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Rahonavis ostromi (Forster, Sampson, Chiappe and Krause, 1998)
is an early bird found in late
Cretaceous
Madagascar that shows a mixture of bird-like and theropod-like
features that strengthen the case for birds as descendents of
theropod
dinosaurs. The partial skeleton consists of
dorsal and
caudal
vertebrae ,
ulna ,
radius ,
synsacrum (fused
vertebrae over the pelvis), shoulder girdle, pelvic girdle,
femur ,
tibia , f
ibula ,
calcaneum ,
astragalus, t
arsals ,
metatarsals and
phalanges . The
overall appearance is bird-like, and Rahonavis is only slightly
larger than Archaeopteryx and smaller than the early bird
Vorona, found in the same quarry. Of particular interest is the
sickle-claw on the second toe - a feature characteristic of
dromaeosaurids
and troodontids
. Because the wing was found nearby but not attached to the rest of
the skeleton, it has been suggested that the wing actually belongs to
Vorona. Forster et al acknowledge the possibility but
consider it unlikely based on the scattered nature of the bird
material from this quarry and the similar appearance of the wing bones
and the remainder of the skeleton. Cladistic analyses both with and
without including the wing give the same result, positioning
Rahonavis close to Archaeopteryx.
A partial skeleton of a primitive bird, Rahona ostromi, gen.
et sp. nov., has been discovered from the Late Cretaceous of
Madagascar. This specimen, although exhibiting avian features
such as a reversed hallux and ulnar papillae, retains
characteristics that indicate a theropod ancestry,
including a pubic foot and hyposphene-hypantra vertebral
articulations. Rahona has a robust, hyperextendible
second digit on the hind foot that terminates in a
sicklelike claw, a unique characteristic of the theropod
groups Troodontidae and Dromaeosauridae. A phylogenetic analysis
places Rahona with Archaeopteryx, making Rahona
one of the most primitive birds yet discovered.
This raven-sized animal belonged to the same group of dinosaurs as
Velociraptor, but it had many bird-like features. Rahonavis lived
about 80 million years ago and had a retractable “sickle-claw” on the
middle toe of each foot. It had feathered wings like a bird but a long
bony tail like Archaeopteryx. |