Edaphosaurus
Name: Edaphosaurus
(Ground lizard).
Phonetic: E-daff-oh-sore-us.
Named By: Edward Drinker Cope - 1882.
Synonyms: Brachycnemius, Naosaurus.
Classification: Chordata, Synapsida, Tetrapoda,
Amniota, Edaphosauridae.
Species: E. pogonias (type), E.
boanerges, E.
colohistion, E.
cruciger, E. novomexicanus.
Diet: Herbivore.
Size: Depending upon the species, between 1 to
3.5 meters.
Known locations: Germany. Czech
Republic. Slovakia. USA - New Mexico - Cutler Formation; Oklahoma -
Garber Formation, Hennessey Formation, Wellington Formation; Texas -
Admiral Formation, Archer City Formation, Arroyo Formation, Belle
Plains Formation, Lueders Formatio, Nocona Formation, Petrolia
Formation, Putnam Formation, Vale Formation; West Virginia - Pittsburgh
Formation.
Time period: Gzhelian of the Carboniferous to the
Wordian of the Permian.
Fossil representation: Many specimens have been
found making this one of the better represented herbivorous pelycosaurs.
Edaphosaurus
is easily one of the more recognisable pelycosaurs,
even if the genus
is often presented in the shadow cast by the much more famous
Dimetrodon.
These two genera of pelycosaur are at opposite ends of
the ecosystem however, with Edaphosaurus being
a plant eater
specialising in low growing vegetation, and Dimetrodon
being ‘the’
big predator of the time. In fact it is quite probable that
Edaphosaurus formed one of the main prey choices for
Dimetrodon given
that these two pelycosaurs share a near identical geographical and
temporal distribution in the fossil record. Both Edaphosaurus
and
Dimetrodon also seem to have been particularly
numerous in the state of
Texas, though both are also known from other locations.
The
name Edaphosaurus is usually listed as meaning
‘ground lizard’,
however, an alternative translation is ‘pavement lizard’, and
this is a reference to the arrangement of teeth inside the mouth.
These are essentially batteries of small peg-like teeth that would
have ground plant matter to a pulp before swallowing. Earlier
interpretations of these tooth batteries were actually of the idea that
they ground molluscs like shellfish, but later analysis of wear
patterns on the teeth have confirmed that plants were the most likely
choice for Edaphosaurus. The teeth at the outer
rim of the mouth were
serrated, greatly helping to shear off fronds of plants.
The
skull of Edaphosaurus is surprisingly small when
compared to the size
of the body, but it should be remembered that with a diet of browsing
upon plants, a large skull would be simply unnecessary. The lower
jaw of Edaphosaurus is very robust and would have
helped as an
attachment for saw closing muscles to process plant matter. The fact
that Edaphosaurus would develop such a strong jaw
might suggest that
Edaphosaurus were eating tougher, more fibrous
plants.
It
is near impossible to talk about Edaphosaurus
without mentioning the
sail that grew in the back. This sail was basically a growth of thin
tissue, perhaps only skin thin, supported by elongated neural
spines. The purpose of this sail still continues to be a source
of debate for palaeontologists well over one hundred years after it was
first described. Many early ideas about the sail have now been
discredited, especially one of the fun ones about how it was a wind
sail that would blow Edaphosaurus across a body of
water. Another
idea about how the enlarged neural spines were anchor points for larger
back muscles is now also not widely accepted as there is no conceivable
purpose for them.
Two
theories that could go either way are predator protection and a fatty
hump to survive times of famine. The sail spines in themselves are
not terribly strong and offer no protection for areas such as the head
or neck. If anything the spines would have given a predator something
to bite onto, but perhaps this was the point. Predatory pelycosaurs
such as Ophiacodon
and Dimetrodon are noted for having very large and
powerful heads, and if a predator got confused by the sail pattern of
an Edaphosaurus and bit into that, it may have
ended up with a
mouthful of sail allowing an Edaphosaurus to
escape. As far as fat
storage is concerned, it is not impossible that the sail could have
served this purpose, but it seems to be quite lightly built for this
function.
The
most tantalizing theory regarding the function of the sail of
Edaphosaurus is thermoregulation that in lay terms
means control of
body temperature. The idea is that when an Edaphosaurus
wanted to
warm up it would align itself side facing the sun so that blood could
be quickly warmed up, and when temperature was right, an
Edaphosaurus could turn so that only the thin edge
faced the sun. In
addition, if an Edaphosaurus got hot it could
flush blood into the
sail to be quickly cooled. Edaphosaurus are also
noted for having
small spiny projections that jut out from the sides of the main
spines, and these are speculated by some to increase wind
turbulence, meaning a much greater cooling effect. The idea of
thermoregulation is not accepted by all however, and at least one
study focused on the neural spines has cast doubt on this theory.
Perhaps
the most likely theory for the sail is that it was there for display.
This includes Edaphosaurus being able to recognise
other individual
Edaphosaurus from other genera sail-backed
pelycosaurs (i.e.
Dimetrodon), different species of their own
genus (each species
having its own pattern/colour set), and even signalling to attract
a mate. It is also possible that the colour of the sail may have
grown more intense at certain times of the year (such as the approach
of the breeding season), or even been made more vivid by an
individual increasing its heart rate to flush more blood into the
sail. In this respect the longer a displaying Edaphosaurus
could
maintain the colour flush, the fitter it was, and the more worthy
it would be to a mate to pass on its genes.
Ultimately
the precise function of the sail is still an open debate, but it is
also worth noting that the sail may have performed double or even
triple duty, fulfilling more than just one purpose. Another fact to
remember is that the colour and patterning of the sail of Edaphosaurus
is still only speculation, and that reconstructions you see
(including the one above) or really just the idea of the artist.
Edaphosaurus
is now the type genus of the Edaphosauridae, a group of pelycosaurs
that are closer to Edaphosaurus in form. It is
generally accepted
that Edaphosaurus evolved from smaller insect
hunting pelycosaurs
like Ianthasaurus
that began to appear at least as far back as the
Carboniferous.
Ctenospondylus, Dimetrodon, Edaphosaurus, Ianthasaurus, Secodontosaurus.
Further reading
- Third contribution to the history of the Vertebrata of the Permian
formation of Texas. - Proceedings of the American Philosophical Society
20:447-461. - Edward Drinker Cope - 1882.
- A Description of Edaphosaurus Cope. -
Permo-Carboniferous vertebrates
from New Mexico. Carnegie Institution of Washington Geological Society
of America Special Paper 181: 71–81. - S. W. Williston & E. C.
Case - 1913.
- Edaphosaurus (Reptilia, Pelycosauria) from the
Lower Permian of
Northeastern United States, with description of a new species. - Annals
of the Carnegie Museum 48 (11): 185–202. - D. S. Berman - 1979.
- Aerodynamics and thermoregulatory function of the dorsal sail of
Edaphosaurus. - Paleobiology 22: 496–506. - S. C.
Bennet - 1996.
- Comparative osteohistology of hyperelongate neural spines in the
Edaphosauridae (Amniota: Synapsida). - Palaeontology 54: 573–590. - A.
K. Huttenlocker, D. Mazierski & R. R. Reisz - 2011.
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