ATH2100LÂ LAB 5: READING
DIRECTIONS: Please read the materials that follow and then complete the Lab 5 Quiz on PILOT.
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By the time you finish reading these materials, you should be able to answer the following questions about primates:
1. What ancestral traits do primates share with other mammals?
2. What derived traits characterize primates compared to other mammals?
3. What is the value of studying primates to understand human evolution?
Primates are mammals (and therefore, so are you!)
Taxonomic classification organizes organisms based on shared characteristics due to common ancestry. The Linnean classification system is a nested hierarchy that becomes more exclusive with each taxonomic level (for example, a phylum contains more groups than a class and so on). Below is the taxonomic classification for modern humans.
Linnean Classification of Human
GENERALÂ KINGDOMÂ AnimaliaÂ (weâ€™re ANIMALS)
PHYLUMÂ ChordataÂ (weâ€™re animals with SPINAL CORDS)
CLASSÂ MammaliaÂ (weâ€™re a kind of spined animal MAMMALS)
ORDERÂ PrimatesÂ (weâ€™re a type of mammal called a PRIMATE)
FAMILY HominidaeÂ (includes us and apes, aka HOMINIDS)
(exclusive)Â SPECIESÂ Homo sapiensÂ (weâ€™re a special group called HUMANS)
From this classification, we see that modern humans are grouped within the order Primates which falls within the class Mammalia. This means that humans are primates, a special type of mammal that shares a common ancestry with OTHER mammals. As a result of this ancestry, primates and mammals share manyÂ ANCESTRAL TRAITS.
Mammals are diverse. On the surface, it may seem hard to find similarities between humans and a dog or cat, etc. However, we all share traits found in our common mammalian ancestor that indicate a closer evolutionary relationship among all animals grouped within the Class Mammalia than other animals.
1.Â Homeothermy/endothermy: Mammals have the ability to regulate body temperature. This means mammals can adapt to different climates.
2.Â Heterodonty: Mammals have different types of teeth. Mammals have four kinds of teeth with different shapes and characteristics:Â incisors,Â canines,Â premolars, andÂ molars. Other animals, such as crocodiles and sharks are homodonts (the teeth are all the same).
3.Â Viviparity: Mammals have internal gestation and give birth to live young (there are a few exceptions). Young are then dependent upon the mother for milk produced byÂ mammary glands.
4.Â Pentadactyly: Mammals have five fingers and toes. The basic structure of the mammalian â€śhandâ€ť and â€śfootâ€ť is similar, but many groups have modified this condition (i.e. ungulates have hooves, felids have paws with claws). Primates retain the primitive structure of pentadactyly.
5.Â Brain: The mammalian brain tends to be larger for body size compared to other vertebrates. Mammals also have a unique area of the brain known as the neocortex. TheÂ neocortexÂ is involved in higher level functions such as spatial reasoning and sensory perception. This area reaches its greatest expansion among primates.
What makes primates different from other mammals?
Primates are defined by a group of features, known asÂ DERIVED TRAITS. Derived traits are modified from the ancestral (in this case, mammalian) condition. The tricky thing about ancestral and derived traits is that their status (or polarity) depends on the context. For example, if we are comparing mammals and primates, the features below are consideredÂ DERIVED. However, if we are comparing different groups of primates, those same features are consideredÂ ANCESTRALÂ because all primates share them.
In the next lab, you will explore more in-depth what distinguishes primates from other mammals. Here are a few key features of primates:
1.Â Vision:Â Vision is the most important sense for most primates. They haveÂ forward-facing eyesÂ andÂ stereoscopic vision. This means that a primateâ€™s eyes are located in the front of the skull. This allows the fields of vision to overlap, and provides depth perception (very important if you primarily live in the trees). Furthermore, the primate eye socket featuresÂ post-orbital closureÂ orÂ aÂ post-orbital bar. You will explore this characteristic more in Lab 6.
2.Â Hands, feet, and limbs: Primates retain the ancestral condition of pentadactyly. They also haveÂ prehensileÂ (gripping) fingers and toes,Â nails instead of clawsÂ (with some exceptions),Â tactile pads, and anÂ opposable thumb. Primates also have very flexible and generalized limbs that allow us to locomote (move) in many different ways.
3.Â Brains and speed of growth: As mentioned above, primate brains are more complex than other mammals, and our brains tend to be larger than expected for body size (this is seen to the extreme among hominins). Primates also featureÂ longer gestationÂ periods andÂ slowerÂ postnatal growthÂ than most other mammals.
The utility of non-primates for understanding evolution
Non-human primates (NHP) are fascinating because they are so like us in both appearance and behavior (and many are very cute!) NHP studies help us to understand:
a) the relationship between dental and skeletal form and their behavioral functions (to reconstruct things like locomotion, group structure, and diet in fossil species),
b) the evolutionary underpinnings of some of our behaviors (tool use, group living, social politics, etc.)
c) evolutionary processes, adaptation, and speciation.
HOWEVER, we have to remember that extant NHP are not â€śliving fossils,â€ť and they were evolving and changing long before hominins (our ancestors) ever came on the scene. Therefore, we must be cautious in our use of NHP as analogies for hominin evolution.