Lecture 6-handout

9/29/08
“Age of Mammals”
“Age of Dinosaurs”
SYNAPSIDS (Carboniferous - Recent)
“PELYCOSAURS”
VARANOPSEIDS/
OPHIACODONTIDS
SPHENACO-
DONTIDS
BIARMO-
SUCHIANS
CASEIDS/
EOTHYRIDIDS
DICYNODONTS
EDAPHOSAURS
NON-MAMMAL
CYNODONTS
GORGONOPSIANS
DINOCEPH-
ALIANS
MAMMALS
THEROCEPH-
ALIANS
CYNODONTS
THERIODONTS
SYNAPSIDA
THERAPSIDS
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“PELYCOSAURS”
• Grade of basal mammal-like reptiles, earliest & most diverse in N Amer
BASAL LINEAGES: Eothyridids, Caseids - small head, pointy nose, BIG NOSTRIL
EOTHYRIDIDS (Permian, TX/OK)
• Carnivores
CASEIDS (Permian, TX/OK, Russia)
• Herbivores (spatulate teeth, barrel-chest)
†Eothyris (Permian, N Amer)
• 1-2 ft long
†Ennatosaurus (Permian, Russia), ~4 ft long.
†Cotylorhynchus (Permian, OK)
• 12+ ft long, 600+ lbs
“PELYCOSAURS”
DERIVED LINEAGES (1)
†VARANOPSEIDS (Carb-Permian, N Amer)
†OPHIACODONTIDS (Carb-Permian, N Amer)
• Earliest fossil synapsids
• Carnivorous, largest animals alive
at this time (3+ m)
• Head shape long, narrow, hatchet-shaped
Skull - ventral view
“PELYCOSAURS”
DERIVED LINEAGES (2): †EDAPHOSAURS
Skull - ventral view
†Edaphosaurus (Permian, N Amer)
• Large (10 ft+) herbivores: tiny head, barrel chest, round peg teeth (on palate, too)
• Sail fin on back - neural spines with crossbars
(spines bear grooves for blood vessels)
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“PELYCOSAURS”
DERIVED LINEAGES (3): †SPHENACODONTIDS
†Dimetrodon (Permian, N Amer)
• Large (10 ft+) carnivores
• Sail fin on back
“PELYCOSAURS”
PALEOBIOLOGY: Limb Posture
†Dimetrodon (Permian, N Amer)
Scapula
(lateral view)
Femur head
(terminal)
Humerus head
(proximal view)
Distal condyles
(ventral)
• All pelycosaurs use SPRAWLING limb posture
• SCREW-SHAPED GLENOID on scapula - head of humerus fits in track
• Head of femur terminal; distal condyles ventral
(directs femur horizontal, shank vertical)
Skull differences
“PELYCOSAUR”
• Lots of “canine” teeth
• Occiput slopes forward
• Large postdentary bones
vs
THERAPSID
• Single large canine tooth
• Occiput slopes back
• Smaller postdentary bones in jaw
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THERAPSIDS
BASAL LINEAGES (1): †BIARMOSUCHIANS (Permian, Russia, S Afr)
†Biarmosuchus (Permian, Russia)
canine
• Most basal therapsid, shows:
• Posterior sloping occiput, expansion of cerebellum
• 1 large canine
• Erect gait
THERAPSIDS
BASAL LINEAGES (2): †DINOCEPHALIANS (Permian, Russia, S Afr)
†Titanophoneus (Permian, Russia)
• “Terrible heads” - tend to have thickened, robust skulls
• Some herbivores, some carnivores (this one carnivorous) THERAPSIDS
BASAL LINEAGES (2): More †DINOCEPHALIANS (Permian, Russia, S Afr)
†Estemmenosuchus (Permian, Russia)
†Moschops (Permian, Russia)
Force transferred
thru occipital condyle
• Herbivores: nipping incisors, small cheek teeth, barrel chest
• Thick skulls, many with ornamentation - head butting? 4
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THERAPSIDS
BASAL LINEAGES (3): †DICYNODONTS (Perm-Triassic, global)
†Lystrosaurus (Perm-Triass, S Afr, Russia, Antarc)
†Dicynodon (Perm, S Afr, Russia)
• Specialized herbivores, shearing beak, lose most or all teeth except tusks
• 70+ taxa, 80-90%specimens in some Permian faunas (5+ sympatric taxa, diff sizes & niches)
• Most die out at end-Perm, Triassic radiation less diverse
THERAPSIDS
DERIVED LINEAGES(1): †GORGONOPSIANS (Perm, S Afr, Russia)
†Inostrancevia (Permian, Russia)
Flattened femur
“sabre” canines
• Dominant predators of Permian; tiger sized (~10 ft, 500 lbs)
• Massive, “sabre” canines
Dorsal view
THERAPSIDS
DERIVED LINEAGES(3): †CYNODONTS (Perm-Recent, includes mammals)
†Cynognathus (Triassic, S Afr)
†Probelesodon (Triassic, S Amer)
Masseter fossa
Bony palate
Many changes closer to mammals:
• Cheeks flare laterally to accommodate larger jaw muscles
• Coronoid develops deep fossa for massester (jaw closing muscles)
• Secondary palate expands**
• Double occipital condyle**
• Even smaller postdentary bones
• BUT, still no single dentary-squamosal articulation. NOT “Mammalia” (rather, “Mammaliamorpha”)**
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THERAPSIDS
“PELYCOSAUR”
THERAPSID
MAMMAL
HEAD
DISTAL
Changes in limb anatomy related to upright posture
• Head offset at angle & spherical, distal condyles rotate terminally
THERAPSIDS
“PELYCOSAUR”
THERAPSID
(Carrier, 1987)
MAMMAL
(Jenkins, 1971)
• Upright posture facilitates shift from lateral bending to dorso-ventral bending in running
(This allows both lungs to fill during running, promoting SUSTAINED ACTIVITY)
THERAPSIDS
DERIVED LINEAGES(3): †CYNODONTS (Perm-Recent, includes mammals)
• Cynodonts typically reconstructed as active predators (or foraging herbivores) 6
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MAMMALS! (or at least, Mammaliaforms...)
(Jurassic-Recent)
†Morganucodon (Jurassic, England)
†Megazostrodon (Jurassic, S Afr)
• Earliest mammaliaform mammals tiny (~15 cm)
• Distinctive features
(1) Precisiely occluding cheek teeth divided into premolars & molars
(2) Cheek teeth have 2 roots
(3) Only 1 set replacement teeth (some teeth only in adult)
(4) Enlarged brain capacity (mostly hearing & smell - nocturnal?)
Trait
Pelycosaurs
Therapsids
Cynodonts
Teeth:
weakly heterodont
increasingly heterodont
strongly hetero
Palate:
no secondary palate
partial
complete
“-apsidy”
small temporal fenestra
enlarged fenestra
vastly expanded
Postdentary bones: present, large
present, reduced
absent
Body size:
Large, ca. 3m
Medium and large (3-5m)
small (eventually)
Occipital condyle:
Single
Double
Double
Posture:
sprawling
intermediate
upright
Kemp (1982)
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When did endothermy evolve?
Endothermy---Body temperature regulated internally.
Homeothermy---Body temperature maintained within
a narrow range.
When did endothermy evolve?
Advantages of endothermy:
1. Independence from environment
(active in colder places, and at NIGHT).
2. Enhanced respiritory capacity
(allows sustained vigorous activity)
3. Speeds growth
When did endothermy evolve?
DISadvantages of endothermy:
1. Energetically expensive:
ca. 70% of calories JUST to stay warm.
Birds & mammals eat ca. 10X more food
than similar sized ectotherms.
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When did endothermy evolve?
Birds & mammals:
Common ancestor ECTOthermic, HETEROthermic.
When did endothermy evolve?
Birds & mammals:
Common ancestor ECTOthermic, HETEROthermic.
ENDO-, HOMEOthermy evolved at least twice.
When did endothermy evolve?
Homeothermy:
Doesn’t require endothermy.
Probably evolved several times.
Result of thermal inertia:
Bigger=relatively smaller surface area.
Slower changes in body temperature.
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When did endothermy evolve?
Late pelycosaurs:
Therapsids:
Features associated with endothermy
1. BONE STRUCTURE
2 types of bone:
1. Lamellar-zonal: Bone laid down in simple layers.
2. Fibro-lamellar (birds & mammals): Similar
layering, but additional canal system to carry blood.
Pelycosaurs: Lammellar-zonal.
Therapsids: Fibro-lamellar.
BUT--lots of diversity, & some modern endos have #1
(and vice versa)....SUGGESTIVE, not definitive.
Features associated with endothermy
2. POSTURE & LIMB SUPPORT
Upright posture expensive, more common in endos.
Maintained by muscle contraction---gives of HEAT.
Therapsids were “hybrids.”
Some modern ectos have similar gaits to endos.
INCONCLUSIVE/WEAK.
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Features associated with endothermy
3. HAIR
Therapsid fossils have SOME indication of hair on skulls,
but similar markings found on hairless ectos.
Features associated with endothermy
4. Brain size
Mammal & bird brains ca. 10 times larger than similar sized
reptiles.
Endothermy requires larger brain?
Therapsids: intermediate.
WEAK.
Features associated with endothermy
5. DIAPHRAGM
Doesn’t fossilize. INCONCLUSIVE.
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Features associated with endothermy
6. SECONDARY PALATE
Reflects increased need of O2?
BUT...crocs have, birds don’t.
Soft palate would do just as well (wouldn’t fossilize).
First see in dicynodonts, but INCONCLUSIVE.
Features associated with endothermy
7. PREDATOR-PREY RATIOS.
Endo carnivores burn lots of calories to stay warm,
community can support fewer.
Features associated with endothermy
7. PREDATOR-PREY RATIOS.
Endo carnivores burn lots of calories to stay warm,
community can support fewer.
Mammal pred:prey ratios usually 2-3% of community.
Ecto pred:prey ratios usually 40-50%.
Pelycosaurs: 45%. Therapsids 15-20%...intermediate.
BUT, must know PREY; MASS more important than
NUMBERS; fossil ratio ≠ true ratio....WEAK.
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Features associated with endothermy
8. BIOGEOGRAPHIC DISTRIBUTION
Therapsids lived at high latitudes; large ectos can’t.
BUT, high latitudes warmer then.
AND, evidence of ectos at same latitudes, same time.
UNCONVINCING
Features associated with endothermy
9. MAXILLARY TURBINALS
Modern mammals (& birds) have turbinals covered with
epithelium.
1. Cleans, humidifies, & WARMS air breathed in.
2. COOLs exhaled air (conserving heat).
As air cools, loses moisture---deposited & absorbed
(conserving water).
“COUNTERCURRENT EXCHANGE” (heat AND moisture)
Works ONLY if body temp. warmer than surrounding air.
NOT found in any ectos, living or extinct.
Most amniote tetrapods:
Lateral walls of nasal cavity exhibit one or more “conchal” projections, which
provide additional surface area for nasal epithelia.
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Ethmoid turbinals (sensory: olfaction)
Maxillary turbinals (heat, moisture retention)
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Features associated with endothermy
9. MAXILLARY TURBINALS
Present in several therapsids.
Pre-mammalian
therapsids were
warm-blooded!
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