Vertebrate Life
PALEOZOIC VERTEBRATES
- SUBGROUP OF PHYLUM CHORDATA
- Chordateshave a stiff, elongate support structure
[called a notochord in primitive chordates] & a hollow, central
nervous system at some stage of their life
- NOTOCHORD IS REPLACED BY VERTEBRAE IN VERTEBRATES
- Chordates & echinoderms probably
evolved from common ancestor
- Oldest Chordates in Burgess Shale (See
Box 10-1, pp. 254-255)
- FIRST VERTEBRATES - FISH
- oldest fossil fish remains - small plates of
jawless fish (Ostracoderms) in Upper Cambrian rocks of Wyoming
- Devonian = "Age of Fish" - great abundance &
diversity of fish
- FIVE (5) CLASSES OF FISH (See Figure 11-8, p. 275)
- Agnatha (jawless fish) - Paleozoic forms called
Ostracoderms because of bony armor
- ONLY MODERN JAWLESS FISH - LAMPREYS & HAGFISH
- Acanthodii & Placodermi (archaic
jawed fish) - jaw evolved from modified gill arch
- Chondrichthyes (cartilaginous fish - sharks,
rays & skates) & Osteoichthyes (bony
fish) [most modern fish]
- BOTH EVOLVED DURING THE DEVONIAN
- Ray-finned Bony Fish - arose in Devonian lakes = Most
modern fish
- Lobe-finned Bony Fish - adapted to drought prone areas
by having sturdy lobe fins for overland movement, nostrils &
lungs; 1 group evolved into Amphibians
- AMPHIBIANS
- still tied to a moist environment; must lay eggs
in water & larva breath via gills
- ichthyostegids (transitional form between fish
& amphibians) evolved during Late Devonian
- labyrinthodonts [from elaborate pattern of teeth](1st
amphibians) evolved during Carboniferous
- modern amphibians & reptiles evolved from labyrinthodonts
- REPTILES
- not dependent on moist environment; "amniotic"
egg (shelled or skinned) protects developing
embryo from drying out
- primitive reptiles (Cotylosaurs) evolved in Early
Pennsylvanian & gave rise to all other reptiles
- advanced reptiles (mammal-like reptiles) evolved
in Permian
- EARLY MAMMAL-LIKE REPTILES (PELYCOSAURS, INCLUDING SAIL-BACKED
FORMS LIKE DIMETRODON) - DOMINANT IN EARLY PERMIAN; BECAME EXTINCT
DURING THE PERMIAN
- ADVANCED MAMMAL-LIKE REPTILES (THERAPSIDS) - DOMINANT IN LATE
PERMIAN
- Had fewer bones in skull, better joint between skull &
neck, enlarged lower jaws, differentiated teeth, limbs
beneath the body, & probably fur (probably were warm-blooded)
- Gave rise to mammals in the Mesozoic
MASS EXTINCTION OF VERTEBRATES AT THE END OF THE PALEOZOIC
- EXTINCTION OF 75% OF AMPHIBIAN & 80% OF REPTILE
FAMILIES
- Extinction of:
- ACANTHODIANS & PLACODERMS [CLASS] & PELYCOSAURS [ORDER]
- SEVERAL CAUSES
- Climate became more severe (colder & drier)
- More dry continents (rain shadows) with
formation of Pangea
MESOZOIC VERTEBRATES
- REPTILES
- Different subclasses are distinguished by
skull structure (See Appendix III)
- ANAPSIDS - NO HOLES on side of skull (TURTLES, extinct PRIMITIVE [stem]
reptiles)
- SYNAPSIDS - 1 HOLE on LOWER SIDE of skull (extinct MAMMAL-LIKE [pelycosaur
& therapsid] REPTILES)
- EURYAPSIDS - 1 HOLE on UPPER SIDE of skull (MOST extinct MARINE [icthyosaur,
plesiosaur, nothosaur, placodont] REPTILES)
- DIAPSIDS - 2 HOLES on side of skull (MOST LIVING [lizard, snake, crocodile,
tuatara] REPTILES, extinct DINOSAURS, extinct FLYING [pterosaur] REPTILES,
& MOSASAURS [extinct marine reptiles])
- Many new reptile types appeared in the Triassic
- TURTLES (Mesozoic turtles had teeth); TUATARAS; CROCODILES
(Cretaceous forms got to be as long as 15 m); LIZARDS & SNAKES
(snakes evolved from lizards by the Cretaceous)
- MARINE & FLYING REPTILES & DINOSAURS (see below)
- THECODONTS (teeth set in sockets) - a MOSTLY BIPEDAL GROUP that
GAVE RISE to CROCODILES, LIZARDS, SNAKES, FLYING REPTILES & DINOSAURS
- The Triassic land fauna was dominated by
therapsids & thecodonts
- DINOSAURS
- Evolved in the Triassic & expanded
& diversified in the Jurassic &
Cretaceous
- Traditionally divided into two orders based on hip structure:
Saurischia (lizard-hipped) & Ornithischia
(bird-hipped)
- Early dinosaurs were mostly Saurichians,
which are divided into 2 suborders
- BIPEDAL CARNIVOROUS THEROPODS & GIANT, 4-FOOTED HERBIVOROUS
SAUROPODS
- Ornithischians are divided into 4 suborders
- STEGOSAURS, ANKYLOSAURS, CERATOPSIANS, & ORNITHOPODS
- ALL WERE HERBIVOROUS WITH THE FRONT TEETH REPLACED BY A BEAK &
CHEEK TEETH ADAPTED FOR CRUSHING COARSE VEGETATION
- ORNITHOPODS, ANKYLOSAOURS & CERATOPSIANS WERE LOW BROWSERS AND
WERE THE DOMINANT HERBIVORES DURING THE CRETACEOUS
- Robert Bakker has suggested that replacement of high browsing sauropods
by low browsing ornithischians aided fast growing angiosperms in replacing
slow growing gymnosperms as the dominant land plant
- Arguments in favor of warm-bloodedness (Endothermy)
- PREDATOR TO PREY RATIOS; ERECT STANCE; RICHLY VASCULARIZED BONES; GROWTH
RATES; SOCIAL BEHAVIOUR & MIGRATION OF HERDS; HAIR ON FLYING REPTILES;
COMPLETE DOMINANCE OVER MAMMALS
- Arguments in favor of cold-bloodedness (Ectothermy)
- DINOSAURS WERE REPTILES & MODERN REPTILES ARE COLD-BLOODED; ERECT
STANCE & VASCULARIZED BONES WERE RESPONSES TO LARGE SIZE; LARGE SIZE
ITSELF
- Still an open question
- IT IS NO LONGER ACCEPTED THAT DINOSAURS WERE SLOW & PONDEROUS;
DINOSAUR BEHAVIOUR PROBABLY LIKE BIRD & MAMMAL BEHAVIOUR
- THEROPODS WERE QUICK & AGILE; LARGE SAUROPODS & ORNITHISCHIANS
ASSEMBLED IN SOCIAL HERDS; SMALLER SAUROPODS & ORNITHISCHIANS BEHAVED
IN A BIRDLIKE WAY
- FLYING REPTILES
- First flying reptiles - gliders
- Pterosaurs - active flyers with maneuvering ability
- WINGS WERE SKIN STRETCHED BETWEEN ELONGATED 4TH FINGER, SIDES OF THE
BODY & REAR LIMBS
- PTERODACTYLOIDS - ADVANCED PTEROSAURS WITH NO TAILS & SOME HAD
ENORMOUS WINGSPANS: - Pteranodon = 7 m; Quetzalcoatlus northropi
= 15.5 m
- PTEROSAURS WERE WARM-BLOODED - FINE HAIR COVERS WELL-PRESERVED PTEROSAURS
- MARINE REPTILES
- Several groups with marine adaptations, including
paddle-shaped limbs, streamlined bodies, & reproductive
adaptations for birth of young at sea
- Euryapsids - PLACODONTS; NOTHOSAURS; PLESIOSAURS (long
necks; short, tailless bodies; flippers); ICTHYOSAURS (MOST FISH-LIKE MARINE
REPTILE [convergent with dolphins])
- Anapsids - SEA TURTLES
- Diapsids - MARINE CROCODILES OCCURRED MOSTLY DURING JURASSIC;
MOSASAURS (SHORT NECKS; LONG BODIES & TAILS)
- BIRDS
- Many reptilian structural characteristics; feathers
probably modified reptilian scales
- Mesozoic birds are toothed
- Probably descended from coelurosaurs (small
theropods: lizard-hipped) during the Jurassic
- Archeopteryx - first fossil bird to be discovered
- EXCEPT FOR ITS FEATHERS, IT WAS DISTINCTLY REPTILIAN - THECODONT TEETH,
LONG TAIL, CLAW-BEARING FREE FINGERS, UNKEELED STERNUM
- Marine birds - no tail but with teeth
- DUCK-, PELICAN-, TERN- & GULL-LIKE FORMS IN THE CRETACEOUS
- WINGLESS SWIMMERS AS WELL
- MAMMALS
- Fossil mammals distinguished from fossil reptiles by differences
in skull structure
|
Reptiles |
Mammals |
| Lower jaw |
several bones |
single bone |
| Jaw-skull joint |
articular-quadrate |
dentary-squamosal |
| Middle-ear bones |
stapes only |
stapes, incus, malleus |
| Teeth |
no differentiation |
fully differentiated |
| Secondary palate |
absent |
well-developed |
- Mammalian orders are distinguished by molars
- Mammals evolved from Cynodont Therapsids
during the Triassic
- Mesozoic Mammals were mostly small, shrew-like,
nocturnal insectivores
- 5 orders during the Triassic & Jurassic
MESOZOIC MASS EXTINCTIONS
- END OF TRIASSIC
- Extinction of:
- LABYRINTHODONT AMPHIBIANS
- MANY REPTILE ORDERS: Primitive reptiles (Cotylosaurs) [Anapsids, leaving
only turtles]; Advanced mammal-like reptiles (Therapsids) [Synapsids];
Placodonts & Nothosaurs (marine reptiles) [Euryapsids]; Thecodonts
[Diapsids]
- END OF CRETACEOUS
- Extinction of:
- MANY REPTILE ORDERS: Plesiosaurs & Ichthyosaurs (marine reptiles)
[the remaining Euryapsids]; Dinosaurs, Pterosaurs & Mosasaurs [Diapsids,
leaving only snakes, lizards, crocodiles & Tuatara]
- EXTRATERRESTRIAL CAUSES
- Meteorite or asteroid impacts
- HIGH CONCENTRATIONS OF IRIDIUM (RARE IN CRUST, RELATIVELY ABUNDANT
IN METEOR-ITES), SHOCKED QUARTZ, SOOT (FROM IMMENSE WILDFIRES), & FERN
POLLEN SPIKE
- DEPOSITION FROM TSUNAMIS
- CRATER BENEATH YUCATAN PENINSULA
- RESULTED IN ACID RAIN, GLOBAL DARKNESS & GLOBAL COOLING FOLLOWED
BY GREENHOUSE WARMING
- ALSO ASSOCIATED WITH LATE DEVONIAN MASS EXTINCITION
- Planet X & The Companion Star Nemesis
- PERIODICITY IN EXTINCTION RATE OF 26-30 MY MAY INDICATE DISTURBANCE
OF THE OORT CLOUD OF COMETS; CONSISTENT WITH MULTIPLE PEAKS IN IRIDIUM
- TERRESTRIAL CAUSES
- Volcanism - abundant during the Cretaceous
(Deccan Traps & Pacific)
- POSSIBLE SOURCE OF IRIDIUM FROM DEEP IN EARTH
- Climate Change - mostly getting colder
(warmer climates are more stable & less stressful)
- Sea Level Change - sea level drops due to a decrease
in seafloor spreading rates
- Disease - dinosaurs from different land masses
mix
CENOZOIC VERTEBRATES
- BIRDS
- Very successful in fully exploiting the aerial
hibitat
- Many large, flightless predatory birds evolved
in the Cenozoic
- MODERN LARGE, FLIGHTLESS BIRDS (ostrich) are HERBIVOROUS
- MAMMALS
- Decimation of reptile faunas at the end of
the Mesozoic opened up new habitat, & a vigorous mammalian
adaptive radiation followed in the early Cenozoic
- THE CENOZOIC IS OFTEN REFERRED TO AS THE "AGE OF MAMMALS"
- THERE WERE 7-8 ORDERS OF MAMMALS IN THE CRETACEOUS, 16-19 ORDERS IN
THE PALEOCENE, AND 24-27 ORDERS IN THE EOCENE
- General decline in the number of mammal orders during later
Cenozoic (24-25 orders in Oligocene, 22 in Miocene, 20 in Pliocene
& Pleistocene, & 18 at present)
- Monotremes (3 species) & Marsupials
(~250 species)
- MONOTREMES - PRIMITIVE MAMMALS (STILL LAY EGGS BUT HAVE
PRIMITIVE MAMMAE)
- Only 3 species remain (duck-billed platypus & 2
echidna species)
- MARSUPIALS ARE POUCHED MAMMALS THAT DEVELOPED EXTENSIVELY
IN AUSTRALIA & SOUTH AMERICA DURING THE TERTIARY
- The Australian marsupials have survived intact
- The S. American marsupials fared well until the Pliocene
- N. American placentals decimated these marsupials (as well
as the native S. American placentals) after uplift of the Isthmus
of Panama
- The opossum is the only remnant of the S. American
marsupial fauna
- Like placental faunas, marsupials exhibit a wide array of modifications
for various habitats & life styles
- Placental Mammals
- ORDER INSECTIVORA (~400 species)
- Insectivores - oldest placental mammals; gave rise
to many other orders
- ORDER EDENTATA (~30 species) - Armadillos, Anteaters
& Sloths
- ORDER PHOLIDOTA - Pangolins (scaly anteaters)
- ORDER TUBULIDENTATA - Aardvarks
- ORDER CARNIVORA (~275 species)
- Carnivore diversification accelerated in the Miocene
in response to changes in herbivores
- ORDER CHIROPTERA (~875 species)
- Bats, only truly flying mammals, comprise the order Chiroptera
- Bats probably 2nd most successful mammal order (>20%
of mammal species)
- ORDER RODENTIA (~1700 species)
- Rodents include a diversified group of burrowing (mice),
aquatic (beaver, muskrat), arboreal (squirrel) & desert-dwelling
(kangaroo rat) animals
- Rodents probably most successful mammal order (>40%
of mammal species)
- ORDER LAGOMORPHA (~65 species) - Rabbits & Hares
- ORDERS PERISSODACTYLA (~16 species), ARTIODACTYLA
(~180 species) & PROBOSCIDEA (~2 species)
- These are the Ungulate (hoofed herbivore) Orders
- Perissodactlys are odd-toed ungulates (horses, rhinoceri &
tapirs) & were dominant during the Eocene
- with the advent of grasses in the Miocene, horses
become more diversified
- the largest land mammal ever, 5 m tall at the shoulder, was Oligocene
to early Miocene hornless rhinoceros Indrichotherium
- Artiodactyls are even-toed ungulates (pigs, hippos, deer, goats,
sheep, cows & camels) & have been the dominant ungulates
since the Oligocene
- Proboscideans are ungulates with trunks (elephants & extinct
mastadons & mammoths)
- Closely related to proboscideans are the ORDERS SIRENIA
(Manatees) and HYRACOIDEA (Hyrax, or cony)
- ORDER DERMOPTERA - Flying lemurs
- ORDER PRIMATES (~175 species)
- Primates include humans, as well as apes, monkeys, tarsiers,
lorises & lemurs
- Primates are divided into 2 suborders - Prosimii
which includes tarsiers, lorises & lemurs; &
Anthropoidea which includes humans, apes &
monkeys
- Prosimians dominated the Early Cenozoic (Paleocene &
Eocene)
- Anthropoids dominated the Late Cenozoic (Oligocene &
Neogene)
- apes (Superfamily Hominoidea, Family Pongidae) are found in Africa
(chimpanzee, gorilla) & Southeast Asia (orangutan, gibbon)
- Humans (Superfamily Hominoidea, Family Hominidae) are
the most numerous & widespread primate
- hominids evolved from ape-like ancestors in Africa about 5 my ago
CENOZOIC MASS EXTINCTIONS
- TWO CENOZOIC MASS EXTINCTIONS
- Eocene
- Followed by an OLIGOCENE-MIOCENE ADAPTIVE RADIATION OF MAMMALS
- Pleistocene
- Marked by EXTINCTION OF LARGE MAMMALS
- CAUSES
- Eocene
- CLIMATE CHANGE: First glacial ice in Antarctica; Sealevel low; Drier
& colder conditions
- EXTRATERRESTRIAL: Planet X & the Companion Star Nemesis
- Pleistocene
- CLIMATE CHANGE
- Climate warmed as ice melted
- Problem is that it had done this many times before
- HUMAN OVERKILL
- PROBABLY a COMBINATION
Study Questions
1. Summarize the details of Paleozoic vertebrate evolution.
2. What are the details of fish evolution (the different fish classes
that evolved, the classes that are extinct & the class that is reduced
in importance)? What was the structure modified to form fish jaws?
3. What were the changes required to adapt to land?
4. What were the characteristics of Paleozoic amphibians?
5. What is the significance of the evolution of the amniote egg?
6. Summarize the details of reptile evolution (progression from primitive
reptiles to advanced mammal-like reptiles).
7. Summarize the details of the terminal Permian mass extinction, including
the vertebrate groups that became extinct & the probable causes.
8. Summarize the way that different reptile subclasses & different
dinosaur orders are distinguished.
9. Summarize the differences between Triassic & Jurassic-Cretaceous
land fauna.
10. Summarize the arguments for & against the warm-bloodedness of
dinosaurs.
11. Summarize the general characteristics of bird evolution during the
Mesozoic and Cenozoic, including the group of dinosaurs that gave rise to
birds, when this occurred, & the nature of the oldest bird fossils.
12. Summarize the characteristics of Mesozoic birds.
13. Summarize the way mammals & reptiles and the way different mammalian
orders are distinguished.
14. Summarize the details of the terminal Triassic & Cretaceous mass
extinctions, including the vertebrate groups that became extinct & the
probable causes.
15. Summarize the general characteristics of the mammalian Cenozoic adaptive
radiation.
16. Briefly summarize the 2 Cenozoic mass extinctions.