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New insights on azhdarchid LK radiation

July 27, 2013

Pterosaur overlords of Transylvania: short-necked giant azhdarchids in Late
Cretaceous Romania

Mark Witton , Matyas Vremir , Gareth Dyke , Darren Naish , Stephen Brusatte &
Mark Norell

Azhdarchid pterosaurs are well known for their frequent attainment of gigantic
wingspans (sometimes over 10m), but are also characterised by a distinctive
anatomical bauplan which is thought to be fairly uniform across the group. This
comprises elongate jaws, long limbs and short wing fingers, as well as
hypertrophied cervical vertebrae, which are perhaps their most defining
features. We present evidence of unprecedented morphological diversity in giant
azhdarchids with EME 315, a large and robust seventh cervical vertebra from the
Maastrichtian Sebeş Formation of Transylvania. The specimen corresponds in
size, histology and proportions with the 10m wingspan Transylvanian azhdarchid,
Hatzegopteryx thambema, and likely represents a member of this genus or an
extremely close relative. Despite its size, EME 315 is proportionally short and
likely represents a cervical III-VII length of only 1.39m. This is comparable to
the neck lengths of much smaller azhdarchids and considerably shorter than our
estimated cervical III-VII length for Arambourgiania philadelphiae (2.3m),
another giant azhdarchid known from cervical remains. We therefore propose that
long necks are not common to all azhdarchids. The robust and short-necked
azhdarchid bauplan may reflect adaptation to predating relatively large animals,
assuming that, as suggested for other azhdarchids, these Transylvanian
pterosaurs foraged terrestrially. Because Transylvanian azhdarchids dwarf
contemporary terrestrial predators by some margin, it is possible that they were
apex predators in Maastrichtian Transylvania. This suggestion conflicts somewhat
with hypotheses that Late Cretaceous pterosaurs were ecologically constrained
and declining into extinction during the Maastrichtian.

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