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Reptile and Mammalian characters
- -Scaly skin
- -2-chambered heart
- -Lay eggs
- -Little parental care
- -Sprawling posture
- -Undifferentiated teeth
- -Small brain
- -Single occipital condyle
- -Single ear bone
- -Multiple lower jaw bones
- -Quadrate-Articular jaw joint
- -Hair for insulation
- -4-chambered heart
- -Live birth, suckle young
- -Extensive parental care
- -Upright posture
- -Precise tooth occlusion
- -Large brain
- -Double occipital condyle
- -Three ear bones
- -Single lower jaw bone
- -Squamosal-Dentary jaw joint
- -only lower temporal opening
- -Earliest amniotes to split from other reptiles
- -Dominant Permian early Triassic reptiles
- -Two subgroups (grades):
- -Pleycosaurs-dominant in early Permian
- 0Therapsids-dominant in late Permina and earlyTriassic
- -Gave rise to mammals in the late Triassic
- Mammal-like advancements over Pelycosaurs:
- -Enlarged temporal openings
- -Supratemporal bone loss
- -Reduction in palatal teeth
- -More forward jaw articulation
- -Notched reflected lamina on angular bone of lower jaw, across which a tympanum was stretched
- -Semi-erect posture
- Began in early Permian with Tetraceratops
- Became abundant in late Permian
Late Permian Therapsids
Zygomatic arch, enlarged dentary, some tooth differentiation, extensive secondary palate, double occipital condyle
Mammalian characters developed gradually in cynodonts and early mammals.
- Advanced therapsids: Cynodonts
- Upright posture allowed for running and breathing at the same time.
Morphology and metabolism in cynodonts
- More upright posture provided for more efficient running but required higher sustained metabolism.
- Reduction then loss of lumbar ribs in advanced cynodonts may represent development of diaphragm for more efficient breathing.
- Upright posture also provided for better running while breathing.
- Evolution of jaw musculature
- t-temporalis muscle
- From reptilian adductor
- Closes jaw quickly
- m-masseter muscle
- New in mammals
- Holds jaw shut tightly Allows lateral chewing
- Advanced Cynodont
- Tooth Occlusion
- -Precise occlusion required to slice food effectively for quick digestion.
- -Developed several times among herbivorous therapsids and later in mammals.
- -Finely-chopped food more surface area to allow enzymatic breakdown and the digestive track to exact energy (for high metabolism).
- Conversion of Jaw Bones to Ear Bones
- -Reptiles have single ear bone, the stapes.
- -Articular and quadrate form primitive jaw hinge.
- -Therapsid dentary expands - forms 2nd jaw hinge with squamosal.
- -In mammals the articular and quadrate bones move into the are to become the malleus and incus.
Advanced Mammal-like Cynodonts
- Tritylodonts (Late Triassic to early Cretaceous)
- -Herbivores with advanced, complex dentition
- -Deep lower jaw and zygomatic arch
- -Temporal part of skull and ilium very mammalian
- Tritheledonts (late Triassic to lower Jurassic)
- -Loss of postorbital bar as in early mammals
- -Loss of fusion between dentaries as in mammals
- -Jaw joint almost entirely squamosal-dentary
- -Girdles and vertbrae very mammal-like
- Very mammal-like, but are specialized herbivores and therefore not direct mammalian ancestors.
- -Poorly known from three genera from South Africa and South America
- -Skull and body mammalian in numerous aspects
- -Dentition suggests insectivory, similar to early mammals
- -Cingulum, or ridge, on lateral edge of upper cheek teeth
- incomplete late Triassic fossils
- -Abelobasileus only from a braincase
- Sharp reduction in size
- -skulls 20-30mm long
- -Body length less than 150mm
- Brain enlarged and enclosed in bone
- -Broad alisphenoid (from reptilian epipterygoid)
- -Orbitosphenoid (new in mammals, behind eye)
- -Periotic (petrosal) - 2 trigeminal nerve branches
- Early Jurassic morganucodonts more complete
- Reptilian jaw joint and extra-dentary lower jaw bones still present, but greatly reduced and used for hearing
- Squamosal/dentary form primary jaw hinge
- Anisognathus-lower jaws narrower than uppers
- Loosely-connected dentaries for chewing on one side
- Chewing occurred in triangular movements
- Teeth formed shearing survaces as they wore down
- Incisors, canines, and premolars each replaced once
- Molars are milk teeth and are not replaced
- -Small, shrew-like body, probably insectivorous
- -No lumbar ribs, suggesting a diaphram
- -forelimb cynodont-like, hindlimb fully mammalian
- -Long ilium, obturator foramen between ischium and pubis
- small body size and carnivorous teeth suggest insectivorous diet.
- Narrow range of body size suggests determinate growth (stops at adulthood).
- Evidence of high metabolism and enlarged sensory parts of the brain suggest they were endothermic and nocturnal.
- Late appearance of teeth suggests they may have suckled young with mammary glands.
- Placentals - fully-developed placenta
- Marsupials - juveniles live in mother's pouch
- Monotremes - living egg-laying mammals
- Multituberculates - odd teeth, early cenozoic
- Symmetrodonts - symmetrical teeth
- Triconotonts - three-cusped teeth
- Docodonts - dumbbell-shaped upper molars
- Morganucodonts - very primitive mammals
Theories of mammalian relationships
- old view=two parallel mammal radiations:
- -Prototherians: morganucodonts, docodonts, triconodonts, multituberculates, montremes
- -Therians: symmetrodonts, marsupials, placentals
- Clatists rejected prototherians as a clade in the 1980s (common characters are primitive).
- Then every possible phylogeny was proposed.
- Amazingly, an mDNA study links montremes to marsupials, to the exclusion of placentals (not supported by osteology).
- Two patterns in skull sidewall structure:
- -Morganucondontids and montremes similar
- -Marsupials and placentals different structure
- "Prototherian" condition primitive, does not demonstrate close relationship.
- But Marsupials and Placentals appear related.
- Kuehneotherium teeth
- -upper molar (a)
- -Lower molar (b)
- Docodon jaw (c)
- -Dumbbell-shaped molars
- Triconodon jaw (d)
- -molars with 3 cusps in a line
- Symmetrodont jaw (e)
- -Middle cusp offset lingually
- Dryolestid jaw and teeth (f)
- -Large coronoid process
- -New angular process
- Jeholodens from early Cretaceous of China
- Sprawling posture and plantigrade foot suggest ground-dweller
- Scapula resembles modern narsupials
- Teeth suggest an insectivorous diet
- Found with a spectacular fauna of dinosaurs and birds in Liaoning
- Most diverse mesozoic mammals
- survived to Eocene in Nebraska
- formed diastema (gap) between incisors and cheek teeth
- Blade-like Premolar 4 expanded and forced out other premolars
- Long fore-aft chewing stroke for grinding tough vegetation
- Grasping feet and strong tail suggest life in trees (arboreal)
- Epipubic bones suggest a pouch
- Lost out in competition with rodents
Characters of an effective chewing apparatus
- -upper and lower teeth need precise occlusion
- -tooth wear leads to changes in shearing fuction
- -Food gets packed between teeth, causing decay
- -cusps form that match between upper/lower teeth
- -minmal tooth replacement for continuity
- -Restructuring for good shearing at all wear stages
- -Basin develops for cusps of occluding tooth to fit in (rather than between two teeth)
- Mammals remained small but diversified during the Mesozoic.
- Improved teeth for chewing to support warm-blooded metabolism.
- Classified based on ear region and tooth shape.
Early Mammal Groups
- Triconodonts - simple teeth with three cusps in a row, the most primitive condition
- Docodonts - dumbell-shaped teeth, wide in skull and narrow in the lower jaw
- Multituberculates - teeth with multiple cusps, and the first tooth in the lower jaw grows and knocks out the others, had a gap in tooth row (like later rodents and rabbits)
The tribosphenic molar
- Culmination of Mesozoic mammal tooth evolution.
- Upper and lower cheek teeth occclude precisely.
- Good shearing from eruption to heavy wear stages.
- Cusps standardized=can be traced to later mammals.
- Starting point in evolution of marsupials and placental mammals.
- Upper molars
- -protocone - medial
- -paracone - anterolater
- -metacone - posterolateral
- Lowre molars
- -protoconid - external
- -paraconid - anteromedial
- -metaconid - posteromedial
- -entoconid - medial
- -hypoconid - lateral
- -hypoconulid - posterior
- The protocone (highest upper cups) fits into talonid basin
- Monotreme mammals
- -Lay and incubate eggs.
- -Suckle young from simple wet spot.
- -Poor thermoregulation
- -Retain interclavicle and coracoids (like reptiles)
- Australia/New Guinea only
- -Poor fossil record.
- -Ancestors unclear
- -Duck-billed platypus and echidna-spiny anteater
- most primitive living mammals
- Lay eggs
- Weak thermoregulation
- Restricted to Australia region
- Duck-billed platypus
- Echidna (spiny ant eater)
- Oldest fossils - Cretaceous of Australia and Paleocen of South America.
- Fossil teeth of early fossil platyplus approach tribosphenic condition.
- Southern cclade (Australosphenida) proposed for monotremes and some other southern hemisphere fossils, but grouping highly controversial.
- Monotremes?=purely Australian with only a brief venture into South America.
Certaceous Therian Ancestors
- Marsupials and placentals=therians.
- Vincelestes close relative - similare coiled cochlea, but lacks tribosphenic molar.
- Deltatheridium=early Metatherian, close relative of marsupials (same tooth replacement).
- Alphadon - didelphid (opossum) similar to living form.
- tooth formula: 3-5/2-4 1/1 3/3 4/4
- Monophyodont (only P3/3 replaced)
- Upper molars have broad lateral cingulum with large stylar cusps
- Lower molars have twinnedhypoconulid and entoconid
- Palatine foramina present
- Reflected angular process
- Coracoid still present
- Epipubic bone present
- Tooth formula: 3/3 1/1 4-5/4-5 3/3
- Diphyodont (all I, C, P replaced)
- Upper molars: crowns wider relative to length
- Palatine foramina absent
- Only in primitive forms
- Coracoid absent
- Epipubic bone absent
Stages of Mammal reproduction
- Monotremes lay eggs like reptiles - lack placenta.
- Marsupials - choriovitelline placenta - creates incompatibility during development.
- -young born prematurely - live in mother's pouch
- -young=lengthy nursing period, which may be why the incisors, canines, and most premolars are not replaced.
- Placentals - chorioallantoic placenta - allows extensive development in the uterus.
- Carry young in external pouch
- Opossums, kangaroos, etc.
- Originated in North America and spread to South america, Antarctica, and Australia
- Mostly replaced by placental mammals except in Australia
History of Marsupials
- Marsupials?=originated in Asia - immediate ancestors there.
- Most Cretaceous marsupial fossils = North America, ~half of late Cretaceous mammals.
- A few marsupials got to Asia and South America, presumably from South America across Antarctica to Australia (these continents still close).
- North American marsupials nearly wiped out in late Permian extinction
- Placentals survived and flourished.
- Didelphids spread North America to Europe, Africa, and Asia in early Tertiary - died out on all three continents in Miocene.
- Also known from South America and Antarctica, and opossums reached Australia by the Eocene.
- Similar opossum teeth from around the world.
- Australian Marsupials
- Distinct clade from other marsupials.
- Australian marsupials evolved in parallel with mammals.
- -Marsupials wolf resembles the placental dog.
- -The marsupial 'lion' resembles saber-toothed cats.
- -Kangaroos and extinct diprotodonts occupy same niche as placental grazers (deer, antelope, cattle).
- Dasyuromorphia - marsupial "mice", cat like dasyures, Tasmania devil, Tazmanian wolf.
- Peramelemorphia - bandicoots
- Notoryctemorphia - marsupial "moles"
- Diprotodontia - 'possums, phalangers, wallabies, kangaroos, koalas, and wombats.
- Last 3 groups=clade - peculiar foot condition (syndactyly) - toe 4 forms main axis; toes 2-3 combined in a sheath and used as a comb
- parallel evolution between marsupial and placental mammals
- Easy to distinguish marsupials from placentals by the pouch, different tooth formulas, etc.
- Both groups fill similar niches on different continents, so evolve superficial similarities.
- fossil australian marsupials
- (a) marsupial lion
- (b) extinct kangaroos
- (c) skydactyl foot
- (d) diprotodont related to wombats
South American Marsupials
- Marsupials common in South America, but also several placental groups (and giant carnivorous birds).
- Evolved with placental shrews, cats, sabertooths, and dogs.
- Didelphimorphia - opossums and relatives
- Paucituberculata - shrew opossum (living) and extinct relatives
- Sparassodonta - extinct dog-like borhyaenids and saber-tooth-cat-like thylacosmilids
- Begin with a generalized body
- -five digits (toes) with phalangeal formula 2-3-3-3
- -a "complete" set of generalized teeth
- Many groups lose and/or specialize toes and teeth
- the earliest placentals were similar to shrews
Primitive Placental tooth formula
- Four groups of teeth
- -incisors, canines, premolars, molars (not replaced)
- Primitve formula 3-1-4-3
- The formula is reduced when the jaw is shortened (the human formula is 2-1-2-3)
- A diastema (gap) develops in most herbivores from the loss of canines and premolars.
Earliest placental mammal
- Discovery of Eomia from liaoning deposits in China extend the placental record back 50 million years into the early Cretaceous.
- Eomaia is shrew-sized and has hair preserved.
- Epipubic bones suggest that it has a pouch like modern monotremes and marsupials.
- The tooth pattern shows it is a placental mammal.
- late cretaceous placentals
- large hindlimbs for hopping
- upper teeth very broad
- Tooth formula I3 C1 P4 M3
- Therian scapula divided by spine, loss of coracoid and interclavicle
Placental Adaptive Ratidation
- After mass extinction at end of Cretaceous many niches open.
- Placental mammals diversified quickly into many forms, some still survive but many quickly went extinct.
- Placental giants quickly appeared but replaced by successive groups of new giants with ancestors of smaller size
- -large mammals reproduce (and evolve) more slowly
- Paleocene mammals of North America
- Multituberculates, insectivores, carnivores, and primates from Montana
Small paleocene placentals
- Leptictids - small, shrew-like insectivores - retain jugal bone (which shrews lose)
- Pantolestids - otter-like mammals=? crushed shellfish
- Apatemyids - large rodent-like incisors but primitive shrew-like cheek teeth
- Anagalids - rabbit-like herbivores - broad molars, high jaw joint, retain postorbital process, -most abundant Paleocene mammals in Asia.
Messel Oil Shales
- Exquisitely preserved fossils including hair.
- Middle Eocene of Germany
- Lepitctidium, a small leptictid (or close relative) -bipedal wiht long tail to balance its body weight.
Early Rooters and Browsers
- Taeniodonts - pig-sized herbivores - short legs, large forefeet and claws for digging
- Tillodonts - up to bear-size - broad teeth (especially incisor 2) for eating tough foods
- Pantodonts - tusked herbivores resembling hippos and even ground sloths, possibly related to tillodonts
- Arctocyonids - dog-like herbivores - strong teeth and claws for digging and eating plants, some adapted for climbing trees.
- Condylarth=early herbivores that gave rise to modern ungulates (horses, cattle, etc.).
- Like "thecodont" it is a term hated by cladists because it represents a grade, and a paraphyletic group.
- Because relationships among early grazers are poorly known, its useful to refer to a suit of similar hebivores.
- Some abundant in Eocene.
- Paleocene herbivores
- (a) Arctocyonid skull
- (b) Periptychid
- (c) Hyopsodontid
- (d) Phenacodontid
- (e) Dinoceratan Uintatherium (=Uintatheres), giants of late Paleocene and early Eocene
- largest paleocene carnivores=hoofed Mesonychids (a), formerly thought to be while relative.
- Creodonts (b-d) most diverse early Cenozoic carnivores, later replaced by Carnivora. This may be a polyphyletic group. The carnassials the (largest shearing teeth) farther back in the tooth row (M1 or 2, m2 or 3) than in the Carnivora (P4, m1)
Northern Placental Adaptive Radiation
Survivors of early radiation - insectivores, carnivores, dermopterans, bats, primates, perissodactyls and rodents. But many early placentals (especially large) went extinct.
Early Insectivores and Shrews
- Mesozoic mammals superficially shrew-like, shrews often considered most primitive living placentals.
- Insectivora based on primitive characters.
- Tenrecs and golden moles now in Afrotheria.
- Shrews (soriconmorphs) arose in Paleocene, relatives moles and hedgehogs arose in Eocen. All insect eaters.
- Moles short, flat humerus and large clawed hands for burrowing.
- Hedgehogs have evolved spines from modified hairs and look like little porcupines.
- Insectivores and Bats
- Oligocene shrew
- shrews tend to lose jugal and zygomatic arch
- giant miocene hedgehog (shown next to living hedgehog)
- Eocene bat Icaronycteris
- Fragementary remains from Paleocene, well-known and fully-developed in Eocene
- (Icaronycteris - Green River Shale, Wyoming)
- -Elongated forelimb bones, ulna and radius fused
- -Fingers 2-5 greatly elongated to support flight membrane
- -Finger 1 short with claw for climbing and hanging
- -Feet turned backward for hanging
- -Eyes large, ears specialized for ecohlocation
- Megachiropterans (large fruit bats) now confirmed by morphology and DNA to form a clade together with Microchiropterans (small insect-eating bats)
- Bats~flying shrews
- Retain all toes and teeth
- Digits 2-4 elongated to support wing membrane
- Digit 1 remains small, with a claw
- Most bats eat insects, some=large fruit eaters
- Xenarthra (extra joints)=extra articulations between some trunk and tail vertebrae.
- Ischium and ilium fused to come caudal vertebrae, probably to strengthen body for digging.
- Edentate (toothless) = frequent loss of teeth.
- Mostly South American, invaded North America
- Retain primitive features: septomaxillary bone, ossified ribs reaching the sternum, low and variable body temperature, primitive reproductive system.
- Armadillos, Glyptodonts, Tree sloths, Ground Sloths, Anteaters.
- Oligocene of South America, five species of tree sloths survive today
- Ground Sloths originated in the Miocene and became giants.
- Megatherium of the Pleistocene reached 6 meters in length.
- Several ground sloths ranged into North America during the Ice Age, as far north as Alaska!
- Some caves filled with sloth dung, often with no bones.
- Glyptodonts armored against phorosrhacids and saber tooth "cats."
- Ground sloths herbivores only
- Megatherium, size of elephant
- Glyptodonts: size of Volkzwagen beetle.
- Anteaters of the world
- Convergent evolution. Pangolins once considered edentates, but no longer.
- Began as small cat-like hunters in Paleocene without ossified auditory bullae.
- Feliforms: ectoympanic bone formed bulla
- -Cats, civets, mongooses, hyaenas, and extinct nimravids
- Caniforms: entotympanic bone formed bulla
- -Dogs and Arctoids (bears, racoons, weasels, and seals)
- Carnassial teeth P4 and m1-good grinding teeth farther back in tooth row (better than creodonts)
- Took over prominence from creodonts in Oligocene, leading to final creodont extinction in Miocene.
- Relationship of creodonts and carnivores hotly debated - two groups may have originated independently.
- Carnivores - slower start - gradually out competed creodonts, resulting in gradual extinction.
- Cats=shortest skulls and lose teeth behind the carnassials for a stronger bite.
- Dots retain longest jaw with no tooth loss, retain crushing postcarnassial teeth.
- Weasels, bears, adn other carnivores fall between extremes.
- Saber canines in several cat lineages. Lower canines generally reduced.
- Smilodon: Holocene saber-tooth cat preyed on large herbivores
One subspecies of (Panthera leo) adapted to Ice age cold - lived in caves in Europe, probably hunting deer, cattle, and horses.
- Late Oligocene of California (a-c)
- Hindfeet rotated backward to work together as a paddle.
- Early forms only semi-aquatic and retain carnassial teeth (d).
- With time teeth become simplified, turning to simple homodont pegs in sea lions (e).
- Seals and sea lions fed on fish.
- Walruses crush shellfish with blunt teeth
- Modern pangolins (scaly anteaters) live in south Asia and north Africa.
- Early fossils are known from Europe and North America.
- Toothless with long tongue
- DNA evidence suggests a relationship to carnivores!
- Major groups appear in early Eocene of North America.
- Brontotheres - giants of early Badland faunas.
- Perissodactyls decline over time in competition with artiodcatyls.
- Mesaxonic feet
- Axis down the middle of toe 3
- Number of toes reduced from 5 to 3 to 1
- Brontotheres (a) sister group to horses - late Eocene giants - North America Badlands National Park.
- Chalicotheres (b) sister group of tapirs and rhinos, horse-like heads, long hooved forelimbs and short clawed hindlimbs - lived until Pleistocene in North America.