Mammals are derived from Synapsid reptiles




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SI A Ecl 365

Worksheet


  1. Mammals are derived from _________________ _________________

    1. Synapsid reptiles



  1. Mammals are ____________________ homeotherms

    1. Endothermic




  1. Mammals have two sets of teeth (________________ and

_______________), which is known as _______________________



    1. Deciduous and permanent

    2. Diphyodonty




  1. Most mammals have _______________________ dentition.

    1. Heterodont



  1. ____________________ were early synapsids and generalized amniotes

    1. Pelycosaurs




  1. Why did “sailbacks” have “sails” or spines?

    1. Sail of Dimetredon derived from enlarged neural spines

    2. Evidence of blood vessels on spines (suggest use for thermal regulation)




  1. True / False All early synapsides had “sails”

    1. False




  1. Describe Therapsids

    1. Both carnivores and herbivorous forms

    2. Wide range of body sizes (10 – 200 kg: dog – cow sized)

    3. Nearly worldwide distribution, including cooler regions

    4. Suggests greater terrestrial dispersal ability, and likely higher metabolic rates

    5. Were dominant in Late Permian with great diversity

    6. Only a few small lineages of small therapsids survived into Triassic




  1. Of therapsids, Cynodonts displayed many mammalian characteristics, name 3.

    1. Carnivorous

    2. Size of large dog

    3. Powerful jaw muscles

    4. Dentary bone formed most of lower jaw (current mammalian condition)

    5. Limbs powerful and beneath body

    6. Heterodont dentition (incisor, canines, molars): thus chewed food, not swallowed whole




  1. What is the most widely accepted mammalian character?

    1. Squamosal-dentary jaw articulation




  1. The ___________________ duct, which is near the eye and secretes oil for preening fur, suggests hair.

    1. Nasolacrimal




  1. Squamosal-dentary jaw articulation evolved from ______________

_____________ (the ancestral condition).



    1. Articular quadrate



  1. What was special about Diarthrognathus?

    1. BOTH reptilian and mammalian jaw articulations!



  1. In mammals, modified ___________ bones transitioned to the inner ear.

    1. Quadrate 

    2.  malleus

    3. Angular 

    4. Already present (in amphibians and reptiles)

      1. jaw

        1. incus, articular, Tympanic membrane, Columella




  1. Describe the anatomical changes in locomotion between ancient reptiles and synapsids.

    1. Ancient reptiles: sprawling posture, with limbs at right-angles to body (elbows out and back)

    2. Synapsids evolved limbs under body

    3. The appendicular skeleton evolved changes to support the weight differently (reduced clavicle, enlarge scapula)

    4. Allows more efficient (and rapid) locomotion (can do more with less muscle mass)




  1. What are the three major groups of mammals?

    1. Monotremata (monotremes)

    2. Metatheria (marsupials)

    3. Eutheria (placentals)




  1. Name 4 characteristics of mammals.

    1. Have hair (keratin) derived from scales

    2. Endothermic homeotherms

    3. Lower jaw a single bone (dentary )

    4. Diphyodonty: two sets of teeth

    5. 4-chambered heart

    6. Mammary glands – emphasizes strong parental care

    7. 3 ear ossicles

    8. Heterodont dentition (most)

    9. Viviparity (most)



  1. Which mammalian group reproduces by laying eggs? Name two examples of these.

    1. Order Monotremata

    2. Platypuses and echidnas



  1. Compare/Contrast Monotremata, Metatheria, and Eutheria.

    1. Monotremata

      1. Egglaying Mammals! - 5 species: platypuses, echidnas (spiny anteaters)

      2. Have hair & mammary glands, and are warm blooded, lower jaw is only dentary, and have 3 middle ear ossicles

      3. No teeth as adults (but juveniles and fossils have them)

      4. The egg is reptilian in structure and development, and contains enough yolk to nourish the developing embryo

      5. Like reptiles, monotremes have cloaca (one passage for urine and feces)

      6. Found only in Australia and New Guinea



    1. Metatharia

      1. 7 orders and 331 species

      2. Include: opossums, kangaroos, koalas, wombats, bandicoots, etc.

      3. Restricted primarily to Southern continents

      4. Born very early in their development; female has short gestation period; yolk sac placenta

      5. Embryonic development is completed in a maternal pouch called a marsupium




    1. Eutheria

      1. 18 orders and 5,082 species

      2. Remaining mammals (horses, cows, dogs, cats, primates, rodents, etc.)

      3. Complete embryonic development within uterus – joined to mother by a ‘true’ placenta

      4. Young are much more developed at time of birth

      5. Great deal of parental care

      6. Includes species adapted for a wide range of habitats and regions

      7. Several major lineages of placental mammals


  1. Embryonic development of Marsupials is completed in a maternal pouch called a _____________________

    1. marsupium

  2. Eutherians (or placentals), complete embryonic development within the

______________ and join to the mother through a ____________ ____________



    1. Uterus, true placenta



  1. True / False Eutherians provide a great deal of parental care to young

    1. True


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