Longisquama
Name:
Longisquama
(Long scales).
Phonetic: Lon-ge-skwar-mah.
Named By: A. G. Sharov - 1970.
Synonyms: X
Classification: Chordata, Reptilia, Diapsida.
Species: L. insignis (type).
Diet: Insectivore.
Size: Uncertain due to incomplete remains.
Preserved elements of the skull and anterior half of the post cranial
skeleton about 4.5 centimetres long.
Known locations: Kyrgyzstan - Madygen Formation.
Time period: Ladinian to early Norian of the
Triassic.
Fossil representation: Almost complete skull
lacking the tips of the snout and lower jaws. Anterior portion of the
postcranial skeleton including cervical (neck) and dorsal (back)
vertebrae, ribs, shoulder girdle and an almost complete forelimb.
Back appendages were found in association with the skeleton. More
specimens of these appendages are known, but only the holotype has
them preserved with the skeleton.
There
are some fossil animals that just seem to be born to confuse us, and
Longisquama is certainly one of these. The partial
post cranial
remains of this diapsid reptile seem to belong to a fairly small
lizard. What really makes this creature bizarre however are the long
appendages that seem to attach to the neural spines of the dorsal
vertebrae. The nature of these appendages has been debated ever since
the creature was first described in 1970, with some considering
them to be elongated scales, and others thinking them to represent
one of the first known appearances of feathers. These
interpretations in turn have not only led to various theories as to how
Longisquama lived, but how it fits in to wider
evolutionary theory.
Since
the early twentieth century a popular idea for the first birds was that
of ‘Proaves’ a fictional creature that was essentially a lizard
with long flight feathers of birds growing from its arms which it used
to glide amongst trees. That creature never actually existed, it
was simply an idea given visual form so that a wider range of people
could understand it. There was no malicious intent, scientists just
wanted to show what they expected the ancestors to birds look like.
The
large appendages of Longisquama were once
interpreted as a double row
of either scales or feathers that extended out to the side to form a
series of ‘wings’. The idea was that Longisquama
used these
appendages to glide amongst the trees, and in turn may represent an
actual ‘Proaves’ that was ancestral to birds. However since last
two decades of the twentieth century the idea that birds originated
from some point within the theropod dinosaurs has become accepted fact
within the wider scientific community. This means that if the
appendages of Longisquama are indeed feathers,
then it is likely that
they are a product of a separate evolution, though even today some
researchers still hold up Longisquama as a member
of a group of
reptiles that are the true ancestors of birds.
More
modern analysis of Longisquama has yielded the
conclusion that there
was just one row of appendages that ran vertical down the back of
Longisquama. If this is true then immediately
the idea that
Longisquama was a glider figuratively flies out of
the window, it
would simply be impossible. Therefore an alternative function for
these appendages would perhaps most obviously be as a display feature,
something that may have helped Longisquama set up
territories and
signal to one another at range, a definitive advantage given the
apparent small size of the body. Another interpretation could be that
the appendages were a scare device that was flashed at the moment that
predators attacked.
There
has been just as much debate over exactly how these appendages where
formed to even if they were actually part of the animal. As briefly
mentioned above, the appendages seem to have attached to the neural
spines of vertebrae (the small spines on the top of the
vertebrae). These appendages then seem to have been rooted inside
follicles in the same way that hairs and feathers are known to. These
appendages have been and continue to be described as elongated scales
and feathers, depending upon the author. The longest of these
appendages seem to have been over thirty centimetres long, much
longer than the perceived full length of the actual body. The more
complete of these seem to curve around at the end so that many authors
describe them as shaped like hockey sticks.
Not
all researchers are convinced that the appendages on the back actually
belonged to the animal, instead suggesting that they may actually be
fronds of a plant and that a lizard may have simply died on top of
them. Indeed, only the holotype specimen is known to have had both
skeleton and appendages preserved together. Further specimens of the
appendages have been found completely separate from further skeletons.
There are two problems with the idea that these appendages are parts
of plants. The first is that when plants are preserved it is usually
as a carbon film, and the appendages of Longisquama
are not preserved
in this way. The second is that there is so far only one plant
preserved in rocks of the Madygen Formation (where Longisquama
fossils are known from), that has fronds that are similar to the
appendages of Longisquama, but these do not have
the distinctive
hockey stick shape.
With
all of the above in mind, the modern interpretation of Longisquama
is
that the appendages were scales, feathers or feather-like structures
that ran in either a single or double row down the back. If
feathers then they might have been more ribbon-like than erect. More
specimens in the future may one day reveal much more of this creature
as well as allow for more accurate reconstructions.
Further reading
- An unusual reptile from the Lower Triassic of Fergana. -
Paleontological Journal 1970(1):112-116 - A. G. Sharov
- 1970.
- Une novelle interprétation de Longisquama insignis,
reptile
énigmatique du Trias supérieur d'Asie centrale [A new interpretation
of Longisquama insignis, an enigmatic reptile
from the Upper Triassic
of Central Asia]. - Comptes Rendus Académie des Sciences du
Paris 305 (serie II): 65–70 - H. Haubold &
E. Buffetaut - 1987.
- Longisquama Fossil and Feather Morphology. -
Science 291
(5510): 1899–1902 - D. M. Unwin & M. J.
Benton - 2000.
- Nonavian Feathers in a Late Triassic Archosaur. - Science
288 (5474): 2202–2205. T. D. Jones, J. A. Ruben,
L. D. Martin, E. Kurochkin, A. Ferduccia, P. F. A.
Maderson, W. J. Hillenius, N. R. Geist &
V. Alifanov - 2000.
- The "Feathers" of Longisquama. -
Nature 408 (6811):
428. - R. R. Reisz & H. -D. Sues - 2000.
- Are current critiques of the theropod origin of birds science?
Rebuttal to Feduccia. - The Auk 120 (2): 550–561. -
R. O. Prum - 2002.
- Pterosaur Science or Pterosaur Fantasy? - Prehistoric Times,
No. 70, pp. 21-23 & 40 - S. C. Bennett -
2005.
- The dorsal appendages of the Triassic reptile Longisquama
insignis: reconsideration of a controversial integument
type. -
Paläontologische Zeitschrift 86 (3): 313–331 - M.
Buchwitz & S. Voigt - 2012.
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