Mammalogy 4764 9/16/2009

Chapter 4

” Mammalian Origins



Amniota Feldhamer Table 4.1 Savage and Long 1986

Major Fig. 3.2, Vaughn, Fig. 4.1, Feldhamer groups Mammalian Origins of Overview Synapsida


Pelycosaurs and


Mesozoic Era appear Feldhamer Fig. 4.2 Era radiate Savage and Long 1986

Pelycosaur , musculature, and teeth Cynodontia -- Advanced, predaceous therapsids Scymnognathus

Early Derived Therapsid/Mammal Primitive

Late Cynodont

Fig. 3.2, Vaughn Fig 4.3 & 4, Feldhamer

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Skeletal transition of

Possibly competition from Pelycosaur Early Cynodonts were -size, last surviving were sized Fig. 4.15 Mammals that survived while Cynodonts went extinct (contemporary) were -sized.

Cynodont Thrinaxodon

Modern Mammal Fig. 3.5, Vaughn Fig. 4.16c, Early Cynodont

Early mammals Changes in land masses Feldhamer 4.11 200 - 250 million years ago Derived characters: Dentary/squamosal jaw articulation Diphyodont 200 MYA 180 MYA Mammary glands Secondary Early Mid- (loss of eggshell) When? Jurassic

65 MYA 135 MYA Early Early Cenozoic

Feldhamer 4.5, 4.9

Skull and teeth of mammals

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Teeth and Dentition of Mammals Teeth Heterodont teeth with different functions

Differentiated on the basis of function, resulting in increased One of the major keys efficiency acquiring and digesting . to success of mammals Teeth occur in 3 bones of skull: Teeth of mammals are , , dentary extremely variable with different diets -- more than other taxa

Feldhamer et al.

Incisors: rooted in premaxilla (upper) and dentary (lower) Additional Notes on Structure Often reduced in number with Not all teeth have enamel over a “diastema” in entire surface of tooth, results in differential wear

Open-rooted teeth grow continuously (e.g., ) Usually canines are lost

Canines: posterior to incisors, canadensis rooted in maxilla, dentary Molars and Premolars Function: piercing/tearing prey, holding, display, fighting vs. Herbivores Structure: moderately to very long Generalizations and exceptions (compared to other teeth), usually simple form (unicuspid), single rooted

Mammals have single canine in each quadrant of jaw if present. Never present in modern , often absent in herbivores

Often used in social displays or fighting.

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Brachydont: Low crowned teeth, typical of Most mammals are diphyodont which means they produce 2 sets of Hypsodont: high crowned teeth, typical of many herbivores teeth during lifetime ( teeth, permanent dentition)

High crown tooth Milk teeth consist of incisors, canines, and premolars. Molars only grow in as

Pattern of tooth replacement/eruption is well-ordered and - specific; tooth eruption schedules can be used for aging mammals

Tooth replacement is vertical except in a few species in which it is horizontal (, , )

Low crown tooth

Vaughn Fig. 2.22

Proboscidea Cheekteeth Cusp Patterns BUNODONT: Separate, rounded cusps for Functional teeth -- consequences of long -- crushing, grinding, typical of omnivores Single tooth active (may be adjacent one too) LOPHODONT: Cusps forming continuous ridges, or lophs, seen in herbivores -- 2nd upper SELENODONT: Cusps as lophs which are crescent- shaped and longitudinal, also in herbivores 40 million years ago

Examples of Selenodont Teeth DENTAL FORMULAS

Gazelle 1. Dental formulae are always given in the : incisors (I), canines (C), premolars (P), molars (M)

2. have 2 incisors, 1 canine, 2 premolars, and 3 molars = I2 C1 P2 M3, in each quadrant of their upper

3. The numbers for each quadrant of the lower jaw are the same; general formula for humans is written I2/2 C1/1 P2/2 M3/3.

White-tailed () 4. To calculate total number of teeth from dental formula, sum these numbers (2+2+1+1+2+2+3+3 = 16) then multiply by 2 16 X 2 = 32 total teeth in adult