1 / 23

Mammals – Part I

VERTEBRATE ZOOLOGY (VZ Lecture29 – Spring 2012 Althoff - reference PJH Chapter 18). Mammals – Part I. Bill Horn. Mammals are… space-age reptiles. THEY ______ & _______ FASTER!!!!. Origins of Mammals. Have to think “synapsids” first….

newman
Télécharger la présentation

Mammals – Part I

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. VERTEBRATE ZOOLOGY (VZ Lecture29 – Spring 2012 Althoff - reference PJH Chapter 18) Mammals – Part I Bill Horn

  2. Mammals are…space-age reptiles.THEY ______ & _______ FASTER!!!!

  3. Origins of Mammals • Have to think “synapsids” first…. • Synapsids thought to have originated at the end of the Paleozoic ~300-290 MYA • Three major radiations: 1) pelycosaurs (~300-250 MYA…now extinct) 2) therapsids (~250-140 MYA…now extinct) 3) mammals (~206 MYA to today) • and considered “mammal-like reptiles • Mammal _________________ peaked in the Cenozoic (starting ~ 90-65 MYA) 1 2 3 1 2

  4. 3 Mammal-like reptilest Mammals 2 1 Fig. 18-2, p489 PJH

  5. Dominance of Mammals • Dominance by mammals occurred during late Cretaceous period…after decline of ruling reptiles…90-65 MYA • Why did Synapid reptiles decline…and mammals flourish? Two explanations have been offered….

  6. Reptiles “out”, Mammals “in”?? • Competition from other reptile groups • Changing climatic conditions

  7. Back to Mammalian Dominance • Specifically, late Cretaceous period to Paleocene epoch • Adaptative __________led to dominance during Cenozoic era

  8. Periods of Extinction & Radiation • MASS Extinction: dinosaurs & reptiles 60-144 mya • Significant extinctions for mammals: 37-58 mya 24-37 mya 100,000 – 2 mya • Significant radiations associated with break-up of Pangaea & continental drift as well as increased faunal and floral diversity…most pronounced during Paleocene(next slide)

  9. “Modern” mammals • Geologic time division when most modernfamilies (aka family diversity) appeared is the Oligocene (37-24 MYA) & Miocene (24-5 MYA) • Oligocene and Miocene may have also represented the period of greatest species diversity as well

  10. Skull Characteristics • Differ from reptiles with development of perforations of temporal portion • Anapsid = no temporal opening vs. • Diapsid = 2 temporal openings, separated by post orbital process vs. • __________ = 1 opening  MAMMALS

  11. Lizards & snake arose from.. MAMMALS arose from… SYNAPSID DIAPSID ANAPSID Lineage lead to turtles

  12. “Better” skull design…advantages • Mammalian skull design (originating from reptilian lineage subclass Synapsida) a) increased freedom for expansion of ____________________ b) selective advantage gained by _______________________ (i.e., less bone, less wt. = bone replaced by opening) or

  13. Synapsid (mammals) Anapsid (primitive amniotes & turtles) Lateral view Adductor muscle Adductor muscle Cross-sectional view More room for “bulging” muscles

  14. Evolutionary Trends in Synapsids • Key change from during evolution of synapsid lineage was crossing of physiological boundary from ectothermy to ________________ • “Changes” from a physiological perspective—which would influence metabolic rate—obviously not fossilized. But changes in skulls and skeletons can offer clues how higher metabolic rates could have been achieved: 1) greater food intake or rate of feeding (FR = food-related) 2) greater respiration rate (AR = activity-related)

  15. Pelycosaur Noncynodont therapsid Cynodont therapsid Early Mammal Megazostrodon Fig. 18-6, p495 PJH

  16. “Mods” • SIZE OF THE TEMPORAL FENESTRA—larger fenestra indicates a greater volume of jaw musculature…also larger temporal fossa • CONDITION OF THE LOWER TEMPORAL BAR—bar of bone owed out from skull behind the orbit indicates presence of masseter muscle. For mammals, zygomatic arch “bows” out • LOWER JAW AND JAW JOINT—change from only about half of lower jaw with teeth to greatly expanded dentary. For mammals, dentary now forms a new jaw joint with skull—coronoid process prominent

  17. “Mods” …con’t • TEETH—specialization of the dentition. Went from homodont to heterodont condition (i.e., differentiated teeth) resulting in change in size, form, and function. Impacts chewing motion as well in combo with #2 • DEVELOPMENT OF SECONDARY PALATE—separates nasal passage from mouth allowing animal to eat and breath at the same time • POSITION OF THE LIMBS—placed more underneath the body

  18. “Mods” …con’t • SHAPE OF THE LIMB GIRDLES—more lightly built girdles than the “mammal-like” reptiles. Mammals have reduced pubis and a rod-shaped ilium….allows more dorsoventral flexion (see 10, too) • SHAPE OF FEET—Shorter toes. Calcaneal heal provides a lever arm for a greater degree of push-off from the gastrocnemius (calf) muscle) • FORM OF VERTEBRAL COLUMN— loss of lumbar ribs , reduction of cervical ribs suggest presence of muscular diaphragm

  19. Classification & Diversity of Mammals CLASS Mammalia ORDERS 29 FAMILIES 153 GENERA ~ 1,200 SPECIES >

  20. EXTANT… mammals Mammal-like reptilest 1 2 3 Fig. 18-2, p489 PJH

  21. 1 • MONOTREMATA order (3 species) “egg-laying” mammals) • MARSUPIALIA infraclass (242 species)(7 orders within “pouched mammals”) • All others-“placental mammals” Infraclass EUTHERIA (eutherians) (4,500-plus species) (21 orders within “placentals”) 2 3

  22. Early Mammal groups Monotremes (egg-layers) Eutherians (placentals) Marsupials (pouched) TIME

More Related