Lesson 4: Moving Around

Question 1

What is a sprawling stance?

Answer 1

lizards, turtles, crocodiles, and salamanders all have a sprawling stance

an animal’s humerus and femur project horizontally, with elbows and knees strongly bent

Question 2

What is an erect stance?

Answer 2

mammals and birds have an erect stance

an animal’s humerus and femur project vertically, such that all the limbs point straight down from their girdles

Question 3

What are the advantages of the erect stance over a sprawling stance?

Answer 3

an erect stance positions the limb bones directly under the body

this allows the limb bones to passively support the body’s weight without muscles having to strain

the weight supporting benefit of an erect posture is more helpful to larger animals that have more weight that needs supporting

another advantage of erect posture is that it allows all 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

Question 4

Why do lizards use a sprawling stance?

Answer 4

holding a “push-up position” forces our forelimbs into a sprawling stance, and it is hard, because supporting our weight with bent arms requires our muscles to do a lot of work

not surprisingly, most animals that have a sprawling posture do not use their limbs to support their weight very often

the life of a lizard is mostly spent resting on its belly

lizards are relatively inactive (compared to mammals and birds) and rise to walk and run infrequently

most lizards are also not very large so they have little weight to support

Question 5

Did dinosaurs have a sprawling or erect stance?

Answer 5

erect and sprawling postures are easy to identify based on limb joints and the articulation angles of limb girdles

dinosaurs stood erect

Question 6

What are cursorial limbs?

Answer 6

limbs specially adapted for fast locomotion

to further increase stride length, cursorial limbs are elongated

in particular, cursorial limbs tend to have very long lower leg bones (the bones below the elbows and knees)

Question 7

What is digitigrade posture?

Answer 7

animals who stand on their toes

Question 8

What is unguligrade posture?

Answer 8

animals that stand only on toenails that have been modified into hoofs

Question 9

What is plantigrade posture?

Answer 9

animals who stand simultaneously on their toes, the flat of their feet, and their heels

in plantigrade animals, the phalanges and metatarsals make contact with the ground

Question 10

What are graviportal limbs?

Answer 10

limbs that are specially adapted for supporting extreme body weight

these limbs have bones that are robust and heavy

limbs also tend to have large feet with large fleshy pads

these big feet and pads provide a solid support base and help to absorb impacts when walking

these limbs tend to be short and, when walking, their joints bend as little as possible

elephants are modern examples

Question 11

What are obligate bipeds?

Answer 11

animals that almost always walk and run on two legs, like birds and adult humans

Question 12

What are obligate quadrupeds?

Answer 12

animals that almost always walk and run on four legs, like turtles and horses

Question 13

What are facultative bipeds?

Answer 13

some animals like, basilisk lizards, walk on all four legs but rise on two legs to run

Question 14

What stance did the ancestor of all dinosaur have?

Answer 14

the ancestor of all dinosaurs was an obligate biped

most dinosaurs remained adapted to carry a majority of their weight on their hind legs and could probably at least stand on only two feet

Question 15

What stance to sauropods, stegosaurs, and ankylosaurs use?

Answer 15

they are obligate quadrupeds

because, even if many of them could stand on two legs, it is unlikely that they frequently attempted to walk bipedally

Question 16

What stance to prosauropods use?

Answer 16

they are tricky to classify

many were probably bipedal, but whether or not they were obligate or facultative bipeds is not always easy to determine

Question 17

What stance did ceratopsians use?

Answer 17

some small ceratopsians were obligate and facultative bipeds, and larger ceratopsians were obligate quadrupeds

Question 18

What stance did pachycephalosaurs and theropods use?

Answer 18

they were obligate bipeds

Question 19

What is the caudofemoralis?

Answer 19

a large muscle present in crocodiles and birds

this muscle pulls backwards on the hind leg and is important for powering birds and crocodiles when they walk and run

the muscle is anchored to the under surface of the ilium, to the caudal vertebrae, and to the chevrons

it attaches, via a tendon, to teh femur

Question 20

What is a the trochanter?

Answer 20

the femora of crocodiles and birds have a prominence of bone, called a trochanter, where the caudofemoralis muscle-ligament attaches

in addition to specially shaped ilia, caudal vertebrae, and chevrons, dinosaurs also have femora with these same trochanters

so we can be sure dinosaurs also had a caudofemoralis

Question 21

What are ichnofossils?

Answer 21

fossils that record traces of biologic activity

fossil footprints, tooth marks, and burrows are examples of ichnofossils

fossil footprints provide the best direct evidence of how dinosaurs moved

Question 22

How are fossil footprints created?

Answer 22

to become fossilized, a footprint must first be made in soft mud

the mud must then dry out and harden

then, to protect the hardened footprint from erosion it must be buried but eventually re-exposed so that paleontologists can identify it

naturally, the odds of this sequence of events happening to any particular footprint are small

Question 23

What are trackways?

Answer 23

often, where on fossil footprint is found so are many others

sometimes an entire series of dinosaur footprints are found

these fossil footprint assemblages are called trackways

Question 24

How has the study of dinosaur trackways helped our understanding of dinosaur posture and locomotion?

Answer 24

it was once widely imagined that bipedal dinosaurs stood and walked in a way not unlike the movie monster Godzilla, with their belly and torsos held vertically above their hips

this posture would have tilted dinosaur tails downward and caused a dinosaur’s tail to drag behind it

dinosaur tail drag marks are rare

we now know that most bipedal dinosaurs held their body in a more horizontal position and that both bipedal and quadrupedal dinosaurs held their tails off the ground

Question 25

What can the trackways of hadrosaurs and iguanodonts tell us about how they walked?

Answer 25

the trackways of hadrosaurs and iguanodonts have deep imprints left by their hind feet and show that these dinosaurs carried most of their weight on their hind legs

however, the trackways of hadrosaurs and iguanodonts also record shallow tracks made by their front feet

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

Question 26

How can trackways be used to determine how fast dinosaurs moved?

Answer 26

when we run, we tend to take long steps, and so do most other animals

as noted previously, longer strides enhance speed

from trackways, we can measure the lengths of dinosaur strides and can usually estimate dinosaur leg lengths from the proportions of their footprints

from these two measurements, it is possible to estimate how fast a dinosaur was moving when its footprints were made

unfortunately, because fossil footprints must be made in mud and because animals seldom run at full speed when stepping through sticky muck, trackways tell us about dinosaur walking speed and not usually about dinosaur running speeds

Question 27

Why are the terms “warm-blooded” and “cold-blooded” misleading?

Answer 27

the blood of a “warm-blooded” animal is not necessarily any warmer than the blood of a “cold-blooded” animal

Question 28

What are ectotherms?

Answer 28

animals that adjust their internal body temperature differences within their environment

for instance, to warm up lizards bask in the sun or on top of hot rocks, and to cool down lizards seek out shade or cool burrows

Question 29

What are endotherms?

Answer 29

animals that regulate their own body temperatures through metabolic processes

to warm up, endotherms burn energy to generate internal heat, and, to cool down, they may sweat or pant

Question 30

What are the costs of being an endotherm?

Answer 30

in order to maintain a constant optimal body temperature, endotherms must expand large sums of energy

pound for pound, this means that endotherms most successfully consume a great deal more food than must ectotherms

due in large part to this significant drawback, most organisms are ectotherms

Question 31

What are the advantages that endotherms have?

Answer 31

endotherms can survive in cold climates, where finding a warm place to absorb heat is impossible

endotherms are always ready for action

although activities like sunbathing may not waste valuable energy they do waste valuable time

Question 32

How do endotherms benefit from insulating integument?

Answer 32

it helps to hold in body heat that they burn energy to produce

Question 33

What is histology?

Answer 33

the technique of slicing samples of bones into very thin sections, such that the internal structure of the bone can be observed under magnification

Question 34

What are osteons?

Answer 34

bone cells

Question 35

What does gigantothermic mean?

Answer 35

it has been suggested that, instead of being endotherms, large dinosaurs were gigantothermic

Question 36

What is the cube square law?

Answer 36

as any shape increases in size, its surface area increases more slowly than its volume

larger animals, therefore, have relatively less surface area than do smaller animals

it is theorized that, even if big dinosaurs were ectothermic, their low ratio of surface area to volume would have prevented them from losing significant heat to the outside world, and, thus, they could have lived active endothermic-like lives without actually needing to produce body heat by burning energy

however, the theory of gigantothermic dinosaurs remains to be proven and lacks supporting evidence