What is a sprawling stance? What kind of animals does this stance refer to
- animal’s humerus and femur project horizontally
- > elbows and knees are strongly bent
-lizards, turtles, crocodiles and salamanders all have sprawling stances
What is an erect stance? What kind of animal has an erect stance
- mammals and birds have what is termed an erect stance
- > in an erect stance, an animal’s humerus and femur project vertically
- > the limbs point straight down from the girdle
What are the advantages of an erect stance over a sprawling one
1) the limb bones are directly under the body
- >this allows the limb bones to passively support the body’s weight without muscles having to strain
- going in a push up positions changes us into a sprawling stance
- > with a sprawling stance, our muscles do a lot of work and it is difficult to maintain
2) Erect stance is more for active animals
- >sprawling stance is for animals that mainly rest on their bellies like lizards do
3) Erect stance allows for the limb bones to contribute to the length of a stride
- >this improves speed
- >because if every step you take is longer, you can potentially cover ground more quickly
Do all modern tetrapods share an ancestor that has a sprawling stance?
-yes
Did birds and mammals evolve their erect stances independently of each other
- yes
- note that dinosaurs had erect postures, not sprawling
What are cursorial limbs?
- they are limbs specially adapted for fast locomotion
- > they are elongated to further increase stride length
- elongation is achieved by having very long lower leg bones
- > leg bones are below the elbows and the knees
What are the two different types of postures associated with cursorial limbs
- digitigrade posture
- > this is when animals stand on their toes
- > eg; cheetahs and ostriches
- unguligrade posture
- > modified toenails
- > the modification results in hoof
- > eg; horses and antelopes
Are humans cursorial?
- no
- > humans simultaneously stand on their toes, flat of their feet and heels
- > this posture is referred to as plantigrade posture
What are graviportal limbs
- specially adapted for supporting extreme body weight
- > they are robust and heavy
- > thye tend to have large feet with large fleshy pads
- > these pads provide a solid support base and help to absorb impacts when walking
Are graviportal limbs short or long
- they are short
- > tend to bend as little as possible whne walking
- > elephants have graviportal limbs
What are obligate bipeds
- they are animals that always walk and run on two legs
- >eg; birds and adult humans
What are obligate quadrupeds
- animals that almost always run and walk on four legs
- >eg; turtles and horses
What are facultative bipeds
- animals that usually walk on all fours but rise to run on all twos
- > eg; basilisk lizards, primatesw, kangaroos
Was the ancestor of all dinosaurs obligate biped
-yes
Are prosauropods bipedal
- many were probably bipedal
- >but whether they are facultative bipeds are hard to determine
How does the size of ceratopsians determine if they are obligate or facultative bipeds
- small ceratopsians were obligate and facultative bipeds
- larger ceratopsians were obligate quadrupeds
What is the caudofemoralis
- it is a large muscle in birds and crocodiles
- > it pulls backward on the hind leg and is important for powering birds and crocodiles when they walk and run
- it is anchored to the under surface of the ilium, to the caudal vertebrae and to the chevrons
- > it attaches via a tendon to the femur
What is the trochanter
- femora of crocodiles and birds have a prominence of bone called the a trochanter
- this is where the caudofemoralis muscle-ligament attaches
- note that dinosaurs had a trochanter
- > so they must have a caudofemoralis
How does the trochanter compare on carnivorous dinosaurs to carnivorous ones
Carnivorous dinosaurs
- > trochanter is located high on the femur
- > this would allow for the caudofemoralis to repeatedly retract quickly
- > this is useful because carnivorous animals depend on their ability to swing their legs fast when sprinting for prey
Herbivore dinosaurs
- > trochanter is located low on the femur
- > this would have reduced the speed at which the caudofemoralis repeatedly retracts
- > but would have resulted in greater endurance, which is useful for herbivores
What are ichnofossils
- they are fossils that record traces of biological activity
- >burrows are all examples of ichnofossils
What are trackways
- this is an entire series of dinosaur footprints that are found
- > trackways helps our understanding of dinosaur posture and locomotion
- it can also tell us how fast dinosaurs moved
- > when we run, we tend tot ake longer steps and so do other animals
- note that trackways made it hard to get sprint speed
- > as dinosaurs would continuously need to sprint in mud for footprints to be made
- > therefore, it only tells us about dinosaur walking speeds and not usually dinosaur sprinting speeds
-lastly, it can sometimes provide insights into other aspects of locomotion
Describe the evidence offered by the trackways of hadrosaurs and iguanodonts
- they have deep imprints left by their hind feet and show that they carried most of their weight on their hind legs
- they also have shallow tracks made up by their front feet
- therefore, it is safe to assume that hadrosaurs and iguanodonts were probably facultative bipeds that walked on all fours most of the time
- > but likely reared up on only their back legs to run
What are ectotherms
- animals that adjust their internal body temperatures through behaviors that depend on temperature differences within their environment
- they are commonly referred to as cold-blooded animals
What are endotherms
- animals that regulate temperature through their metabolic processes
- > they burn energy to generate internal heat, and to cool down they may sweat or pant
-they are commonly referred to as warm-blooded animals
