Chapter 6 Outline
INTRODUCTION TO STEGOSAURIA (ROOF LIZARD)
- CHARACTERISTICS
- ROWS OF OSTEODERMS THAT SOMETIMES DEVELOPED INTO SPINES AND PLATES
ALONG THE NECK, BACK AND TAIL
- QUADRAPEDAL LIMB POSTURE
- LONG, THIN, RELATIVELY SMALL HEADS WITH SMALL TEETH THAT SUGGEST HERBIVORY
- SHORT, MASSIVE FORELIMBS AND LONG, COLUMNAR HINDLIMBS THAT GIVES A
PROFILE SLOPED STRONGLY FORWARD AND DOWNWARD
- Toes ended in broad hooves
- THREE TO NINE METERS IN LENGTH; 300 TO 6500 KILOGRAMS
- GEOLOGICAL RANGE & DIVERSITY
- MIDDLE JURASSIC TO EARLY LATE CRETACEOUS (~170 - 95 MILLION YEARS)
- MAXIMUM DIVERSITY - 7 SPECIES DURING THE LATE JURASSIC
- A dozen species (11 genera) throughout their time on earth
- FOUND IN NORTH AMERICA, EUROPE, CHINA, INDIA AND AFRICA
HISTORY OF STEGOSAUR DISCOVERIES
- 19TH CENTURY (1870's)
- EUROPE
- 2 genera from upper Jurassic beds
- NORTH AMERICA
- Stegosaurus from upper Jurassic Morrison Formation
- 20TH CENTURY
- AFRICA
- Kentrosaurus from upper Jurassic units of the
Tendaguru area of Tanzania (before WWI)
- 1 other genera from upper Jurassic-lower Cretaceous beds of southern
Africa (during WWII)
- CHINA
- 5 genera (6 species) from middle Jurassic, upper Jurassic
and lower Cretaeous units (1959, 1970's, 1980's)
- INDIA
- 1 genus from upper Cretaceous units (1979)
STEGOSAUR PALEOBIOLOGY AND PALEOECOLOGY
- STANCE AND GAIT
- SHORT, MASSIVE FORELIMBS AND LONG, COLUMNAR HINDLIMBS SUGGEST STEGOSAURS
WERE NOT BUILT FOR GREAT SPEED
- EATING
- STEGOSAURS HAVE A MIX OF CHARACTERISTICS, SOME OF WHICH SUGGEST SOPHISTICATED
ORAL FOOD PROCESSING AND OTHERS OF WHICH SUGGEST SIMPLE ORAL FOOD PROCESSING
COMBINED WITH INTERNAL FOOD BREAKUP
- Sophisticated oral food processing
- A HORN-COVERED BEAK (RHAMPHOTHECA) COVERED THE FRONTS OF THE UPPER
AND LOWER JAWS AND WAS USED TO CROP OR STRIP FOLIAGE FROM PLANTS
- STEGOSAURS SEEM TO HAVE HAD CHEEKS
- Simple oral food processing combined with internal food breakup
- TEETH ARE RELATIVELY SMALL, SIMPLE, AND TRIANGULAR AND APPARENTLY DID
LITTLE GRINDING (LACK WELL-DEVELOPED WEAR SURFACES ON CROWNS) AND
- JAW MUSCLES SEEM TO BE WEAK
- SO PERHAPS STEGOSAURS HAD A GIZZARD PACKED WITH STONES TO GRIND FOOD
(like some birds, crocodiles, sauropods and psittacosaurs)
- Gastroliths have not been found associated with Stegosaur skeletons,
however
- STEGOSAURS HAVE A NARROW SNOUT, SUGGESTING A FAIR DEGREE OF FOOD SELECTIVITY
- Posture suggests Stegosaurs were principally low-browsers (less
than 1 meter)
- Bakker argues that some Stegosaurs could have reared up on their
hind legs, using their tail as a third "leg" to from a tripod,
to feed higher up in trees (2 - 4 meters)
- Center of gravity near hips and hind limbs supported nearly 80% of
body weight
- BRAINS
- STEGOSAURS HAD SMALL BRAINS BASED ON BRAIN CASTS - BRAINS WERE ONLY
AN ESTIMATED 0.001% OF BODY WEIGHT
- Relatively large olfactory bulbs suggest Stegosaurs had a good sense
of smell
- STEGOSAURS HAD AN ENLARGEMENT OF THE SPINAL CORD CANAL IN HIP VERTEBRAE
- Marsh and others suggest this enlargement housed a second brain
(to control the back legs and tail)
- Giffin has recently shown that the enlargement was probably used
for a glycogen body, as occurs in some living birds
- BEHAVIOUR
- STEGOSAUR SOCIAL BEHAVIOUR MOSTLY UNKNOWN
- No nests, eggs, or hatchlings
- Only a few juvenile and adolescent specimens
- Some sexual dimorphisms among adults
- NUMBER OF RIBS FORMING SACRUM
- Kentrosaurus appears to have lived in herds
- MASS ACCUMULATION OF DISARTICULATED BUT ASSOCIATED FOSSILS AT TENDAGURU
- PLATES AND SPINES
- MOST STEGOSAURS HAVE AT LEAST ONE ROW OF SPINES OR PLATES (only in
the case of Stegosaurus ) ALONG THEIR BACK & ALL HAVE PAIRS
OF SPINES AT THE END OF THE TAIL
- Spines and plates were embedded in skin (they were osteoderms),
and not articulated with vertebrae
- STEGOSAURUS MAY HAVE BEEN ABLE TO ROTATE ITS PLATES FROM A FOLDED
DOWN TO ERECT POSITION ACCORDING TO BAKKER
- IMPORTANCE OF SPINES AND PLATES
- Protection and defense
- PARTICULARLY TAIL SPIKES AND PARASCAPULAR SPINES
- Display
- SHAPES AND PATTERNS OF PLATES AND SPINES ARE NEARLY ALWAYS SPECIES
SPECIFIC
- Thermoregulation
- STEGOSAURUS PLATES ARE COVERED WITH AN EXTENSIVE PATTERN OF
GROOVES, AND THE INSIDES ARE FILLED WITH A HONEYCOMB OF CHENNELS, PROBABLY
FOR CONVEYING BLOOD VESSELS
- PLATES WERE PROBABLY ARRANGED IN ALTERNATING PAIRS AS INDICATED BY
WIND TUNNEL EXPERIMENTS
- NOTE - JUVENILES MAY NOT HAVE DEVELOPED PLATES, PRESUMABLY BECAUSE
THEY DID NOT NEED THEM FOR DISPLAY OR THERMOREGULATION
- SPINES PROBABLY DEVELOPED FOR PROTECTION & DEFENSE INITIALLY -
DISPLAY & THERMOREGULATION WOULD HAVE DEVELOPED LATER