Vertebrate Zoology Mr. Walker BHS Rodents to Bats Vertebrate Zoology Mr. Walker BHS

Evolution Rodents evolved some time around the end of the Cretaceous period about 65 million years ago.

Order: Rodentia The single largest group of mammals is the Rodentia. Most non-flying mammals are rodents: There are about 1,500 living rodent species (out of about 4,000 living mammals overall). 

Household pets? Most people are familiar with mice, rats, hamsters, and guinea pigs, which are commonly kept as pets.  Also includes beavers, muskrats, porcupines, woodchucks, chipmunks, squirrels, prairie dogs, marmots, chinchillas, voles, lemmings, and many others. 

Diversity Rodents are found native on all continents except Antarctica. One particular family of rodents, the Muridae, contains over 1100 species: over a quarter of all mammal species are rats, mice, voles, muskrats, lemmings, hamsters, gerbils, and other members of the Muridae. The capybara (shown at right), another South American species, is the largest living rodent. About the size of a pig, and reaching a maximum weight of 50 kg (110 pounds), the capybara is truly a rodent of unusual size.

Structural Adaptations Despite their great species diversity, all rodents share common features. Rodents have a single pair of incisors in each jaw, and the incisors grow continually throughout life. The incisors have thick enamel layers on the front but not on the back; this causes them to retain their chisel shape as they are worn down. Behind the incisors is a large gap in the tooth rows; there are no canines, and typically only a few molars at the rear of the jaws. Rodents gnaw with their incisors by pushing the lower jaw forward, and chew with the molars by pulling the lower jaw backwards. In conjunction with these chewing patterns, rodents have large and complex jaw musculature, with modifications to the skull and jaws to accommodate it.  Like some other mammal taxa, but unlike rabbits and other lagomorphs, male rodents have a baculum (penis bone).

Habitat Most rodents are herbivorous, but some are omnivorous, and others prey on insects. Rodents show a wide range of lifestyles, ranging from burrowing forms such as gophers and mole rats to tree-dwelling squirrels and gliding "flying" squirrels, from aquatic capybaras and muskrats to desert specialists such as kangaroo rats and jerboas, and from solitary organisms such as porcupines to highly social organisms living in extensive colonies, such as prairie dogs and naked mole rats (right).

Disease (Dz) carriers Rodents cost billions of dollars in lost crops each year, and some are carriers of human diseases such as bubonic plague, typhus, and Hanta fever. However, various rodent species are economically important as sources of food or fur in many parts of the world, and others are used extensively in biomedical research.

Idaho Squirrels Red Squirrels Fox Squirrels

Chiroptera (hand-wing)

Vertebrate Flight True flight is found in 3 vertebrate groups. Reptiles (Pterosaurs etc) Aves Mammalia Many vertebrate glider groups, including mammals, frogs, geckos, lizards, snakes, and fish.

Bat Evolution Date to Eocene epoch (50 mya) There are no intermediate forms - earliest bats are good bats. Underived characters include 38 teeth (compared to 44 for underived eutherian number). Earliest bat fossils are from the early Eocene of North America: Icaronycteris index As is often the case in biology, there has been a rather ugly controversy concerning the evolutionary history of the Big Bats (megachiropteran) and small bats(microchiroptera). Are they diphyletic or monophyletic?

Order Chiroptera The only true flying mammals worldwide suborders 17 families 170 genera 850 species suborders Megachiroptera-flying foxes of tropics Microchiroptera-worldwide

Some Weirdness. Bats do a number of interesting morphological things. Musculature differences. Forearm specialization. Modification of the shoulder. Hind limb rotation. Tricks w/ echolocation.

Characteristics Can carry rabies Small bats eat insects Large bats eat fruit Vampire bats (3 species) feed on blood:live in Central and South America 14 Species of Bats in Idaho

Little Brown Myotis Myotis lucifugus

Little Brown Myotis Just the facts: 6-9 grams may live to 25 years favors ponds and streams for foraging forages at about 13 mph, 3-6 m above ground mate in early autumn; fertilization in spring upon rousing; 50-60 day gestation move to maternity colonies of hundreds born after 30 minute labor in late May weighing1.5 grams reaches sexual maturity at 8 mos.

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Silver Haired Bat Lasionycteris noctivagans Feeds on small to medium sized flying insects over small water bodies in conifer forests. Found throughout Idaho

Big Brown Bat Eptesicus fuscus

Hoary Bat Lasiurus cinereus

Vampire Bat

Megachiroptera Pteropodidae 36 genera and 154 species of tropical and subtropical Old World fruit and nectar feeding bats. Predominantly nocturnal, with body sizes ranging from 15g to 1.6Kg. They do not echolocate like micro-chiroptera, they are specialized for feeding on fruit and nectar (note teeth and palates: they do not consume pulp), and they have odd eye structures.

Echolocation True echolocation occurs only in the Microchiroptera. Sound is produced in the larynx. Sound is emitted through the nose or the open mouth. Echolocation works in a similar way to sonar. Bats make calls as they fly and listen to the returning echoes to build up a sonic map of their surroundings. The bat can tell how far away something is by how long it takes the sounds to return to them. These calls are usually pitched at a frequency too high for adult humans to hear naturally. Human hearing ranges from approximately 20Hz (cycles per second) to 15 to 20 kHz (1000Hz) depending on age. In comparison, some bats can hear sounds up to 110 kHz in frequency. By emitting a series of often quite loud ultrasounds that either sweep from a high to low frequency or vary around a frequency, bats can distinguish objects and their insect prey and therefore avoid the object or catch the insect. Individual bat species echolocate within specific frequency ranges that suit their environment and prey types. This means that we can identify many bats simply by listening to their calls with bat detectors.