Another overview of Mammal's Evolution

1. EVOLUTION OF MAMMAMLS
Mammals Mystery
By
Muhammad Tahir Waseem
Rol. 28
7th Semester

2. SUMMAMRY
 “How Mammals evolved?
 Late paleozoic or early mesozoic
 Evolutionary hierarchy
 Amniotes
 Synapsids
 Therapsids

3. THE DARK AGE OF MAMMALS
 Mesozoic era
 Dinosaurs
 Mammals like reptiles
 Nocturnal

4. DEFINITION OF MAMMALS
 Mammals use two bones for
hearing that all
other amniotes use for eating.
 In the mammal configuration, the
quadrate and articular bones are
much smaller and form part of the
middle ear. Note that in mammals
the lower jaw consists only of
the dentary bone.

5.  Mammals also have a double Occipital condyle;
they have two knobs at the base of the skull that fit
into the topmost neck vertebra, while other
tetrapods have a single occipital condyle.

6. THE ANCESTRY OF MAMMALS

7. AMNIOTES
 The first fully terrestrial vertebrates were amniotes.
 Eggs had internal membranes that allowed the
developing embryo to breathe but kept water in.
 Middle Carboniferous

8. SYNAPSIDS
 Identification
 Holes behind each eye
 Purpose
 Made the skull lighter without sacrificing strength.
 Provided attachment points for jaw muscles.
 Saved energy by using less bone

9. THERAPSIDS
 Therapsids descended from pelycosaurs in the
middle Permian
 They differ from pelycosaurs in several features of
the skull and jaws, including larger temporal
fenestrae and incisors that are equal in size.
 Progress towards an erect limb posture.
 Gradual development of a bony secondary palate.

10. THERAPSIDS FAMILY
 Only the dicynodonts, therocephalians, and
cynodonts survived into the Triassic.

11. CYNODONTS
 Arose in the late Permian.
 Cynodonts' mammal-like features include further
reduction in the number of bones in the lower jaw, a
secondary bony palate, cheek teeth with a complex
pattern in the crowns, and a brain which filled the
endocranial cavity.
 Trirachodon

12. FROM CYNODONTS TO CROWN MAMMALS
 Mesozoic synapsids that had evolved to the point of
having a jaw joint composed of the dentary and
squamosal bones are preserved in few good
fossils, mainly because they were mostly smaller
than rats.

13. Docodonta
Crown
group Mammals
Mammaliaformes Prozostrodon
Cynodonts

14. DOCODONTS
 Among the most common Jurassic
mammaliaforms.
 Noted for the sophistication of their molars.
 Castorocauda- A fish eating docodont.

15. AUSTRALOSPHENIDA 12OMYA
 Appear to have tribosphenic molars.
 Monotremes are thought to be evolved from them.

16. MONOTREMES
 Teinolophos, from Australia, is the earliest known
monotreme.
 It was also a basal monotreme and predated the
radiation of modern monotremes.

17.  Monotremes have some features that may be
inherited from the cynodont ancestors:
Like lizards and birds, they use the same orifice to
urinate, defecate and reproduce ("monotreme"
means "one hole").
 They lay eggs that are leathery and uncalcified, like
those of lizards, turtles and crocodilians.


18. MULTITUBERCULATES
 Rodents of the Mesozoic.
 They existed for approximately 120 million years
 but were eventually outcompeted by rodents,
becoming extinct during the early Oligocene.
 Their "molars" have two parallel rows of tubercles.

19. THERIA
 Theria ("beasts"), is the clade originating with the
last common ancestor of
the Eutheria (including placentals)
and Metatheria(including marsupials).
 No interclavicle.
 Tribosphenic molars.

20. METATHERIA
 The living Metatheria are all marsupials.
 Didelphimorphia first appeared in the late
Cretaceous and still have living representatives.
 The best-known feature of marsupials is their
method of reproduction.
 The mother develops a kind of yolk sack in her
womb that delivers nutrients to the embryo.
 Embryosof bandicoots, koalas and wombats additi
onally form placenta-like organs that connect them
to the uterine wall.

21.  Pregnancy is very short, typically four to five weeks.

22. EUTHERIA
 Early Cretaceous have also been classified as
eutherian birth.
 study also reported that eutherians did not
significantly diversify until after the catastrophic
extinction at the Cretaceous–Paleogene boundary,
about 66 million years ago.
 From a paleontologist's point of view, eutherians
are mainly distinguished by various features of their
teeth, ankles and feet.