorn Basin, Wyoming has recovered significant new material of the plesiosaur Tatenectes laramiensis. The majority of cryptocleidoid plesiosaurs have been recovered from Middle and Upper Jurassic units (Oxford and Kimmeridge Clays, respectively) in the United Kingdom, but Tatenectes laramiensis is one of at least two cryptocleidoids known from the Upper Sundance Member of the Sundance Formation (Oxfordian) of North America. Although poorly known, they bear directly on both the phylogeny and biogeography of the cryptocleidoid plesiosaurs. Here we describe new fossil material of Tatenectes, and reevaluate the phylogenetic position of this genus based on all …
Neoteny And The Plesiomorphic Condition Of The Plesiosaur Basicranium, F. Robin O’Keefe
Neoteny And The Plesiomorphic Condition Of The Plesiosaur Basicranium, F. Robin O’Keefe
F. Robin O’Keefe
The purpose of this paper is to describe the condition of the braincase in stratigraphically early and morphologically primitive plesiosaurs. Information on the braincase of plesiomorphic taxa is important because it establishes the polarity of characters occurring in more derived plesiosaurs. This paper begins with a short review of braincase anatomy in stem-group sauropterygians. Data on braincase morphology of the plesiomorphic plesiosaur genera Thalassiodracon and Eurycleidus are then presented and interpreted via comparison with other plesiosaurs, stemgroup sauropterygians, and stem diapsids (Araeoscelis). Early diapsids are relevant because plesiosaur skulls more closely resemble early diapsids than stem-group sauropterygians in several key …
Evidence Of Pachyostosis In The Cryptocleidoid Plesiosaur Tatenectes Laramiensis From The Sundance Formation Of Wyoming, Hallie P. Street, F. Robin O’Keefe
Evidence Of Pachyostosis In The Cryptocleidoid Plesiosaur Tatenectes Laramiensis From The Sundance Formation Of Wyoming, Hallie P. Street, F. Robin O’Keefe
F. Robin O’Keefe
In this paper we present evidence for pachyostosis in the cryptocleidoid plesiosaur Tatenectes laramiensis Knight, 1900 (O'Keefe and Wahl, 2003a). Pachyostosis is not common in plesiosaurs and is particularly rare in non-pliosaurian plesiosaurs, although enlarged gastralia were first recognized in Tatenectes by Wahl (1999). This study aims to investigate the nature of the disproportionately large gastralia of Tatenectes m greater depth, based on new material. A recently discovered partial skeleton consisting of a dorsal vertebral series, ribs, gastralia, and a complete pelvic girdle was collected from the Jurassic-aged Sundance Formation of the Bighorn Basin in Wyoming during the summer of …
On The Cranial Anatomy Of The Polycotylid Plesiosaurs, Including New Material Of Polycotylus Latipinnis, Cope, From Alabama, F. Robin O’Keefe
On The Cranial Anatomy Of The Polycotylid Plesiosaurs, Including New Material Of Polycotylus Latipinnis, Cope, From Alabama, F. Robin O’Keefe
F. Robin O’Keefe
The cranial anatomy of plesiosaurs in the family Polycotylidae (Reptilia: Sauropterygia) has received renewed attention recently because various skull characters are thought to indicate plesiosauroid, rather than pliosauroid, affinities for this family. New data on the cranial anatomy of polycotylid plesiosaurs is presented, and is shown to compare closely to the structure of cryptocleidoid plesiosaurs. The morphology of known polycotylid taxa is reported and discussed, and a preliminary phylogenetic analysis is used to establish ingroup relationships of the Cryptocleidoidea. This study also presents new material referable to Polycotylus latipinnis from the Mooreville Chalk Formation of Alabama. This skeleton is largely …
The Vertebrate Fauna Of The Upper Permian Of Niger. Iv. Nigerpeton Ricqlesi (Temnospondyli: Cochleosauridae), And The Edopoid Colonization Of Gondwana, J. Sebastien Steyer, Ross Damiani, Christian A. Sidor, F. Robin O’Keefe, Hans C.E. Larsson, Abdoulaye Maga, Oumarou Ide
The Vertebrate Fauna Of The Upper Permian Of Niger. Iv. Nigerpeton Ricqlesi (Temnospondyli: Cochleosauridae), And The Edopoid Colonization Of Gondwana, J. Sebastien Steyer, Ross Damiani, Christian A. Sidor, F. Robin O’Keefe, Hans C.E. Larsson, Abdoulaye Maga, Oumarou Ide
F. Robin O’Keefe
We describe the edopoid temnospondyl Nigerpeton ricqlesi from the Upper Permian Moradi Formation of northern Niger on the basis of two partial skulls and tentatively associated postcranial material. This crocodile-like taxon displays several edopoid characters states such as a long prenarial region with enlarged premaxillae, elongated vomers, large, posteriorly tapering choanae, and a jugal that broadens anteriorly. Nigerpeton possesses a unique carnivorous dentition. It is autapomorphic in its possession of an extremely elongate snout bearing a maxillary bulge that accommodates three hypertrophied caniniform teeth, inner premaxillary tusks, and anterior paired fenestrae, which pierce the skull roof. In addition, both the …
A New Partial Skeleton Of A Cryptocleidoid Plesiosaur From The Upper Jurassic Sundance Formation Of Wyoming, Benjamin C. Wilhelm, F. Robin O’Keefe
A New Partial Skeleton Of A Cryptocleidoid Plesiosaur From The Upper Jurassic Sundance Formation Of Wyoming, Benjamin C. Wilhelm, F. Robin O’Keefe
F. Robin O’Keefe
Cryptocleidoid plesiosaurs from the Upper Jurassic are well known from the Oxford Clay (Callovian) of the United Kingdom. The plesiosaurs of the nearly coeval Sundance Formation (Oxfordian) of North America are poorly known, but are thought to include two cryptocleidoid taxa:Pantosaurus striatus and Tatenectes laramiensis. Here we present two specimens recently recovered from the Bighorn Basin of Wyoming. The first specimen comprises three articulated adult cervical vertebrae and fragments of a fourth. This specimen preserves a posteriorly directed cervical neural spine, a character diagnostic of Pantosaurus striatus. It also resembles Pantosaurus in the morphology of its cervical rib articulations. The …
Cranial Anatomy And Taxonomy Of Dolichorhynchops Bonneri New Combination, A Polycotylid (Sauropterygia: Plesiosauria) From The Pierre Shale Of Wyoming And South Dakota, F. Robin O’Keefe
F. Robin O’Keefe
The taxonomic identity of two well-preserved polycotylid plesiosaur skeletons from the Pierre Shale of far northern Wyoming and southern South Dakota has been controversial since their discovery. Originally referred to Dolichorhynchops osborni, the material was almost immediately christened Trinacromerum bonneri Adams 1997; more recently the material has been referred toPolycotylus. Recent preparation of the well-preserved skull of one specimen permits detailed examination of the cranial morphology of this animal for the first time, and allows for its inclusion in a cladistic analysis of the Polycotylidae. This analysis reveals a stable sister-taxon relationship with Dolichorhynchops osborni. However, the taxon possesses a …
A Plesiosaur Containing An Ichthyosaur Embryo As Stomach Contents From The Sundance Formation Of The Bighorn Basin, Wyoming, F. Robin O’Keefe, Hallie P. Street, Jean Pierre Cavigelli, John J. Socha, R. Dennis O'Keefe
A Plesiosaur Containing An Ichthyosaur Embryo As Stomach Contents From The Sundance Formation Of The Bighorn Basin, Wyoming, F. Robin O’Keefe, Hallie P. Street, Jean Pierre Cavigelli, John J. Socha, R. Dennis O'Keefe
F. Robin O’Keefe
Herein we report the discovery of an ichthyosaur embryo from the Upper Member of the Sundance Formation (Oxfordian) of the Bighorn Basin, Wyoming. The specimen is the first known ichthyosaur embryo from the Upper Jurassic, and is the first Jurassic ichthyosaur embryo from North America. The embryo was discovered in close association with the abdomen of an articulated partial plesiosaur skeleton, and several lines of evidence support the interpretation of the embryo as plesiosaur stomach contents. The small size and extremely poor ossification of the embryo indicate that the animal was probably not a neonate. Although the taxonomic affinities of …
The Vertebrate Fauna Of The Upper Permian Of Niger—Iii, Morphology And Ontogeny Of The Hindlimb Of Moradisaurus Grandis (Reptilia, Captorhinidae), F. Robin O’Keefe, Christian A. Sidor, Hans C. E. Larsson, Abdoulaye Maga, Oumarou Ide
The Vertebrate Fauna Of The Upper Permian Of Niger—Iii, Morphology And Ontogeny Of The Hindlimb Of Moradisaurus Grandis (Reptilia, Captorhinidae), F. Robin O’Keefe, Christian A. Sidor, Hans C. E. Larsson, Abdoulaye Maga, Oumarou Ide
F. Robin O’Keefe
We describe hindlimb elements of the large captorhinid Moradisaurus grandis (Reptilia: Captorhinidae) recently collected from the Upper Permian Moradi Formation of north-central Niger. This description is based primarily on an associated partial skeleton comprising a hemimandible, vertebral column, and partial left and nearly complete right hindlimb. Additionally, we report on a well-preserved, articulated, and essentially complete juvenile pes that provides important information on the ontogeny of the captorhinid tarsus. The hindlimb of Moradisaurus is stout and more massively built than in any other known captorhinid. The femur displays several features interpreted as adaptations to the demands of large body size, …
Preliminary Report On The Osteology And Relationships Of A New Aberrant Cryptocleidoid Plesiosaur From The Sundance Formation, Wyoming, F. Robin O’Keefe, William Wahl Jr.
Preliminary Report On The Osteology And Relationships Of A New Aberrant Cryptocleidoid Plesiosaur From The Sundance Formation, Wyoming, F. Robin O’Keefe, William Wahl Jr.
F. Robin O’Keefe
The cryptocleidoid plesiosaur Tatenectes laramiensis, new genus, is described from the Redwater Shale Member of the Sundance Formation, Narrona County, Wyoming. The holotype of this species was a partial skeleton that has since been lost. A neotype is designated that preserves the same elements present in the holotype. A second specimen is referred to the taxon, and this specimen includes cranial material. The preserved cranial elements are the left squamosal, a partial right frontal, several isolated teeth, the parasphenoid, and large portions of the left and right pterygoids. The skull shares many traits with that of Kimmerosaurus, a cryptocleidoid plesiosaur …
Morphologic And Ontogenetic Patterns In Elasmosaur Neck Length, With Comments On The Taxonomic Utility Of Neck Length Variables, F. Robin O’Keefe, Norton Hiller
Morphologic And Ontogenetic Patterns In Elasmosaur Neck Length, With Comments On The Taxonomic Utility Of Neck Length Variables, F. Robin O’Keefe, Norton Hiller
F. Robin O’Keefe
Elasmosaur cervical vertebrae are common fossils, but their taxonomic utility is limited due to a lack of understanding concerning their shape within and among taxa. In this paper, we analyze data from complete elasmosaur necks in an attempt to quantify and understand the variation in centrum dimensions. In accord with previous studies, variation in cervical centrum shape is found to stem from at least three sources: ontogeny, intracolumn variation, and intercolumn or taxonomic variation. Ontogenetic variability seems reminiscent of that seen in Cryptoclidus, with an overall positive allometry in the length of all centra that is accentuated in the mid-cervical …