Homework to be emailed to valenciabiologyhw@gmail.com
-
Desribe the 4 unique characteristics of chordates
- Compare and
contrast members of Agnatha, Placadermi, and Chondrichthyes
- Summarize the
evidence supporting the fact that amphibians evolved from
crossopterygians
- List the
distinguishing characteristics of members of the class Aves and explain
any special adaptations for flight
- Compare and contrast the four main evolutionary lines of placental mammals
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Fishes that have swim bladders can regulate their density and, thus, their buoyancy. There are two types of swim bladder: physostomus and physoclistus. The ancestral version is the physostomus version, in which the swim bladder is connected to the esophagus via a short tube (Figure 34.1). The fish fills this version by swimming to the surface, taking gulps of air, and directing them into the swim bladder. Air is removed from this version by "belching." The physoclistus version is more derived, and has lost its connection to the esophagus. Instead, gas enters and leaves the swim bladder via special circulatory mechanisms within the wall of the swim bladder.
Rank the following fish, from most to least, in terms of the amount of energy it must use to maintain its position (depth) in the water column over the long term.
1. physoclistus fish
2. physostomus fish
3. chondrichthyan fish
7. If a physoclistus fish removes gas from its swim bladder, this fish's density cannot actually change until that gas arrives at the _______________
8. Which shark structure is most analogous to a swim bladder full of gas?
9. When a shark stops swimming, it does which of the following?
1. sinks
2. quickly dies
3. oxygenates its blood less effectively
10.This phylogenetic tree indicates that birds are most closely related to _____.
11. This phylogenetic tree indicates that the most recent common ancestors of reptiles, birds, and mammals are _____.
Vertebrate Lecture Notes--animals 3 A
and 3 B
By the end of the Cambrian period, some 540 million years ago
An astonishing variety of animals inhabited Earths oceans
One of these types of animals
Gave rise to vertebrates, one of the most successful groups of animals
-One hypothesis for the origin of fish-like chordates is paedomorphosis of the tadpole larva.
-This seems to have happened once in the origin of larvaceans, which are small, planktonic urochordates that retain the postanal tail, etc., throughout their lives.
-This may have happened at least one other time, giving rise to the rest of the chordates.
The Chordates have four distinguishing characteristics:
- Pharyngial gill slits
- Muscular postanal tail (for locomotion)
- Notochord (which keeps the body from telescoping)
- A dorsal, hollow nerve tube (which coordinates movement)
Note that 3 of these are associated with locomotion
-Phylogeny of Chordates
- The chordates as a group are pretty diverse in form, too, containing some members that are decidedly un-vertebate like.
-The Urochordata appear to be the sister group to the lineage that contains the vertebrates
Urochordates are sedentary or slow-moving animals
Tunicates (sea squirts) are attached to the bottom as adults and use a huge pharyngial basket (with gill slits) to filter the water much like a clam.
Salps are free-floating filter feeders, also using their pharynx and gill slits
So wheres the tail?
-The other three chordate characteristics are found in the larval stage the tadpole larva. It is the dispersal stage for tunicates, which cannot move as adults. As the dispersal stage, the tadpole larva has the postanal tail, notochord, and dorsal nerve tube.
- But even so, where did fish come from?
-One hypothesis for the origin of the rest of the chordates from a urochordate-like ancestor: paedomorphosis (also known as paedogenesis)
-Paedomorphosis is a phenomenon in which sexual maturity is achieved in the larval or juvenile body form. Either maturation is accelerated, or body development is prolonged (maybe forever).
-Evolutionary changes in relative rates of development are common. The Mexican axlotl is a paedomorphic salamander that keeps its gills and swimming tail throughout its life.
The animals called vertebrates
Get their name from vertebrae, the series of bones that make up the backbone
There are approximately 52,000 species of vertebrates
Which include the largest organisms ever to live on the Earth
Chordates have a notochord and a dorsal, hollow nerve cord
Vertebrates are a subphylum of the phylum Chordata
Chordates are bilaterian animals
That belong to the clade of animals known as Deuterostomia
Two groups of invertebrate deuterostomes, the urochordates and cephalochordates
Are more closely related to vertebrates than to invertebrates
Derived Characters of Chordates
All chordates share a set of derived characters
Although some species possess some of these traits only during embryonic development
Notochord
The notochord
Is a longitudinal, flexible rod located between the digestive tube and the nerve cord
Provides skeletal support throughout most of the length of a chordate
Notochord
In most vertebrates, a more complex, jointed skeleton develops
And the adult retains only remnants of the embryonic notochord
Dorsal, Hollow Nerve Cord
The nerve cord of a chordate embryo
Develops from a plate of ectoderm that rolls into a tube dorsal to the notochord
Develops into the central nervous system: the brain and the spinal cord
Pharyngeal Slits or Clefts
In most chordates, grooves in the pharynx called pharyngeal clefts
Develop into slits that open to the outside of the body
These pharyngeal slits
Function as suspension-feeding structures in many invertebrate chordates
Are modified for gas exchange in aquatic vertebrates
Develop into parts of the ear, head, and neck in terrestrial vertebrates
Muscular, Post-Anal Tail
Chordates have a tail extending posterior to the anus
Although in many species it is lost during embryonic development
The chordate tail contains skeletal elements and muscles
And it provides much of the propelling force in many aquatic species
Tunicates
Tunicates, subphylum Urochordata
Belong to the deepest-branching lineage of chordates
Are marine suspension feeders commonly called sea squirts
Tunicates most resemble chordates during their larval stage
Which may be as brief as a few minutes
As an adult
A tunicate draws in water through an incurrent siphon, filtering food particles
Early Chordate Evolution
The current life history of tunicates
Probably does not reflect that of the ancestral chordate
Lancelets
Lancelets, subphylum Cephalochordata
Are named for their bladelike shape
Lancelets are marine suspension feeders
That retain the characteristics of the chordate body plan as adults
Gene expression in lancelets
Holds clues to the evolution of the vertebrate form
Craniates are chordates that have a head
The origin of a head
Opened up a completely new way of feeding for chordates: active predation
Craniates share some common characteristics
A skull, brain, eyes, and other sensory organs
Derived Characters of Craniates
One feature unique to craniates
Is the neural crest, a collection of cells that appears near the dorsal margins of the closing neural tube in an embryo
Neural crest cells
Give rise to a variety of structures, including some of the bones and cartilage of the skull
The Origin of Craniates
Craniates evolved at least 530 million years ago
During the Cambrian explosion
The most primitive of the fossils
Are those of the 3-cm-long Haikouella
In other Cambrian rocks
Paleontologists have found fossils of even more advanced chordates, such as Haikouichthys
Hagfishes
The least derived craniate lineage that still survives
Is class Myxini, the hagfishes
Hagfishes are jawless marine craniates
That have a cartilaginous skull and axial rod of cartilage derived from the notochord
That lack vertebrae
Vertebrates are craniates that have a backbone
During the Cambrian period
A lineage of craniates evolved into vertebrates
Derived Characters of Vertebrates
Vertebrates have
Vertebrae enclosing a spinal cord
An elaborate skull
Fin rays, in aquatic forms
Lampreys
Lampreys, class Cephalaspidomorphi
Represent the oldest living lineage of vertebrates
Have cartilaginous segments surrounding the notochord and arching partly over the nerve cord
Lampreys are jawless vertebrates
Inhabiting various marine and freshwater habitats
Fossils of Early Vertebrates
Conodonts were the first vertebrates
With mineralized skeletal elements in their mouth and pharynx
Armored, jawless vertebrates called ostracoderms
Had defensive plates of bone on their skin
Origins of Bone and Teeth
Mineralization
Appears to have originated with vertebrate mouthparts
The vertebrate endoskeleton
Became fully mineralized much later
Gnathostomes are vertebrates that have jaws
Today, jawless vertebrates
Are far outnumbered by those with jaws
Derived Characters of Gnathostomes
Gnathostomes have jaws
That evolved from skeletal supports of the pharyngeal slits
A. Vertebrate jaws evolved from skeletal supports of pharyngeal slits
1. Animals that replaced jawless vertebrates, and are Gnathostomes.
2. Members of group have two pairs of fins.
3. Jaws and fins allowed fish to become active in pursuit of food and in biting off chunks of flesh.
4. Jaws evolved from modifications of skeletal elements of anterior pharyngeal gill slits.
Other characters common to gnathostomes include
Enhanced sensory systems, including the lateral line system
An extensively mineralized endoskeleton
Paired appendages
Fossil Gnathostomes
The earliest gnathostomes in the fossil record
Are an extinct lineage of armored vertebrates called placoderms
Another group of jawed vertebrates called acanthodians
Radiated during the Devonian period
Were closely related to the ancestors of osteichthyans
Chondrichthyans (Sharks, Rays, and Their Relatives)
Members of class Chondrichthyes
Have a skeleton that is composed primarily of cartilage
The cartilaginous skeleton
Evolved secondarily from an ancestral mineralized skeleton
The largest and most diverse subclass of Chondrichthyes
Includes the sharks and rays
Most sharks
Have a streamlined body and are swift swimmers
Have acute senses
A second subclass
Is composed of a few dozen species of ratfishes
Ray-Finned Fishes and Lobe-Fins
The vast majority of vertebrates
Belong to a clade of gnathostomes called Osteichthyes
Nearly all living osteichthyans
Have a bony endoskeleton
Aquatic osteichthyans
Are the vertebrates we informally call fishes
Control their buoyancy with an air sac known as a swim bladder
Fishes breathe by drawing water over four or five pairs of gills
Located in chambers covered by a protective bony flap called the operculum
Ray-Finned Fishes
Class Actinopterygii, [Ac-tin-o-ter-y-gi-i ] the ray-finned fishes
Includes nearly all the familiar aquatic osteichthyans
The fins, supported mainly by long, flexible rays
Are modified for maneuvering, defense, and other functions
Lobe-Fins
The lobe-fins, class Sarcopterygii
Have muscular and pectoral fins
Include coelacanths, lungfishes, and tetrapods
Tetrapods are gnathostomes that have limbs and feet
One of the most significant events in vertebrate history
Was when the fins of some lobe-fins evolved into the limbs and feet of tetrapods
Derived Characters of Tetrapods
Tetrapods have some specific adaptations
Four limbs and feet with digits
Ears for detecting airborne sounds
The Origin of Tetrapods
In one lineage of lobe-fins
The fins became progressively more limb-like while the rest of the body retained adaptations for aquatic life
Extraordinary fossil discoveries over the past 20 years
Have allowed paleontologists to reconstruct the origin of tetrapods
Amphibians
Class Amphibia
Is represented by about 4,800 species of organisms
Most amphibians
Have moist skin that complements the lungs in gas exchange
Order Urodela
Includes salamanders, which have tails
Order Anura
Includes frogs and toads, which lack tails
Order Apoda
Includes caecilians, which are legless and resemble worms
Amphibian means two lives
A reference to the metamorphosis of an aquatic larva into a terrestrial adult
Amphibians represent the first truly tetrapod vertebrates
first to move about and support themselves on land
All amphibians have bony skeletons
Most have 4 limbs, except Caecilians (limbless) and Sirens (forelimbs only)
Many have webbed feet
Typically the glandular skin is smooth, moist, and lacks scales
Caecilians have concealed dermal scales
One advance associated with a more terrestrial existence is the refinement of the ear
the amphibian ear, unlike that of fishes, consists of three components
Inner ear, middle ear, outer ear
There is increased sensitivity to accommodate airborne sounds
Gas exchange occurs through lungs, gills, and/or the skin
Some salamanders have no lungs (secondarily lost)
Adults have double circulation
Both a pulmonary and a systemic circuit
Heart has three chambers
Two atria and one ventricle
Some mixing of oxygenated and deoxygenated blood occurs in ventricle
The evolution of the tetrapod limb was the third major hallmark in vertebrate evolution
In early forms, these limbs represented modified Sarcopterygian pectoral and pelvic fins
Development of limbs required only a few minor modifications
elongation of proximal elements into long-bones of limbs
Proliferation of more distal elements into bones of feet
Elaboration of pectoral and pelvic girdles (for anchoring the limbs)
Early locomotion was probably very crude
Orientation of limb did not effectively allow body to be raised above substrate
Limbs acted as pivot points rather than for propulsion. Modern salamanders still move about in this way.
Emergence on to land required adaptations to accommodate desiccation
amphibians have an external layer of skin, the stratum corneum, that consists of a single layer of dead cornified cells
Reduces water loss through skin to some extent
However, amphibian eggs are very vulnerable to desiccation
Hence, amphibians are reproductively constrained to exist in moist environments.
Fertilization is external in anuran and some urodelids
most salamanders have external fertilization, but no copulation
Males deposit a spermatophore which is picked up by the female and placed into a spermatheca (in wall of cloaca)
Eggs are fertilized as they pass through the cloaca
Most amphibians are oviparous
-females lay eggs
Some amphibians undergo direct development in the egg
-embryos pass through larval stage in the egg and emerge from the egg as miniature versions of the adults.
In most amphibians, the young must pass through a larval stage
larvae are aquatic with external gills
In a few forms, the adults will retain larval characteristics
= neoteny
A very few forms are viviparous
the females retain the eggs in their bodies until they are ready to hatch.
It is clear that amphibians evolved from some lineage of Sarcopterygian fishes
-However the details of this origin remain obscure
One fossil group, from the Crossopterygian lineage, that provides a good candidate for amphibian origins are the Rhipidistians [rı˘pı˘-dı˘ste―-nz]
shared many characteristics with fossil amphibians
Limb/fin structure, jaw structure, both had labyrinthodont teeth
the arrangement of skull bones is similar
the amphibian limb can be derived from the fin structure
the rhipidistians lived in shallow freshwater lakes and almost certainly had lungs and breathed air
both rhipidistians and early amphibians have a similar structure to their teeth - called a labyrinthodont pattern from the complex folding of the walls of the pulp cavity
rhipidistians were the only fish which had developed an opening to the nostrils inside the mouth - a feature which is found in all the land vertebrates.
However, recent mitDNA evidence shows that modern amphibians are more similar to lungfishes (Dipnoi) than to Coelacanths (Crossopterygii)
this suggests a different origin for the amphibians
Critics reject this argument based on certain methodological arguments
Though actual origins are uncertain, it is clear that there was plenty of selective pressure for amphibians to emerge onto land
the Devonian was a period of tremendous climatic fluctuation
Wet and dry spells dry spells would have set up intense competition in aquatic habitats, would favor an ability to move from one pond to another, oxygen poor waters would favor air-breathing
Also, at this time, there was a tremendous radiation of arthropods into the terrestrial environment
Centipedes, millipedes, spiders, insects, etc.
This would create an open niche in a relatively low-competition terrestrial environment
Lastly, the ability to temporarily move out of water would allow early amphibians a means of escaping from aquatic predators.
The fossil record of amphibians includes two extinct subclasses
Labyrinthodontia and Lepospondyli
The earliest fossil amphibians belonged to the Labyrinthodontia
Labyrinthodonts first appeared in the upper Devonian
were the most abundant and diverse amphibians though the Carboniferous, Permian, and Triassic
Some were quite large, reaching a length of 5 feet.
Most were aquatic or primarily aquatic
Many retained fish-like tails, some retained internal gills
Several groups of Labyrinthodonts existed, two were important for vertebrate evolution
Anthracosaurs represented a small group but are important because they are believed to be ancestral to reptiles
Temnospodylians were common during Permian and are suggested to be ancestral to modern Amphibians
origins
The other fossil subclass was Lepospondyli
represent a group of small, salamander-like amphibians that appeared in the Carboniferous and Permian.
Though superficially similar to salamanders, they are not believed to be closely related to any living amphibians
Based on unique structure of the vertebrae
Living Amphibians
Modern amphibians all belong to the Subclass Lissamphibia
First appeared in Triassic about 200 mya
First true frog Jurassic (190 mya)
First salamander Jurassic (145 mya)
First Caecilians Jurassic (195 mya)
Because many forms have delicate skeletons, they dont preserve well.
Thus the fossil record is rather poor
As a result the evolutionary relationships among living taxa are poorly understood
Amniotes are tetrapods that have a terrestrially adapted egg
Amniotes are a group of tetrapods
Whose living members are the reptiles, including birds, and the mammals
A phylogeny of amniotes
Derived Characters of Amniotes
Amniotes are named for the major derived character of the clade, the amniotic egg
Which contains specialized membranes that protect the embryo
The extraembryonic membranes
Have various functions
Allantois. (a˘-la˘nto―-ı˘s )) The allantois is a disposal sac for certain metabolic wastes produced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ
Chorion. [kτre―-o˘n] The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell.
Amnion. The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock.
Yolk sac. The yolk sac contains the
yolk, a stockpile of nutrients. Blood
vessels in the yolk sac membrane transport
nutrients from the yolk into the embryo.
Other nutrients are stored in the albumen Amniotes also have other
terrestrial adaptations
Such as relatively impermeable skin and the ability to use the rib cage to
ventilate the lungs
Early Amniotes
Early amniotes
Appeared in the Carboniferous period
Included large herbivores and predators
Reptiles
The reptile clade includes
The tuatara, lizards, snakes, turtles, crocodilians, birds, and the extinct
dinosaurs
Reptiles
Have scales that create a waterproof barrier
Lay shelled eggs on land
Most reptiles are ectothermic
Absorbing external heat as the main source of body heat
Birds are endothermic
Capable of keeping the body warm through metabolism
Temperature Relationships in Animals -Why are temperature relationships
important for land animals?
-Its hard to get moving when it is cold
-Few reptiles live at high altitudes and high latitudes, and if they do, they
often undergo hibernation during winter.
-But do lizards really fit all of the cold-blooded stereotypes?
-Lizards arent always cold blooded. They can maintain relatively high body
temperatures even higher than some birds an mammals and body temperature can
exceed air temperature
Body Temperature Cold-blooded
Body temperature = environmental temp.
Warm blooded
Body temperature usually > environmental temp.
But the source of body heat does differ between lizards and birds or mammals.
They dont generate their own heat, but instead take up heat from the sun, or
from rocks.
Source of Body Heat
Ectotherm
Body temperature depends on environment
Endotherm
Body temperature depends on internal source of heat
-Lizards and other living reptiles can regulate their body temperature
behaviorally, by exposing themselves to the sun, or to warm surfaces. They are
truly ectothermic, but are still capable of maintaining constant, high body
temperatures,
under a certain range of
conditions.
Temperature Relationships in Animals: Summary
-Most fish:
Cold-blooded, poikilothermic, ectotherms
-Lizards & Snakes:
Warm-blooded (often), homeothermic (often), ectotherms (typically)
-Birds & Mammals:
Warm-blooded, homeothermic, endotherms helps to permit an active lifestyle
in a range of environmental conditions, but at an energetic cost.
-Dinosaurs?
Modeled after lizards and other ecothermic reptiles?
The Origin and Evolutionary Radiation of Reptiles
The oldest reptilian fossils
Date to about 300 million years ago
The first major group of reptiles to emerge
Were the parareptiles, which were mostly large, stocky herbivores
As parareptiles were dwindling
The diapsids [dı―-a˘psı˘d] were diversifying
The diapsids are composed of two main lineages
The lepidosaurs [le˘pı˘-do―-sτrz] and the archosaurs[δrko―-sτrz]
The dinosaurs
Diversified into a vast range of shapes and sizes
Included the long-necked giants called the theropods
Traditionally, dinosaurs were considered slow, sluggish creatures
But fossil discoveries and research have led to the conclusion that dinosaurs
were agile and fast moving
Paleontologists have also discovered signs of parental care among dinosaurs
Early Dinosaurs
Archosaurs replaced synapsid/reptile groups
Two major groups of reptiles
modern lizards and snakes
archosaurs
crocodiles, birds, dinosaurs, flying reptiles, many archic reptiles
archosaur radiation produced many unusual beasts
first true dinosaurs
small (< 1m) bipedal
hind limbs upright
Dinosaur groups
Two major groups based on pelvis shape
Saurischian (lizard-hipped)
sauropods (brontosaurus, etc.)
theropods (two-legged carnivores)
birds eventually developed from this line
Ornithiscian (bird-hipped)
all herbivorous
Anklyosaurs
Stegosaurs
Hadrosaurs, Pachycephalosaurs
Iguanodonts
Ceratopsids
The K-T extinctions
Extinctions were severe
Evidence is different for different groups
Dinosaurs, pterosaurs, many plants went extinct
Severe extinctions of coccolithoids and forams, brachiopods and ammonites
Microfossils tended to phase out slowly however, beginning millions of years
before the boundary
Tropical groups suffered most
Ammonites declining long before the boundary
Mammals cross nearly unscathed, but shift to placentals
Bulk of evidence indicates gradual decline over K
Impact hypothesis
Giant meteor impact
first suspected from Gubbio, Italy iridium layer
iridium rare element on earth, more abundant in meteors
iridium layer found all over the world now
shocked quartz another impact indicator?
Chixalub crater in the Yucatan, Mexico
suspected of being THE K-T impact
Mechanism for extinctions
dust hung in atmosphere and blocked sunlight, initiated global cooling
plants would die, triggering food chain collapse
total event may have lasted less than 50 years
Volcanic hypothesis
Gradual extinction record a problem for impact
Massive volcanic eruptions suggested
Deccan traps of India and flood basalts in Brazil
dated to last 500,000 yrs before KT boundary
would pump lots of ash and sulfuric acid into atmosphere
iridium also enriched in mantle rocks and volcanics
And the jury says...
Arguments are still going on
gradual extinctions seem to fit volcanic hypothesis
but complexities abound
neither model seems to completely account for all evidence
both events might have contributed to the declines
Lepidosaurs
One surviving lineage of lepidosaurs
Is represented by two species of lizard-like reptiles called tuatara
The other major living lineage of lepidosaurs
Are the squamates, [skwa―ma―tz] the lizards and snakes
Lizards
Are the most numerous and diverse reptiles, apart from birds
Snakes are legless lepidosaurs
That evolved from lizards
Turtles
Turtles
Are the most distinctive group of reptiles alive today
Some turtles have adapted to deserts
And others live entirely in ponds and rivers
All turtles have a boxlike shell
Made of upper and lower shields that are fused to the vertebrae, clavicles,
and ribs
Alligators and Crocodiles
Crocodilians
Belong to an archosaur lineage that dates back to the late Triassic
Birds
Birds are archosaurs
But almost every feature of their reptilian anatomy has undergone modification
in their adaptation to flight
Derived Characters of Birds
Many of the characters of birds
Are adaptations that facilitate flight
A birds most obvious adaptations for flight
Are its wings and feathers
The Origin of Birds
Birds probably descended from theropods
A group of small, carnivorous dinosaurs
By 150 million years ago
Feathered theropods had evolved into birds
Archaeopteryx
Remains the oldest bird known
Living Birds
The ratites, order Struthioniformes
Are all flightless
The demands of flight
Have rendered the general body form of many flying birds similar to one
another
Foot structure in bird feet
Shows considerable variation
Mammals
Developed from latest Late Triassic synapsids
remained mouse-sized
did not compete with dinosaurs in their niches
developed mammary glands
endothermic and homothermic--required high food intake
jaw muscles and teeth well adapted for catching prey
soft palate to separate breathing from eating passages
Mammals
mid-Cretaceous divergence into two groups
placentals (young carried in uterus until ready for birth)
marsupials (pouched mammals)
young crawl to pouch to finish development
» oppossum, kangaroo, koala, etc.
Mammals are amniotes that have hair and produce milk
Mammals, class Mammalia
Are represented by more than 5,000 species
. The earliest mammals evolved from reptiles about 220 million years ago.
Therapsids gave rise to mammals.
. Major groups of mammals:
a. Monotremes lay eggs and produce milk, but have no nipples.
- Platypus, echidna
b. Marsupials born early in embryonic development; climb to mothers pouch
and attach to a nipple.
- Opossum, kangaroo
c. Eutherians long pregnancy with embryonic attachment to mother in uterus
via placenta
Derived Characters of Mammals
Mammary glands, which produce milk
Are a distinctively mammalian character
Hair is another mammalian characteristic
Mammals generally have a larger brain
Than other vertebrates of equivalent size
Early Evolution of Mammals
Mammals evolved from synapsids
In the late Triassic period
The jaw was remodeled during the evolution of mammals from nonmammalian
synapsids
And two of the bones that formerly made of the jaw joint were incorporated
into the mammalian middle ear
Living lineages of mammals originated in the Jurassic
But did not undergo a significant adaptive radiation until after the
Cretaceous
Mammals
Mammals appeared in the Triassic period, as part of a lineage of small,
nocturnal therapsids. The feature distinguishing them was the transformation of
the the quadrate and articular bones to the incus and malleus.
-Mammalian characteristics acquired before transition to true mammals:
-Endothermy? (as indicated by turbinate bones)
-Mammalian gait (limbs tucked under body)
-Mammalian characteristics that could have appeared before the transition to
mammals:
-Hair (as insulation for endothermy, and for sensation by touch at night)
-Lactation (signs of lips in some pre-mammalian therapsids; supply of
high-energy food for endothermic young)
-Increase in size of cerebral cortex (associated with olfaction in nocturnal
animals)
-Appearing after the transition:
-Viviparity
While mammals persisted throughout the Mesozic era (the Age of Reptiles), they
were not the dominant large land animals. Some of the major lineages of mammals
appeared during this time.
-Monotremes are egg-laying mammals, but they produce milk in a slit. Young
lap milk.
-Marsupials are viviparous, but young are born poorly-developed, and depend on
lacatation for nourishment as they develop. The young suck milk.
Our lucky stars.
Strong evidence for a large extraterrestrial impact on earth 65 million years
ago, marking the end of the Cretaceous period.
-Probably the cause of mass extinctions at this time, including the dinosaurs
(except birds)
-This may have allowed the diversification of mammals as the predominant large
land animals.
Monotremes and Marsupials
Monotremes
Monotremes
Are a small group of egg-laying mammals consisting of echidnas and the
platypus
Monotremata (mon-uh-TREEM-ah-tuh)
Prototheria, (pro―to―-thξre―-Qnz ) retention of various reptilian features
Two families:
Ornithorhynchidae (OR-nith-oh-RIN-kuh-dee) and Tachyglossidae (TAK-ih-GLOS-suh-dee
)
Monotremata = one opening
Cloaca, common opening of fecal, urinary and reproductive tracts
Rubbery-shelled eggs (permeable)
Monotremata cont
Eggs are small, incubated for 10 to 11 days
Neonates have well developed forelimbs and shoulders
Monotremata cont
No teats
Pectoral girdle has coracoid, precoracoid, and interclavicle bone (similar to
Therapsid reptile)
Homeotherm - low - 32 C
Sperm are fiiform (threadlike) and testis structures similar to reptile
Pectoral girdle
Ornithorhynchidae
OR-nith-oh-RIN-kuh-dee
Duck-billed platypus
Semiaquatic, semifossorial
Near freshwater lakes and rivers, east coast of Australia and Tasmania
Feed on invert., fish and amphibians
Adult male 1.7 kg, female smaller
Short dense fur covers all but bill, feet, and underside of tail
Bill is soft and pliable, with nostrils at tip
Has tactile receptors to sense electric field generated by muscle contraction
of prey
Ornithorhynchidae cont
Has small eyes and ears
Pentadactyle (five-toed) and manus (forefoot) is webbed
Long claws for digging burrow
Ornithorhynchidae cont
Spur on hind limb connect to venom gland in thigh
Platypus has no pouch, female incubate eggs in burrow
Neonates have molariform teeth, shed before emerge from burrow
Keratinized pads
Milk is secreted onto tufts of hair
Ornithorhynchidae cont
Tachyglossidae
Short-beaked echidna (Tachyglossus)
Australia, New Guinea, and Tasmania
6 kg
Long-beaked echidna (Zaglossus)
Forested highland of New Guinea
10 kg
Feed on ants, termites, and insects - ground to paste between tongue and spiny
palatal ridge
Have scooplike claws on feet to break anthills and burrows
Ankle spur not venomous
Tachyglossidae cont
Beak contains electroreceptors
Guard hairs modified to become spines
Mucus that coat tongue to make it sticky
No teeth at any stage of development
Have a pouch for incubating eggs
Marsupials
Characterized by marsupium
Only 50% of species have permanent pouch
Litters that weigh 1% of mothers body mass
Eutherians: litters weigh 50% of mothers BM
Have well-developed stylar shelf
Marsupials
Marsupials
Include opossums, kangaroos, and koalas
A marsupial is born very early in its development
And completes its embryonic development while nursing within a maternal pouch
called a marsupium
In some species of marsupials, such as the bandicoot
The marsupium opens to the rear of the mothers body as opposed to the front,
as in other marsupials
In Australia, convergent evolution
Has resulted in a diversity of marsupials that resemble eutherians in other
parts of the world
Marsupials cont
Lower basal metabolic rate (BMR) - 70% of comparable sized eutherians
Slower postnatal growth
Smaller relative brain size
No true flight, no fossorial herbivores, large marsupial carnivores are
extinct
Marsupial reproduction
Bifurcated reproductive tract (female) and bifurcated penis (male)
Choriovitilline placenta
Limited intrauterine development time and accelerated development of muscular
forelimb
Precludes forelimb from becoming hooves, flippers, or wings
Marsupial reproduction cont
Paired sperm in New World marsupials
Marsupium - open anteriorly or posteriorly, folds of skin
Best developed in arboreal species, and species that burrow or jump
Neonate (no more than 1 g) climb to a teat
Once attached, teat swells, keeping neonate in place
Zoogeography
Living marsupials occur in NA, Central and SA, Australasia
Marsupials are thought to have originated in North America
Oldest fossils dating 100 mya
Panamanian land bridge developed 2 to 5 mya, major interchange of fauna
65 mya, marsupials moved from SA through Drake Passage to Antartica and
Australasia
Australian marsupials evolved in relative isolation from eutherians
Orders and Families
7 orders and 18 extant families
Polyprotodonts - unshortened mandible, lower incisors small and unspecialized
Diprotodont - shortened mandible with first pair of lower incisors enlarged to
meet upper incisors
Didactylous - unfused toes, each in own skin sheath
Syndactylous - skeletal elements of 2nd and 3rd toes in common skin sheath
Dentition
Digits
Numbat
Dasyuromorphia cont
Phascolarctidae (fas-koh-LARK-tuh-dee)
Koala
Vombatidae (vom-BAT-uh-dee )
Wombat - powerful burrower 30 kg
Grazing herbivore, dentition open-rooted
Macropodidae (ma-crow-POD-uh-dee )
Kangaroos and wallabies
Grazing herbivores
Similar to artiodactyls
Molar hypsodont*, mesial drift of cheekteeth
*high-crowned teeth and enamel which
extends past the gum line .
This provides lots of extra material for wear
Eutherians (Placental Mammals)
Compared to marsupials
Eutherians have a longer period of pregnancy
Young eutherians
Complete their embryonic development within a uterus, joined to the mother by
the placenta
Phylogenetic relationships of mammals
The major eutherian orders
Primates
The mammalian order Primates include
Lemurs, tarsiers, monkeys, and apes
Humans are members of the ape group
Derived Characters of Primates
Most primates
Have hands and feet adapted for grasping
Primates also have
A large brain and short jaws
Forward-looking eyes close together on the face, providing depth perception
Well-developed parental care and complex social behavior
A fully opposable thumb
Living Primates
There are three main groups of living primates
The lemurs of Madagascar and the lorises and pottos of tropical Africa and
southern Asia
The tarsiers of Southeast Asia
The anthropoids, which include monkeys and hominids worldwide
The oldest known anthropoid fossils, about 45 million years old
Indicate that tarsiers are more closely related to anthropoids
The fossil record indicates that monkeys
First appeared in the New World (South America) during the Oligocene
The first monkeys
Evolved in the Old World (Africa and Asia)
New World and Old World monkeys
Underwent separate adaptive radiations during their many millions of years of
separation
The other group of anthropoids, the hominoids
Consists of primates informally called apes
VI. Primates and the evolution of Homo sapiens
A. Primate evolution provides context for understanding human origins
1. Hands and feet adapted for grasping. Possess opposable thumb.
2. Large brains allow complex social behavior.
Figure 34.35 (p. 708) A phylogenetic tree of primates.
B. Hominid lineage diverged from other primates about 7 million years ago.
Humans compared to other hominids:
a. Brain size large size allows development of language and social behavior.
b. Jaw shape shortened to give a flatter face.
c. Bipedalism = walking on two legs.
- Frees hands to do other things.
- Eyes set higher; can see farther
Hominoids
Diverged from Old World monkeys about 2025 million years ago
Humans are bipedal hominoids with a large brain
Homo sapiens is about 160,000 years old
Which is very young considering that life has existed on Earth for at least
3.5 billion years
Derived Characters of Hominids
A number of characters distinguish humans from other hominoids
Upright posture and bipedal locomotion
Larger brains
Language capabilities
Symbolic thought
The manufacture and use of complex tools
Shortened jaw
The Earliest Humans
The study of human origins
Is known as paleoanthropology
Paleoanthropologists have discovered fossils of approximately 20 species of
extinct hominoids
That are more closely related to humans than to chimpanzees
These species are known as hominids
Hominids originated in Africa
Approximately 67 million years ago
Early hominids
Had a small brain, but probably walked upright, exhibiting mosaic evolution
Two common misconceptions of early hominids include
Thinking of them as chimpanzees
Imagining human evolution as a ladder leading directly to Homo sapiens
Australopiths
Australopiths are a paraphyletic assemblage of hominids
That lived between 4 and 2 million years ago
Some species walked fully erect
And had human-like hands and teeth
Bipedalism
Hominids began to walk long distances on two legs
About 1.9 million years ago
Tool Use
The oldest evidence of tool usecut marks on animal bones
Is 2.5 million years old
Early Homo
The earliest fossils that paleoanthropologists place in our genus Homo
Are those of the species Homo habilis, ranging in age from about 2.4 to 1.6
million years
Stone tools have been found with H. habilis
Giving this species its name, which means handy man
Homo ergaster
Was the first fully bipedal, large-brained hominid
Existed between 1.9 and 1.6 million years
Homo erectus
Originated in Africa approximately 1.8 million years ago
Was the first hominid to leave Africa
Neanderthals
Neanderthals, Homo neanderthalensis
Lived in Europe and the Near East from 200,000 to 30,000 years ago
Were large, thick-browed hominids
Became extinct a few thousand years after the arrival of Homo sapiens in
Europe
Homo sapiens
Homo sapiens
Appeared in Africa at least 160,000 years ago
The oldest fossils of Homo sapiens outside Africa
Date back about 50,000 years ago
The rapid expansion of our species
May have been preceded by changes to the brain that made symbolic thought and
other cognitive innovations possible
Birds
Birds are archosaurs
But almost every feature of their reptilian anatomy has undergone modification
in their adaptation to flight
Derived Characters of Birds
Many of the characters of birds
Are adaptations that facilitate flight
A birds most obvious adaptations for flight
Are its wings and feathers
The Origin of Birds
Birds probably descended from theropods
A group of small, carnivorous dinosaurs
By 150 million years ago
Feathered theropods had evolved into birds
Archaeopteryx
Remains the oldest bird known
Living Birds
The ratites, order Struthioniformes
Are all flightless
The demands of flight
Have rendered the general body form of many flying birds similar to one
another
Foot structure in bird feet
Shows considerable variation
Mammals
Developed from latest Late Triassic synapsids
remained mouse-sized
did not compete with dinosaurs in their niches
developed mammary glands
endothermic and homothermic--required high food intake
jaw muscles and teeth well adapted for catching prey
soft palate to separate breathing from eating passages
Mammals
mid-Cretaceous divergence into two groups
placentals (young carried in uterus until ready for birth)
marsupials (pouched mammals)
young crawl to pouch to finish development
» oppossum, kangaroo, koala, etc.
Mammals are amniotes that have hair and produce milk
Mammals, class Mammalia
Are represented by more than 5,000 species
. The earliest mammals evolved from reptiles about 220 million years ago.
Therapsids gave rise to mammals.
. Major groups of mammals:
a. Monotremes lay eggs and produce milk, but have no nipples.
- Platypus, echidna
b. Marsupials born early in embryonic development; climb to mothers pouch
and attach to a nipple.
- Opossum, kangaroo
c. Eutherians long pregnancy with embryonic attachment to mother in uterus
via placenta
Derived Characters of Mammals
Mammary glands, which produce milk
Are a distinctively mammalian character
Hair is another mammalian characteristic
Mammals generally have a larger brain
Than other vertebrates of equivalent size
Early Evolution of Mammals
Mammals evolved from synapsids
In the late Triassic period
The jaw was remodeled during the evolution of mammals from nonmammalian
synapsids
And two of the bones that formerly made of the jaw joint were incorporated
into the mammalian middle ear
Living lineages of mammals originated in the Jurassic
But did not undergo a significant adaptive radiation until after the
Cretaceous
Mammals
Mammals appeared in the Triassic period, as part of a lineage of small,
nocturnal therapsids. The feature distinguishing them was the transformation of
the the quadrate and articular bones to the incus and malleus.
-Mammalian characteristics acquired before transition to true mammals:
-Endothermy? (as indicated by turbinate bones)
-Mammalian gait (limbs tucked under body)
-Mammalian characteristics that could have appeared before the transition to
mammals:
-Hair (as insulation for endothermy, and for sensation by touch at night)
-Lactation (signs of lips in some pre-mammalian therapsids; supply of
high-energy food for endothermic young)
-Increase in size of cerebral cortex (associated with olfaction in nocturnal
animals)
-Appearing after the transition:
-Viviparity
While mammals persisted throughout the Mesozic era (the Age of Reptiles), they
were not the dominant large land animals. Some of the major lineages of mammals
appeared during this time.
-Monotremes are egg-laying mammals, but they produce milk in a slit. Young
lap milk.
-Marsupials are viviparous, but young are born poorly-developed, and depend on
lacatation for nourishment as they develop. The young suck milk.
Our lucky stars.
Strong evidence for a large extraterrestrial impact on earth 65 million years
ago, marking the end of the Cretaceous period.
-Probably the cause of mass extinctions at this time, including the dinosaurs
(except birds)
-This may have allowed the diversification of mammals as the predominant large
land animals.
Monotremes and Marsupials
Monotremes
Monotremes
Are a small group of egg-laying mammals consisting of echidnas and the
platypus
Monotremata (mon-uh-TREEM-ah-tuh)
Prototheria, (pro―to―-thξre―-Qnz ) retention of various reptilian features
Two families:
Ornithorhynchidae (OR-nith-oh-RIN-kuh-dee) and Tachyglossidae (TAK-ih-GLOS-suh-dee
)
Monotremata = one opening
Cloaca, common opening of fecal, urinary and reproductive tracts
Rubbery-shelled eggs (permeable)
Monotremata cont
Eggs are small, incubated for 10 to 11 days
Neonates have well developed forelimbs and shoulders
Monotremata cont
No teats
Pectoral girdle has coracoid, precoracoid, and interclavicle bone (similar to
Therapsid reptile)
Homeotherm - low - 32 C
Sperm are fiiform (threadlike) and testis structures similar to reptile
Pectoral girdle
Ornithorhynchidae
OR-nith-oh-RIN-kuh-dee
Duck-billed platypus
Semiaquatic, semifossorial
Near freshwater lakes and rivers, east coast of Australia and Tasmania
Feed on invert., fish and amphibians
Adult male 1.7 kg, female smaller
Short dense fur covers all but bill, feet, and underside of tail
Bill is soft and pliable, with nostrils at tip
Has tactile receptors to sense electric field generated by muscle contraction
of prey
Ornithorhynchidae cont
Has small eyes and ears
Pentadactyle (five-toed) and manus (forefoot) is webbed
Long claws for digging burrow
Ornithorhynchidae cont
Spur on hind limb connect to venom gland in thigh
Platypus has no pouch, female incubate eggs in burrow
Neonates have molariform teeth, shed before emerge from burrow
Keratinized pads
Milk is secreted onto tufts of hair
Ornithorhynchidae cont
Tachyglossidae
Short-beaked echidna (Tachyglossus)
Australia, New Guinea, and Tasmania
6 kg
Long-beaked echidna (Zaglossus)
Forested highland of New Guinea
10 kg
Feed on ants, termites, and insects - ground to paste between tongue and spiny
palatal ridge
Have scooplike claws on feet to break anthills and burrows
Ankle spur not venomous
Tachyglossidae cont
Beak contains electroreceptors
Guard hairs modified to become spines
Mucus that coat tongue to make it sticky
No teeth at any stage of development
Have a pouch for incubating eggs
Marsupials
Characterized by marsupium
Only 50% of species have permanent pouch
Litters that weigh 1% of mothers body mass
Eutherians: litters weigh 50% of mothers BM
Have well-developed stylar shelf
Marsupials
Marsupials
Include opossums, kangaroos, and koalas
A marsupial is born very early in its development
And completes its embryonic development while nursing within a maternal pouch
called a marsupium
In some species of marsupials, such as the bandicoot
The marsupium opens to the rear of the mothers body as opposed to the front,
as in other marsupials
In Australia, convergent evolution
Has resulted in a diversity of marsupials that resemble eutherians in other
parts of the world
Marsupials cont
Lower basal metabolic rate (BMR) - 70% of comparable sized eutherians
Slower postnatal growth
Smaller relative brain size
No true flight, no fossorial herbivores, large marsupial carnivores are
extinct
Marsupial reproduction
Bifurcated reproductive tract (female) and bifurcated penis (male)
Choriovitilline placenta
Limited intrauterine development time and accelerated development of muscular
forelimb
Precludes forelimb from becoming hooves, flippers, or wings
Marsupial reproduction cont
Paired sperm in New World marsupials
Marsupium - open anteriorly or posteriorly, folds of skin
Best developed in arboreal species, and species that burrow or jump
Neonate (no more than 1 g) climb to a teat
Once attached, teat swells, keeping neonate in place
Zoogeography
Living marsupials occur in NA, Central and SA, Australasia
Marsupials are thought to have originated in North America
Oldest fossils dating 100 mya
Panamanian land bridge developed 2 to 5 mya, major interchange of fauna
65 mya, marsupials moved from SA through Drake Passage to Antartica and
Australasia
Australian marsupials evolved in relative isolation from eutherians
Orders and Families
7 orders and 18 extant families
Polyprotodonts - unshortened mandible, lower incisors small and unspecialized
Diprotodont - shortened mandible with first pair of lower incisors enlarged to
meet upper incisors
Didactylous - unfused toes, each in own skin sheath
Syndactylous - skeletal elements of 2nd and 3rd toes in common skin sheath
Dentition
Digits
Didelphimorphia die-delf-uh-MOR-fee-uh
Single family, Didelphidae
New World distribution
Terrestrial burrowers, semiarboreal
Solitary and opportunistic feeders
Most specialized didelphid, water opossum (aquatic, webbed hind feet,
marsupium watertight during dives)
Didelphimorphia morphology
Paired spermatozoa
Pentadactyly, with primitive metatherian dental formula 5/4, 1/1, 3/3, 4/4 =50
Polyprotodont and didactylous
Have sparsely haired prehensile tails and opposable pollex (thumb on forefoot)
Some have incrassated tail (store fat in the base)
Paucituberculata paw-see-too-ber-KYOO-lah-tuh
Single family, Caenolestidae kee-noh-LESS-tuh-dee
Shrew or rat opossum
Dense vegetation of northwestern S. America
Nocturnal, insectivorous or omnivorous, and terrestrial
Paired spermatozoa
Paucituberculata morphology
Small, shrewlike
Long rostrum, adult weigh 40g
No marsupium
Didactylous, only New World marsupial that is diprotodont
Lower canine vestigial
Microbiotheria my-crow-bio-THER-ee-uh
Single family, Microbiotheriidae
One species, monito del monte (Dromiciops gliroides)
South central Chile in beech/bamboo forest
Small, 16-30g
Have prehensile tail and pouch
Greatly inflated auditory bullar
Called colocolos by natives, bad omen
Dasyuromorphia (das-ih-yoor-oh-MOR-fee-uh)
Small to medium sized, incl. carnivorous species (Tasmanian devil and quoll)
Polyprotodont and didactylous
Canines well-developed, have carnassial dentition
Tails never prehensile
3 families: Thylacinidae, Myrmecobiidae, Dasyuridae
Numbat
Dasyuromorphia cont
Peramelemorphia per-uh-mel-eh-MOR-fee-uh
Bandicoots and bilbies - Australasia
2 families, Peramelidae and Peroryctidae
Terrestrial omnivores
Have chorioallantoic placenta (no villi)
Short compact body with long pointed rostrum
Bandicoots have well-developed patella (kneecap) and no clavicle
Polyprotodont
Marsupium opens posteriorly
Diprotodontia (dih-pro-toh-DON-she-uh)
8 families, 116 species
Diprotodont, syndactylous
In arboreal diprotodonts, first two digits of forefeet oppose the other three
digits - schizodactylous
Hallux (big toe) opposable (not in terrestrial species)
Phascolarctidae (fas-koh-LARK-tuh-dee)
Koala
Vombatidae (vom-BAT-uh-dee )
Wombat - powerful burrower 30 kg
Grazing herbivore, dentition open-rooted
Phalangeridae (fah-lan-JER-uh-dee)
Brushtail possum, cuscus
Long prehensile tail, excellent climbers
Potoroidae (pot-uh-ROY-dee)
Bettongs, potoroos
Weak prehensile tail
Upper canine well developed
Have embryonic diapause
Macropodidae (ma-crow-POD-uh-dee )
Kangaroos and wallabies
Grazing herbivores
Similar to artiodactyls
Molar hypsodont*, mesial drift of cheekteeth
*high-crowned teeth and enamel which
extends past the gum line .
This provides lots of extra material for wear
Burramyidae (bur-ruh-MY-uh-dee )
Pygmy possum - smallest possum
7-50g
Exhibit embryonic diapause
Acrobatidae (ak-crow-BAH-tuh-dee )
Feathertailed glider and feather-tailed possum
New Guinea
Stiff, featherlike hairs on side of tails
Feathertailed glider - smallest gliding mammal (10-14g)
Both species nectivorous with brush-tipped tongue
Exhibit embryonic diapause
Pseudocheiridae (soo-doh-KY-ruh-dee)
Slow-moving, ringtail possum
Feed on leaves, aboreal
Molars are selenodont (elongated)
Schizodactylous digits
Prehensile tail
Have marsupium
Petauridae (pet-OR-uh-dee)
Striped possums and wrist-winged gliders
Petaurus similar to NA gliding squirrels
Prehensile tail, opposable hallux
Have marsupium
Diprotodont but molars bunodont
Tarsipedidae
(tar-sih-PED-uh-dee)
Honey possum
12 g
Nectivorous
Long pointed rostrum with brush-tipped tongue, small peglike teeth
Prehensile tail, hallux opposable, pads on digits for gripping branches
Delayed implantation
Notoryctemorphia (noh-toh-rik-teh-MOR-fee-uh )
Marsupial mole
Secretive, completely fossorial, eats beetles and larvar
Similar to eutherian talpids and chrysochlorids
Swim through ground, substrate collapse behind, no permanent tunnels
Spend time aboveground too, active both day and night
Fusiform, scooplike claw, thick keratinized nasal shield (pushing dirt)
Cervical vertebrae fused, no pinna, vestigial eye
Notoryctemorphia cont
Epipubic bone reduced
Molars zalambdodont (v-shaped)
Eaten by aborigines
Eutherians (Placental Mammals)
Compared to marsupials
Eutherians have a longer period of pregnancy
Young eutherians
Complete their embryonic development within a uterus, joined to the mother by
the placenta
Phylogenetic relationships of mammals
The major eutherian orders
Primates
The mammalian order Primates include
Lemurs, tarsiers, monkeys, and apes
Humans are members of the ape group
Derived Characters of Primates
Most primates
Have hands and feet adapted for grasping
Primates also have
A large brain and short jaws
Forward-looking eyes close together on the face, providing depth perception
Well-developed parental care and complex social behavior
A fully opposable thumb
Living Primates
There are three main groups of living primates
The lemurs of Madagascar and the lorises and pottos of tropical Africa and
southern Asia
The tarsiers of Southeast Asia
The anthropoids, which include monkeys and hominids worldwide
The oldest known anthropoid fossils, about 45 million years old
Indicate that tarsiers are more closely related to anthropoids
The fossil record indicates that monkeys
First appeared in the New World (South America) during the Oligocene
The first monkeys
Evolved in the Old World (Africa and Asia)
New World and Old World monkeys
Underwent separate adaptive radiations during their many millions of years of
separation
The other group of anthropoids, the hominoids
Consists of primates informally called apes
Hominoids
Diverged from Old World monkeys about 2025 million years ago
Humans are bipedal hominoids with a large brain
Homo sapiens is about 160,000 years old
Which is very young considering that life has existed on Earth for at least
3.5 billion years
Derived Characters of Hominids
A number of characters distinguish humans from other hominoids
Upright posture and bipedal locomotion
Larger brains
Language capabilities
Symbolic thought
The manufacture and use of complex tools
Shortened jaw
The Earliest Humans
The study of human origins
Is known as paleoanthropology
Paleoanthropologists have discovered fossils of approximately 20 species of
extinct hominoids
That are more closely related to humans than to chimpanzees
These species are known as hominids
Hominids originated in Africa
Approximately 67 million years ago
Early hominids
Had a small brain, but probably walked upright, exhibiting mosaic evolution
Two common misconceptions of early hominids include
Thinking of them as chimpanzees
Imagining human evolution as a ladder leading directly to Homo sapiens
Australopiths
Australopiths are a paraphyletic assemblage of hominids
That lived between 4 and 2 million years ago
Some species walked fully erect
And had human-like hands and teeth
Bipedalism
Hominids began to walk long distances on two legs
About 1.9 million years ago
Tool Use
The oldest evidence of tool usecut marks on animal bones
Is 2.5 million years old
Early Homo
The earliest fossils that paleoanthropologists place in our genus Homo
Are those of the species Homo habilis, ranging in age from about 2.4 to 1.6
million years
Stone tools have been found with H. habilis
Giving this species its name, which means handy man
Homo ergaster
Was the first fully bipedal, large-brained hominid
Existed between 1.9 and 1.6 million years
Homo erectus
Originated in Africa approximately 1.8 million years ago
Was the first hominid to leave Africa
Neanderthals
Neanderthals, Homo neanderthalensis
Lived in Europe and the Near East from 200,000 to 30,000 years ago
Were large, thick-browed hominids
Became extinct a few thousand years after the arrival of Homo sapiens in
Europe
Homo sapiens
Homo sapiens
Appeared in Africa at least 160,000 years ago
The oldest fossils of Homo sapiens outside Africa
Date back about 50,000 years ago
The rapid expansion of our species
May have been preceded by changes to the brain that made symbolic thought and
other cognitive innovations possible
Marine vertebrates
Early Mesozoic had primitive bony fish
Modern teleost fishes
developed by late Jurassic
highly mobile jaws and swim bladder
Marine reptiles (not dinosaurs)
plesiosaurs (long necked fish-catchers)
icthyosaurs (fish-lizards, dolphin-like reptiles)
mosasaurs (related to monitor lizards)
Marine vertebrates