FERNS, HORSE TAILS AND THE LIKE
These are fossil spore-bearing plants which developed a series of vessels that form a conducting apparatus for moving fluids and nourishment through their tissue. Common types of pteridophyts are the ferns, the horse tails, and the club mosses. Geologic range is Carboniferous to recent in general. Fossil plants are prized in a fossil collection because specimens are often leaves, bark or sometimes even flowers that leave little to the immigration and make great display items that can be appreciated even by someone who has little experience with fossils. Besides, fossil plants are usually easy to collect from layers of thinly laminated shales which split open with the tap of a chisel or splitting hammer.
Calamities, a horse tail rush, grew to heights of up to forty (40) feet. Although it is related to the modern horsetail, Calamities cisti actually looked something like a pine tree . It had upward-slanting slender branches arranged concentrically around the trunk in rows spaced several feet apart, and conifer-like needles arranged in whorls around ends of the branches. Though reaching significant heights, the trunk lacked substantial mass, being composed mostly of pithy reed-like tissue, with about the strength of a rolled-up newspaper. Consequently, they tended to fall over very easily, unless supported by neighboring plants or by accumulating sediments. In sandstones, this plant is usually seen as casts of the hollow trunks and stems,while in finer sediments such as shale the leaves can be preserve as an impression and carbon film, showing exquisite detail. A great living exhibit of horsetails can be seen at the entrance to the cave at the Arizona-Sonora Desert Museum.

Pennsylvanian fossil Calamites cisti

Horsetail rushes are living fossils,
related to calamites.
Lepidodendron (also known as the "scale tree") is an extinct genus of primitive, vascular, arborescent (tree-like) plant related to the Lycopsids (club mosses) reaching a heights of over 180 ft (54 m), and the trunks were often over 6 ft (1.8 m) in diameter. Lepidodendron had tall, thick trunks crowned with a cluster of narrow leaves. The leaves were spirally-arranged and ended in cones. The tightly packed diamond-shaped leaf scars were left by leaves as they dropped off the trunks and stems of the tree fern as it grew. In some Carboniferous (coal-age) deposits in Arizona, fossils of these and related lycopods are most interesting and common fossils in shales and accompanying Carboniferous coal deposits. By the Mesozoic era, the giant clubmosses had died out so don't expect to find them in any of our Mesozoic rock formations.

Coal age swamp showing tall tree ferns and the horsetail rush calamites.

Fossil bark of Lepidodendron showing leaf scars
FERNS
FERNS are a very ancient family of plants: early fern fossils predate the beginning of the Mesozoic era, 360 million years ago. As we know them now, most ferns are leafy plants that grow in moist areas under forest canopy.
Ferns are "vascular plants" with well-developed internal vein structures that promote the flow of water and nutrients. Unlike the other vascular plants, the flowering plants and conifers, where the adult plant grows immediately from the seed, ferns reproduce from spores and an intermediate plant stage called a gametophyte.
COAL
Coal is a sedimentary rock composed of plant debris (and occasionally material from other creatures) that was deposited in a bog or swamp that had little biological activity at its bottom. This led to preservation of the plant leaves, stems, pollen and other structures, although with continued burial these structures become much less distinct. Time and pressure combine with chemical changes to turn the plant material into coal. Fluctuating sea-levels during the Carboniferous contributed to the preservation of many coal environments. Coal deposits are common in Arizona's Cretaceous rocks. While coal itself contains few immediately recognizable fossil plants, non-marine sedimentary rocks of nearly every kind can contain fossil plants, and even some marine sediments may contain such specimens. Good specimens of plants can be collected from the fine-grained, dark, non-marine shales or sandstone in rocks such as those in the photo here, which are often associated with coal beds. For some reason, the rock beds directly above coal layers are usually much more productive than beds between or below coral zones.
This photo brings to mind an interesting question: What environmental change occurred to cause such an abrupt change in environment seen by the sudden end of the swampy conditions and the appearance of massive accumulation so quartz sand seen directly above the coal?
BROADLEAF PLANTS

Spermatophytes include the most highly organized plants, all of which are seed producing. The division includes the gymnosperms, plants whose seeds are unprotected by coverings (the trees and shrubs, mostly evergreens which produce cones), and the angiosperms, the flowering plants. Spermatophytes range in general from the Carboniferous to the recent. Broadleaf plants: Leaves of deciduous trees are abundant in Late Cretaceous rocks. Cycads, having an odd place in the kingdom of plants, resembled a palm, not not a palm's close relative. Cycads have a much closer kinship to the Ginkgo, another living fossil that we can grow in many of our backyards today.

The cycad shown on the right was abundant in the Mesozoic, and likely its tough, waxy leaves were one of the main sources of food for many of the herbivorous dinosaur of the time.

Trunk of a Cretaceous Cycad. Such fossils have been found in the Turney Ranch Formation on the flanks of the Whetstone Mountains.
CONIFERS
The state fossil of Arizona is a type of petrified wood called . This name come from its relationship to the modern araucarias (Norfolk Island Pine and Monkey Puzzle Tree) although how closely related to them it may be is an open question. This wood is the mineralized remains of large trees that grew in Arizona during the Triassic Period, about 220 million years ago. The most famous of these deposits, the Chinle Formation, produces the beautiful agatized logs which are preserved at Petrified Forest National Park, but related fossil wood is found in many parts of Arizona, especially in Cretaceous rocks. Other petrified wood in Arizona can be found in Cenozoic rocks where conditions led to the burial of millions of trees, which over time, turned to stone. Early in the last century, tens of thousands of fossil logs at the Petrified Forest were mined and crushed into powder for the sandpaper industry. It's all protected now.
 NORFOLK ISLAND PINE A nearly identical conifer Araucarioxylon arizonicum is found in Arizona's Triassic-age Petrified Forest National Park
COLLECTING THE FOSSIL PLANTS
It's one thing to dig a hole
in a sandstone or shale outcrop and find fossil leaves but getting them out of the ground in good shape is a trick and takes a bit of practice. . It's the most difficult part of leaf excavation. Because fossil leaves often occupy a horizontal plane (anywhere from a paper-thin layer to meters thick), getting them out in good shape to them requires clearing the overburden.
Carbon film of leaf split from shale
Once the proper stratigraphic layer has been located, the collector's objective is to quarry as large a slab of fossiliferous rock as possible. Ideally, rock strata lying above the fossiliferous zone should be removed with pick and shovel and discarded downslope. This method is often disregarded by collectors because of the time and trouble required for quarrying, and so is responsible for the many fragmented specimens in both private and museum collections.
This can be done with several tools: pickaxes, your flat-ended rock hammer, and shovels. In other words, you've got to start with housekeeping, and nobody gets any really good plant fossils if they don't have a clean quarry surface, best an area about three meters square. From that point, you can use a hammer and flat chisel to split the bedded rocks along the surface planes that will become obvious once you start learning the nature of the rock you're dealing with. One in a hundred leaf fossils, especially deciduous tree-leaves, will be complete enough to knock your sock off when you first see it. But persistence will pay off and you'll come home with some museum-quality specimens for your collection.
Fossil Plant Bible for the Collector

After quarrying of excess debris is completed, plant-bearing strata should be removed in large slabs which are then split along bedding planes. In plant deposits, this process is easily accomplished because of the natural cleavage produced by the plants themselves; a fossil, such as a leaf, essentially is a deposit of carbon or iron oxide film between rock layers which prevents one layer "sticking" to the other when the sediments are being deposited and transformed over time into shale or sandstone. Various wide-edged chisels and putty knives are best for splitting most plant fossil producing rocks. Plant fossils found as float or on talus slopes are usually of poor quality and not valuable to the collector. A collector should make every effort to find the strata from which these specimens are weathering.

Fossil Plant Preparation

Often, and its unavoidable, you'll likely develop cracks right through a fossil plant in shale when you're collecting them in the field. When this happens, use a good rock glue such as PaleoBond that you should have with you. It's a lot easier to carry a small vial of PaleoBond to repair specimens rather than trying to do this back in your lab. Why? Because contact points, the surface of the crack most often crumbles a bit during transportation, no matter how well you wrap and pack your broken fossil. The exact fit between pieces is often lost and the it is really frustrating and often impossible to repair a fossil from a number of fragments wrapped in newspaper. And use the proper glue; many glues or preservatives discolor the rock after a few years in storage years in storage, or will peal from the specimen and you're back to having useless fragments, or worse, some lovely swamp-green or pastel-colored fossils in your collection!

Heavy coatings of any kind of varnish, shellac, or plastic will ruin plant specimens and should only be used as a preservation technique when a plant fossil cannot hold together on its own.

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