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© 2010 Dinosauria International Ten Sleep Report Series No. 1 tooth crowns, these studies, have speculated that branch stripping may have been employed. Stripping would require the swallowing of virtually complete vegetation without being processed into a lump through mastication. Then this vegetation must be pushed by muscle contractions in a twenty to thirty foot long neck. This strip and swallowing process seems highly improbable, unless the plant material is small fern sized foliage. Effective oral processing of plant material requires that the food be chewed into a lump for throat muscle to push against, thereby making swallowing possible. It is clear that Morrison diplodocids were incapable of chewing plant material with their front teeth. Therefore, it is believed that the reduced dentition was part of a feeding system, which incorporated a type of rostral bill. A The Rostral Bill The presence of a rostral bill is supported by the following suite of characters: rostral crest, nasal repositioning, the premaxillae and maxillae transversely extended and flattened, loss of teeth, presence of distinct grooves, channels, pits and foramina on the surface bone of the upper and lower jaws. The rostral crest is a bilaminar structure created by the median ridges of the caudal extensions of the premaxillaries. The prominence of this crest originates behind the anterior maxillary foramen and extends posteriorly terminating just before the narial opening. The crest is distinctly sculpted and flanked on both sides by shallow grooves. Its dorsal surface is somewhat flat, and tapers anteriorly. The best example of this crest is preserved in the skull CM 11161 (Fig 26 C), and a reconstruction of this apomorphy is illustrated in Fig 4. A similar structure is present in the mud probing Boat-bill Heron (Cochlearius cochlearius), a nocturnal wading species. In the Boat-bill Heron, its bony crest is designed to structurally reinforce the overlying ramphotheca bill while facilitating its digging and scooping use. The development of an interfenestra bridge dividing the preantorbital from the antorbital fenestrae not only strengthens that skull area (Witmer 1997) but also to extend the continuous flattened surface area of the premaxillae and maxillae that helps to forms a duck billed shaped rostrum. This rostral bill in Amphicoelias may have been formed by durable keratinous ramphotheca or by reinforced or thickened epidermal tissue, which may have possessed a degree of leather-like flexibility. This rostral bill probably covered the snout in areas of the premaxilla, maxilla and dentary. Additionally, it is possible that a cutting edge or notch existed on the long post dental diastema, which, as indicated on the skull, may have been created by the angle of the ventral border along the maxilla and quadrajugal contact, and from the dorsal ridge of the dentary. The Fig 28 A-C, A-B. Comparison of mid cervical ribs in Amphicoelias “brontodiplodocus” belonging DQ-TY and DQ-PE from Dana Quarry. Note the proportionately more robust rib and massive, well developed, laterally extending parapophyses in DQ-PE (posterior end of rib is not shown) compared with the elongated overlapping ribs in DQ-TY. C. cervicals belonging to DQ-SB, an adult specimen displaying a shortened length compared with DQ-TY. B C 38
Amphicoelias “brontodiplodocus” Galiano and Albersdörfer interfenestral bridge may have strengthened considerably this cutting edge. This rostral bill, probably unique in design, may have resembled and functioned both like a duck’s bill and a turtle’s beak. In Amphicoelias a unique and unusual feature exists in skulls preserving the palatal region. The median edges of the pterygoid bones contact at a steep angle creating a deeply arched palate (Holland 1924, McIntosh and Berman 1975). A possible explanation for the development of this interesting feature may be to increase the open space of the mouth to help in the rake and scoop filter feeding process by being able to take in greater amounts of food matter. The propalinal jaw motion may have worked in conjunction with the tongue in pushing water or mud through the mouth. As in a duck or flamingo bill equipped with fine ridges, the teeth in Amphicoelias “brontodiplodocus”may have had several functions. One function would be the incorporation of these thin teeth into a rostral bill to form ridges necessary for dabbling, which is another mode of filter feeding. Dabbling for soft aquatic vegetation, algae, snails, clams, insect larvae, and crustaceans is an energy efficient way of consuming highly nutritious foods in large quantities. The inter-dental spaces create a comb-like structure that may have functioned as a straining apparatus in the imbedded teeth. Bottom feeding may have represented a second function in the use of the protruding slender elongate teeth for probing in soft mud, nipping, racking and manipulating. In addition, the square shaped or duck billed snout would increase the scooping action efficiency during dabbling and bottom feeding. The section of the jaws behind the teeth may have had a keratin cutting edge for slicing and reducing larger food matter into manageable pieces, in the same way turtles use the side of their jaws which are equipped with double rows of sharp ridges for shearing and chopping. We are not alone in these ideas, Hass (1963 /p. 148) concluded: “I see only one source of food which could fulfill the nutritional requirements of such large animals (as Diplodocus): an invertebrate occurring in large numbers and large enough to be strained out by the very coarse device of pencil-like fence of the dental series-relatively soft-shelled crustaceans of fairly large size and such enormous density that they could mechanically be scooped or raked out of the water, or as another alternative, relatively thin-shelled temporarily floating mollusks like lymnaeids, ampullariids or some other primitive pulmonates which have to surface in huge numbers in lagoon-like bodies of fresh water. Lamellibranches could, in a similar way, have been sifted out of the soft mud of the bottom. Pulmonates very often form whole rafts at the surface of stagnant waters if the oxygen content in deeper water is getting low, especially under hot conditions… I would infer, therefore that the big sauropods depended on animal food, and I think that mollusks (or perhaps some very large crustaceans, living in enormous numbers) could have been the basic food of these gigantic animals, which lived and fed wholly or partially submerged”. Similar ideas were also presented in Dodson (1990) and Stevens and Parrish (2005) for diplodocids, without factoring the presence of a rostral bill. With the ability to wade, Amphicoelias “brontodiplodocus” may have had access to a larger menu of food compared with other contemporary herbivores. During seasonal migrations from one body of water to another when it could not rake and scoop, filter feed or dabble for microscopic aquatic plants and animals, Amphicoelias “brontodiplodocus” may have taken advantage of its long neck and specialized bill to feed in both low and high vegetation with a selective picking and browsing capability not available to other dinosaurs. Fungi, fruit, tree sap, and insects may have been some of the sought-after foods. To reach tall trees, temporary tripod standing may have been easy for them. Nasal Repositioning The presence of a rostral bill in Amphicoelias “brontodiplodocus” is also evident in the harmonious character complex seen in the cranial skeleton. Principally these characters include the posterior-dorsal position of the opening for the external nares above the orbits, modification and caudal elongation of the premaxillae, and size reduction of nasal bones. Many vertebrate species with reduced or absent dentition evolve beaks or bills as an alternative efficient lightweight food processing mechanism. As a developmental consequence of this feeding mechanism, the nasal opening must be relocated behind the area of the continually growing horny keratin in order to the protect the air passages from obstruction. Virtually all bird species have their nostril openings located at the posterior end of their bill or beak but always in front of the nasal-frontal hinge. Several duckbilled hadrosaurs also show backward, close to the orbit, repositioning of the nasal openings. The highly speculative and sometimes controversial nasal position in diplodocids (Coombs 1975, Witmer 2001, and others) can be explained as a response to a neomorphic structure such as a keratin bill, and not as an adaption seen in animals that are truly aquatic (Bakker 1971, Bakker 1986). The position of the nasal opening is compelling evidence in favor of a rostral bill structure, which seems to have been overlooked in discussions attempting to explain this unique dinosaur trait. The external shape of this bill structure may have extended the snout considerably. The caudally placed nasal opening may have also aided in the ability to simultaneously breath while filter feeding during long periods of wading by Amphicoelias “brontodiplodocus”. The posterior position of the 39
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