As well as old leases, you should keep anything that documents the landlord-tenant relationship or supports the items you report on your tax return. If the IRS audits your tax return and you cannot produce the correct verification documents, you may be liable for additional tax and penalties.
The facet joints link the vertebrae together and give them the flexibility to move against each other. The facets are the bony knobs that meet between each vertebra. There are two facet joints between each pair of vertebrae, one on each side.
The head and shoulders of the Elasmosaurus most likely acted as a rudder. If the animal moved the front of the body in one direction, it would cause the rest of the body to move in that direction. Thus, Elasmosaurus could not have swum one way and move its head and neck another way, horizontally or vertically.