Biology Reference
In-Depth Information
suggesting seasonal rainfall and slightly open vegetation (tropical forest;
T in fi g. 2.10).
In the midcontinent region, low to moderate topographic diversity pro-
vided uplands (as opposed to highlands), swampy lowlands, and aquatic
habitats. Otoliths from a Maestrichtain fi sh (
Vorhisia vulpes
) in the Fox
Hills Formation of South Dakota suggest the near-shore waters of the epi-
continental sea were brackish (70-80 percent seawater), and temperatures
in the open marine waters were about 18°C (Carpenter et al. 2003). The
Dakota Formation (Albian, Early Cretaceous) of Kansas and Minnesota con-
tains plants similar to the fern family Marattiaceae (Hu et al. 2006). The
modern species grow along streams in shaded, wet, tropical, and subtropi-
cal habitats. Also present are Nymphaeaceae (
Aquatifolia fl uitans
) and Ca-
bombaceae (
Brasenites kansense
; Wang and Dilcher 2006), as well as
Isöetes
(quillwort, a fern-allied plant; Skog et al. 1992) and the aquatic fern
Mar-
silea
(Skog and Dilcher 1992). Other reports of Cretaceous aquatics include
the fl oating ferns
Azolla
and
Salvinia
(Hall 1974), Nymphaeales/Nymphaea-
ceae (Friis et al. 2001; Gandolfo et al. 2004), and
Trapago
, a fl oating rosette
of unknown affi nity (Stockey and Rothwell 1997). The Nymphaeaceae is
also known from the late Paleocene Almont fl ora of North Dakota (Taylor
et al. 2006). Early and middle Eocene fl oras include
Isöetes
,
Salvinia
,
Dec-
odon
(Dillhoff et al. 2005; Little and Stockey 2003),
Nelumbo
, and
Porosia
,
an extinct fl oating aquatic angiosperm. The Nelumbonaceae and aquatic
ferns (
Paleoazolla
,
Marsilea
,
Regnellidinum
) occur in the Late Cretaceous La
Colonia Formation, Chubut, Argentina (Gandolfo and Cúeno 2005), so the
aquatic ecosystem was widespread in the Cretaceous and Paleogene of the
New World.
An interesting plant from the Late Cretaceous Lance and Hell Creek for-
mations of Wyoming was originally described as a fi g (
Ficus ceratops
), but
it is most similar to the modern
Guarea
(e.g.,
G. chichon
; fi g. 5.3a, b). Both
Ficus
and
Guarea
grow in the American tropics and subtropics. In the earli-
est Paleocene the vegetation from a site near Denver was a paratropical rain
forest, with MAT 22.2°C
2°C, and MAP 2250 mm (Johnson and Ellis
2002). The paleoclimate is based on leaf physiognomy where 69 percent
of the ninety dicot species had leaves that were entire margined, and forty-
eight species had drip tips.
In summary, eight ecosystems formed the plant communities of North
America north of Mexico toward the end of the Cretaceous. There was a
polar broad-leaved deciduous forest, notophyllous broad-leaved evergreen
forest, paratropical rain forest, tropical forest, aquatic, and herbaceous
bog/marsh/swamp communities. Also, there must have been versions of
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