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Paleo Lab 11 - Mammals

Paleo Lab 11 - Mammals - PALEO LABORATORY 11 PAGE 1 PALEO...

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PALEO LABORATORY # 11, PAGE 1 PALEO LAB # XI - MAMMALS Class Mammalia According to modern biological classification, mammals are warm-blooded, hairy vertebrates which suckle their young. Since none of these features are preserved in the fossil record, it would seem difficult to distinguish the older mammal groups from their therapsid ancestors. However, mammals can be distinguished paleontologically by the fact that their lower jaw (mandible) consists of a single bone (the dentary) which is received by the squamosal bone of the skull. In reptiles two different bones (the articular of the mandible and quadrate of the skull) are involved in jaw articulation. The teeth of mammals are much more complex than the simple, peg- or blade-like teeth of other tetrapods. They are used extensively in identification of fossil mammals, since a species of that class can typically be determined on the basis of a single, isolated molar tooth! Mammals may be divided into three modern subclasses: the Monotremata, Marsupialia and Eutheria. In addition, there are a number of Mesozoic mammal types that cannot be placed within the modern subclasses. These include triconodonts, symmetrodonts, panthotheres and multituberculates; groups primarily known from tiny isolated teeth of Jurassic or Cretaceous age. EXERCISE # 1 - Mammal Teeth A. Label the incisors, canines, premolars and molars on the drawing provided. B. What is the difference between premolars and molars? EXERCISE # 2 - Mammal Bones Label the bones indicated on the illustration. Compare this illustration with the mounted skeleton of Felis domesticus (TSU VP 664; on shelf). Be able to recognize the individual bones on this “real” specimen. Monotremes The monotremes are curious, toothless, egg-laying mammals very similar in anatomy to the therapsid reptiles. They are very rare in the fossil record and are largely confined to the Pleistocene and Recent of Australia. They seem to represent an archaic sideline of mammalian evolution. Only two genera of monotremes are alive today, the duckbill platypus and spiny echidna. The duckbill platypus ( Ornithorhynchus) is semiaquatic and resides in Australian lakes and streams. It uses its bill to feed on invertebrates. The spiny anteaters, or echidnas ( Tachyglossus) are hedgehog-like spiny egg-layers. They feed mainly on ants and termites. Jaw fragments from the Early Cretaceous may pertain to monotremes. Other fossils include Obdurodon (Miocene) and in the Plio-Pleistocene several specimens are known, including the giant echidna Zaglossus. EXERCISE # 3 - Observe the skull of the platypus, Ornithorhynchus anatinus TSU VP 576). A.How do monotremes differ from other groups of mammals?
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B.Based on skull morphology, how can the platypus skull be differentiated from those of other mammals?
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