The Ginkgo tree is another of the "living fossils" but it's surprisingly well known and familiar. You'll probably recognize them on city streets by the waxy, wide green leaf and by the fleshy, ping pong ball sized fruit with the large pit that smells like vomit.
Ginkgo trees are the national tree of China and typically have a leaf that is wide and fan shaped that drops in the winter, similar to deciduous trees. However, the leaves are very primitive with simple veins. Unlike most tree species common in the U.S., the Ginkgo is dioecious, meaning trees are male or female. Female ginkgoes produce seeds which are covered in a fleshy coating that contains butyric acid, also found in rancid butter, which is what gives it the nasty smell. For this reason some cites have removed the female trees or, in some extreme cases, all the trees because of complaints from the smell or the slippery conditions caused by the fruits pulp. It's a slow growing tree but very hardy and adapts to most temperate climates well. It is my favorite tree and I planted one in my backyard when I moved into my house.
Fossils of Ginkgo leaves are first found in the Jurassic period in sediments from central Asia. At least two species have been identified from this time but there were as many as five or six species identified in the Northern Hemisphere during the Cretaceous. After the KT extinction event, Ginkgoes seemed to go into decline around the world. In the Paleocene there was only one species left, Ginkgo adiantoides, and it is considered to be polymorphic (having many different looks). In this way it accounts for both the fan shaped leaves of Ginkgo adiantoides and the thin finger-like leaves of Ginkgo dissecta. By the late Miocene it had disappeared from North America and (5 million years later) Europe, retreating into China. There it persevered in marginal habitats until being discovered by humans. It was cultivated by Buddhist monks for generations until it started to be brought out into the wider world by 1100 AD. It spread back into Europe and America in the 1700's as plantings. Today you will often find the only living species, Ginkgo biloba, planted along streets in cities as decorative trees. They actually thrive in the polluted city air and tolerate the salt used to thaw ice in the winter and thus are a perfect fit. There are even some that survived the atomic bombing in Hiroshima! Finally, Ginkgo biloba reputedly has medicinal value and is marketed as being good for memory and the seeds are used in some traditional Chinese and Japanese foods.
Here are some modern leaves from my backyard Ginkgo biloba tree. Notice the differences in the shape and "lobes" of the leaves.
You can see that the leaves that are "split" or "lobed" are typically at the very ends of the branches.
In fact the most typical fan shaped leaves are found closer to the trunk on my tree. There are some exceptions of course:
After seeing these examples on my single tree I more readily accept the theory that Ginkgo biloba and the thin finger-like leaves of Ginkgo dissecta likely came from the same tree, but from different parts.
Onto the fossils! This is a Ginkgo adiantoides from the Paleocene aged Sentinel Butte formation of North Dakota.
And this is a Ginkgo dissecta from the Eocene aged Tranquille shale in British Columbia, Canada
For more info about Ginkgos, check out the Paleobotany.org website
Another great page with lots of pics and even some fossil wood: The Ginkgo Pages
There is a Ginkgo Petrified Forest in Washington State.