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| An illustration of the a stout, short-bodied, four-legged animal with a short tail and short neck. |
Discovery News /Long before
dinosaurs, something was digging intricate homes and roads underground. While life on Earth
240 million years ago flourished in the seas and on land, the underground
worlds discovered in Morocco are the oldest example of such communal
subterranean structures from a low-latitude area.
The burrows,
described in the latest issue of the journal Palaios, are the world’s second
oldest known communal burrows. The oldest, from South Africa, only predate
these by 5 million years.
It's possible that a
similar animal created both structures.
"You should
imagine the tracemaker as a stout, short-bodied, four-legged animal with a
short tail and short neck," lead author Sebastian Voigt told Discovery
News. "The trunk was about 20-25 centimeters (8-10 inches) in length. We
have to assume that it had five sturdy digits with claws suitable for digging
into moderately soft sediment."
Funded by the German
Research Foundation, ichnologist Voigt from the Institute of Geology at TU
Bergakademie Freiberg and his colleagues studied the burrows, located in red
beds of the Argana Basin in central Morocco. The architecture consists of
numerous openings, exists, tunnels and chambers.
"The Argana
burrows do not have any equivalent in the fossil record or among extant
burrowing vertebrates," Voigt said. "Their chambers are exceptionally
complex structures and two-fold winded tunnels have never been observed
anywhere else."
Based on this
arrangement and what can be inferred about the burrow makers, the scientists
think the underground world served as a retreat, permitting escape from
predators. Although dinosaurs were not yet around, huge fast-running crocodiles
with long legs were in the area, as evidenced by fossil finds. Close relatives
of today's lizards, snakes and tuataras were also around, along with relatives
of birds and dinosaurs.
The site's geology
as well as the burrow's design also suggests the animals headed underground to
tolerate weather extremes.
"During the
Triassic, the region probably was a semiarid large inland basin," Voigt
explained. "Rivers were slowly flowing after episodic rain fall.
Streambeds were flat and completely dry for lengthy periods. Loose vegetation
covered the banks of the streams. It was hot during the day and cold in the
night."
The smooth floor of
the tunnels reveals they were well used, with the animals probably gathering
food, such as plants, roots and insects, at the surface during nighttime.
Burrows made by
individual animals, such as fish, date to early Paleozoic periods, indicating
this behavior was very important since practically the beginning of complex
animal life on the planet. Voigt suspects it first evolved to permit escape
from environmental extremes, particularly drought.
It seems that
whenever animals could dig to escape, they did. Some dinosaurs dug burrows. One
of the limitations is having the right substrate. In the case of the Moroccan
animals, the conditions were perfect for digging. The burrows there were
constructed in riverbank sandy substrates intermixed with moist overbank mud.
Molly Miller, a
professor of earth and environmental sciences at Vanderbilt University, told
Discovery News, "This is an exciting discovery. The careful description
and analysis make a convincing case that the burrows provided shelter to
numerous animals."
She added, "It
demonstrates that the development of complex tetrapod behavior in response to
challenging environmental conditions goes back over 200 million years. It has a
very long history!"
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