Lesson 4: moving around Flashcards
sprawling stance
An animal’s humerus and femur project horizontally, with elbows and knees strongly bent
Supporting weight with bent arms requires our muscles to do a lot of work
Examples: Lizards, turtles, crocodiles, and salamanders
Erect stance
An animal’s humerus and femur project vertically, such that all the limbs point straight down from their girdles
This allows the limb bones to passively support the body’s weight without muscles having to strain
Allows all the limb bones to contribute to the length of a stride this improves speed
Most tetrapods had an erect stance
Example: Mammals and birds
Cursorial limbs
Adapted for fast locomotion
Are elongated
Tend to have very long lower leg bones (the bones below the elbows and knees)
Often stand on their toes (digitigrade posture, which Ornithomimids like raptors have), or stand only on toenails that have been modified into hoofs (unguligrade posture
Cursorial limbs and digitigrade posture examples
Cheetahs and ostrich
Cursorial limbs and unguligrade posture.
Horses and antelopes
Humans are not cursorial
Plantigrade posture
We stand simultaneously on our toes, the flat of our feet, and our heels
The phalanges and metatarsals make contact with the ground
Graviportal limbs
Specially adapted for supporting extreme body weight
Have bones that are robust and heavy
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
Example: elephants
Obligate bipeds
Animals that almost always walk and run on two legs
Examples: Birds and humans
Most small ornithopods
Obligate quadrupeds
Animals that almost always walk and run on four legs
Examples: Horses
Sauropods, stegosaurs, and ankylosaurs
Facultative bipeds
Walk on all four legs but rise on two legs to run
Example: basilisk lizards
Caudofemoralis
A large muscle in many birds and in crocodiles
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
Trochanter
The femora of crocodiles and birds have a prominence of bone, called a trochanter
It is where the caudofemoralis muscle-ligament attaches
On most theropods, the trochanter is located high on the femur
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
Process of bone on the femora of crocodiles and birds where the caudofemoralis muscle-ligament attaches
Ichnofossils
Are fossils that record traces of biological activity. Fossil footprints, tooth marks, and burrows
Fossil footprints provide the best direct evidence of how dinosaur moved. 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 palaeontologists can identify it.
Sometimes an entire series of dinosaur footprints are found. These fossil footprint assemblages are called trackways
Endotherm
-Are animals that regulate their own body temperatures through metabolic processes like burning energy to generate internal heat, and, to cool down, they may sweat or pant
Endotherms must expend large sums of energy to maintain a constant optimal body temperature
Can survive in cold climates
Are always ready for action
Dinosaurs are endothermic
The bones of dinosaurs also support the conclusion that they were endotherms.
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
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
The study of bone microstructure as it relates to bone growth
Osteons
bones
Gigantothermic
Instead of being endotherms, large dinosaurs were
Cube square law
As any shape increases in size, its surface area increases more slowly than its volume
A mathematical principle that explains the discrepancy in the relative change of surface area and volume as an object grows or shrinks; as the size of an object increases its volume increase by a factor of three, while its surface area increase by only a factor of two
Theory about ectothermic dinosaur
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
Graviportal
Foot and limb posture specially adapted for supporting extreme body weight. e.g. elephants
Ichnology
The study of trace fossils (like footprints, old burrows)
