In this lab, you will learn to identify the skulls of the mammals listed below.  The first list is the genera whose skulls you will be expected to be able to identify during a quiz at the end of this lab period as well as during the exam at the end of the semester.  The second list includes the species whose skulls you will be expected to be able to identify during the exam at the end of the semester, but will not be used in the quiz at the end of the lab period.  Use the STUDY AID FOR SKULLS to find the distinguishing characteristics of the skulls.  Work on these characteristics BEFORE the lab period.  Be especially attentive to number of teeth and family or order characteristics, as these may be particularly helpful to some students.

QUIZ AND EXAM

Didelphis
Scalopus
Lepus
Sylvilagus
Erethizon
Myocastor
Castor
Marmota
Cynomys
Dipodomys
Chaetodipus
Geomys
Reithrodontomys
Sigmodon
Neotoma
Ondatra
Cryptotis
Notiosorex

EXAM ONLY 
Sciurus
Spermophilus
Glaucomys
Perognathus
Rattus
Mus
Peromyscus
Onychomys
Baiomys
Microtus 

STUDY AID TO SKULLS

ORDER DIDELPHIMORPHIA

Didelphidae

Didelphis
1. 50 teeth (DF = 5/4, 1/1, 3/3, 4/4)
2. molars are tuberculosectorial (bearing cusps arranged in asymetrical triangles)
3. angular process inflected inwardly
4. nasals are long and expanded on the forehead in diamond shape
5. palatine has several foramina
6. jugal extends backward far enough to help form mandibular fossa
7. prominent sagittal crest

Talpidae-zygomatic arches complete, first incisors moderately enlarged projecting directly downward, teeth white

Scalopus
1. 36 teeth (DF = 3/2, 1/0, 3/3, 3/3)
2. auditory bullae completely formed

Soricidae-zygomatic arches incomplete, first incisors greatly enlarged and projecting conspicuously forward, anterior teeth tipped reddish or blackish

Blarina
1. 32 teeth (DF = 3/1, 1/1, 3/1, 3/3)
2. skull robust and strong, bones heavy
3. prominent sagittal crest
4. behind enlarged anterior teeth, 5 unicuspid teeth, first 2 of same size, 3 and 4 of same size but smaller than first two, 5th is minute

Cryptotis
1. 30 teeth (DF = 3/1, 1/1, 2/1, 3/3)
2. behind enlarged anterior teeth, 4 unicuspid teeth varying in size (last one is minute)
3. all teeth pigmented except last unicuspid

Notiosorex
1. 28 (DF = 3/2, 1/0, 1/1, 3/3)
2. Upper teeth 8 on each side, 3 unicuspid teeth above

Leporidae-28 teeth (DF = 2/1, 0/0, 3/2, 3/3)

Lepus
1. interparietal absent in adults
2. supraorbital processes broadly triangular and winglike

Sylvilagus
1. interparietal triangular shaped in adults
2. supraorbital processes narrower and more strap-shaped frequently touching or fusing with cranium

ORDER RODENTIA-incisors 1/1, diastema, side of rostrum not extensively fenestrated, number of teeth variable

Erethizontidae

Erethizon
1. infraorbital foramen exceeding foramen magnum in size
2. upper cheek teeth tilted to outside, lower teeth tilted inwardly
3. toothrows converge anteriorly
4. nasals tapered posteriorly, terminating well behind premaxilla at midorbit
5. paroccipital processes small, vertical and terminating above level of bottom of bullae
6. angular process arising at level of M₂
7. large coronoid process
8. depression between orbits
9. 20 teeth (DF = 1/1, 0/0, 1/1, 3/3)

Myocastoridae

Myocastor
1. infraorbital foramen exceeding foramen magnum in size
2. upper cheek teeth tilted to outside, lower teeth tilted inward
3. toothrows converge anteriorly
4. posterior ends of nasals terminate near ends of premaxilla
5. Paroccipital process greatly enlarged and projects beyond bottom of bullae
6. Angular process of mandible arising opposite P4, forming a broad shelf

Castoridae

Castor
1. reduced postorbital processes
2. infraorbital foramen small and inconspicuous
3. teeth hypsodont with complicated pattern of enamel loops
4. heavy zygomatic arch
5. 20 teeth (DF = 1/1, 0/0, 1/1, 3/3)

Sciuridae-teeth brachydont, crowns tuberculate (with rounded elevations), and capped with enamel, infraorbital foramen small and inconspicuous relative to size of skull, well-developed postorbital processes, number of teeth variable

Tamias
1. infraorbital foramen pierce zygomatic plate
2. postorbital processes small and extend posteriorly
3. 20 teeth (DF = 1/1, 0/0, 1/1, 3/3)

Marmota
1. infraorbital foramen passes between zygomatic plate and side of rostrum
2. dorsal profile almost straight, slightly depressed between postorbital processes
3. postorbital processes of frontals approximately at right angles to main axis of skull
4. skull broad, flattened dorsally
5. 22 teeth (DF = 1/1, 0/0, 2/1, 3/3)

Cynomys
1. infraorbital foramen passes between zygomatic plate and side of rostrum
2. dorsal profile convexed, not depressed between postorbital processes
3. postorbital processes of frontal directed obliquely backward
4. zygomata flattened horizontally and converging anteriorly
5. upper tooth rows strongly convergent posteriorly
6. lambdoidal crest prominent
7. molars much wider than longer
8. 22 teeth (DF = 1/1, 0/0, 2/1, 3/3)

Glaucomys
1. zygomatic arches compressed vertically
2. large tubercle (bump) situated on lower side of infraorbital foramen
3. interorbital region relatively narrow and indented on each side with a v-shaped notch

Spermophilus
1. infraorbital foramen passes between zygomatic plate and side of rostrum
2. dorsal profile convexed, not depressed between postorbital processes
3. postorbital processes of frontal directed obliquely backward
4. zygomata flattened horizontally and converging anteriorly
5. upper tooth rows approximately parallel
6. molars not greatly widened
7. lambdoidal crest weakly to moderately developed
8. postorbital processes more wide spreading
9. interorbital and postorbital widths approximately equal
10. large tubercle (bump) situated on lower side of oval or triangular infraorbital foramen
11. 22 teeth (1/1, 0/0, 2/1, 3/3)

Sciurus
1. infraorbital foramen passes between zygomatic plate and side of rostrum
2. dorsal profile convexed, not depressed between postorbital processes
3. postorbital processes of frontal directed obliquely backward
4. zygomata compressed vertically and more or less parallel
5. interorbital region relatively wide and not V-shaped
6. anterior border of orbit ventrally opposite M¹
7. two transbullar septa
8. tubercle (bump) on infraorbital foramen
9. number of teeth variable [S. niger-20 teeth (1/1, 0/0, 1/1, 3/3); S.carolinensis-22 teeth (1/1,0/0,2/1,3/3)]

Heteromyidae-infraorbital foramen small and inconspicuous, and situated well in frontof zygomatic plate, perforation through nasal septum connecting left and right infraorbital foramina through rostrum, nasal projecting anteriorly to incisors, 20 teeth (1/1, 0/0, 1/1, 3/3)

Dipodomys
1. mastoid region (auditory bullae) greatly inflated
2. zygomatic processes of maxillaries broadly expanded dorsally
3. upper incisors grooved

Chaetodipus
1. mastoid region (auditory bullae) not greatly inflated but visible dorsally
2. upper incisors grooved
3. broad zygomatic arch
4. interparietal very broad

Perognathus
1. mastoid region more inflated than in Chaetodipus, encroaching noticeably onto dorsal surface of skull and extending posteriorly beyond occipital
2. upper incisors grooved
3. interparietal narrower than interorbital region

Geomyidae-infraorbital foramen small and inconspicuous and situated on side of rostrum well in front of zygomatic plate, no perforation through nasal septum, nasals not projecting anterior to incisors, incisors strong and chisel-like

Geomys
1. upper incisors grooved
2. wide spreading zygomatic arches
3. long constricted rostrum
4. long external ear tubes
5. 20 teeth (1/1, 0/0, 1/1, 3/3)

Dipodidae-infraorbital foramen oval in shape, crowns of molars brachydont and with complicated pattern of enamel loops

Zapus
1. upper incisors grooved
2. 18 teeth (1/1, 0/0, 1/0, 3/3)

Muridae-infraorbital foramen V-shaped, crowns of molars either hypsodont and with prismatic (triangles or loops with sharp angles; geometric-like) crown patterns or brachydont and cuspidate (having cusps), 16 teeth (1/1, 0/0, 0/0, 3/3)

Rattus
1. supraorbital and temporal ridges present
2. upper incisors not notched from side view
3. molar teeth capped with enamel and upper molars with cusps arranged in 3 longitudinal rows (transverse ridges which run from side to side)

Mus
1. supraorbital and temporal ridges absent
2. upper incisors notched in side view
3. molar teeth capped with enamel and upper molars with cusps arranged in 3 longitudinal rows (transverse ridges which run from side to side)

Reithrodontomys
1. upper incisors grooved
2. cheek teeth rooted and bearing 2 cusp rows
3. skull rounded in profile

Sigmodon
1. upper incisors smooth
2. molar teeth with flat crowns consisting of cusps elongated into transverse lophs with M₂ and M₃ lophs forming sigmoid (S) shaped pattern
3. infraorbital foramen has notched border on dorsal side (encapsulated when viewed from above)

Peromyscus
1. upper incisors smooth
2. coronoid processes weak or only moderately large
3. palate ending at plane of M³
4. infraorbital foramen with straight dorsal border
5. molars with 2 cusp rows (outer and inner rows staggered)

Baiomys
1. upper incisors smooth
2. anterior cusp of M1 intermediate in alignment between the two rows of cusps
3. skull never exceeding 20 mm in length

Onychomys
1. upper incisors smooth
2. coronoid process large, broad and strongly recurved
3. anterior cusp of M¹ aligned with outer row of cusps
4. high-cusped cheek teeth

Neotoma
1. cheek teeth with crowns bearing prismatic patterns of dentine
2. M¹ and M² with middle loop undivided, extending completely across tooth
3. supraorbital and temporal ridge present
4. infraorbital foramen notched on dorsal border
5. cranium not constricted abruptly in interorbital region

Ondatra
1. cheek teeth with crowns bearing prismatic patterns of dentine
2. M¹ and M² with middle portion divided into a number of sharp-angled triangles
3. dorsal border of infraorbital foramen virtually straight
4. cranium abruptly constricted in interorbital region
5. basal length (front of incisive foramen to middle of foramen magnum) > 50 mm
6. postorbital processes nearly right-angled in shape and projecting into orbit as thin-edged shelves

Synaptomys
1. cheek teeth with crowns bearing prismatic pattern of dentine
2. M¹ and M² with middle portion divided into a number of sharp-angled triangles
3. cranium abruptly constricted in interorbital region
4. dorsal border of infraorbital foramen virtually straight
5. basal length < 45 mm
6. upper incisors grooved near lateral margin
7. zygomata slightly expanded in middle

Microtus
1. cheek teeth with crowns bearing prismatic pattern of dentine
2. M¹ and M² with middle portion divided into a number of sharp-angled triangles
3. cranium abruptly constricted in interorbital region
4. dorsal border of infraorbital foramen virtually straight
5. basal length < 45 mm
6. posterior border of palate supported by sloping median spine elevating palate above level of palatal pits
7. upper incisors not grooved
8. M² with four triangular islands of dentine surrounded by enamel 
9. M³ with three transverse loops