Fossil Roots and Burrows

In general, to distinguish roots from burrows, we look for:

(a) plant material or structures (roots)

(b) diameter (relatively constant in burrows, frequently irregular
in roots, with secondary segments usually having a narrower
diameter than primary segments)

(c) branching style (usually lateral, i.e., more or less T-shaped in
burrows; either lateral or dichotomous, i.e., Y-shaped, in roots)
(Exception: Y-shaped branching is very common in crustacean

(d) structure of fill (active in some burrows; passive in originally
open burrows and in root cavities)

(e) enlarged junctions (e.g., in Thalassinoides)

Exceptions abound; nature is prolific and inventive. But a marked
difference in diameter between primary and secondary segments,
and a Y-shaped branching style without enlarged junctions, are
usually good indicators of a root origin even in the absence of
plant matter.

Dr. Andrew K. Rindsberg

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St. Louis Pennsylvanian Fossils of the Altamont Formation