Chicago Archaeopteryx informs on the early evolution of the avian bauplan
Abstract
Here we report on the nearly complete and uncrushed 14th specimen of Archaeopteryx. Exceptional preservation and preparation guided by micro-computed tomographic data make this one of the best exemplars of
this iconic taxon, preserving important data regarding skeletal
transformation and plumage evolution in relation to the acquisition of
flight during early avian evolution. The ventrolaterally exposed skull
reveals a palatal morphology intermediate between troodontids1 and
crownward Cretaceous birds2,3. Modifications of the skull reflect the
shift towards a less rigid cranial architecture in archaeopterygids from non-avian theropods. The complete vertebral column reveals paired
proatlases and a tail longer than previously recognized. Skin traces on
the right major digit of the hand suggest that the minor digit was free
and mobile distally, contrary to previous interpretations4. The
morphology of the foot pads indicates that they were adapted for
non-raptorial terrestrial locomotion. Specialized inner secondary
feathers called tertials5,6 are observed on both wings. Humeral tertials
are absent in non-avian dinosaurs closely related to birds, suggesting
that these feathers evolved for flight, creating a continuous
aerodynamic surface. These new findings clarify the mosaic of traits
present in Archaeopteryx, refine ecological predictions and elucidate
the unique evolutionary history of the Archaeopterygidae, providing
clues regarding the ancestral avian condition.
Full text:
https://www.researchgate.net/publication/391739196
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