Proposal (8) to South American Classification Committee
Change linear sequence of orders to place Galliformes and
Anseriformes after Tinamiformes
Synopsis: An accumulating body of independent evidence indicates
that the (1) the Galliformes and Anseriformes are sister taxa, and (2) they
represent the earliest branch in the living class Aves after the palaeognaths.
These two orders have traditionally been separated by the Falconiformes and
placed after a group of orders (Gaviiformes to Ciconiiformes) that almost
certainly appeared later in avian evolution. To maintain these two orders in
their traditional places in linear sequences obscures patterns of avian
evolution.
Background: See Sibley-Ahlquist (1990) tome for an unsynthesized
compilation of pre-1990 literature. I noted that although Beddard's 1898 review
concluded that both (1) and (2) above were correct, this was not generally
recognized, and it seems that the current linear sequence has been maintained
in most classifications for most of the 20th Century. A study of cranial
morphology led Simonetta (1963) to suggest a sister relation between
Anseriformes and Galliformes. But I think it was Sibley and Ahlquist's results
(1990) that provided the first prominently recognized genetic data for this
relationship and the basal origin of the two orders. We did not make this
change in AOU (1998) because we require multiple independent data sets to
revise at the family/order level, especially one that affects linear sequence
so radically.
New data: Now we have multiple independent data-sets
that support the original Sibley-Ahlquist finding. Here's a quote from Cracraft
(2001; Proc. Royal Soc. London 268: 459-469):
"There is compelling evidence from
immunological distances (Ho et al. 1976), amino-acid sequences from
conservative alpha crystallin genes (Caspers et al. 1997), DNA hybridization
(Sibley & Ahlquist 1990), whole and partial mitochondrial gene sequences
(Mindell et al. 1997; Van Tuinen et al. 2000), nuclear gene sequences (Groth
& Barrowclough 1999) and morphological characters (Cracraft 1988;
Dzerhinsky 1995, Livezey 1997; Cracraft & Clark 2001) that the Galliformes
and Anseriformes are each other's closest relative (united in a group called
Galloanserae) and are the basal sister group to all remaining neognaths, the
Neoaves (see Cracraft & Clarke [2001] for a review)."
Two
parts of this proposal require separate evaluation:
1. Sister
relationship of Galliformes and Anseriformes: I am unable to find any
recent data set that refutes this. In addition to the papers cited by Cracraft,
Harshman's (1994) reanalyses of the Sibley-Ahlquist DNA hybridization data
supported their original finding. Waddell et al.'s (1999) analysis of mtDNA
sequences supported the sister relationship of duck + chicken (compared to
rhea, ostrich, falcon, and passerine). Zusi and Livezey (2000)'s analysis of
cranial morphology supported this relationship (and explained problems in
previous analyses that did not find this relationship). Johnson's (2001)
analysis of cytochrome b supported the Galliformes-Anseriformes clade to the
exclusion of 703 species of birds from an exceptional range of families and
orders. Müller and Weber's (1998) analysis of tongue musculature also supported
the sister relationship of Galliformes and Anseriformes. Ericson's (1997)
analysis of osteological characters was ambiguous: he was unable to corroborate
their sister relationship but also was unable to refute it.
2. Basal
position in Neognaths: Support for this is not as solid. Mindell et al.
(1997), Härlid et al. (1998), Waddell et al. (1999), and Johnson et al. (2001)
found that Passeriformes were basal to all Neognaths or even all living birds.
These studies can be faulted, as the authors themselves often pointed out, for
combinations of limited taxon sampling, rooting the tree with distantly related
alligator sequence, or assuming equal rates of mtDNA evolution within lineages.
The analysis of van Tuinen et al. (2000) showed very strong support for the
Galloanserae as the sister to all other Neognathae. They used complete
mitochondrial gene sequences from 3 genes from 41 taxa spanning a broad
taxonomic range, and also sequence data from a nuclear gene from representatives
of 32 taxa (including all avian orders); thus their analysis stands apart from
the others in depth and breadth of sampling. They also explained why the
paraphyly of the neognaths found by the Mindell lab was an artifact of poor
taxon sampling. Also, Zusi and Livezey (2000)'s analysis of cranial morphology
supported a basal position of the Galloanserae. These studies, in conjunction
with the studies cited by Cracraft, in my opinion provide sufficient evidence
for the basal position of the Galloanserae.
Recommendation: I am by no means an expert on higher-level phylogeny. With
varying degrees of misunderstanding, I recognize that all the studies above can
be faulted to varying degrees for incomplete taxon sampling, tree-rooting
problems, failure to provide bootstrap support, use of only one analytical
paradigm (parsimony vs. likelihood), problems in character-coding, etc. Yet,
standing on the sidelines, my view is that it is statistically impossible that
so many independent and heterogeneous analyses would arrive at the same
conclusion (Galloanserae clade) by chance or artifact alone. (Besides, I like
the best-tasting birds all bunched together, early in the sequence; if you've
tasted ostrich or tinamou, you know what I mean.) I am less comfortable with
the basal position of the Galloanserae, but because retaining the Galloanserae
in one of the two linear positions currently occupied by Anseriformes or
Galliformes is not supported by any data other than tradition, I think that
moving them to follow the Tinamiformes is actually a conservative action, given
that it has received major support.
V. Remsen, June 2001
Literature Cited (in part)
Dzerhinsky,
R. Y. 1995. Evidence for common ancestry of Galliformes and Anseriformes.
Courier Forsch. Senckenberg 181: 325-336.
Ericson,
P. G. P. 1997. Systematic relationships of the Palaeogene family
Presbyornithidae (Aves: Anseriformes). Zool. J. Linn. Soc. 121: 429-483.
Groth,
J. G. & G. F. Barrowclough. 1999. Basal divergences in birds and the phylogenetic
utility of the nuclear RAG-1 gene. Mol. Phylogenetics Evolution 12: 115-123.
Härlid,
A., A. Janke, and U. Arnason. 1998. The complete mitochondrial genome of Rhea
americana and early avian divergences. J. Mol. Evol. 46: 669-679.
Harshman,
J. 1994. Reweaving the tapestry: what can we learn from Sibley and Ahlquist
(1990)? Auk 111: 377-388.
Johnson,
K. P. 2001. Taxon sampling and the phylogenetic position of Passeriformes:
evidence from 916 avian cytochrome b sequences. Syst. Biol. 50: 128-136.
Livezey,
B. C. 1997. A phylogenetic analysis of basal Anseriformes, the fossil Presbyornis,
and the interordinal relationships of waterfowl. Zool. J. Linn. Soc. 121:
361-428.
Mindell,
D. P. et al. 1997. Phylogenetic relationships among and within select avian
orders based on mitochondrial DNA. Pp. 213-247 in Avian molecular
evolution and systematics (D. P. Mindell, ed.). Academic Press, San Diego.
Mindell,
D. P. et al. 1999. Interordinal relationships of birds and other reptiles based
on whole mitochondrial genomes. Syst. Biol. 48: 138-152.
Müller,
W. and E. Weber. 1998. Re-discovery of a supposedly lost muscle in
palaeognathous birds and its phylogenetic implications. Mitt. Mus. Nat.kd.
Berlin, Zool. Reihe 74: 11-18.
Van
Tuinen, M., C. G. Sibley, and S. B. Hedges. 2000. The early history of modern
birds inferred from DNA sequences of nuclear and mitochondrial ribosomal genes.
Mol. Biol. Evol 17: 451-457.
Waddell,
P.J. et al. 1999. Assessing Cretaceous superordinal divergence times within
birds and placental mammals by using whole mitochondrial protein sequences and
an extended statistical framework. Syst. Biol. 119-137.
Zusi,
R.L. and B. C. Livezey. 2000. Homology and phylogenetic implications of some
enigmatic cranial features in galliform and anseriform birds. Annals Carnegie
Museum 69: 157-193.
___________________________________________________________________________________________
Comments
(from Carla Cicero to AOU CLC on same proposal): " Date:
Mon, 11 Feb 2002 15:36:45 -0800 - I read the Cracraft and Clarke paper on
"The basal clades of modern birds" over the weekend. The paper
primarily analyzes - or re-analyzes - a suite of 44 morphologic characters, and
discusses those as well as molecular data to address 4 major questions. Here's
a summary, for what it's worth: (1) Monophyly of modern birds, using as
outgroups Ichthyornis, Hesperornis, and outgroups outside of those fossil
clades (they don't specify) - Strongly supported (99%) by 16 derived
morphologic characters, 8 of which were unambiguously optimized on tree. They
also discuss other morphologic characters that are now found to be
synapomorphic at other levels. Three amino acid replacements in
alpha-crystallin A are consistent with neornithine monophyly. (2) Monophyly of palaeognaths
- Strongly supported (100%) by 5 derived characters, all unambiguously
optimized on tree. They also discuss other morphologic characters (previously
proposed for monophyly) that are found to be synapomorphic at other levels, or
where polarity unclear. Four molecular data sets support monophyly of palaeognaths:
immunological distances, 2 derived amino acid replacements in alpha-crystallin
A, DNA hybridization, RAG-1 sequences (3) Monophyly of neognaths - Strongly
supported (100%) by 11 derived characters, 6 of which are unambiguously
optimized on tree. Two molecular data sets consistent with monophyly of
neognaths include 2 amino acid replacements in alpha-crystallin A, and RAG-1
sequences. (4) Monophyly of Galloanseres - Strongly supported (100%) by 12
derived characters, 11 of which are unambiguously optimized on tree. They also
review synapomorphies postulated by Livezey (1997) to support monophyly of
Galloanseres (some, not all, incorporated by Cracraft and Clarke; others not
included pending further comparative analysis within neognaths and outgroups).
Molecular data that support monophyly include: immunological distances, DNA
hybridization, DNA sequences from alpha-A and alpha-B-crystallin genes, RAG-1
sequences, unpublished mtDNA and RAG-2 sequences. Furthermore, 3 amino-acid
replacements in alpha-crystallin A are consistent with a neognath clade that
excludes Galloanseres, and a 5-codon deletion in RAG-1 also diagnoses this
clade. They state: "Whereas a sister group relationship between palaeognaths
and neognaths is strongly supported by a variety of data, the basal divergences
of the neognaths has remained controversial. Recently, however, interpretations
of both molecular and morphological data have begun to converge on the
hypothesis that Galliformes and Anseriformes are sister taxa and are together
the sister group of all other neognaths...Although no viable alternative
hypothesis...has been put forth, a monophyletic Galloanseres has been doubted by
some (e.g., Feduccia 1996). In particular, Ericson (1996) questioned the
validity of many of the morphological characters listed above, and in a later
study (1997) on the systematic position of Presbyornis
placed Galliformes as the sister group of other neognaths and imbedded the
Anseriformes deep within the neognaths in a clade also containing ciconiiforms.
However, as already noted, Livezey (1997) examined many of the same taxa during
a parallel study of Presbyornis, used
a much larger morphological data set than Ericson (1997), especially for the
skull, and concluded that the morphological evidence supported a monophyletic
Galloanseres...Thus, a broad suite of data, from many independent sources, all
point to a monophyletic Galloanseres. These data now place a substantial
homoplasy burden on all other hypotheses..." They go on to talk about
problems with rooting and taxon sampling in molecular studies. Basically, their
conclusion is that we can confidently place Galloanseres as sister to a clade
of other Neognathes, but relationships of the latter are still poorly
understood. This is nothing new, but their paper is a nice summary of the data.
Though Galliformes and Anseriformes may be sister taxa in a cladistic sense
(i.e., supported by numerous derived morphologic as well as molecular
characters), which makes them closest living relatives, they are not closely
related. Nonetheless, in view of the fact that they have been evolving
independently for a very long time, the number of characters shared by these groups
is surprising - more so than the differences between them.