Ornithischia

*- pelvis opisthopubic - process of pubis is rotated bacwards to lie close to and parallel with the ischium

*- presence of predentary bone

*-presence of palbebral bone (this bone crosses outside of eye socket

*-ossified tendons above the sacral region

*-cheek teeth leaf-shaped with triangular crown and constricted roots

*-coronoid processes behind tooth row on lower jaw

*-jaw joint set below level of upper tooth row

*-at least 5 sacral vertebrae

-small prepubic process along pubis

-long preacetabular process on ilium

  Genasauria

*-reduction in size of openings in lateral jaw bones (mandibular fenestra)

*-muscular cheeks indicated by positioning of tooth rows

-loss of gastralia

    Thyreophora

*-jugal bone (one of cheek bones) has a transverse process below eye

*-parallel rows of dermal armor

       Eurypoda

-reduction of 4^th trochanter

-short stocky metatarsal and metacarpel bones

-shortened post acetabular process on ilium

-loss of phalanx on digit IV of foot

-special horns fuse margins of eye socket

-enlargement forward portion of ilium

             Stegausauridae

*-rows of bones (osteoderms) that sometimes developed into spines and plates along back, neck and tail

*-quadrapedal, short forelimbs with long columnar hind limbs

*-long thin, relatively small head

*-Back vertebrae very tall neural arches and highly angled transverse processes

-sacrum 5 or 6 fused vertebrae

             Ankylosauria

*-closure of antorbital and upper temporal openings

-ossification and fusion of keeled plate onto side of jaw

-fusion of first tail vertebrae to sacral vertebrae and ilium

                       -closure of hip joint 

*- Low wide skull

*- Cheek teeth deeply inset

*- Body encased in armor plates

*- Fusion of armor to skull, masking cranial sutures

- Secondary closure of acetabulum

- Horizontal rotation of ilium

- Reduction in size of pubis

- Low neural spines on dorsal vertebrae

- Short limbs. Hindlimbs > Front limbs by about 50%

Group Broken into two families:1. Nodosauridae 2. Ankylsauridae. Based primarily on presence of bone club on tail, but many other characters also.

Marginocephalia

     Pachycephalosauria

Characters:

*1. Posterior edge of skull roof overhangs occiput

*2. Thickened skull roof. Frontal and parietal bones are thickened.

*3. Skull fore-shortened anterior-posteriorly

                       - frontal excluded from orbital margin

                       -tubercles on posterolateral margin of squamosal

                         -double ridge-and-groove articulations on dorsal vertebrae

                              elongate sacral ribs

4. Squamosal broadly expanded on deep occiput

5. Anterior and medial walls of orbits ossified

6. Dorsal vertebrae have distinctive double ridge-in-groove articulation between successive vertebrae.

7. Bundle of ossified tendons surrounds distal part of tail

8. Slender scapula much longer than humerus

*9. Small pubis not part of acetabulum

*10. Ornamentation external skull surface.

Group Broken into two groups: ? Now appears dome-headed derived from flat-headed

                                   1. Homalocephalidae = flat-headed

                                   2. Pachycephalosauridae = dome-headed

    Ceratopsia: “horn-faced dinosaurs”

-Primary character rostral bone - unique cap on snout with parrot-beak shape.

                       Psittacosaurus “parrot lizard” - transitional bipedal form

                                   1. Short preorbital region on skull

                                   2. High external nares

                                   3. Broad lateral premaxillary process

                                   4. Loss of digit 5 on hand

                                   5. Loss of antorbital opening

    Neoceratopsia

          Characters:     1. All quadrapedal

                                   *2. Fully developed frill (parietal bone)

                                   *3. Upwardly hooked lower beak

                                   4. Reduction/loss of premaxillary teeth

                                   5. Sharply keeled rostral bone

                                   *6. Fusion first 3 cervical vertebrae

                                   7. Short projection of lower jaw beyond jaw joint

                                   *8. Head proportionally large.

Protoceratopsidae - disputed as monophyletic group - ?progressive series

                                   Small bodied forms- e.g. Leptoceratops, Protoceratops

         Ceratopsidae:

          Characters:     *1. Very large skulls

                                   *2. Long horns and extensive frills

                                   *3. Complex dental battery

                                   4. Secondary roof over brain case

                                   5. Double rooted teeth

               Centrosaurinae

                     Characters:     *1. Short squamosals (square)

                                               *2. Long nasal horn

                                               *3. Short brow horns

                                               4. Long and narrow opening on top of skull roof

                                               *5. Rounded epocciptals decorating rim of frill

                                               6. Bony fingers projecting back into nares

                        Genera: Centrosaurus, Styracosaurus, Pachyrhinosaurus

                Chasmosaurinae

                     Characters:     *1. Long squamosals

                                               *2. Large orbital horns

                                               *3. Short nasal horn

                                               4. Thickening of bones of snout

                                               5. Enlargement of rostral bone

                                               6. Key-shaped opening between frontal bones

                                               *7. Epioccipitals broad based and triangular

                                               8. Large connical epijugal bone on flared cheeks

                       Genera: Chasmosaurus, Torosaurus, Triceratops, Anchiceratops

Ornithopoda

          Characters:     *1. Pronounced offset of the premaxillary tooth row relative to maxillary

                                   2. Cresencentric parocciptal process

*3. Depression of mandibular condyle beneath level of upper and lower tooth row

*4. Elongation of the lateral process of the premaxilla to contact the lacrimal and or prefrontal bones.

                     Heterodontosauridae

                        Characters:*1. Large canine-like tooth present upper and lower jaw

                                               2. High crowned teeth with chisel-shaped crown

                                               3. Long arms with large manus

                                               4. Prominent dental battery

                                   Genera: Heterodontosaurus

     Euornithopoda

          Characters:     1. Absence of prominent boss in cheek region

                                   2. High angle between prepubic process and body of pubis

                                   *3. Loss of fenestra lower jaw

                                   *4. Elongation of prepubic bone

                                   5. Presence of obturator process on ischium

                                   *6. Pleurokinetic skulls

                                   7. Modification of the orbital margin

           Hysilophodontidae

              Characters:*1. Retain premaxillary teeth (many)

                                   2. Loss of ridges on chisel shaped cheek teeth

*3. Ossification of more forwardly placed ribs where fuse to sternum

                                   4. Development of rod-shaped pre-pubic bone

                       Genera: Hypsilophodon

          Iguanodontidae

                Characters:*1. Eversion of the oral margin of the predentary

                                   2. Enlargement of external nares

                                   3. Reduction of antorbital opening

                                   4. Denticulate margin of predentary

                                   *5. Loss of premaxillary teeth

                                   6. Reduction of bones of digit 2

                                   *7. Predentary bone with two processes that project backwards

                                   8. Loss phalanx 3^rd digit

                                   9. Compressed blade-shaped prepubic process

                       Genera: Iguanodon, Camptosaurus Ouranosaurus

          Hadrosauridae

               Characters: *1. 3 or more teeth per tooth position

                                   2. Repositioning of antoorbital fenestra

                                   3. Loss of opening between quadrate and quadratojugal bones

                                   *4. Loss of first digit in hand

                                   5. Increase in number of sacral vertebrae

                                   *6. Observe free palpebral bone in eye

                                   *7. Wider and more elongate snout than Iguanodontidae

                                   8. Relatively the longest forelimbs of the Ornithopoda

                     Hadrosaurine

                          Characters: *1. Flat-headed forms with crest of solid bone

                                               2. Highly flared snout

                                               *3. Circumnarial depression

                                               4. Eight or more sacral vertebrae

                             Genera: Edmontosaurus, Maiasaura

Lambeosaurines

                          Characters: *1. Hollow crested forms

                                               2. Truncated forward margin of jugal bone

                                               *3. Footed ischium

4. High angle between crown and root of the teeth of lower jaw

                                               5. High neural spines

                               Genera: Parasaurolophus