[Taxacom] mangroves, angiosperm origins etc.

[John Grehan]

Below is just a small follow up not for those interested in such
perspectives (there are at least 2-4 I know of and perhaps there are a few
more) another excerpt from Croizat (and apologies for any typos) on the
nature and significance of the 'mangrove' environment both ecologically and
biogeographically (and by consequence, for evolution in general). The
freshwater cetaceans presents an intriguing possibility for the future, for
just as their ancestors could have been mangrove inhabitants whose habitat
become totally submerged, now are being uplifted again to become freshwater
organisms, and perhaps in the future terrestrial once again? (yes, pure
undisciplined speculation on my part).
John Grehan

Croizat 1968 180

The distinction between true mangroves and near-mangroves would in
geological ages past be not quite as trenchant as it is today, considering
the constant increase in salinity in the seas and oceans. The point is
worth mentioning, for it applies in a way also to the immediate present. To
explain: the land south of Cabo Corrientes in Chocó (Colombia on the
Pacific) is characterized by Murphy, R.C. (in the Geogr. Rev. 29: 13-14,
1939; see additionally Meggers, Evans & Estrada in Smithsonian Contr.
Anthropology 1: 11.1965) as “The maritime Chocó, a flooded lowland of
perpetual rain, of which selva and morasses, of hundreds of streams, many
or most of which pour into the Pacific through multiple mouths. *The line
between earth and ocean becomes tenuous*, for the greater part of the shore
is fringed with a maze of mangrove-covered flats and islands, separated by
a network of *esteros* and grading into shifting bars and shallows which in
many places extend for miles offshore” (italics mine). The counterpart of
this description is to be read in: de Wavrin, Cez les Indiens de Colombie
34: 1953. Dealing with the Northern Chocó, de Wavrin writes: “Les rives de
l’Atrato sont basses. Il faut pénétrer assez loin, vers l’intérieur des
terres, pour trouver les premières hauteurs. N’empêche que le fleuve a un
lit stable et profond…Le dauphin est inconnu…Les requins abondent…Il est de
même de cette autre variété de squales: les poisons-scie”. [The banks of
the Atrato are low. It is necessary to penetrate far enough, towards the
interior of the grounds, to find the first heights. Nevertheless, the river
has a stable and deep bed ... The dolphin is unknown ... The sharks abound
... It is the same of this other variety of sharks: the saw fish - JRG
'translation'].  Here uplift has taken place, and the river cut itself a
deeper bed (in the basin of Río Sucio, a right-side affluent of the Atrato
River, de Wavrin observed marine shells (op. cit. 27) embedded in rock),
sharks and sawfishes swim upstream remounting the Atrato up to about Quidbó
(op. cit, 34), that is, for 250 km (some 150 miles). It must be a very old
habit with these fishes, given the setup of land and sea at this end of the
world.  Naturally, landscapes of the sort must have teemed in the
palaeogeography of early angiospermous development, it being most likely,
for example that the shores on both sides of Tenasserim (as of our maps),
the South China Sea, the Banda Sea, New Guinea, The Palaus/Marianas/Western
Carolines, the approaches of New Caledonia, etc., had in the Cretaceous
environmental status to match the Western and Northern Chocó of our days.
Of course, “porpoises” (dauphins as de Wavrin calls them) could not be
found in the Atrato. *Inia* and *Sotalia*, the two genera of fresh-water
Cetacea found in Tropical America (Hershkovitz, Smiths, Inst., U.S. Natl.
Mus. Bull. 246, 1966) belong to the Amazonian sector. Dispersal is here as
everywhere clear, logical, repetious whether in the past of present, so at
least for the naturalist who has some smattering of records and geography.