Proposal (626) to South
American Classification Committee
Recognize
rheas as an order, Rheiformes
The higher classification of the
ratites and tinamous has been turbulent through the decades, with just about
every permutation possible in terms of ranking schemes. Our current classification treats the Rheidae
as a family in the order Struthioniformes, implicitly following many
classifications that treat all the ratites in a single order. Our footnote reads as follows:
Recent genetic data (Harshman et al. 2008, Phillips et al. 2010,
Smith et al. 2012) indicate that the Struthioniformes is paraphyletic with
respect to the Tinamiformes. Cracraft
(2013) elevated the rheas to ordinal rank, Rheiformes, as in some older
classifications. Proposal badly needed to change SACC
classification to reflect this.
Rather than transfer Rheidae to the
Tinamiformes, or Tinamidae to Struthioniformes, Cracraft (2013) elevated rheas
to the rank of order, along with ostriches, tinamous, and kiwis, and placed
cassowaries and emus in the same order.
He placed Rheiformes and Tinamiformes adjacent in the linear sequence.
Recommendation: I personally favor
recognizing all these ancient lineages at the rank of order regardless of their
inter-relationships given their age relative to other taxa ranked as orders, so
would vote for this regardless of tinamou-rhea sister relationship. Regardless, the genetic data require treating
these two lineages at the same rank, and so I recommend elevating the rheas to
the rank of order. Treatment of the
rheas in their own order actually follows many classifications, including even
the online Merriam-Webster dictionary, so this is not a radical proposal.
References:
CRACRAFT, J. 2013.
Avian higher-level relationships and classification:
nonpasseriforms. Pp. xxi-xliii in The Howard and Moore Complete
Checklist of the Birds of the World, 4th Edition, Vol. 1.
Non-passerines (E. C. Dickinson & J. V. Remsen, Jr., eds.). Aves Press,
Eastbourne, U.K.
(see SACC Biblio for the others)
Van Remsen, March 2014
======================================================
Comments
from Stiles: “YES.
Given the age of all these lineages as well as the distinctive features of the
birds themselves, a separate order for the rheas seems eminently reasonable.”
Comments from Nores: “YES. If Ratites do not form a
monophyletic group, a separate order for the rheas seems quite reasonable.”
Comments from Zimmer: “YES, for reasons stated in the proposal.”
Comments
from Pacheco: “YES. The suggested treatment seems most appropriate
instead to gather Tinamous and Rheas in expanded Struthioniformes.”