Lesson 4: Moving Around Flashcards
What is a sprawling stance?
lizards, turtles, crocodiles, and salamanders all have a sprawling stance
an animal’s humerus and femur project horizontally, with elbows and knees strongly bent
What is an erect stance?
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
What are the advantages of the erect stance over a sprawling stance?
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
Why do lizards use a sprawling stance?
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
Did dinosaurs have a sprawling or erect stance?
erect and sprawling postures are easy to identify based on limb joints and the articulation angles of limb girdles
dinosaurs stood erect
What are cursorial limbs?
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)
What is digitigrade posture?
animals who stand on their toes
What is unguligrade posture?
animals that stand only on toenails that have been modified into hoofs
What is plantigrade posture?
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
What are graviportal limbs?
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
What are obligate bipeds?
animals that almost always walk and run on two legs, like birds and adult humans
What are obligate quadrupeds?
animals that almost always walk and run on four legs, like turtles and horses
What are facultative bipeds?
some animals like, basilisk lizards, walk on all four legs but rise on two legs to run
What stance did the ancestor of all dinosaur have?
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
What stance to sauropods, stegosaurs, and ankylosaurs use?
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
What stance to prosauropods use?
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
What stance did ceratopsians use?
some small ceratopsians were obligate and facultative bipeds, and larger ceratopsians were obligate quadrupeds
What stance did pachycephalosaurs and theropods use?
they were obligate bipeds
What is the caudofemoralis?
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
What is a the trochanter?
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
What are ichnofossils?
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
How are fossil footprints created?
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
What are trackways?
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
How has the study of dinosaur trackways helped our understanding of dinosaur posture and locomotion?
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
What can the trackways of hadrosaurs and iguanodonts tell us about how they walked?
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
How can trackways be used to determine how fast dinosaurs moved?
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
Why are the terms “warm-blooded” and “cold-blooded” misleading?
the blood of a “warm-blooded” animal is not necessarily any warmer than the blood of a “cold-blooded” animal
What are ectotherms?
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
What are endotherms?
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
What are the costs of being an endotherm?
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
What are the advantages that endotherms have?
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
How do endotherms benefit from insulating integument?
it helps to hold in body heat that they burn energy to produce
What is histology?
the technique of slicing samples of bones into very thin sections, such that the internal structure of the bone can be observed under magnification
What are osteons?
bone cells
What does gigantothermic mean?
it has been suggested that, instead of being endotherms, large dinosaurs were gigantothermic
What is the cube square law?
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
