Rodentia.docx

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Department
Ecology & Evolutionary Biology
Course
EEB388H1
Professor
Engstrom
Semester
Fall

Description
Rodentia  Very large radiation  Variety of food habits and styles, typically herbivorous or granivorous, but many are omnivorous o Example: deer mice => most common rodent in Ontario o Refuted to be granivorous, but they mostly eat insects, fruit, and carrion (if they have access to it) o Rodents, in general, fill small herbivore niche  Incredibly difficult to classify within the order in terms of using morphology o The same type of skull morphology occur over and over again as convergences and parallelisms => rampant within the order o Within the order of rodents, you see a lot of conflicting classifications o Main classification of suborders was based on origin of masseteric musculature => muscle that is meeting the cranium and lower jaw for mastication o Complicated in rodents because they have a single pair of large, rootless incisors o Muscles are complex because when the incisors are working, the molars are disengaging vice versa  Hystricomorphous rodents have a large infraorbital foramen o Big hole in front of zygomatic arch o One of the masseteric muscles is passing right through it and originating in the lower jaw o Found primarily in Africa, Asia, and South America o Evolved in isolation primarily in African and South America when those continents were isolated from others o South American hystricomorphs were the only rodents in that continent prior to the GAI  There were also no ungulates in South America  Rodents filled ungulate-like niche => the largest rodent in the world (Capybara) in South America o Arrived in South America are approximately the same time as Platyrrhines arrived in South America  But how they got there is unknown because the two continents (Africa and South America) were separated at the time of origin of these two groups  Dispersal event => both hystricomorph and platyrrhine monkeys arrived there at around the same time  Sciurimorphous rodents do not have this big foramen, just a shield o Masseteric muscle originates of the arch o Squirrel-like rodents => have been difficult to classify because they are plesiomorphic rodents in terms of musculature and very hard to place phylogeny  Castorimorpha o Beavers (and sometimcs geomyodiae)  Myomorpha o The typical rats that we see in civilization o Largest suborder and over half of all rodents are in this suborder o Worldwide distribution  Most primitive rodent = Aplodontidae o One genus, one species o Does not live in the mountains (even though it is called “Mountain beaver”) o Typically placed in its own suborder but it IS in sciurimorph o Most primitive sciurimorph o Primarily herbivorous  They re-ingest their feces o Typical sciurognathous jaw, but have more teeth than typical sciuirds  Sciuridae o Three major groups => ground, tree squirrels, and flying squirrels  It was thought that flying squirrels evolved many times because they are found in many places => gliding evolved multiple times? NO they
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