Biology Reference
In-Depth Information
plates, all moving westward from the Mid-Atlantic Ridge, but at different
rates. The Caribbean plate is moving at the comparatively slow rate of about
1.8-2 cm each year, North America at 3.0 cm, and South America at 3.3 cm.
The result is a progressively eastward position of the Caribbean plate vis-à-
vis the two other plates. After a submerged Cretaceous origin, the principal
period of emergence occurred when the island arc collided with the stable
Bahamas Platform in the Eocene about 45 Ma. Some islands fragmented
further, others collided, and new ones emerged later, particularly in the
Miocene. The prevalent view now is that the original arc was never continu-
ous and never formed a complete land connection between the continents.
This allows a greater role for dispersal in explaining the distribution and
speciation of organisms in the Antilles (Heinicke et al. 2007).
Near the time of initial encounter of the volcanic island arc with the
Bahamas Platform, a land fragment representing proto-northern Cuba was
part of the North American Plate located along its southern edge. Another
fragment on the Caribbean plate consisted of proto-southern and -western
Cuba, and it collided with northern Cuba in the late Paleocene to early
Eocene with the contact represented by the Pinar Fault. Parts of Cuba were
above water in the middle Eocene, as shown by spores and pollen of some
forty-six terrestrial plants identifi ed from the Saramaguacán Formation.
The Cauto Fault is the contact between proto-Cuba and another fragment
made up of eastern Cuba, northern Hispaniola, and Puerto Rico. The Ba-
hamas Platform is curved, so when the western edge of the volcanic arc
encountered the platform, this edge slowed fi rst, affi xing eastern Cuba to
the rest of the island, while the remaining part of the arc continued to move
eastward. The distribution and relationships of
Adelia
(Euphorbiaceae) and
other genera are consistent with the composite North American / Caribbean
plate origin of Cuba (De-Nova and Sosa 2007). Northern Hispaniola (Haiti
and the Dominican Republic) and Puerto Rico separated next. These events
were taking place in the late Oligocene and Miocene between about 28
and 20 Ma.
An extensive fl ora of middle Oligocene age (30 Ma) is known from
Puerto Rico and includes 91 species of macrofossils and 165 kinds of spores
and pollen. There has been some question as to whether Puerto Rico had
emerged by this time, but the extensive terrestrial vegetation of the San
Sebastian Formation shows that at least parts were fully above water in
the middle Oligocene. Southern Hispaniola, the elongated “South Island”
(fi g. 2.27), was added on to northern Hispaniola in the middle Miocene
(15 Ma) through movement of one of the many Caribbean micro- or
subplates. The contact is marked by the present Cul-de-Sac / Enriquillo Ba-
