Chapter 9 Outline
INTRODUCTION TO CERATOPSIA (HORNED FACE)
- CHARACTERISTICS
- SHARP, PARROTLIKE BEAK (FORMED BY ROSTRAL BONE AT THE TIP OF THE SNOUT)
- LARGE SHEET OF BONE CALLED THE FRILL EXTENDING FROM THE BACK OF THE
SKULL
- Epoccipitals, long spikes or lump of bones, ornament
the margin of the frill in some genera
- LARGE, AGGRESSIVE-LOOKING HORN CORES
- Some ceratopsians had 2, one over each eye, &
a third over the nose; some had a nose horn and no eye horns;
several had roughened bone over the nose and eyes; some had no
horns at all
- IMPRESSIVE DENTAL BATTERY FOR SLICING PLANT MATERIAL
- QUADRUPEDAL LIMB POSTURE AMONG LATER AND LARGER CERATOPSIANS
- Bipedal stance for earlier and smaller ceratopsians
- FORELIMBS SHORTER THAN HINDLIMBS; BOTH PAIRS MASSIVE (AMONG QUADRUPEDAL
FORMS)
- Toes ended in broad hooves
- FIVE TO NINE METERS IN LENGTH; UP TO 7000 KILOGRAMS (LARGER CERATOPSIANS)
- Smaller Ceratopsians were about 2 meters long
- GEOLOGICAL RANGE & DIVERSITY
- EARLY TO LATE CRETACEOUS (~115 - 65 MILLION YEARS)
- MAXIMUM DIVERSITY - 22 GENERA DURING THE LATE CRETACEOUS
- At least 23 genera (and many more species) throughout their
time on earth
- Only Psittacosaurus from Early Cretaceous
- FOUND IN NORTH AMERICA, MONGOLIA, CHINA AND KAZAKHSTAN
HISTORY OF CERATOPSIAN DISCOVERIES
- 19TH CENTURY (1870's, 1880's, 1890's)
- NORTH AMERICA
- Triceratops & Torosaurus from Wyoming,
as well as Centrosaurus (initially identified
as Monoclonius ) from Montana
- 20TH CENTURY
- NORTH AMERICA
- Centrosaurus (based on much better material)
from Canada and 1 other genus from Wyoming (1904, shortly after)
- Styracosaurus , Chasmosaurus , Leptoceratops
, 1 other genus from Canada, and 1 other genus from Montana
(1913, 1914)
- Pentaceratops from New Mexico and Arrhinoceratops
from Canada (1923, 1925)
- Pachyrhinoceratops and 1 other genus from Canada (1940's,
1950's)
- 3 genera (1980's, 1990's)
- ASIA
- Protoceratops & Psittacosaurus (1920's)
and 1 other genus (1950's) from Mongolia, China &
Russia
- Bagaceratops and 3 other genera (1980's, 1990's) from
Mongolia, China & Kazakhstan
CERATOPSIAN DIVERSITY
- TWO CLADES OF CERATOPSIANS - PSITTOCOSAURIDAE AND NEOCERATOPSIA
- PSITTACOSAURIDAE
- BIPEDAL DINOSAURS, ABOUT 2 M LONG
- ONE GENUS, AT LEAST 7 SPECIES
- HAVE CLOSE AFFINITIES WITH BIPEDAL PACHYCEPHALOSAURIA (WHICH TOGETHER
WITH CERATOPSIANS FORMS THE CLADE MARGINOCEPHALIA) AND ORNITHOPOD DINOSAURS
(WHICH TOGETHER WITH MARGINOCEPHALIANS FORM THE CERAPODA CLADE OF ORNITHISCHIAN
DINOSAURS)
- Implies that quadrupedal stance in most Ceratopsians is a return
to the ancestral condition for Tetrapoda as a whole
- NEOCERATOPSIA
- UNCLEAR WHETHER SMALL, HORNLESS (OR SMALL, BLUNT NASAL HORN) "PRIMITIVE"
GENERA (INCLUDING Protoceratops , Leptoceratops , &
Bagaceratops ) FORM A CLADE (CALLED PROTOCERATOPSIDAE) OR NOT
- Sereno argues that sequential evolution of these "primitive"
genera leads to the clade of large horned Ceratopsians (called Ceratopsidae)
- CERATOPSIDAE
- TWO CLADES - CHASMOSAURINAE & CENTROSAURINAE
- CHASMOSAURINAE
- Long frills with horns over the eyes & nose
- Includes Chasmosaurus , Pentaceratops , Arrhinoceratops
, Triceratops & Torosaurus
- CENTROSAURINAE
- Short frills without horns over the eyes, but with nose horns or
bosses
- Includes Centrosaurus , Styracosaurus & Pachyrhinoceratops
CERATOPSIAN PALEOBIOLOGY AND PALEOECOLOGY
- EATING
- CERATOPSIANS HAD SOPHISTICATED ORAL FOOD PROCESSING EQUIPMENT &
CHEWED WELL
- A hooked rhamphotheca suggesting selectivity in food choice
- A dense cluster of cheek teeth that were constantly replaced as
they wore down
- VERTICAL OCCLUSION FOR SLICING AND DICING OF FOOD
- A sturdy coronoid process
- THIS LARGE VERTICAL PROTRUSION ON THE LOWER JAW ALLOWED ATTACHMENT
OF A GREAT MASS OF JAW-CLOSING MUSCALATURE
- Fleshy cheeks
- Note: All of these attributes are similar to those of hadrosaurids
and of modern herbivorous mammals (like sheep, cows & horses)
- CERATOPSIANS APPARENTLY DID NOT HAVE A SOPHISTICATED INTERNAL DIGESTIVE
SYSTEM, AS SUGGESTED FOR STEGOSAURS, ANKYLOSAURS, & PACHYCEPHALOSAURS
- The remainder of the Ceratopsian digestive tract does not appear
to have been dispropotionately large
- Psittacosaurus is the only Ceratopsian (or Ornithischian)
with gastroliths
- CERATOPSIANS PROBABLY BROWSED NO MORE THAN 2 METERS ABOVE THE GROUND
- CERATOPSIANS PROBABLY DID NOT FEED ON CYCADS AND PALMS, BUT INSTEAD
ON A VARIETY OF SHRUBBY ANGIOSPERMS (FLOWERING PLANTS), FERNS, AND PERHAPS
SMALL CONIFERS
- The browsing of Ceratopsians and other large, low-browsing herbivorous
dinosaurs may have contributed to the extraordinary rise of flowering plants
during the Late Cretaceous
- LOCOMOTION
- ORIENTATION OF THE FORELIMBS IS PROBLEMATIC
- Bakker reconstructs Ceratopsian forelimbs as fully erect
- Others reconstuct Ceratopsian forelimbs with a more spawling posture
- MAXIMUM SPEEDS: 20-40 KPH (12.5-25 MPH), AVERAGE 30-35 KPH (~20 MPH)
- WALKING SPEEDS: 2-4 KPH (1-2.5 MPH)
- BEHAVIOUR
- FUNCTION OF HORNS
- Interspecific: defense
- Intraspecific: display, ritualized combat, establishment
of dominance & defense of territories
- PUNCTURE WOUNDS ON FACES, FRILLS AND BODIES OF CERATOPSIANS (PRESERVED
IN AT LEAST 5 SPECIMENS) SHOW THAT HORNS WERE USED IN INTRASPECIFIC COMBAT
- FUNCTION OF FRILLS
- Attachment of jaw muscles (suggested by Ostrom in 1966)
- Sexual dimorphism in size and shape of adult frills among Protoceratops
, Centrosaurus & Chasmosaurus indicates a display
component in the development of frills, scallops and spikes
- STUDIES OF PROTOCERATOPS SHOWS THAT FRILL GROWTH OCCURS
AT SEXUAL MATURITY
- SOCIAL BEHAVIOUR
- Many, if not all, Ceratopsians lived in herds at least
part, if not all, of the year
- EVER INCREASING CATALOG OF BONEBEDS (mass accumulation of single species)
- NOW KNOWN FOR AT LEAST 9 SPECIES
- MINIMUM NUMBER OF INDIVIDUALS MAY EXCEED OVER 100 FOR SEVERAL BONE
BEDS
- Brains less than size expected of a similarly sized crocodilian
or lizard
- LARGER THAN SAUROPODS, ANKYLOSAURS AND STEGOSARUS
- Small, "primitive" Ceratopsians may have
used their small frills as a visual dominance symbol, and then used
their small, blunt nasal horns to ram the flanks of their opponents
- Larger Ceratopsians developed more elaborate frills and horns
- LONG-FRILLED CHASMOSAURINES PROBABLY EMPHASIZED FRILL DISPLAY WITH
INCLINATION OF THE HEAD AND NODDING OR SHAKING THE HEAD SIDE-TO-SIDE
- Failure of frill display would lead to frontal engagement of nasal
and brow horns, with shoving and charging determining the winner
- SHORT-FRILLED CENTROSAURINES MAY HAVE USED THEIR NASAL HORNS MORE READILY
- EXCEPTIONS: STYRACOSAURUS IS A CENTROSAURINE BUT HAS LONG FRILL
MARGIN SPIKES & MAY HAVE DEPENDED MORE ON FRILL DISPLAY; TRICERATOPS
IS A CHASMOSAURINE WITH A SECONDARILY SHORTENED FRILL & COMBAT MAY
HAVE TAKEN PLACE WITHOUT EXTENSIVE FRILL DISPLAY