Some Types of Plant Fossils T H E B O TA N I C G A R D E N O F S M I T H C O L L E G E

Much of what we know about the form and structure of extinct plant species comes from fossils. Four major types of plant fossils are:

Fossil Pecopteris fronds PHOTO BY PAMELA DODS; SPECIMEN FROM THE BENESKI MUSEUM, AMHERST COLLEGE

Compression and impression fossils originate in wet areas where plant parts become quickly buried by sediment, the weight of which squeezes out and flattens the plant material, leaving impressions in the fine-grained sediment. In some cases plant carbon or cuticle (waxy, water-repellent coating) also remain within the impression.

Permineralized fossils result from infiltration of the plant tissue by water containing dissolved minerals. Over time, if the minerals precipitate, a rock forms that preserves the plant in three dimensions with detail down to the cellular level.

Petrified tree in Petrified Forest National Park in Arizona

Man standing next to fossilized Sigillaria trunk in a coal Polished petrified wood from Arizona mine in France PHOTOS BY PAMELA DODS; SPECIMENS FROM THE BENESKI MUSEUM, AMHERST COLLEGE

ALEXANDER WINCHELL, SKETCHES OF CREATION, NEW YORK, NY:

HARPER & BROTHERS, 1870

Polished petrified wood from Arizona PHOTOS BY PAMELA DODS; SPECIMENS FROM THE BENESKI MUSEUM, AMHERST COLLEGE

Above: Fossil wood from Madagascar PHOTO BY JAMES ST. JOHN

Petrified Calamites trunk

Right: Flower of Strychnos Unaltered plant remains can occur electri in Dominican Republic

PHOTO BY GEORGE POINAR where microbial activity, which would amber

normally destroy plant remains, is inhibited by freezing, salinity, or acidity. Below: Hymenaea protera leaf

PHOTO BY GEORGE POINAR

in Dominican Republic amber Examples can be found in deep lake sediments, in amber (fossilized plant resin), and in pack rat middens, where animal nests made of plants become encased in crystallized urine.

Casts of plants can form when sediment infiltrates into cavities left by the decay of buried plant parts. Casts preserve the three-dimensional shape of the plant parts but are without internal structure. Casts of ancient trees are among the most impressive plant fossils.

Lepidodendron fossil branch in rusty siltstone, found in Ohio PHOTO BY JAMES ST. JOHN Above and below, Lepidodendron trunk surface casts PHOTOS BY GHEDOGHEDO

Fossil leaves of Ginkgo PHOTO BY GHEDOGHEDO

Fossil leaves and branches of Sphenophyllum miravallis PHOTO BY WOUDLOPER

Pack rat midden found in Utah PHOTO BY LARRY L. COATS

Calamites canniformis pith cast of hollow stem PHOTO BY PAMELA DODS;

SPECIMEN FROM THE BENESKI MUSEUM,

AMHERST COLLEGE