Many of the most important and diagnostic mammalian characteristics serve to further intelligence and sensibility, promote endothermy, or to increase the efficiency of reproduction or the securing and processing of food.

Basic structural body plan is inherited from Therapsid mammal-like reptiles.

Survival through mammalian evolution was perhaps due to their ability to move and to think more quickly than their Archosaurian counterparts.

Morphological trends were toward structural simplification:
    • skull and jaw bones lost or reduced in size
    • limbs and limb girdles simplified, reduced, and less laterally splayed

Fossil record provides little evidence on when endothermy actually developed.

Diagnostic or Distinguishable Characteristics of Mammals:

Soft Tissues
Skin glands:  Mammalian skin contains several kinds of glands not found in other vertebrates.
    Mammary Glands: Provide nourishment for the young during their postnatal period of rapid growth.
    Milk Composition: Milk composition varies with species:
    Cow’s milk 85% H2O
    Dry weight 20% Fat
                     20% Proteins
                     60% Sugars - largely lactose
    also have sweat, sebaceous, scent, and musk glands

Hair: bodies of mammals typically covered with hair, which has no structural homology in other vertebrates.
    - perhaps developed before a scaly covering lost in Therapsid reptiles
    - consist of dead epidermal cells that are strengthened by keratin

Fat and energy storage:
Fat and adipose tissue but are of vital importance as:
    • energy storage
    • a source of heat and water
    • thermal insulation
    Lives of many mammals punctuated by times of crisis when food is in short supply or energy demands are usually high

Circulatory system:
    Highly efficient system with four-chambered heart acting as a double pump
        The RIGHT side receives venous blood from the body and pumps it to the lungs for oxygenation.
        The LEFT side receives oxygenated blood from the lungs and pumps it to the body.
    Erythrocytes biconcave, enucleated disk as possible mechanisms for increased oxygen-carrying capacity.

Respiratory system:
    Lungs are large and, together with the heart, virtually fill the entire thoracic cavity.
    Movements of air into and out of the lungs and volume of exchange due primarily to muscular diaphragm.

Reproductive system:
    Both ovaries are functional and the ova is fertilized in the oviducts.
    Embryo develops within the uterus and lies within a fluid-filled amniotic sac
    Nourishment for embryo comes from the maternal blood stream via placenta
    Male testes typically contained within the scrotum outside the body cavity

Brain:
    Enlargement of the brain’s cerebral hemisphere
   Neopallium - functions as center for sensory stimulus and initiation of motor activity

Sense organs:
    Sense of smell acute as a result of development of the turbinate bones
    Olfactory lobes enlarged in carnivorous and insectivores but lost in porpoises and dolphins
    Hearing highly developed due to three middle ear bones: malius, incus, stapes, and external pinnae.
   Tapetum lucidum - reflective structure within choroid that improves night vision by reflecting light
   Vibrissae - tactile hairs/whiskers in the muzzles and lower legs of some mammals.

Digestive system:
    salivary glands are present -specialized in anteaters: mucilaginous material makes the tongue sticky

Musculature system:
    Limb and trunk musculature highly plastic
    Variations for high speed locomotion

The Skeleton
Basic changes from Reptiles to Mammals
    • simplification of skeletal elements
    • reduction in the size and number of bones
    • limbs and girdle systems simplified
    • axial skeleton becomes more rigid
    • ossification of large parts of the skeleton
    • development of epiphysis and diaphyses
    Skull
    • increased brain case size
    • sagittal and lambdoidal crest increased
    • temporal muscle origin
    • zygomatic arch protects eyes and provides an origin for the masseter
    • turbinal bones within the nasal cavity (improved smell/saturation of air)
    • foramina allow passage of cranial nerves
    • 3 middle ear ossicles
    • dentary bone articulates directly with the squamosal
    • hyoid apparatus supports trachea, larynx, and base of the tongue
    Teeth:
    • Heterodonty - specialized for feeding/diet
    • Originate in the premaxilla, maxilla, and dentary
    • Dentine covered by enamel
    Axial skeleton - limbs and girdles:
    • five well-differentiated vertebrae: cervical, thoracic, lumbar, sacral, caudal
    • sternum well developed to form a rigid rib cage
    • limb motion generally restricted to fore-aft directions in distal joints; more solid hip and shoulder attachments
    • pelvic girdle has characteristic shape: illium projecting forward and ischium and pubis back - all solidly fused
    • standard pattern of bones in manus and pes (hand and foot) 2-3-3-3-3

Diagnostic Mammalian Traits:

Pelage = hair
Ears
Mammary glands
Diaphragm
Left aortic arch
Enucleated erythrocytes
3 middle ear bones
Single dentary
Dentary/squamosal jaw articulation

Studying the evolution of Mammals:
    • helps us understand where and why they are distributed
    • understand evolution
    • understand our past

Geologic Time
 
 

Eras:
   Precambrian or Protozoic- to 570mya
        First life - algae, bacteria, worms
   Paleozoic (old) - 570 - 225mya
        Age of fishes
   Mesozoic (middle) - 225 - 65mya
        Age of reptiles  ~20 reptilian orders
   Cenozoic (recent) - 65mya to present
        Age of mammals  ~30 mammalian orders

Mesozoic mammals tended to be somewhat insignificant - limited fossil evidence indicated holding  to conservative mouse-like form and quadrupedal locomotion

Dramatic adaptive burst following the extinction of the dinosaurs

Why so many mammals in such a short time?
   Plate tectonic and continental drift
Mesozoic - Pangea 230 mya
               Laurasia - Europe and Asia - northern
               Gondwanaland - India, S. America, Africa, Antarctica, Australia, southern

When mammals arose, continents were fairly close together
    - pieces breaking off with groups of mammals
    - different conditions evolved different mammals
    - geographic isolation

Mammals evolved from Synapsid reptiles

1. old reptile group
2. past its peak prior to dinosaurs
3. competition from other reptiles
4. named for skull type
5. two important orders - Pelycosauria (primitive) and Therapsida (advanced)

1. allow jaw muscles to bulge
2. more surface area for muscle attachment
3. lighter skull
4. opening thickened around edges due to pressures

Order Pelycosauria 1. primitive order that gave rise to the Therapsids 2. first group to depart radically from the basic reptilian design = 300mya 3. “bowl lizards” pelvic structure allowed organs to be carried off of the ground- increased agility 4. many changes in size, teeth, skulls, jaw musculature 5. many forms evolved 6. may have had increased body temperature, appetites, and feeding effectiveness

Dimitrodon 1 1/2 - 3m long Predaceous - jaws deep, bigger muscles, canines developing and lots of sharp teeth - no true heterodonty Unique sail structure - display and/or thermoregulation. Order Therapsida 1. term refers to characteristic mammal-like arch of the cheekbone- may be for harder bite 2. size variable from a rat to a bear 3. limbs thin, and body raised off ground- faster, more active? 4. secondary palate developing 5. dentary becoming larger 6. phalangeal formula develops 2-3-3-3-3 7. chemical communication develops- sites for well developed vomeronasal organs 8. fossils suggest smooth instead of scaly skin- no indications of hair 9. thought to have laid eggs, but no remains have been located egg guarding =» egg brooding =» egg retention =» live birth 10. milk evolved from secretions to keep humidity high in egg brooders? 11. middle ear bones developed- allowed for higher frequencies to be heard: hearing sounds of insects - insectivory- (maybe) - tooth differentiation

Order Therapsida; Infraorder Cynodontia (dog tooth)

- basal stock for mammals
- about 2m in length
- highly cursorial (limbs rotated)
- well developed secondary palate
- reduction in number of lumbar ribs = probable development of diaphragm
- elevated metabolism . . . Why?
    • diaphragm present - efficient respiration, more active
    • locomoter efficiency
    • histiological bone examination - no growth rings, Haversian canals - cell deposition, vessel patterns
    • location of fossils - 60° latitude, no good hibernation sites for some, must produce heat to survive
    • homeothermy - insulation, sweat glands = hair??  Evidence for hair vibrissae pits on cynodont skulls
    • heterodonty - came with increased locomoter efficiency - probably with increased oxygen uptake

Greater mastication prior to swallowing - increased surface area for better enzyme action

Dentary-Squamosal jaw articulation developing with reduction of the quadrate and articular - become free to aid in transmission of sounds and vibrations.

Secondary palate increased surface area of the nasal cavity
    - allowed for simultaneous mastication and respiration
    - warm, moisturize, and clean air
    - increase sense of smell - chemical smells/pheromones (vomeronasal organ)

Masseter muscle has essentially the same attachment as in modern mammals - insertion on lateral surface of dentary and originates on the zygomatic arch; enhanced control of transverse jaw movement.

First Mammals - after Cynodonts
    ~ 10cm long
    20-30gm
    long snouts
    rows of complex teeth - probably insectivorous
    partially arboreal
    probably nocturnal - favored by endothermy

Early mammals were small - at least an order of magnitude smaller than Cynodonts
     - arose in Triassic
     - stayed small with Cretaceous (140mya)

Why stay small?
    - competition from moderate-sized non-dinosaur reptiles (turtles, crocodiles) - probably not, lived in different habitats
    - competition from small immature dinosaurs - carnivorous when young
    - lacked sophisticated evaporative cooling mechanism
    - more important features were evolving than size:  maternal care, soft anatomy, and physiology each demonstrated by similarities between therians and non-therians

Mesozoic Mammalian Radiation
Current evidence indicates that mammals probably evolved monophyletically from cynodont reptiles

Early mammals displayed structural features that distinguish them from even the most advanced cynodonts:

1. In species of like body size, the morganucodontid brain was three or four times larger than that of even the most advanced therapsids, a reflection perhaps of greater neuromuscular coordination and improved auditory and olfactory acuity.
2. The condyle of the dentary bone fit into the glenoid fossa of the squamosal bone.
3. The cheek teeth were differentiated into premolars and molars, and the premolars were probably preceded by deciduous teeth.
4. Chewing was on one side of the jaw at a time, and the lower jaw on the side involved in chewing followed a triangular orbit as viewed from the front
5. During chewing, the inner surface of the upper molars sheared against the outer surface of the lower molars.
6. The cochlear region of the skull was far larger and more conspicuous ventrally than in cynodonts.
7. Body weight, probably 20 to 30 grams, was an order of magnitude smaller than in any Middle Triassic cynodont .
8. The pelvis was esscntially mammalian, with a rodlike ilium and a small pubis .
9. As part of a series of specializations allowing rotary head movement, the dens of the axis was large and protuberant and fit into the atlas.
10. The thoracic and lumbar vertebrae arched dorsally, the thoracic vertebrae had narrow, posteriorly directed neural spines, and the lumbar vertebrae bore dorsally directed neural spines.

Early radiation best described as a dichotomy between two early groups, the Kuehneotheriidae and Morganucodontidae.
 

Morganucodontidae - basic triconodont molar - may have evolved triconodons, docodonts, and monotremes. Kuehneotheriidae- triangular molars - may have given rise to the therians (symmetrodonts, pantotheres, marsupials, and eutherians)

 Increasing evidence indicates more complex relationships among early mammals - only the monotremes, marsupials, and eutherians survive today.
 

Order Triconodonta - late Triassic early cretaceous - one of the oldest primitive prototherians - predaceous - largest = house cat size - heterodont - 14 teeth in dentary - canines large - molar cusps 3, arrangement in front-to-back row Order Docodonta - late Jurassic - roughly quadrate teeth -cusp not aligned anterioposteriorly Order Symmetrodonta - late Triassic to late Cretaceous - probably predaceous - 3 fairly symmetrical cusp

 

Order Multituberculata - first appeared in the late Jurassic period to Tertiary - first mammalian herbivores - wide spread in both the old and new worlds - Ecologically equivalent to rodents - strongly built lower jaw with attachment for powerful jaw muscles - 2 or 3 incisors - diastema in front of premolars, 3 parallel cuspules - olfactory lobes enlarged

It has been generally accepted that eutherians and metatherian mammals evolved from the Order Pantotheria
    - profile of the ventral border of the dentary bone is interrupted by an angular process
    - the lower molar has a posterior “heel” which is separated by the talonid
    - the trigonid section of the pantotheric lower molar and the triangular upper molar resemble the corresponding teeth of some primitive eutherians and metatherians

During the Cretaceous, land dwellers were banned from intercontinental movement by oceans and seaways
    - populations of mammals on different continents evolved in isolation under different environmental conditions
    - earliest known marsupials are from late Cretaceous Canada, Westerns N.A. and Peru.
    - mammalian radiation coincided with a burst of flowering plants (Angiosperms), Lepidoptera (moths and butterflies), Isoptera (termites), and Coleoptera (beetles).
 
 

Partial Classification of Mammals                    ? = Extinct

Kingdom Animalia
    Phylum Chordata
    Subphylum Vertebrata
        Class Mammalia
            Subclass Prototheria
                Infraclass Eotheria ?
                    Order Tricodonta ?
                        Family Morganneodontidae ?
                    Order Docodonta ?
                        Family Docodontidae ?
                Infraclass Ornithodelphia
                    Order Monotremata
                        Family Tachyglossidae
                        Family Ornithorhynchidae
                Infraclass Allotheria ?
                    Order Multituberculata ?
                        (?) Family Haramyidae ?
            Subclass Theria
                Infraclass Trituberculata ?
                    Order Symmetrodonta ?
                        Family Kuchneotheriidae ?
                    Order Pantotheria ?
                Infraclass Metatheria - all marsupial mammals
                Infraclass Eutheria - all placental mammals
 
 

Monotremes and Marsupials can easily be considered apart from other mammals

Marsupials diverged from Eutherians ~100mya
 
 

Represented by three genera, each with a single species. Monotreme translates into "one-hole" - refers to the presence of a cloaca, a single reproductive/excretory outlet

Monotremes retain many reptilian traits:

• egg-layer - incubate in a bird-like fashion
• extra bones in pectoral girdle - more rigid than therians’ interclavicle, clavicles, precoracoids, coracoids
• epipubic bones
• splayed stance and carriage
• no lacrimal bones
• reproductive tract
• cloaca, shell gland, penis-no baculum, seminal vesicles, prostate, testis abdominal
• cervical ribs
• lack vibrissae
• brain not well developed - no corpus collosum, reduced convolutions
• no auditory bullae - surrounded by tympanic rings
• lack mammae - no nipples - young suck milk from two lobules in a temporary pouch

Refers to the diet of many, but . . . taxonomic uncertainty and disagreements on classification are causing many problems - the order serves as a convenient "catch-all"

Most primitive eutherian order

Third largest order with ~77genera and 400spp.

Originally thought to have evolved in Old World (Europe and Asia) and moved into the New World

- usually small
- long narrow snout
- 5 clawed digits
- usually short, close-set fur
- anterior vena cavae paired
- pinnae small to absent
- minute eyes - some covered with skin
- scrotum when present anterior to penis
- most insectivorous
- terrestrial, fossorial, semiaquatic
- plantigrade - heels touch ground when walking

Second largest order of mammals with ~170 genera and 850 species

Characterized as the only mammal to have evolved true flight

Represents the most poorly understood/misunderstood groups of mammals

Relatively recent biological research has revealed:

• extraordinarily complex social behavior, including harems maintained by males and complex vocalizations
• coordinated neuromuscular and behavioral adaptations allowing detailed perception of prey and their environments by the use of sound
• unsurpassed ability to conserve daily energy or survive through periods of stress by drastic reduction of metabolic rates

Frequently abundant members of temperate faunas but reach their highest densities and greatest diversities in tropical and subtropical areas

Bats occupy a number of terrestrial environments, including:

• temperate, boreal, and tropical forest
• grasslands
• chaparral
• deserts
• also man-made structures afford excellent roost sites and agricultural areas having high insect abundance

Because of their small size, ability to fly, delicate structure, and greatest abundance in tropical areas where fossilization rarely occurs, but fossils are rare
 

Icaronycteris index - from Eocene beds in Wyoming the oldest known undoubtable bat material first described by Jepsen in 1966 claws on the first 2 digits of the hand fairly short, broad wings Other fossils prove insectivory during Eocene - moth scales in gut Late Eocene and Oligocene deposits in France have shown evidence for Microchiroptera families Emballonuridae, Megadermatidae, Rhinolophidae, and Vespertilionidae Megachiroptera appeared in Oligocene in Italy

Fossil record shows little change in some families since Eocene, indicating good adaptations to their particular environments - a sharp contrast to Oligocene horses which were sheep-sized and 3-toed

The most important feature about bats is their adaptation for flight
 

bones of the arm and hand (except thumb) are elongated and slender

 

flight membranes extend from the body and hind limbs to the arm and the 5th digit, between the fingers, from the hind limbs to the tail, and from the arm to the occipitopollicalis muscle - patagia

 

the hind foot is free from flight membranes, which may extend to the ankle Uropatagium (tail membrane) may not always be present as in the tail - multiple combinations

 

ears usually have some form of a tragus - flap in the front part of the ear - different shapes in different species

 

Calcar may or may not be present - bony element extending off the foot which helps to support the uropatagium - may also be keeled (cartilagenous extension)

 

Shoulder Modifications: enlarged tuberosity of the humerus locks against the scapula at the top of the upstroke

• serratus anterior muscle tips lateral edge of scapula downward to help power downstroke
• adductor and abductors of the forelimb raise and lower the wings (major muscles of flight) contrast with flexors and extensors of terrestrial mammals
• the clavicle articulates proximally with the enlarged manubrium and distally with the acromion process and base of the coracoid process

• rotated either 90 to the side from the typical mammalian posture - reptilian posture - or 180? - spiderlike posture - used for suspending the animal upside down
• reduced to conserve weight
• fibula usually reduced
• support for the uropatagium, in the form of the calcar

• considerable advantage in metabolic economy to reduce distal components of the wing - must move faster as compared to proximal portion
• light wings are easier to control with speed and precision during rapid maneuvers associated with chasing insects
• movement of the elbow and wrist joints limited to one plane - elimination of musculature involved in rotation and bracing
• extension and flexion of the wing transferred from distal muscles of the forearm and hand to large proximal muscles (pectoralis, biceps, triceps)
• addition of connective tissues with muscle reduction to "automatically" extend the chiropatagium with extension of the elbow

ORDER PRIMATES

Primates represent the 7^th largest order with 51 genera and 168sp

• 16 genera and 50 species in the New World
• often considered to be the most important mammals (ego)
• no one denies that modern man is primate yet . . .
• few people understand why man is classified with animals such as the tree shrew, loris, and aye aye
• anthropologist have difficulty in defining what man is
• primates (living or fossil) are defined by an overall pattern
• The fossil record is from the:
• Palocene and Oligocene of North America and Europe
• Miocene of Africa and Europe
• Pleistocene and recent of South America, Asia, Africa, and Madagascar

Order Scandentia - tree shrews as primates

• Appearance - don't look like primates but internally primate-like, can't base on superficial appearances
• Multiple breast pairs - have them but reduced in number, 1-3 pairs primitive condition
• Muzzle too long - but shorter than most insectivores - baboon’s long
• External and middle ear - external human-like, middle ear primate-like
• Olfaction - rely on hearing, primates are more vision oriented with increase in brain section for vision
• Vision - poor binocular but retina is primate-like
• Throat-chest scent glands - lower primates scent mark
• Nonprehensile feet and hands / not opposable but is moveable
• No baculum or os clitoris bones - neither do humans
• Multiple births - primates don't usually, but more primitive groups do
• Maturation period too short - mature quickly rather than slowly - lots of differences in recognized primates
• Brain size relatively large in proportion to the body
• Blood/serological test closer to primates
• Social behavior poorly developed

Rhinarium - fleshy pad with moisture glands on end of nose - cool and wet

Most nonhuman primates occur in tropical areas - because of cultured and biological plasticity man adapts to most biomes
 
 

Centers around adaptation to tree life and arboreal existence, secondarily evolved for life on the ground

Qualities to exploit forest canopies:

• behavioral plasticity - adaptation allows change at a second’s notice

• general anatomy - "plain"
• neurologically complex
• individuality - nervous system allows quick thinking
• large cerebral centers devoted to hands, thumbs, and vocal areas

• grasping extremities - holding on in trees
• opposable thumbs and toes
• pentadactyl
• grip powerful and precise, claws reduced to nails and more sensitive, friction ridges/callouses

• good vision - eyes in the front of the head

• nose reduced or rostrum dropped to move nose out of the field of view
• mobile limbs - propelled through the trees

ability to hold body erect - stand up to free the hands

Xenarthrans (armadillos, sloths, anteaters): underwent tertiary radiation in South America

Pholidota (pangolins) and Tubulidentata (aardvark): Old World groups, each of which has conservatively maintained a single structural plan.

 

Not of great importance but are remarkably interesting because of their unique structure and unusual ecological roles, large fossil types, and remarkable Tertiary radiation in South America

All share a series of distinctive morphological features:

• extra zygopophysis-like articulation (Xenarthrous) which brace the lumbar vertebrae
• incisors and canines absent
• cheek teeth, when present, lack enamel and each has a single root - continuous growing
• brain case usually long and cylindrical
• the hind foot is usually five-toed
• forefoot has two or three prominant toes with large claws

An ancient, profitable (and honorable) occupation

Appeared in the early Paleocene (Creodonts) before most of the recent mammalian orders

Probably evolved in response to the food resources offered by expanding array of herbivores

Most recent carnivores are predaceous and have a remarkable sense of smell

General Characters:

• larger brain case
• good sense of smell
• well-developed canines
• small incisors - usually 3/3
• shearing and crushing teeth
• many have carnassial pair P⁴/m₁
• cheek teeth vary
• "long faced" - P 4/4, m 2/3 - dogs, bears
• "short faced" - P 2/2, m 1/1 - cats
• transverse mandibular fossa - good for biting, not for grinding
• reduced or absent clavicle
• plantigrade or digitigrade
• well-developed scent glands

 

Mysticeti - baleen whales 11spp.

Odontoceti - toothed whales 67spp.

Noted as being mammals that are most fully adapted to aquatic life

Fossil information indicates cetaceans are an old and successful group:

• swimming ability
• capacity to echolocate in many
• social behavior

intelligence?

About half of all mammals currently alive are rodents

Plants are the most abundant food source - rodents adapted as herbivores to take advantage of this food supply

30 families
418 genera
~1750 species

Why so successful?

• nearly cosmopolitan in distribution
• exploit a broad spectrum of foods
• important members of most terrestrial faunas
• often reach extremely high population densities
• small size to utilize shelters and escape predation
• high fecundity - large number of offspring, some survive
• rapid population turnover - natural selection operates quickly

• Oldest from Paleocene of North America
• Ischyromyidae - represented by only a few teeth
• Eumegamys - largest known rodent about size of hippo, skull ~2 ft long
• Castoroides - Pleistocene beaver from Mississippi river valley ~7 ft long

Early divergence of suborders based on mandibles - Split by Tullburg (1899) and Wood (1985)

• single pair in each jaw
• roots and pulp cavities open and evergrowing
• outside enamel, inside dentine rub against each other - differential wear produces chisel edge
• good for gnawing, grasping and holding, piercing

• highly variable
• premolars may or may not be present
• some ever-growing, some rooted

Dentition best suited for herbivory but varies

Protrogomorphs

• Masseter muscles originate entirely on the zygomatic arch toward the placement of the origin of at least one division of the masseter on the rostrum
• represented only by Aplodontia rufa (Aplodontidae)

Sciuromorphs

• The insertion of the anterior part of the lateral masseter is shifted onto the anterior surface of the zygomatic arch and the adjacent part of the rostrum - improved gnawing and grinding
• The temporalis muscle is relatively large and the coronoid process is moderately well developed
• occurs in Sciuridae and Castoridae

Hystricomorphs The origin of the medial masseter from the zygomatic arch to an extensive area on the side of the rostrum passes through the often greatly enlarged infraorbital foramen occurs in Dipodidae and most Hystricognaths

Myomorphs

• The anterior part of the lateral masseter originates on the highly modified anterior extension of the zygomatic arch and the anterior part of the medialmasseter originates on the rostrum and passes through the somewhat enlarged infraorbital foramen
• occurs in many members of the Sciurognathi, including all members of the family Muridae

Cheek teeth and incisors perform distinctively different functions - musculature is required to move the lower jaws into power positions for teeth to function - "division of labor"

Rabbits, hares, and pikas are not a very diverse group but are important members of many terrestrial communities, and are nearly cosmopolitan in distribution and were only absent from Antarctica, Australia, and southern South America

Two families with 13 genera and 80 species

• Leporidae - rabbits and hares
• Ochotonidae - pikas

• Leporidae underwent most of it's early evolution in the Oligocene and Miocene of North America
• Ochotonidae originated in Eurasia and developed largest number in North America

Not a taxonomic term but is a general term for a large group of cursorial forms

The name implies that a hoof is present

Two Orders:

Perissodactyla - horses, rhinos, tapirs - "odd toed"
Artiodactyla - pigs, peccaries, hippos, camels, deer, antelope, cattle, sheep, goats - "even toed"

Exceptional cursorial ability - Why?

• evolved at same time Miocene grasslands were developing
• open country
• needed speed to avoid predators in the absence of trees

• reached peak in Eocene with their greatest diversity
• declined through Miocene
• few alive today

• peaked in Miocene following adaptive radiation
• may have out-competed Perissodactyls

Two factors determine speed:

• length of stride
• rate of stride (#/time)

Length of stride:
1) Lengthen the limb

• metacarpals and metatarsals elongate and fused - cannon bone
• other limb bones elongated

2) Loss or reduction of clavicle

• loss of clavical frees scapula and shoulder joint from a strongly fixed attachment to axial skeleton

\ scapula free to pivot and rotate about a point near its center allowing leg to move farther during stride
\ absorbs shock of foot striking ground and not transfered to entire body

• well developed muscles attached to spine
• flexed when legs under body , extended when legs outstretched

1) Extra joints

• total speed of foot depends in part upon the speed of each joint and the number of joints

\ each new joint = increase foot speed
\ greater number of joints moving in the same plane also increases the speed of the limb

• Digitigrade/Unguligrade - lift head off ground
• Phalanges and metapodials
• Scapula free
• Flexion of spine

• proximal migration of muscle masses
• gets weight away from extremites
• concentrates center of gravity
• insertion points migrate proximally - the closer the muscle to the insertion point the faster the response
• distal parts lighter (fewer muscles) - less energy needed to start/stop - oftern associated with a reduction in the bones
• plane of movement limited to one - fewer muscles needed

Mammals with no reduction in limb elements
 

Ungulates
 

4) Other specializations

Nuchal ligament
• heavy band of elastin connective tissue
• anchored to neural spine and occipital of skull
• helps to support head

Springing ligament
• found in both front and back feet
• evolved from muscles that flex digits
• originates on proximal 1/3 of cannon bone and inserts on phalanges
• foot on ground ® phalanges extended by weight, ligament stretched
• weight off foot ® ligament springs back and foot flips backwards

\ increases speed of foot without adding muscles

Feeding Specializations for Herivorous Diets:
1) Cheek teeth

• large teeth with complex occlusal surfaces
• premolars molariform - hypsodont
• diastema
• elongated jaw for broader teeth

• lack enzymes to digest cellulose - uses bacteria
• retention time varies but is long
• 30 - 45 hours in Perissodactyles
• 70 - 100 hours Artiodactyls

Microflora and Fauna:

• in caecum of Artiodactyls
• # bacteria est. 10¹⁰ - divide every 20 min.
• protozoa est. 10⁶ - divide every 2-3 days
• originally thought to only digest cellulose
• Also
• synthesizes vitamin B
• makes amino acids, simple proteins
• split urea into ammonia, fix N to make amino acids
• decompose complex carbohydrates, convert to fatty acids
• produce large quantities of CO₂ and Methane

General pattern of stomach activity:

• fill stomach rapidly and retire to safe spot to digest
• stomach large with 4 chambers
• rumen - paunch
• reticulum - honeycomb tripe
• omasum - psalterium
• abomasum - stomach of other mammals
• food swallowed into rumen and churned with micro flora and fauna
• regurgitated to mouth (cud) and chewed to mix with micro flora/fauna
• reswallowed
• mixed between rumen and reticulum
• enters omasum
• compressed and mixed more, 60 - 70% H₂O absorbed

enters abomasum - enzymatic hydrolysis of food and micro flora/fauna