ZOO 4910 Lecture Notes - Lecture 17: Giraffidae, Deer, Bovidae
2 May 2018
School
Department
Course
Professor
Bovid families
○
Living bone inside sheath
○
Keratin covered
○
Fused to skull with connective tissue
○
Present on males and some females
○
Grow throughout life
○
Horns:
•
Only in cervids (deer, moose, elk)
○
One single bone (no keratin layer)
○
Velvet covered until mature
○
Stimulated annually by hormones
○
Sexually selected, only in males
○
Shed annually
○
Antlers:
•
Presence of bone may or may not be fused to
body
!
Epidermis may persist, be temporary or never
be present
!
Some are covered in keratin
!
*see slide -structure of headgear
○
No hair or fuzz (epidermis) on horns
!
Fused to bone
!
Cervidae
○
Keratin -epidermis and fuzz -bone
!
Not fused
!
Bovidae
○
Covered by epidermis (no keratin)
!
Not fused
!
Giraffidae (ocitones?)
○
Fused
!
Keratin -epidermis -bone
!
Antilcapridae (prong horns)
○
Ontogeny:
•
One of the smallest ungulates, does not grow
antlers
!
Mouse deer:
○
Lacks antlers as well
!
Musk deer:
○
Mouse deer is basal species
!
Headgear has independently evolved four times
in a unique way (intermediate species)
!
Morphological phylogeny: 4 independent origins
○
1origin and one loss
!
More parsimonious explanation
!
Evolved once following mouse deer
divergence, and was loss in musk deer
divergence
!
Molecular phylogeny:
○
Phylogeny:
•
Physical Weapons: Headgear
Most vertebrates have undifferentiated teeth
•
Most mammals and few other groups (dinosaurs) display
differentiated teeth (heterodont dentition)
•
Tusks = modified canine teeth
○
--> diversity and disparity
○
In mammals, teeth are specialized as incisors, canines,
premolars, and molars
•
Opisthoglyphous: posterior, fixed
!
Proteroglyphous: anterior, fixed
!
Solenoglyhous: anterior, hinged
!
Canal hold venom gland
□
Have to chomp on prey to insert venom
□
Increase in complexity
□
Most complex
!
Can be longer
!
Hinged fangs: spring out when mouth is
opened
□
*see cross section of fangs
!
Teeth can be used to deliver chemical weapons
○
Ingested/passively encountered
□
Possibly collected in specialized
structured
□
No specialized mechanism of delivery to
recipient
□
Typically a single molecular entity or
compound with specific action
□
Poisons:
!
Housed and produced in specialized
structures
□
Associated with delivery device
(morphological convergence)
□
Active delivery to recipient
□
Typically multipart blend of compounds
with complex effects
□
Venoms:
!
Poisons vs Venoms:
○
Snake fangs have large diversity and disparity
in terms of complexity
!
Causes gland to compress and
release venom when snake strikes
prey
!
Venom gland is located in cheek pouch
which is surrounded by compressor
muscle
□
The venom gland pushes venom into the
secondary venom duct and the venom
moves down the venom canal within the
fang for release
□
Structure:
!
Synthesis and Delivery:
○
Regulation co-opted from pancreatic functions
!
Massive expansion of toxin genes via gene
duplication
!
To increase diversity of toxins within
each individual "cocktails"
□
Other compounds are being included in
venom to at synergistically with other
toxins
□
Positive selection = neofunctionalization
!
--> response in prey evolution
□
*understanding diversity of snake venom
can help understand arms race between
toxicity and resistance in prey
□
Diversity as a result of coevolutionary arms
race
!
Sequencing the genome of King Cobra venom:
○
Due to enormous variation in
toxins within venom
!
It is hard to develop rattlesnake
antivenom
□
In regions where they overlap,
there is still a large difference in
the variation of different toxins and
how variable they are within the
range
!
Local adaptation
!
Conservation
considerations
!
More time for
evolutionary arms race
!
Harder to develop
antivenom
!
Extensive geographic
variation in venom
◊
Rattlesnake: 30% sequences
associated with toxin
!
Could identify more toxins
◊
Less variability
◊
Recent invader without
time to locally adapt?
!
Same venom
phenotype throughout
range
!
Antivenom easier to
develop
!
Almost no geographic
variation in venom
◊
Coral snake: 47.5% sequences
associated with toxin
!
Found instances where both range of
species overlap
□
Ex. Diamondback rattlesnake and eastern coral
snake
!
Geographic variation in venom:
○
Venom is primarily used for prey capture
!
Complex mixture of bioactive proteins and
polypeptides
!
Multiple physiological, pharmacological and
biochemical modes of action
!
Inhibits acetylcholine release --> inhibits
neural impulses from nerve to muscle
fibers
□
Leads to paralysis and respiratory failure
□
Neurotoxins:
!
Depolarize muscles and cause necrosis in
muscle tissue
□
Myotoxins:
!
Haemolytic -->lyse rbcs, excessive
hemorrhaging
□
Anti-coagulant --> intracranial
hemorrhage
□
Pro-coagulant --> potential activators =
rapid blood clotting
□
Hemotoxins:
!
Prey capture:
○
Contains all types of venom
□
EXTREMELY venomous
□
Venom gland runs along body
!
Diversity:
○
Can be used as treatments
!
Venom collected from cobras was tested for
ability to counteract symptoms of arthritis
!
Validated measure of pain
□
High snake venom --> significant
decrease in writhing response compared
to control
□
Subjected mice to acetic acid writhing assay
!
Venom in medicine:
○
Venom:
•
Physical Weapons: teeth
Accumulated in skin, or specialized cells within skin or
organs
•
Obtained from environment
•
Used in predator defense
•
Causes membrane to depolarize
!
Triggers muscle contraction
!
Enables impulse to travel along nerve
!
Blocks: voltage gated Na2+ channel
○
Paralytic neurotoxin
!
Synthesized by marine bacteria
!
Selectively blocks Na2+ channels of nerves,
skeletal and cardiac muscles
!
Factors:
○
Some species have evolved TTX resistant Na2+
channels (puffer fish, California newts)
○
TTX is 10,000x more toxic than cyanide
○
TTX is 2-3x stronger than venom of most potent
snake (inland Taipan from Australia)
○
Pufferfish TTX is concentrated in the liver and
roe
!
Fugu meat is a sushi delicacy
!
Farmed fungu does not have TTX, added afrer
!
Initial: euphoria, with numbness/tingling lips
!
Nausea
□
Paralysis of limbs/respiratory muscles
□
Lose ability to swallow or move mouth
□
Lose of brain stem reflexes
□
Then:
!
Fatality rates: 50-80% within 30 minutes
!
TTX Poisoning:
○
Hypothesis: newts are warning that they are
dangerous (poisonous)
!
Energetically expensive to produce toxin
but needed to remain safe from predation
□
--> evolution of toxin within intermediate
levels
□
Predicts that stabilizing selection will
result in a population of newts, with just
enough TTX for protection, but not too
much to reduce fitness
□
Discovered that newts contain a large amount
of TTX in their body
!
Co-evolutionary arms race against snake
species (garter snakes) --> why newts are
so toxic
□
Variation
!
Heritability
!
Differential reproductive success
!
Substrate for natural selection (TTX
production vs resistance):
□
TTX levels vary among
newts, and substantially
among newt population
◊
Garter snakes have
variability in resistance to
eating newts
◊
Variation:
!
Newts are not getting toxins
from their diets
◊
Snake siblings raised in lab
have similar TTX resistance
◊
Heritability:
!
Newt TTX increases survival
◊
Snakes are immobile at risk
after eating newts (less likely
to escape own predator)
◊
Fitness:
!
Therefore, TTX levels vary among
newts, and substantially among newt
populations
□
Are they co-evolving in their weaponry
and defence?
□
More likely to be eaten
!
Produce more
offspring
!
Too little TTX production:
◊
Less likely to be eaten
!
Produce fewer
offspring
!
Too much TTX production:
◊
Newts trade-off:
!
Unable to eat toxic
newts
!
Higher crawling speed
!
Too little TTX resistance:
◊
Able to eat toxic newts
!
Lower crawling speed
!
Too much TTX resistance:
◊
Snake trade-off:
!
--> evidence for co-evolutionary
arms race
Are there trade-offs between costs and
benefits of toxicity and resistance?
□
Hypothesis 2: newts are defending against a
TTX resistant predator
!
Three dead hunters and a coffee pot:
○
Tetratoxin (TTX):
•
Chemical Weapons: Poisons
Physical and Chemical Weaponry
Friday,*November* 24,*2017
12:28*PM
Bovid families
○
Living bone inside sheath
○
Keratin covered
○
Fused to skull with connective tissue
○
Present on males and some females
○
Grow throughout life
○
Horns:
•
Only in cervids (deer, moose, elk)
○
One single bone (no keratin layer)
○
Velvet covered until mature
○
Stimulated annually by hormones
○
Sexually selected, only in males
○
Shed annually
○
Antlers:
•
Presence of bone may or may not be fused to
body
!
Epidermis may persist, be temporary or never
be present
!
Some are covered in keratin
!
*see slide -structure of headgear
○
No hair or fuzz (epidermis) on horns
!
Fused to bone
!
Cervidae
○
Keratin -epidermis and fuzz -bone
!
Not fused
!
Bovidae
○
Covered by epidermis (no keratin)
!
Not fused
!
Giraffidae (ocitones?)
○
Fused
!
Keratin -epidermis -bone
!
Antilcapridae (prong horns)
○
Ontogeny:
•
One of the smallest ungulates, does not grow
antlers
!
Mouse deer:
○
Lacks antlers as well
!
Musk deer:
○
Mouse deer is basal species
!
Headgear has independently evolved four times
in a unique way (intermediate species)
!
Morphological phylogeny: 4 independent origins
○
1origin and one loss
!
More parsimonious explanation
!
Evolved once following mouse deer
divergence, and was loss in musk deer
divergence
!
Molecular phylogeny:
○
Phylogeny:
•
Physical Weapons: Headgear
Most vertebrates have undifferentiated teeth
•
Most mammals and few other groups (dinosaurs) display
differentiated teeth (heterodont dentition)
•
Tusks = modified canine teeth
○
--> diversity and disparity
○
In mammals, teeth are specialized as incisors, canines,
premolars, and molars
•
Opisthoglyphous: posterior, fixed
!
Proteroglyphous: anterior, fixed
!
Solenoglyhous: anterior, hinged
!
Canal hold venom gland
□
Have to chomp on prey to insert venom
□
Increase in complexity
□
Most complex
!
Can be longer
!
Hinged fangs: spring out when mouth is
opened
□
*see cross section of fangs
!
Teeth can be used to deliver chemical weapons
○
Ingested/passively encountered
□
Possibly collected in specialized
structured
□
No specialized mechanism of delivery to
recipient
□
Typically a single molecular entity or
compound with specific action
□
Poisons:
!
Housed and produced in specialized
structures
□
Associated with delivery device
(morphological convergence)
□
Active delivery to recipient
□
Typically multipart blend of compounds
with complex effects
□
Venoms:
!
Poisons vs Venoms:
○
Snake fangs have large diversity and disparity
in terms of complexity
!
Causes gland to compress and
release venom when snake strikes
prey
!
Venom gland is located in cheek pouch
which is surrounded by compressor
muscle
□
The venom gland pushes venom into the
secondary venom duct and the venom
moves down the venom canal within the
fang for release
□
Structure:
!
Synthesis and Delivery:
○
Regulation co-opted from pancreatic functions
!
Massive expansion of toxin genes via gene
duplication
!
To increase diversity of toxins within
each individual "cocktails"
□
Other compounds are being included in
venom to at synergistically with other
toxins
□
Positive selection = neofunctionalization
!
--> response in prey evolution
□
*understanding diversity of snake venom
can help understand arms race between
toxicity and resistance in prey
□
Diversity as a result of coevolutionary arms
race
!
Sequencing the genome of King Cobra venom:
○
Due to enormous variation in
toxins within venom
!
It is hard to develop rattlesnake
antivenom
□
In regions where they overlap,
there is still a large difference in
the variation of different toxins and
how variable they are within the
range
!
Local adaptation
!
Conservation
considerations
!
More time for
evolutionary arms race
!
Harder to develop
antivenom
!
Extensive geographic
variation in venom
◊
Rattlesnake: 30% sequences
associated with toxin
!
Could identify more toxins
◊
Less variability
◊
Recent invader without
time to locally adapt?
!
Same venom
phenotype throughout
range
!
Antivenom easier to
develop
!
Almost no geographic
variation in venom
◊
Coral snake: 47.5% sequences
associated with toxin
!
Found instances where both range of
species overlap
□
Ex. Diamondback rattlesnake and eastern coral
snake
!
Geographic variation in venom:
○
Venom is primarily used for prey capture
!
Complex mixture of bioactive proteins and
polypeptides
!
Multiple physiological, pharmacological and
biochemical modes of action
!
Inhibits acetylcholine release --> inhibits
neural impulses from nerve to muscle
fibers
□
Leads to paralysis and respiratory failure
□
Neurotoxins:
!
Depolarize muscles and cause necrosis in
muscle tissue
□
Myotoxins:
!
Haemolytic -->lyse rbcs, excessive
hemorrhaging
□
Anti-coagulant --> intracranial
hemorrhage
□
Pro-coagulant --> potential activators =
rapid blood clotting
□
Hemotoxins:
!
Prey capture:
○
Contains all types of venom
□
EXTREMELY venomous
□
Venom gland runs along body
!
Diversity:
○
Can be used as treatments
!
Venom collected from cobras was tested for
ability to counteract symptoms of arthritis
!
Validated measure of pain
□
High snake venom --> significant
decrease in writhing response compared
to control
□
Subjected mice to acetic acid writhing assay
!
Venom in medicine:
○
Venom:
•
Physical Weapons: teeth
Accumulated in skin, or specialized cells within skin or
organs
•
Obtained from environment
•
Used in predator defense
•
Causes membrane to depolarize
!
Triggers muscle contraction
!
Enables impulse to travel along nerve
!
Blocks: voltage gated Na2+ channel
○
Paralytic neurotoxin
!
Synthesized by marine bacteria
!
Selectively blocks Na2+ channels of nerves,
skeletal and cardiac muscles
!
Factors:
○
Some species have evolved TTX resistant Na2+
channels (puffer fish, California newts)
○
TTX is 10,000x more toxic than cyanide
○
TTX is 2-3x stronger than venom of most potent
snake (inland Taipan from Australia)
○
Pufferfish TTX is concentrated in the liver and
roe
!
Fugu meat is a sushi delicacy
!
Farmed fungu does not have TTX, added afrer
!
Initial: euphoria, with numbness/tingling lips
!
Nausea
□
Paralysis of limbs/respiratory muscles
□
Lose ability to swallow or move mouth
□
Lose of brain stem reflexes
□
Then:
!
Fatality rates: 50-80% within 30 minutes
!
TTX Poisoning:
○
Hypothesis: newts are warning that they are
dangerous (poisonous)
!
Energetically expensive to produce toxin
but needed to remain safe from predation
□
--> evolution of toxin within intermediate
levels
□
Predicts that stabilizing selection will
result in a population of newts, with just
enough TTX for protection, but not too
much to reduce fitness
□
Discovered that newts contain a large amount
of TTX in their body
!
Co-evolutionary arms race against snake
species (garter snakes) --> why newts are
so toxic
□
Variation
!
Heritability
!
Differential reproductive success
!
Substrate for natural selection (TTX
production vs resistance):
□
TTX levels vary among
newts, and substantially
among newt population
◊
Garter snakes have
variability in resistance to
eating newts
◊
Variation:
!
Newts are not getting toxins
from their diets
◊
Snake siblings raised in lab
have similar TTX resistance
◊
Heritability:
!
Newt TTX increases survival
◊
Snakes are immobile at risk
after eating newts (less likely
to escape own predator)
◊
Fitness:
!
Therefore, TTX levels vary among
newts, and substantially among newt
populations
□
Are they co-evolving in their weaponry
and defence?
□
More likely to be eaten
!
Produce more
offspring
!
Too little TTX production:
◊
Less likely to be eaten
!
Produce fewer
offspring
!
Too much TTX production:
◊
Newts trade-off:
!
Unable to eat toxic
newts
!
Higher crawling speed
!
Too little TTX resistance:
◊
Able to eat toxic newts
!
Lower crawling speed
!
Too much TTX resistance:
◊
Snake trade-off:
!
--> evidence for co-evolutionary
arms race
Are there trade-offs between costs and
benefits of toxicity and resistance?
□
Hypothesis 2: newts are defending against a
TTX resistant predator
!
Three dead hunters and a coffee pot:
○
Tetratoxin (TTX):
•
Chemical Weapons: Poisons
Physical and Chemical Weaponry
Friday,*November* 24,*2017 12:28*PM
Bovid families
○
Living bone inside sheath
○
Keratin covered
○
Fused to skull with connective tissue
○
Present on males and some females
○
Grow throughout life
○
Horns:
•
Only in cervids (deer, moose, elk)
○
One single bone (no keratin layer)
○
Velvet covered until mature
○
Stimulated annually by hormones
○
Sexually selected, only in males
○
Shed annually
○
Antlers:
•
Presence of bone may or may not be fused to
body
!
Epidermis may persist, be temporary or never
be present
!
Some are covered in keratin
!
*see slide -structure of headgear
○
No hair or fuzz (epidermis) on horns
!
Fused to bone
!
Cervidae
○
Keratin -epidermis and fuzz -bone
!
Not fused
!
Bovidae
○
Covered by epidermis (no keratin)
!
Not fused
!
Giraffidae (ocitones?)
○
Fused
!
Keratin -epidermis -bone
!
Antilcapridae (prong horns)
○
Ontogeny:
•
One of the smallest ungulates, does not grow
antlers
!
Mouse deer:
○
Lacks antlers as well
!
Musk deer:
○
Mouse deer is basal species
!
Headgear has independently evolved four times
in a unique way (intermediate species)
!
Morphological phylogeny: 4 independent origins
○
1origin and one loss
!
More parsimonious explanation
!
Evolved once following mouse deer
divergence, and was loss in musk deer
divergence
!
Molecular phylogeny:
○
Phylogeny:
•
Physical Weapons: Headgear
Most vertebrates have undifferentiated teeth
•
Most mammals and few other groups (dinosaurs) display
differentiated teeth (heterodont dentition)
•
Tusks = modified canine teeth
○
--> diversity and disparity
○
In mammals, teeth are specialized as incisors, canines,
premolars, and molars
•
Opisthoglyphous: posterior, fixed
!
Proteroglyphous: anterior, fixed
!
Solenoglyhous: anterior, hinged
!
Canal hold venom gland
□
Have to chomp on prey to insert venom
□
Increase in complexity
□
Most complex
!
Can be longer
!
Hinged fangs: spring out when mouth is
opened
□
*see cross section of fangs
!
Teeth can be used to deliver chemical weapons
○
Ingested/passively encountered
□
Possibly collected in specialized
structured
□
No specialized mechanism of delivery to
recipient
□
Typically a single molecular entity or
compound with specific action
□
Poisons:
!
Housed and produced in specialized
structures
□
Associated with delivery device
(morphological convergence)
□
Active delivery to recipient
□
Typically multipart blend of compounds
with complex effects
□
Venoms:
!
Poisons vs Venoms:
○
Snake fangs have large diversity and disparity
in terms of complexity
!
Causes gland to compress and
release venom when snake strikes
prey
!
Venom gland is located in cheek pouch
which is surrounded by compressor
muscle
□
The venom gland pushes venom into the
secondary venom duct and the venom
moves down the venom canal within the
fang for release
□
Structure:
!
Synthesis and Delivery:
○
Regulation co-opted from pancreatic functions
!
Massive expansion of toxin genes via gene
duplication
!
To increase diversity of toxins within
each individual "cocktails"
□
Other compounds are being included in
venom to at synergistically with other
toxins
□
Positive selection = neofunctionalization
!
--> response in prey evolution
□
*understanding diversity of snake venom
can help understand arms race between
toxicity and resistance in prey
□
Diversity as a result of coevolutionary arms
race
!
Sequencing the genome of King Cobra venom:
○
Due to enormous variation in
toxins within venom
!
It is hard to develop rattlesnake
antivenom
□
In regions where they overlap,
there is still a large difference in
the variation of different toxins and
how variable they are within the
range
!
Local adaptation
!
Conservation
considerations
!
More time for
evolutionary arms race
!
Harder to develop
antivenom
!
Extensive geographic
variation in venom
◊
Rattlesnake: 30% sequences
associated with toxin
!
Could identify more toxins
◊
Less variability
◊
Recent invader without
time to locally adapt?
!
Same venom
phenotype throughout
range
!
Antivenom easier to
develop
!
Almost no geographic
variation in venom
◊
Coral snake: 47.5% sequences
associated with toxin
!
Found instances where both range of
species overlap
□
Ex. Diamondback rattlesnake and eastern coral
snake
!
Geographic variation in venom:
○
Venom is primarily used for prey capture
!
Complex mixture of bioactive proteins and
polypeptides
!
Multiple physiological, pharmacological and
biochemical modes of action
!
Inhibits acetylcholine release --> inhibits
neural impulses from nerve to muscle
fibers
□
Leads to paralysis and respiratory failure
□
Neurotoxins:
!
Depolarize muscles and cause necrosis in
muscle tissue
□
Myotoxins:
!
Haemolytic -->lyse rbcs, excessive
hemorrhaging
□
Anti-coagulant --> intracranial
hemorrhage
□
Pro-coagulant --> potential activators =
rapid blood clotting
□
Hemotoxins:
!
Prey capture:
○
Contains all types of venom
□
EXTREMELY venomous
□
Venom gland runs along body
!
Diversity:
○
Can be used as treatments
!
Venom collected from cobras was tested for
ability to counteract symptoms of arthritis
!
Validated measure of pain
□
High snake venom --> significant
decrease in writhing response compared
to control
□
Subjected mice to acetic acid writhing assay
!
Venom in medicine:
○
Venom:
•
Physical Weapons: teeth
Accumulated in skin, or specialized cells within skin or
organs
•
Obtained from environment
•
Used in predator defense
•
Causes membrane to depolarize
!
Triggers muscle contraction
!
Enables impulse to travel along nerve
!
Blocks: voltage gated Na2+ channel
○
Paralytic neurotoxin
!
Synthesized by marine bacteria
!
Selectively blocks Na2+ channels of nerves,
skeletal and cardiac muscles
!
Factors:
○
Some species have evolved TTX resistant Na2+
channels (puffer fish, California newts)
○
TTX is 10,000x more toxic than cyanide
○
TTX is 2-3x stronger than venom of most potent
snake (inland Taipan from Australia)
○
Pufferfish TTX is concentrated in the liver and
roe
!
Fugu meat is a sushi delicacy
!
Farmed fungu does not have TTX, added afrer
!
Initial: euphoria, with numbness/tingling lips
!
Nausea
□
Paralysis of limbs/respiratory muscles
□
Lose ability to swallow or move mouth
□
Lose of brain stem reflexes
□
Then:
!
Fatality rates: 50-80% within 30 minutes
!
TTX Poisoning:
○
Hypothesis: newts are warning that they are
dangerous (poisonous)
!
Energetically expensive to produce toxin
but needed to remain safe from predation
□
--> evolution of toxin within intermediate
levels
□
Predicts that stabilizing selection will
result in a population of newts, with just
enough TTX for protection, but not too
much to reduce fitness
□
Discovered that newts contain a large amount
of TTX in their body
!
Co-evolutionary arms race against snake
species (garter snakes) --> why newts are
so toxic
□
Variation
!
Heritability
!
Differential reproductive success
!
Substrate for natural selection (TTX
production vs resistance):
□
TTX levels vary among
newts, and substantially
among newt population
◊
Garter snakes have
variability in resistance to
eating newts
◊
Variation:
!
Newts are not getting toxins
from their diets
◊
Snake siblings raised in lab
have similar TTX resistance
◊
Heritability:
!
Newt TTX increases survival
◊
Snakes are immobile at risk
after eating newts (less likely
to escape own predator)
◊
Fitness:
!
Therefore, TTX levels vary among
newts, and substantially among newt
populations
□
Are they co-evolving in their weaponry
and defence?
□
More likely to be eaten
!
Produce more
offspring
!
Too little TTX production:
◊
Less likely to be eaten
!
Produce fewer
offspring
!
Too much TTX production:
◊
Newts trade-off:
!
Unable to eat toxic
newts
!
Higher crawling speed
!
Too little TTX resistance:
◊
Able to eat toxic newts
!
Lower crawling speed
!
Too much TTX resistance:
◊
Snake trade-off:
!
--> evidence for co-evolutionary
arms race
Are there trade-offs between costs and
benefits of toxicity and resistance?
□
Hypothesis 2: newts are defending against a
TTX resistant predator
!
Three dead hunters and a coffee pot:
○
Tetratoxin (TTX):
•
Chemical Weapons: Poisons
Physical and Chemical Weaponry
Friday,*November* 24,*2017 12:28*PM
Document Summary
Presence of bone may or may not be fused to body. Epidermis may persist, be temporary or never be present. One of the smallest ungulates, does not grow antlers. Headgear has independently evolved four times in a unique way (intermediate species) Evolved once following mouse deer divergence, and was loss in musk deer divergence. Most mammals and few other groups (dinosaurs) display differentiated teeth (heterodont dentition) In mammals, teeth are specialized as incisors, canines, premolars, and molars. Teeth can be used to deliver chemical weapons. Have to chomp on prey to insert venom. Hinged fangs: spring out when mouth is opened. Typically a single molecular entity or compound with specific action. Typically multipart blend of compounds with complex effects. Snake fangs have large diversity and disparity in terms of complexity. Venom gland is located in cheek pouch which is surrounded by compressor muscle. Causes gland to compress and release venom when snake strikes prey.
