recovered clades are well supported on the basis of osteological evidence, such as the New
and Old World quail (Perdicini) and the grouse (Tetraonidae) (see Dyke et al. 2003 for
details of this analysis).
Including the two Lower Eocene taxa Gallinuloides and Paraortygoides within the
phylogenetic analysis resulted in no changes to original tree topology (not shown), and an
increase in tree length of just six steps. However, markedly different placements for the
two taxa are suggested—Paraortygoides (Figure 12.6) is hypothesized to be a basal (perhaps
the most basal) representative of the order, whereas Gallinuloides (Figure 12.6) is placed in
a more derived position towards the crown of Galliformes (Figure 12.6). This conclusion
is of interest because, almost without exception, previous workers have considered
Gallinuloides to be a member of, or closely related to, the basal galliform clade Cracidae
(Tordoff and Macdonald 1957; Brodkorb 1964; Ballmann 1969).
The ages of included fossils—what do these imply?Although it is possible to view a number of the early fossil representatives of the
neornithine clades in a phylogenetic context, in terms of the pattern of the radiation of
modern birds, what do the placements of these taxa imply with respect to the two
alternative hypotheses outlined above? Although acceptance of a hypothesis in which the
bulk of the neornithine radiation occurred in the early Tertiary (Feduccia 1995, 1999)
would require taking the known fossil record at face value—the noted lack of Neornithes
in the later stages of the Mesozoic would then present evidence for their absence (Cracraft
2001)—it could be that both hypotheses are, to some extent, correct. Perhaps, as has
been suggested, some clades diverged deep in the Cretaceous and then were maintained at
low diversity until after the K-T boundary (Cooper and Fortey 1998; Cracraft 2001).
Workers have used the fossil record and the phylogeny of Neornithes in different ways in
order to address this problem. On the basis of some limited phylogenetic placements for
fossils and the spatial pattern of extant taxa within phylogenetic topologies, Cracraft
(2001) argued that both of these lines of evidence support a Cretaceous divergence for
neornithine clades on the Southern Hemisphere continents. On the other hand,
Bleiweiss’s (1998) stratigraphic gap analysis of the published fossil record of three
putatively related clades of Neornithes (Apodiformes, Caprimulgiformes, and
Strigiformes) supported the probability of their divergence as late as the Tertiary.
Whatever the outcome of specific debates regarding the taxonomy of individual
specimens claimed to be neornithine and from the Mesozoic (Stidham 1998; Dyke and
Mayr 1999), the fossil record, when evaluated in a phylogenetic context, does appear to
support a pre-Tertiary divergence for at least the more basal clades— Palaeognathae,
Galliformes plus Anseriformes. I have argued elsewhere (Dyke 2001a) that the placement
of well-represented fossil taxa (such as Presbyornis and Gallinuloides) from the early Tertiary
within crown-groups of the most basal major clades of Neornithes must imply the
divergence of these clades at an earlier time. Further evidence for this inference simply comes
from the proximity of these Tertiary fossils to the K-T boundary (less than 10 million
years in some cases) and from the fact that the vast majority of material claimed as
neornithine from the Mesozoic has also been placed within more basal clades (Dyke
2001a). Of course divergence estimates tell us nothing about diversity changes and hence the
BASAL RADIATIONS WITHIN THE NEORNITHES 279