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© 2010 Dinosauria International Ten Sleep Report Series No. 1 of the new information provided by the Dana sample of Amphicoelias “brontodiplodocus” Amphicoelias “brontodiplodocus” The Dana specimens are sufficiently distinct morphologically to warrant the recognition of a new species, A. “brontodiplodocus”. Amphicoelias “brontodiplodocus” differs from Amphicoelias altus (including its synonyms), by the following characters: antorbital fenestra proportionately small; proatlas present; neural spine bifurcate past C 9 ; cervical ribs elongate, overlapping past centrum length; prezygapophysis on caudal vertebrae short; unfused clavicles present; ossified calcaneum; and claws tapered. Amphicoelias “brontodiplodocus” differs from Amphicoelias “Suuwassea” emilieae in lacking the following characters: no post parietal foramen, “optic” foramen not conjoined, neural spine bifurcation past C 9, and neural spines anteriorly positioned on cervical centra C 3-5. It is understood that the extraordinary completeness and preservation of the A. “brontodiplodocus” sample may be a factor in providing distinguishing characters that may be present but have not been documented in A. altus and A. emilieae. If proven to be the case, then all these species can be considered as one under A. altus. Thus, we recognize two or possibly three Amphicoelias species, a more primitive form A. “brontodiplodocus” in the lower part of the Morrison and a more derived species A. altus in the upper part. Both type specimens of Diplodocus hayi and Eobrontosaurus yahnahpin compare favorably in certain aspects with Amphicoelias “brontodiplodocus” and may offer taxonomically suitable names in a study which attempts to identify individual variation, sexual dimorphism and ontogeny. A possible third species A. emailieae may prove to be valid. Whether A. “brontodiplodocus” and A. altus overlap in time is not known. However, future discoveries of more complete specimens, particularly from classic upper Morrison localities, may close the morphological gap between A. “brontodiplodocus” and A. altus. Although this study recognizes a new taxon, we do not designate a type specimen until a suitable specimen is accessioned into an institution. The species name is used only for the purpose of communication and discussion in this report, and to call attention to the morphological distance and osteological uniqueness of the Dana sample. It is understood that the name A. “brontodiplodocus” is temporary and unofficial, and therefore should be considered a nomen nudum in accordance with ICZN guidelines. RECONSTRUCTION OF LIFE HABITS AND PALEOECOLOGY OF AMPHICOELIAS Since their initial discovery scientists have speculated about the life habits of sauropods in opposing scenarios. Originally they were depicted as feeble brained, solitary, aquatic reptiles, and then in later years, as herding animals with complex behavior, living in open dry savannah environments (Coombs 1975, Dodson 1990). Current speculation, based on Dana discoveries, portrays diplodocids somewhere in the middle of these two scenarios. They were highly evolved creatures well suited to extensive overland travel but preferring to live and feed in watery shore environments, a niche filled primarily by today’s wading birds. The key adaption for this niche is the ability to travel from one body of water to another. In the case of birds, flying is their method of travel, while diplodocids are perfectly adapted for terrestrial locomotion (Bakker 1971, Coombs 1975, Alexander 1985, Carrano 2005, and others). Therefore, long distance travel may have been possible. The ability to migrate and to explore new resources confers a substantial ecological advantage to a species so that it is not restricted to a habitat in the same way aquatic animals are to water. This form of opportunistic feeding may have varied their food intake regionally and seasonally. Long before duckbilled hadrosaurs, wading birds, and specialized pterosaurs, the shore or wetland habitats may have been dominated by diplodocids throughout most of the Late Jurassic and Early Cretaceous Periods. Pterosaur diversity is well represented in the Cretaceous Period with many species displaying filter feeding capabilities. Fossil evidence for the existence of wading birds is not known until the Eocene, in the Green River Formation, Wyoming and the Messel oil shale pit near Frankfurt, Germany where a large diversity of species have occupied this niche until today. The Skull Of systematic importance, the Dana Quarry braincase of DQ-EN displays a clear basipterygoid fossa, a feature associated solely with specimens identified as Diplodocus (Wilson 2002, Whitlock et al 2010). On the other hand, Balanoff, et al (2010) considers the presence of this feature a sauropod plesiomorphy retained in Apatosaurus. The basipterygoid recess or fossa in the DQ-EN cranium can be described as a clear depression, circular in outline located at the base where the pterygoid processes converge. This feature is also present in CM 11255, CM 11161, CM 26552, the holotype braincase of Diplodocus hayi HMNS 175 (Holland 1906), and the braincase BYU 17096 identified as Apatosaurus. Whether, this feature represents a species, gender, or ontogenetic trait remains questionable, however, its present distribution suggests that it is a synapomorphy of 36
Amphicoelias “brontodiplodocus” Galiano and Albersdörfer the genus Amphicoelias. One of the most extraordinarily derived features in Amphicoelias is the microcephalomorphic condition of its skull. The skull in DQ-BS measures approximately 35.56 cm (14 inches) relative to its estimated body length of 24.38 m. (80 feet), which amazingly calculates to approximately 1.4 % of body length. Among quadruped animals, Amphicoelias may have evolved, proportionately, the smallest known skull, paralleling the proportions found in birds and toothless mammalian edentates. The braincase is also incredibly small which apparently, in life, housed a brain no larger than a man’s thumb (measured from the base at the wrist). During preparation, matrix sand carefully removed and saved from Einstein’s braincase measured 80 cubic centimeters (4.88 cubic inches) or approximately less than half of a cup in volume. DQ-EN is a massive individual specimen from the Dana Quarry, almost the size of the American Museum of Natural History “Brontosaurus” skeleton. Like microchip technology, this reduced sized brain must be respected as an organ optimized to maintain its substantially complex body morphology. This also needs to be acknowledged as a derived sauropod character. Apatosaurus brain morphology is the subject of a recently published research by Balanoff, et al (2010) . The cranial skeleton in Amphicoelias “brontodiplodocus” is lightweight in construction, featuring thin bones, proportionately large openings, and nearly toothless upper and lower jaws, all to minimize the cantilever weight stress the long neck had to support. The skull reconstruction (Fig 26B) of Amphicoelias “brontodiplodocus” (DQ-BS) accurately depicts how the animal holds its head naturally, taking into account the ventral position of the occipital condyle. This is critical in that it shows two important features of these amazing creatures not previously described. With head held in this position, its eyes would see without obstruction, and they were clearly stereoscopic, positioned like those in birds. This is best appreciated when the skull is examined in front view. All the other known Diplodocid skulls may be incorrectly reconstructed or preserved distorted, as they do not seem to show this feature to the same degree. The other feature is orientation, which is determined by identifying the top of the head in connection with orbital position. The occipital condyle in Amphicoelias “brontodiplodocus” is not directed back so to hold the head in a more horizontal plane as in most other dinosaurs. Therefore, in a relaxed pose the head is held with the snout pointing down, while the frontal bones (top of skull) are kept horizontal to the ground. So, when it points its head to look straight ahead, the anterior neck vertebrae automatically must flex forward below the Fig 27 Illustration depicts the head of Amphicoelias “brontodiplodocus” in an inverted feeding position as indicated by the right angle of the occipital condyle to the long axis of skull. skull. This tends to agree with the idea that the entire neck was not kept rigid and low to the ground. Head and neck posture in sauropods is the subject of debate (Taylor et al 2009, Stevens and Parrish 2005). The downward angle of the occipital condyle allows the skull to be held in an inverted position when the neck is lowered while feeding (Fig 27) . The Feeding System Amphicoelias “brontodiplodocus” and other diplodocids display a unique dental morphology somewhat reminiscent of the specialization seen in certain insectivorous mammals (e.g., Proteles, Manis), which share a significant reduction or loss in the number of cheek teeth with weak slender jaws. In these animals chewing has been effectively abandoned as an adaption to feed on small and relatively soft foods such as insects. The feeding preferences might have been for similar types of foods in A. “brontodiplodocus”. The tooth crowns in Amphicoelias “brontodiplodocus” have been greatly simplified. They have narrowed, and like the roots, elongated. In other words the individual teeth are long and slender, and situated in the jaws evenly spaced and slightly prognathous so as to appear like the teeth in a rake or comb. Descriptions by Holland (1924) point out similar features in the dentition belonging to the skulls CM 11161 and CM 11162. Like the incisors in mammals, the teeth are retained only in the front edges of the upper and lower jaws. These dental features are derived compared with the more primitive sauropods, Camarasaurus and Brachiosaurus, and point to a unique feeding adaptation. Analyses based on cranial structure, dental micro wear and feeding mechanisms (Barrett and Upchurch 1994 & 1995, Calvo 1994, Christiansen 2000, Upchurch and Barrett 2000, Sereno and Wilson 2005) concluded that the diplodocid dentition does not interlock, and the jaws are used primarily in a back and forth movement. To explain the labial wear on diplodocid 37
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