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molecular-clock analyses. Furthermore, we
have not included any internal calibra-
tions within Cichlidae, so that our relaxed-
molecular-clock estimate of the evolution-
ary time scale for the group is truly inde-
pendent of its fossil record, which contrib-
utes to our palaeontological estimates of
divergence times (see §2).
3. Results
Our three approaches to estimating a
time scale of cichlid origin and diversifi-
cation yield overlapping CIs that diverge
significantly from the predictions made by
the Gondwanan vicariance biogeographic
hypothesis, and are discussed in turn in
§3a,b (figure 1).
(a) Palaeontological time scales for cichlid evolution electronic supplementary material, table S2).
The distribution of cichlid-bearing fos-
sil horizons, combined with an empiri-
cally informed function describing fossil
recovery potential, indicates an age of
origin for cichlids in the Late Cretaceous
or Palaeocene. If only the records of land-
masses that are currently inhabited by
cichlids are considered, the time of origin
of the clade is estimated as 59.2 Ma (95%
CI: 56.1-67.6 Ma). By contrast, a slightly
younger age estimate of 57.8 Ma (95% CI:
56.1-62.4 Ma) is obtained if the record of
all Gondwanan landmasses is considered.
Restricting the scope of analysis to con-
sider articulated remains alone provides
a more conservative means of estimating
the time of origin for cichlids, because
early members of this group might not be
recognized on the basis of less diagnos-
tic skeletal debris. Point estimates for the
timing of cichlid origin under this approach
do not change drastically from those
obtained using the entirety of the cichlid
10 facebook.cichlids.org.au
fossil record, but the upper bounds of
the CIs do increase by more than 10 Ma.
Depending on the scope of geographical
analysis, we estimate the time of cichlid
origin based only on articulated remains as
ranging from 59.8 Ma (95% CI: 56.1-75.1
Ma; landmasses inhabited by modern cich-
lids) to 60.2 Ma (95% CI: 56.1-77.8 Ma; all
Gondwanan landmasses). The Gondwanan
vicariance hypothesis requires a pre-
Eocene record of cichlids that is roughly
10-30 times worse than their recorded
fossil history, with rescaled recovery poten-
tials conditioned on point estimates for
the origin of the group at 135 Ma ranging
from 2.8-3.3% (all fossils) to 6.6-6.9%
(articulated fossils only) of their original
values. Classical confidence intervals deliver (b) A molecular time scale for cichlid evolution
similar results to the Bayesian estimates (see
Analysis of outgroup ages provides broadly
similar estimates for the timing of cichlid
origin to those derived from the distribu-
tion of cichlid fossil horizons, in terms of
both the magnitude of point estimates
and the degree of uncertainty surround-
ing them. We find a mean age of 60.7 Ma
(95% CI: 46.8, 90.1 Ma) using the old-
est possible fossil ages for outgroups.
The time scale for cichlid origin is predict-
ably more recent using the youngest pos-
sible fossil ages for outgroups, but only
slightly so, with a mean age of 57.0 Ma
(95% CI: 46.8-81.2 Ma). Using this same
approach, it is also possible to determine
probable times of origin for a series of more
inclusive clades that contain Cichlidae:
Ovalentaria, Percomorpha, Acanthopterygii,
Acanthomorpha, Eurypterygii, Euteleostei
andTeleostei. This exercise implies that no
crown acanthomorph lineages are likely
to be sufficiently ancient to have vicariant
Gondwanan distributions, as we estimate
the age of the group as between 106.4Ma
(95% CI: 98.5-132.2Ma) and 109.2Ma (95%
CI: 98.5-136.0Ma). The most restrictive
group containing cichlids that we can date
with this method and which is of sufficient
apparent antiquity to have been affected by
the initial rifting of Gondwana is Eurypterygii,
the radiation containing Acanthomorpha,
Myctophiformes and Aulopiformes [25].
Our estimates for the time of origin for
this major teleost clade range between
131.1Ma (95% CI: 104.9-163.2Ma) and
142.1 Ma (95% CI: 126.2-166.2 Ma).
The phylogeny of Ovalentaria and the
major cichlid lineages inferred from the 10
nuclear genes is similar to previous molec-
ular and morphological analyses [8,10,19],
with Etroplinae (India, Madagascar)
resolved as the earliest-diverging clade
and Ptychochrominae (Madagascar) as the
sister lineage to the unnamed clade that
contains the African (Pseudocrenilabrinae)
and Neotropical (Cichlinae) cichlid line-
ages (figure 1; electronic supplementary
material, figure S1). The 10 nuclear gene
phylogeny preserves the parallels between
patterns of cichlid interrelationships and
the fragmentation history of Gondwana
that has led to the prominence of vicari-
ance biogeographic scenarios for this lin-
eage [9]. However, the Bayesian random
local molecular-clock analyses yield age
estimates for the origin of cichlids consist-
ent with those derived from analysis of
fossils alone (figure 1 and table 1; elec-
tronic supplementary material, figure S1).