Igneous rocks 

 formed by crystallization directly from molten material. This molten material is called magma when it is below the surface, and lava once it reaches the surface 

*no fossils found

 Sedimentary rocks 

Clastic: 

 erosion, subsequent deposition, and lithification of pre-existing rocks 

or

 precipitation of minerals from seawater 

*fossils found here

 Metamorphic rocks 

 Under conditions of intense heat and pressure, pre-existing rock can be physically and 

chemically altered 

* Fossils are less commonly found in metamorphic rocks, but are often distorted. 

1. In-turned femoral head

2. Opposable thumb

3. Perforate acetabulum

4. S-shaped neck

5. Characteristic pelvis with back-turned pubis

6. Predentary bone in lower jaw

7. Ossified tendons along part of vertebral column

8. Teeth inset from margin of jaws (indicating the presence of muscular cheeks)

Expanded crown in premaxillary teeth

Asymmetrical distribution of tooth enamel

Expanded shelf at back of skull

Rostral bone present on upper jaw to form sharp beak

Large, spike-like caniniform tooth in dentary bone

Armor made of bony scutes that cover back and/or flanks

 Tibia shorter than femur

The anterior portion of the ilium is much longer than the posterior portion

Scutes form interlocking mosaic that covers most of body

Scutes enlarged to form two rows of large plates extending along vertebral column

Articulation of skull and jaw well below the level of the tooth row

Pachycephalosauria

Skull roof greatly thickened to form solid “dome” that is usually surrounded by various bumps

and tubercles

Occipital plate rotated beneath skull

described Mosasaurus and first correctly identified it as a giant fossil lizard