Geography Reference
In-Depth Information
tion, as the key factor to explain their biotic evolution, especially during the Creta-
ceous (Russell 1993; Sampson et al. 1998); however, Sereno (1997, 1999) con-
cluded that continent-level vicariance was rare and unimportant to explain dino-
saurian biogeographic patterns. Upchurch et al. (2002) undertook a TPCA to ana-
lyze the biogeography of dinosaurs in order to detect the presence of repeated
area relationships that may indicate vicariance.
Upchurch et al. (2002) used TreeMap (Page 1994c) to analyze the taxon-area
cladograms of Ornitischia and Saurischia. They analyzed nine time slices of vari-
ous durations: Mesozoic, Late Triassic, Jurassic, Early Jurassic, Middle Jurassic,
Late Jurassic, Cretaceous, Early Cretaceous, and Late Cretaceous. For each time
slice, the taxon-area cladograms were pruned so that only taxa present at the rel-
evant time were retained.
Only three analyses passed a randomization test, indicating that the patterns
for the Middle Jurassic, Late Jurassic, and Early Cretaceous were highly unlikely
to have arisen by chance (
fig. 7.1
). General area cladograms for Middle and Late
Jurassic (
fig. 7.1a-d
)
contained only four areas, reflecting the poor sampling of
taxa for several continents. They display the same relationships for the areas in
common (Asia, Europe, and Africa). The Early Cretaceous general area clado-
gram (
figs. 7.1e
and
7.1f
) contains six areas and differs from that of the Late
Jurassic regarding the relationships of Europe. Incongruities between the three
general area cladograms result from the conflicting relationships of Europe and
SouthAmericarelativetotheothercontinents.Accordingtotheauthors,thefailure
of the Late Triassic and Early Jurassic analyses may reflect the current selec-
tion of areas that are suitable for the detection of continent-level vicariance, given
that Pangaea remained largely intact until the Middle Jurassic. Additionally, poor
sampling may be largely responsible for obscuring area relationships.
When Upchurch et al. (2002) compared the results of their analysis with paleo-
geographic reconstructions, they found that the greatest incongruence concerns
the position of South America in the Middle Jurassic. According to the general
area cladogram, Europe and Africa were more recently in contact with each other
than either was with South America, conflicting with paleogeographic reconstruc-
tions that suggest that Africa and South America constituted a continuous area
throughout the Jurassic and into the Cretaceous. It is conceivable that some non-
marine barrier separated South America and Africa during the Middle Jurassic, but
there is no geological evidence. It seems more probable that the problem lies with
the apparent biogeographic signal. Another incongruity is the lack of a clear group
of Laurasian areas in the general area cladograms, but this may be more apparent
than real because Laurasia may have constituted a single continuous continent di-
vided by epicontinental seas into a number of separate landmasses. The different
positions of Europe in the general area cladograms of the Late Jurassic and Early
Cretaceous may indicate the convergence of two previously depauperate areas.
This is consistent with previous studies that showed that the regression of the Tur-
