Ctenosauriscus
Name:
Ctenosauriscus.
Phonetic: Ten-oh-sore-is-cus.
Named By: Kuhn - 1964.
Synonyms: Ctenosaurus koenei.
Classification: Chordata, Reptilia,
Archosauria, Crurotarsi, Rauisuchia, Paracrocodylomorpha,
Poposauroidea, Ctenosauriscidae.
Species: C. koeneni (type).
Diet: Uncertain, but presumed carnivore.
Size: Uncertain due to incomplete remains. but
sail is roughly 1.4 meters long.
Known locations: Germany, Lower Saxony.
Time period: Olenekian of the Triassic.
Fossil representation: Dorsal and caudal vertebrae,
ribs and shoulder girdle preserved on two slabs.
Ctenosauriscus
is the type specimen of the Ctenosauriscidae, a group of sail
backed rauisuchian
archosaurs that also include others such as
Arizonasaurus.
Ctenosauriscidae however is only known from post
cranial remains that reveal it had a large sail on its back. Like in
related reptiles, this sail was supported by the enlarged neural
spines of the vertebrae. The neural spines in the anterior half of
the sail curved slightly forwards, while the posterior half curved
slightly backwards. Altogether Ctenosauriscus
possessed the largest
known back sail in its group while also being one of the first members
of the Ctenosauriscidae to enter the fossil record.
It
was once considered that the tall neural spines were thought to have
been to absorb the stresses involved in walking upon two legs however
this explanation is now considered highly unlikely. First off the
only bipedal reptiles known to have enlarged neural spines are
dinosaurs like Spinosaurus
and Acrocanthosaurus
and here it’s
certain that the neural spines did not become enlarged for this
purpose. Additionally there are other related rauisuchians that have
similar back structures yet also remain quadrupedal. Finally the very
position of the sail would have shifted the centre of gravity further
forward, making a bipedal posture even less likely.
Sails
are often thought to have been for the purpose of thermoregulation,
the idea being that a larger surface area enables a faster heat
exchange with the surrounding environment to either warm up or cool
down the animal. While possible, the neural spines that support the
sail in Ctenosauriscus are quite robust, and the
structure itself may
have been for more than temperature regulation. It’s plausible that
the sail may have been a fat reserve for storing excess fat.
Rauisuchians
like Ctenosauriscus appear in the early Triassic,
only a few million
years after the biggest single extinction event in the planets
history, even bigger than the one that ended the dinosaurs. Animals
that could adapt to harsher living conditions would have had an
advantage over those that could not, and a fat hump, which may or
may not have also helped with temperature regulation as well as even
display would have allowed animals equipped with this feature to more
easily survive.
As
mentioned above, the sail in Ctenosauriscus is so
far the largest
known in the group, but more importantly it was already well
established in what is currently the first known genus to exist. The
ancestor (or ancestors) that led to this development may have
started adapting several million years earlier at the time of the
Permian-Triassic extinction event. Further fossils from around this
time would be needed to confirm this however, and until this time it
remains only a theory.
Further reading
- Ungel�ste Probleme der Stammesgeschichte der Amphibien und Reptilien.
- Jahreshefte des Vereins f�r vaterl�ndische Naturkunde in W�rttemberg
118/119:293-325. - O. Kuhn - 1964.
- Ctenosauriscus koeneni (v. Huene) und der
Rauisuchier von Waldshut -
Biomechanische Deutung der Wirbels�ule und Beziehungen zu Chirotherium
sickleri Kaup. - Stuttgarter Beitr�ge zur Naturkunde, Serie B
(Geologie
und Pal�ontologie) 261: 1–18. - K. Ebel, F. Falkenstein. F-O. Haderer
& R. Wild - 1998.
- The Sail-Backed Reptile Ctenosauriscus from the
Latest Early Triassic
of Germany and the Timing and Biogeography of the Early Archosaur
Radiation. - PLOSone - Richard J. Butler, Stephen L. Brusatte, Mike
Reich, Sterling J. Nesbitt, Rainer R. Schoch & Jahn J. Hornung
- 2011.
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