Lesson 6: Attack and Defense Flashcards
How were horns, spikes, and armor used as defense by herbivorous dinosaurs?
having horns or spikes is a common strategy used by modern animals
horns of buffalo and rhinos or the spiky quills of porcupines make them dangerous prey to attack
even if predators succeed at killing such prey, they may be seriously injured in the process
What are deterrents?
weapons like horns and spikes, beyond their usefulness in defending prey when attacked, are also deterrents
they discourage predators from choosing to attack in the first place
armor, like the shell of a turtle, can also be a deterrent because it makes the animal difficult to eat, and therefore not worth the effort
large size can be a defense entirely on its own
What deterrents did giant sauropods use to avoid predators?
giant sauropods may have lacked horns and armor, but their sheer size would have made them formidable prey
like modern elephants, giant sauropods could have trampled even their largest potential predators, and, although they were not armed with spikes and clubs, sauropods could have dealt severe blows with their massive tails
How are cursorial limbs a defense against predators?
being able to outrun and/or outmaneuver potential predators keep prey safe and avoids a physical fight altogether
based on their hind limb proportions, ornithomimids and many small ornithopods are cursorially adapted, and it is likely that these dinosaurs made use of their speed when threatened
however, predators can also make use of speed, and long limbs in a carnivore can be seen as a predatory adaptation
How do cryptic adaptations help prey to avoid predators?
cryptic adaptations allow potential prey to go a step further and avoid even being seen by predators
crypsis is the ability of an animal to avoid detection, and cryptic adaptations include camouflage color patterns, hiding behaviors, and odor-making chemicals
crypsis is difficult to judge from only fossil evidence
because cryptic adaptations are widespread among modern animals, it is reasonable to assume that cryptic adaptations were also wide spread among dinosaurs
however, relying primarily on crypsis as a predator defense is more common among small animals, which are able to hide more easily behind environmental structures, than among large animals, and it is unlikely that crypsis was the sole predator defense of any large herbivorous dinosaurs
it is difficult to demonstrate that any dinosaur species used cryptic adaptations like camouflage, because color and color patterns are not usually preserved in dinosaur fossils and “hiding” isn’t something that can be fossilized
What defenses cannot be observed through the fossil record?
like crypsis, many defenses, including chemical weapons and intimidating displays, are difficult to detect from fossil evidence
some modern animals use bright colors or false eyes to scare predators away, or to clearly label themselves as toxic or otherwise dangerous
given the diversity of dinosaurs, it is more likely that some dinosaurs, it is more likely that some dinosaurs used such defenses then that no dinosaurs did
What is finite element analysis?
a technique that has been used by paleontologist to help evaluate hypotheses about the functions of many dinosaur adaptations
finite element analyses are computer simulations that apply set material properties to a digital object and that report data on how stresses are dispersed through the object, when a force is applied at a particular point
How was finite element analysis carried out to evaluate the hypothesis that the tail cubs of ankylosaurs were used as weapons?
the reasoning behind this study was that, if ankylosaur tail cubs were used as weapons, it is likely that the tail cubs were able to withstand large impact forces without breaking, whereas, if ankylosaur tail cubs were not used as weapons, it would be very unlikely that the tail cubs were adapted in such a way as to withstand large impact forces
the tail club of the ankylosaur Euoplocephalus was digitally scanned, and this digital model was them imported into a finite element analysis program
the digital tail cub model was given material properties equivalent to that of bone
to stimulate a tail club strike, the force of a Euoplocephalus tail swing was estimated and was applied to a point on the outer surface of the digital tail club model
the results showed that the resulting stresses across the tail club were insufficient to damage the tail club
thus, the study concluded that ankylosaur tail clubs were capable of serving as weapons, and this supports the hypothesis that weapons were the function of the tail clubs
How can paleontologists determine how well a dinosaur could see, hear, and smell?
the brain cases of dinosaurs offer some clues, because the sizes of different regions of the brain relate directly to the strength of specific senses
eye size can be estimated from the size of the orbits, and the inner ear cavity of the skull offers many clues to the strength of a dinosaur’s hearing
What adaptations serve the sensory needs of prey?
herbivores, who are concerned with avoiding being snuck up on by predators, benefit from a wide field of view
for this reason, herbivores often have eyes positioned on the sides of their heads
this prevents the field of vision of one eye from redundantly overlapping with the field of vision of the other eye and maximizes how much of its surrounding an animal can see at one time
What adaptations serve the sensory needs of predators?
predators benefit from being able to maximize their perception of a single target
often, but by no means always, predators have eyes that are positioned near each other and that both face forward
this causes the field of vision of both eyes to overlap and grants the predator stereoscopic vision
What is stereoscopic vision?
allows an animal to see the same object with both eyes, and thus to see it from two slightly different angles, which improves the animal’s ability to judge depth
other animals besides predators may benefit from enhanced depth perception, and stereotypic vision is also common among animals that fly and climb
What are ambush predators?
lie in wait until prey comes within striking distance
a good example of this kind of hunting strategy is a crocodile, waiting for prey to enter the water, then lunging
What are stealthy predators?
stalk and pursue prey, and may rely on stealth to approach quietly and strike
What are pursuit predators?
still others, like wolves, may pursue prey over long distances, using their endurance to tire out and eventually overtake their prey
What are social predators?
some hunters work cooperatively in order to acquire prey that would be too difficult to kill on their own, and we call these social predators
What is the importance of the “Fighting Dinosaurs” fossil in Mongolia?
this amazing fossil pair seems to be a snapshot of a Velociraptor in the midst of killing a Protoceratops, and provides support for the use of the sickle-shaped toe claw as a predatory adaptation
this is one of the best examples of an interaction between two dinosaurs that we know of
based on this fossil, we might guess that Velociraptor was a solitary hunter
however, maybe other Velociraptor were present, but were able to escape whatever killed the Fighting Dinosaurs
What are agonistic behaviors?
it is common for members of the same species to fight over territory, mates, food resources, and for social rank within a group
fighting and aggressive displays between members of the same species are called agonistic behaviors
because agonistic behaviors are common, so are adaptations that facilitate them
What is ritualized agonistic combat?
this kind of competition that determines which of two individuals is the strongest without either combatant risking serious injury is a special kind of agonistic behavior
Why is it adaptive for predators to form groups?
predators that form packs may be able to cooperatively bring down prey that is too dangerous or difficult to be attacked by an individual
it is usually more difficult to sneak up on an alert group than on a single alert individual
Why is it adaptive for prey to form groups?
prey that band together in a herd benefit from the additional sets of watchful eyes (and alert ears and noses)
some prey herds may also mount collective offenses against predators that would be too dangerous to challenge alone
What is the evidence for dinosaurs forming groups?
from trackways and monospecific bonebeds
some sauropod and ornithopod trackways show many sets of footprints, all from the same species of dinosaur and all heading in the same direction
these trackways suggest that the dinosaurs that made them were traveling together as a group
What are monospecific bonebeds?
large accumulations of fossil bones that are all from multiple individuals of the same species
monospecific bonebeds are known for many kinds of dinosaurs, including ceratopsians, hadrosaurs, and tyrannosaurs
monospecific bonebeds are often interpreted as nonrandom samples, and an explanation is needed for why only one species is included
What are some explanations of why monospecific bonebeds form?
one obvious explanation for this nonrandom sample is that the particular species was traveling in a group and that the group collectively met the fate that ultimately resulted in their fossilization (such as dying in a flash flood, a mud or rock slide, or a massive volcanic ash fall)
sometimes we find articulated skeletons in close association with one another, and this is strong support for social behavior
How can skeletal adaptations for attack and defense change ontogenetically?
juvenile Pinacosaurus lacked the heavy armor of adult ankylosaurs, which may be why they lived in groups of juveniles
juvenile Tyrannosaurs may have employed different hunting strategies compared to adults
juvenile Tyrannosaurs had proportionally longer legs, which would have made them more fleet-footed than the stockier, more heavy-built adults
What does the presence pathologies tell us about the interactions between dinosaurs?
they can include healed injuries or other evidence of diseases, such as infections, cancer, or arthritis
the cause of many pathologies can have multiple interpretations, so it is important to be cautious when extrapolating from evidence of pathologies
What is nonlethal face biting?
several Tyrannosaur skulls show signs of healed bite marks that can only have been made by other Tyrannosaurs
because the injuries had time to heal, these bite marks cannot have been formed by a Tyrannosaur killing and feeding on the carcass of another
nonlethal face biting is a common agonistic behavior among modern carnivores, such as crocodiles, and so Tyrannosaurs may have engaged in a similar behavior
