[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Limusaurus (Theropoda: Ceratosauria) digits not a clue to avian digit identity

Ben Creisler

A new online paper:

Geoffrey Guinard (2015)
Limusaurus inextricabilis (Theropoda: Ceratosauria) gives a hand to
evolutionary teratology: a complementary view on avian manual digits
Zoological Journal of the Linnean Society (advance online publication)
DOI: 10.1111/zoj.12329

It is widely accepted that birds are rooted within theropod dinosaurs.
However, there is controversy between palaeontological and
developmental data regarding manual digit identities of birds and
their tetanuran ancestors (I, II and III vs. II, III and IV). To
resolve this conflict, the principle of a frame-shift has been
considered. Identities of digits I–III would develop on condensations
2–4. Nevertheless, the discovery of the basal Ceratosauria Limusaurus
inextricabilis has been used as a reference to define the digital
identity of Tetanurae as II–IV. The new concept of evolutionary
teratology states that certain anatomical structures identified in
evolutionary lineages are viable developmental anomalies (‘adaptive’
or not), becoming part of the considered groups. The features of
Limusaurus' forelimb match teratological characterization. This
diagnosis, associated with the variations previously identified in
derived Ceratosauria taxa (Carnotaurinae), underline an anatomical and
developmental independence (regarding evolutionary conserved
mechanisms) compared with Tetanurae and therefore birds. Consequently,
Limusaurus should not be used as a reference concerning the identity
of avian manuals digits. Evolutionary teratology supports identities
I, II and III of the tetanuran manus via a frame-shift that did not
occur in the Ceratosauria lineage.