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Systematics affinities of fossil wood

Taxonomy is a way to organize and classify living organisms based on their shared characteristics. It helps scientists understand the relationships between different species and how they are related to one another. In taxonomy, scientists group organisms into categories called taxa. The highest level is the kingdom just like you have different kingdoms in the world (e.g., Animal Kingdom, Plant Kingdom).

To learn about systematics and naming organisms and reconstructing the evolutionary history of life, visit here

Like living organisms, fossil wood can be classified and organized using taxonomy. Paleobotanists categorize fossil wood based on its shared characteristics and evolutionary relationships. They examine various features of the fossil wood to determine its classification.

The three common types of petrified wood found are conifers (gymnosperms), dicots (e.g., mango tree, teak, magnolia, oak), and monocots (palm stems).

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Monocot 

Dicot

Conifer

without resin canals

Conifer

with resin canals

The figure displays microscopic photos of various fossil woods found in Wyoming, including palm, dicot, and conifer wood.

Classifying fossil wood

The primary level of taxonomy for fossil wood is the family. Families are groups of similar organisms that share certain characteristics. For example, Lauraceae (cinnamon, avocado) has oil cells, Anacardiaceae (mango, cashew) has radial ducts in wood, and Pinaceae (pine) has resin canals.

 

Within each family, there are genera (singular: genus). Genera are more specific groups of closely related organisms. Lastly, within each genus, there are species. Species are the most specific level of classification and refer to individual types of fossil wood. They are identified by their unique microscopic features. By using taxonomy to classify fossil wood, scientists can better understand the different types of trees that existed in ancient times and how they were related. It helps them organize and study the rich history of plant life on Earth.

Monocot stem

The most common monocot found petrified is palm.  Most fossil of petrified palm stem is known as "Palmoxylon".

Palmoxylon  fiber is composed of scattered vascular bundles embedded in a groundmass of parenchyma cells.

Each fibrovascular bundle contains cells adapted for: conducting water, transporting food made in photosynthetic tissues, and providing structural support. For identify the palm stems from their anatomical characters, please visit Palm ID

The fossil Palmoxylon found near Big Sandy Reservoir, north of Farson, Wyoming grew along the shores of Lake Gosiute approximately 50 million years ago in a subtropical/tropical environment. This is in sharp contrast to the sagebrush steppe ecosystem that dominates the high plains desert in this region today.

Dicot woods

 

The two groups, monocots and dicots derive their name from the number of cotyledons or seed leaves that the embryo uses to absorb nutrients as it sprouts from the seed. Monocots such as palms, grasses and orchids have one seed leaf, while dicots, such as oaks, maples, and sunflowers have two. Dicot wood refers to the type of wood derived from dicotyledonous plants, which are a group of flowering plants with two seed leaves. Dicot wood is characterized by its distinct growth rings, composed of xylem and phloem tissues. It often exhibits a porous structure with vessels or pores visible under a microscope. The identification of dicot wood involves analyzing various anatomical features such as vessel size, arrangement, and distribution of parenchyma cells. These characteristics aid in distinguishing different species and understanding the evolutionary history of dicotyledonous plants.

The silicified wood exhibits indistinct growth rings, an indication that it was growing in an environment that lacked significant seasonal changes in temperature or in the availability of water. The small water conducting vessels become clearly visible at 150x and are found individually or in groups of up to four.  For identify the dicot woods from their anatomical features, please visit  Inside Wood Database

Gymnosperms

is derived from the Greek roots Gymnos (= naked) + sperma (= seed). The term "gymnosperm" describes a group of plants whose seeds are not enclosed within a protective fruit or ovary. Gymnosperms include plant species such as conifers, cycads, ginkgoes, and gnetophytes, which have seeds that are typically borne on the surface of cones or similar structures. Therefore, the name reflects the characteristic of these plants having exposed, naked seeds. 

 

 Arborescent gymnosperms, like dicots, form stems constructed as solid woody cylinders. Cupressinoxylon is considered to be in the cypress family and constructed woody stems from secondary growth. Gymnosperms are a rare find at the Blue Forest and this specimen, in contrast to the previous one, did not retain its bark and exhibits distinct growth rings. The Schinoxylon and Cupressinoxylon specimens were found in the same deposit not far from each other. The lack of bark and distinct growth rings may indicate that the gymnosperm was growing at higher elevation and was transported to Lake Gosiute where it became fossilized.

The water conducting cells making up the wood or secondary xylem of gymnosperms are almost exclusively tracheids. The tracheids of gymnosperms are typically smaller than vessels and are arranged in radially aligned rows. Many fossil wood enthusiasts use Identifying Wood by Bruce Hoadley to become familiar with terminology used in basic wood identification (Hoadley, 1990).

It is important to note that serious scientific identification of silicified trunks and stems often requires the use of thin sections made in transverse, radial, and tangential orientations; even so, many categories of arborescent plant life can be recognized in transverse view alone (Viney, 2008). Exploring the microscopic world of silicified plant fossils opens up a new world of enjoyment and study that includes learning to identify fossil tissues and cells.

References

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