Lesson 4: Moving Around

Question 1

What is a sprawling stance? Give some examples of animals that use it.

Answer 1

In a sprawling stance, an animal’s humerus and femur project horizontally, with elbows and knees strongly bent. Ex, lizards, turtles, crocodiles, and salamanders.

Question 2

What is an erect stance? Give some examples of animals that use it.

Answer 2

In an erect stance, an animal’s humerus and femur project vertically, such that all the limbs point straight down from their girdles. Ex, mammals and birds.

Question 3

What are some advantages of an erect stance over sprawling stance?

Answer 3

1. 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.
2. It also allows all the limb bones to contribute to the length of a stride. This improves speed.

Question 4

All modern tetrapods share an ancestor that had a ___ stance. Birds and mammals evolved their ___ stances independently of each other.

Answer 4

Sprawling and erect.

Question 5

Did dinosaurs sprawl like crocodiles and lizards, or stand erect like mammals and birds? How do we know>

Answer 5

Erect and sprawling postures are easy to identify based on limb joints and the articulation angles of limb girdles. The evidence is clear. Dinosaurs stood erect.

Question 6

What are cursorial limbs?

Answer 6

Cursorial limbs are 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? What are examples?

Answer 7

When cursorial animals stand on their toes, like cheetahs and ostriches.

Question 8

What is unguligrade posture? What are examples?

Answer 8

When cursorial animals stand on toenails that have been modified into hoofs, like horses and antelope.

Question 9

Humans are not ___, and we stand simultaneously on our toes, the flat of our feet, and our heels ( ___ posture).

Answer 9

Cursorial and plantigrade.

Question 10

What is plantigrade posture?

Answer 10

In plantigrade animals, the phalanges and metatarsals make contact with the ground.

Question 11

Do dinosaurs have cursorial adaptations?

Answer 11

Some dinosaurs show cursorial adaptations, in particular the ornithomimid theropods. Ornithomimids have a digitigrade stance and long metatarsals.

Question 12

What are graviportal limbs?

Answer 12

Graviportal limbs are specially adapted for supporting extreme body weight. Graviportal limbs have bones that are robust and heavy. Graviportal 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. Graviportal limbs tend to be short and, when walking, their joints bend as little as possible. Elephants are modern examples of animals with graviportal limbs.

Question 13

Animals that almost always walk and run on two legs, like birds and adult humans, are termed ___ ___. Animals that almost always walk and run on four legs, like turtles and horses, are termed ___ ___.

Answer 13

Obligate bipeds and obligate quadrupeds.

Question 14

Some animals like, basilisk lizards, walk on all four legs but rise on two legs to run. Such animals are termed ___ ___.

Answer 14

Facultative bipeds.

Question 15

The ancestor of all dinosaurs was an obligate ___.

Answer 15

Biped.

Question 16

We classify sauropods, stegosaurs, and ankylosaurs as obligate ___.

Answer 16

Quadrupeds.

Question 17

Prosauropods are tricky: many were probably ___, but whether or not they were obligate or facultative ___ is not always easy to determine.

Answer 17

Bipedal and bipeds.

Question 18

Some small ceratopsians were obligate and facultative ___, and larger ceratopsians were obligate.

Answer 18

Bipeds and quadrupeds.

Question 19

Pachycephalosaurs and theropods were obligate ___. Most small ornithopods were also obligate ___. Our understanding of the postures of large ornithopods, including hadrosaurs and iguanodonts, has changed over the years. Both of these groups have strong hind legs that are significantly longer than their front limbs. This indicated a ___ stance; however, fossil footprints reveal a different story,

Answer 19

Bipeds, bipeds, and bipedal.

Question 20

What is the caudofemoralis?

Answer 20

The caudofemoralis pulls backwards on the hind leg and is important for powering birds and crocodiles when they walk and run. The caudofemoralis 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.

Question 21

What is a trochanter?

Answer 21

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 22

Based on the size of the various anchor points, we can also say that some dinosaurs, like many theropods and hadrosaurs, had a large caudofemoralis relative to the other proportions of their bodies. This tells us that these dinosaurs were adapted for greater hindlimb power and were probably strong runners. Compare the position of the muscle attachment between the two.

Answer 22

On most theropods, the trochanter is located high on the femur. A high muscle attachment would have allowed the caudofemoralis to repeatedly retract quickly – a useful adaptation for carnivorous animals that depend on their ability to swing their legs fast when sprinting after prey. On hadrosaurs, the trochanter is located further down on the femur (as it is in most herbivorous dinosaurs). This would have reduced the speed at which the caudofemoralis could have repeatedly retracted but would have granted the muscle better endurance, because each retraction would have pulled with greater leverage.

Question 23

What are ichnofossils?

Answer 23

Ichnofossils are fossils that record traces of biologic activity. Fossil footprints, tooth marks,
and burrows are all examples of ichnofossils.

Question 24

Fossil footprints provide the best direct evidence of how dinosaur moved. How do they become fossilized?

Answer 24

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 reexposed so that palaeontologists can identify it.

Question 25

Side fact: How many years did dinosaurs rule?

Answer 25

160 million years.

Question 26

What are trackways?

Answer 26

Often, where one 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 27

How did bipedal dinosaurs hold their bodies?

Answer 27

Most bipedal dinosaurs held their body in a more horizontal position and that both bipedal and quadrupedal dinosaurs held their tails off the ground. As evidenced by a lack of tail track fossils.

Question 28

Discuss the tracks of hadrosaurs and iguanodonts (changed the notion on whether they were primarily bipedal or quadrupedal).

Answer 28

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 29

What are ectotherms?

Answer 29

Ectotherms are animals that adjust their internal body temperatures through behaviors that depend on 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 30

What are endotherms?

Answer 30

Endotherms are 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 31

What are the costs of being an endotherm?

Answer 31

Being an endotherm comes with a high cost. In order to maintain a constant optimal body temperature, endotherms must expend 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, not endotherms.

Question 32

What are the benefits of being an endotherm?

Answer 32

1. Endotherms can survive cold climates.
2. Endotherms are always ready for action, day or night.
3. Although they pay an energy cost, endotherms also do not need to take frequent stops and can maintain high activity levels.

Question 33

What support is there for dinosaurs being endotherms?

Answer 33

1. The limbs of dinosaurs, which appear well adapted for the more active lifestyle of endotherms.
2. Some dinosaurs had simple hair-like feathers. Endotherms benefit from insulating integument to help hold in the body heat that they burn energy to produce.
3. When it comes to being large land-living carnivores and herbivores, endotherms tend to outcompete ectotherms. So, the overall pattern of dinosaur ecological success is most consistent with this idea.
4. Dinosaur histology studies show that dinosaur bones grew fast and that dinosaur osteons were arranged like those of endotherms.

Question 34

What is histology?

Answer 34

Histology is 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 35

What are osteons?

Answer 35

Bone cells are called osteons.

Question 36

How do osteons differ in endotherms and ectotherms?

Answer 36

Endotherms grow their bones more quickly and have their osteons arranged in a different pattern than ectotherms.

Question 37

It has been suggested that, instead of being endotherms, large dinosaurs were ___.

Answer 37

Gigantothermic.

Question 38

What is Gigantothermic?

Answer 38

As any shape increases in size, its surface area increases more slowly than its volume. This is called the cube square law. 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.