Why was the evolution of a vascular system critical to the invasion of the land by plants? What were the first plants to make the transition, and what were their characteristics?

Plants evolved in various ways and got various adaptations which assisted them to cope with various problems on dry land. One of the most essential adaptation was the evolution of vascular tissues which carry water as well as minerals to the leaves of the plant (Peng Xu 7). The development of the vascular system also helped in giving the plants an increased stature. The mechanical support given to the plant by the vascular system is critical in the ability of the plant to survive on land.

Some of the oldest plants to develop a vascular system was the Cooksnia plant. This plant had stems that were forked into two. They did not have leaves. The algae also were some of the earliest plants to make the transition. Algae have a spore case known as sporangia. These characteristics helped them to adapt to their environment.
How might a paleontologist determine whether a fossil lower jaw containing teeth belonged to a mammal rather than a reptile?

A paleontologist studies the records of life which have been left as fossils. A paleontologist is able to differentiate the fossil lower jaw of a mammal from that of a reptile by observing the arrangement of the teeth. For instance, mammals have teeth which vary greatly in shape and size while reptiles have teeth which are more or less uniform in shape and size.

Besides, in reptiles, the lower jaw has various different bones which are connected on the skull bone as well as the angular bone of the jaw. This is different in mammals as the lower jaw has only one bone and it hinges to the quadrate of the skull. By observing these characteristics, it is possible for the paleontologist to determine whether a fossil lower jaw containing teeth belonged to a mammal or reptile.