Horaffia, new diapsid marine reptile from Middle Triassic of Germany (free pdf)

[Ben Creisler <bcreisler@gmail.com>]

Ben Creisler
bcreisler@gmail.com

A new paper in open access:


Nicole Klein & Hans Hagdorn (2014)
Humerus morphology and histology of a new marine reptile (Diapsida)
from the Muschelkalk-Keuper-Grenzbonebed (Middle Triassic, Ladinian)
of Southwest Germany.
Palaeodiversity 7: 23-38
http://www.palaeodiversity.org/pdf/07/02Palaeodiversity_7-14_Klein_3.pdf



A survey in the collection of the Muschelkalkmuseum Ingelfingen
revealed a growth series of five humeri from  the Grenzbonebed
collected from localities in northeastern Baden-Württemberg (Southwest
Germany). The Grenzbonebed is a tempestitic condensation horizon at
the base of the Keuper that contains prefossilized vertebrate fossils
reworked during a 100 ka minor sedimentary cycle. The humeri share a
unique but simplified morphology due to adaptation to aquatic life.
They are very robust and pachyostotic and have a dorsopreaxially
elongated margin, a massive and ventrally protruding triangular
proximal head as well as a preaxially slanted asymmetrical distal end.
A detailed morphological comparison with humeri of other Triassic
marine reptiles showed that they differ from humeri of all known taxa,
including those of placodonts such as Paraplacodus, Placodus,
Cyamodus, and Henodus. However, an analysis of the bone microstructure
and histology revealed a close relationship with the humeri of
Cyamodus, despite of distinct morphological differences. The five
humeri and humeri of Cyamodus share a plexiform radiating
fibro-lamellar bone tissue with moderate to high vascular density in
the middle and outer cortex and a poorly developed medullary region,
indicating osteosclerosis. Contrary to the pachyostotic humeri from
the Grenzbonebed, Cyamodus humeri are not pachyostotic, thus
suggesting different modes of locomotion in a similar shallow marine
environment. The histological features of the pachyostotic humeri from
the Grenzbonebed, which could point to placodont or pistosauroid
affinities, respectively, are no reliable phylogenetic markers because
convergent evolution of bone tissue is common among aquatic
vertebrates sharing a similar environment and life style. Due to the
unique humerus morphology the establishment of a new taxon, Horaffia
kugleri gen. et sp. nov., is justified, although the remains are too
poor to include them into a phylogenetic analysis or to assign them to
a certain group.