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Giant Scorpions and Dino Breath

To: dinosaur@usc.edu
From: Ben Creisler (bh480@scn.org)
Subject: Giant Scorpions and Dino Breath

In Tom Holtz's reply to a query about giant scorpions, he
assumed the giant scorpion must have been a eurypterid
--a giant sea scorpion. However, it's likely the questioner was
thinking of Pulmonoscorpius, a giant TERRESTRIAL scorpion
recently discovered in Scotland. This critter could reach about
70 cm (2.5 ft.) long. The reference is:

Jeram, A. J. 1994. Scorpions from the Visean of East Kirkton,
West Lothian, Scotland, with a revision of the infraorder
Mesoscorpionina. Transactions of the Royal Society of
Edinburgh: Earth Sciences. 84: 281-299.

It was also briefly discussed in New Scientist magazine:
Taylor, Michael. 1994.  Amphibians that came to stay.
New Scientist (Feb. 1994) 141 (1912): 21-24.

See David Norman's Prehistoric Life page 109 for
a picture of a part of a claw of Pulmonoscorpius next to the
controversial tetrapod (amniote?) Westlothiana. (A word of
warning based on recent experience. Norman's book mixed up the
dates on the amphibians Gerrothorax and Paracyclotosaurus,
which lived during the Late Triassic, NOT the Carboniferous.
This error caused problems for a yet-to-appear book that
I did some research for--the artist already had created a
Carboniferous scene that mixed in Triassic forms,
using Prehistoric Life as a reference.)

Pulmonoscorpius looked pretty much like modern
desert-dwelling scorpions but was not nocturnal and
had large lateral compound eyes designed for hunting
in daylight. Given its size, it's possible it occasionally
preyed on the little tetrapods of its day (Early Carboniferous),
but that's speculation. It had one mean stinger!

Since this reply is far off the topic of dinosaurs, I plead there
is a connection.  From time to time the argument has been
made that Earth's atmosphere must have had a much higher
level of oxygen during the Mesozoic that permitted dinosaurs
to thrive and reach gigantic size. The air may also have been
thicker, permitting giant pterosaurs to fly. However, most
vertebrate paleontologists I am aware of don't think the biological case
for enhanced oxygen and thicker air can be made based on
the assumption that dinosaurs and pterosaurs couldn't have
lived under current atmospheric conditions. The geochemical
evidence, including the supposed oxygen content preserved
in Cretaceous amber, remains controversial, though there
seems to be good evidence for higher carbon dioxide levels
at various times during the Mesozoic.

The biological case for higher oxygen/thicker air seems
easier to make for the Carboniferous.  Modern insects and
other terrestrial arthropods appear to face a size limit
based on their respiratory tract (a system of tubes or in
some forms book lungs). The presence of truly gigantic land
arthropods such as Arthropleura (almost 2 meters long!),
Meganeura (a dragonfly-like flier), Megarachne (a gigantic spider)
and Pulmonoscorpius indicate they were able to oxygenate
their tissues as well as much smaller modern arthropods and
were thus able to give early tetrapods a run for their money.
In some sense, Arthropleura was the "sauropod" of its day,
a huge plant eater able to eat large quantities of low
quality plant food. Preserved stomach contents indicate it
ate the pith out of the early tree-like plants such as lycopods--
it likely used bacteria in a large gut to break down the
tough tissues. (I recall a juvenile book that came out a
few years ago, though, that depicted Arthropleura clasping  a
Westlothiana in its jaws to eat it!!)