Rodentia--rodents I. Characteristics 1/1 ever-growing, curved incisors with beveled tips and enamel on anterior surface only no canines and a large diastema




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Order RODENTIA--rodents

I. Characteristics

1. 1/1 ever-growing, curved incisors with beveled tips and enamel on anterior surface only

2. no canines and a large diastema between the incisors and the cheekteeth (Figure 13-2)

3. Specialized zygomasseteric structure (Figs. 13-2, 13-3, 13-5)

A. Protrogomorphous

B. Sciuromorphous

C. Myomorphous

D. Hystricomorphous


4. Two types of lower jaw angle (Figure 13-4)

A. Sciurognathous

B. Hystricognathous


II. Families

1. Family Aplodontidae--Sewellel or mountain beaver (Figs. 13-6, -7, - 8)

A. protogomorphous, sciurognathous

B. dental formula 1/1,0/0,2/1,3/3

C. cheek teeth evergrowing, with a simple pattern

D. flattened, triangular skull shape; flask-shaped auditory bullae

E. stocky body; limbs short, no external tail

2. Family Sciuridae--tree squirrels, ground squirrels (marmots, prairie dogs), "flying" squirrels

A. sciuromorphous, sciurognathous

B. dental formula 1/1,0/0,1-2/1,3/3

C. cheek teeth rooted, with prominent cusps or ridges

D. supraorbital (incomplete postorbital) process large

E. tail generally long and bushy except in most ground squirrels


3. Family Castoridae--beaver (Figure 13-12, -13)

A. sciuromorphous, sciurognathous

B. dental formula 1/1,0/0,1/1,3/3

C. cheek teeth hypsodont, with prominent ridges; more or less parallel rows

D. tail large, broad and flat

E. hind feet webbed

F. large bodied

G. long guard hairs overly a fine, dense underfur.





4. Family Geomyidae--pocket gophers



  1. sciuromorphous, sciurognathous

  2. infraorbital foramen on rostrum, small, visible in lateral view

  3. zygomatic arch robust

  4. dental formula 1/1,0/0,1/1,3/3

  5. external, furred cheek pouches

  6. eyes and pinnae very small

  7. forefoot with powerful claws

  8. thickset body

  9. tail short





5. Family Heteromyidae--pocket mice, Kangaroo rats (Figs. 13-16, -17)

  1. sciuromorphous, sciurognathous

  2. infraorbital foramen relatively large, pierces the rostrum, visible in lateral view

  3. dental formula 1/1,0/0,1/1,3/3

  4. external, furred cheek pouches

  5. pinnae evident

  6. infraorbital foramen small, on rostrum.


6. Family Dipodidae--jumping mice, jerboas

A. hystricomorphous, sciurognathous

B. dental formula 1/1, 0/0, 1-0/0, 3/3

C. jumping mice are small, have a long tail, and long hind limbs







Superfamily Muridoidea--rats and mice (including murids and cricetids)

A. myomorphous, sciurognathous

B. dental formula 1/1, 0/0, 0/0, 3/3


7. Family Muridae--: Old World rats and mice [Figs. 13-28 to -32]



  1. occlusal pattern of cheek teeth forms chevrons by connecting three transverse cusps.




  1. Family Cricetidae

  2. Subfamily Sigmodontinae: New World rats and mice

    1. anterior cheek tooth with, at most, two pairs of cusps opposite each other; pairs may be united to form lophs.





  1. Subfamily Arvicolinae [Microtinae]: voles, lemmings, and muskrats

    1. complex occlusal pattern of cheek teeth of acute triangles; teeth are rootless

    2. frequently with compact body and short tail

    3. muskrats have a long, laterally compressed tail and partially-webbed hind feet.







HYSTRICOMORPHA

11. Family Pedetidae--springhaas

A. hystricomorphous, sciurognathous [Fig.13-34]

B. dental formula 1/1,0/0,1/1,3/3

C. cheekteeth are evergrowing with a simplified crown pattern


12. Family Erethizontidae--American porcupines [Fig. 13-42]

A. hystricomorphous, hysticognathous, but with angular process deflected internally

B. dental formula 1/1,0/0,1/1,3/3

C. pelage conspicuously spiny, with barbs

D. Tubercles on pads of manus to increase traction

E. paroccipital process short, never extending below bulla




13. Family Myocastoridae--nutria

A. hystricomorphous, hysticognathous

B. dental formula 1/1,0/0,1/1,3/3

C. hind feet webbed

D. tail round and scaly

E. paroccipital process long







14. Family Cuniculidae--pacas



  1. hystricomorphous, hysticognathous

  2. dental formula 1/1,0/0,1/1,3/3

  3. large rugose cheek plate, outer surface of zygomatic arch pitted; inner surface with deep depression.

15. Family Chinchillidae--chinchillas



  1. hystricomorphous

  2. angular process delicate and not strongly hysticognathous

  3. auditory canal oriented vertically and with accessory foramina at base

  4. dental formula 1/1,0/0,1/1,3/3

  5. cheekteeth evergrowing, pattern of lamellar plates










Order LAGOMORPHA-rabbits, hares, pikas

Characters

A. 2/1 incisors (Fig. 13-53)

B. fenestrated maxilla

C. scrotum anterior to penis (as in marsupials)

D. soles of feet entirely furred

E. hypsodont cheek teeth



FAMILIES

1. Family Ochotonidae--pikas (figs. 13-56, 13-57)

A. pinna short, no tail, short limbs

B. maxilla with one large fenestra

C. no supraorbital process


2. Family Leporidae--rabbits and hares (Fig. 13-58)

A. pinna long, pointed, tail distinct, hindlimbs long

B. highly fenestrated (lattice-like perforations) maxilla (fig 17.2); squamosals and parietals weakly fenestrated

C. supaorbital process present



What is the dental formula of leporids?




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