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Pebas 17 Ma

The Amazon River is the world’s largest river and it has the world’s largest drainage basin—the vast Amazon rainforest, which stretches from the Andes in the west, to the Guiana Highlands to the north and the Brazilian Highlands in the south.   The great river drains east into the Atlantic Ocean….but it was not always so.  Before the Andes Mountains rose, the river drained west into the Pacific.  Throughout the Cenozoic, the mouth of the river moved up around the continent.  Thirteen million years ago, during the Miocene, the river drained north into the Caribbean through a huge tropical swamp–the Pebas mega-wetlands–which covered over one million square kilometers of what is now the Amazon Basin.

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An illustration of Pebas Corocodilians–Gnatusuchus is underwater, gobbling clams (art by Javier Herbozo)

Like today’s Amazon Basin, the Pebas mega-wetland was a great riverine rainforest.  And yet the ecosystem was very different from what is there today.  The marshes and swamps were filled with bivalve mollusks that thrived in the oxygen-poor waters.  Predators evolved to feed on these clams and mussels…and what predators!  This is Gnatusuchus, a caiman with spherical teeth for crushing open shellfish. Can you imagine biting through the shell of a clam?  Just thinking about it makes my jaw hurt and my teeth feel broken.  Yet Gnatusuchus bit through heavy shells for every meal!

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A life-sized reconstruction of the gigantic Purussaurus

The crocodilian grew to lengths of 1.5 meters (about 5 feet) and had a short round shovel-shaped mouth to focus maximum force on biting through clams.  Life in the Pebas was not all basking and clam feasts for Gnatusuchus.  The reptile was hardly the only reptile in the swamp, but was instead one genus among a hyper-diverse group of crocodilians including giant toothy predators capable of eating Gnatusuchus.  One of these predators, Purussaurus neivensis grew to be 12.5 metres (41 ft) in lengt—making it a rival of the great Mesozoic crocodilians like Phobosuchus (maybe I should have mentioned this horrifying monster first, instead of alluding to him after the clam-eater, but Ferrebeekeeper is interested in mollusks and their predators not in giant crocodiles: this is not Peter Pan, my friend).  There were also piscivorous crocodilians with long scissor snouts foll of hooked teeth (like modern gharials), and even little crocodilians on stilt-like legs that ran around plucking up small prey in the manner of pipers or herons.

anatosuchus-size

Seven million years ago, the Pebas began to change from swamps to channels as Amazonian drainage became spread through an even more enormous basin. Still, the diversity of the creature that lived there became a heritage for the contemporary Amazon, arguably the most diverse ecosystem in the world today.

A magnificent Bald Cypress towering over Weston, West Virginia

When I was on vacation last week, I took some pictures of the tree in my grandparents’ garden, a magnificent bald cypress (Taxodium distichum).  Whereas the Norway maple in my back yard is like a rat or a pigeon (ubiquitous and worthless–yet amazing for its hardiness and success) the bald cypress is huge, ancient, and stately–a monarch among the trees.  Bald cypresses, which are native to the great southern wetlands of the United States, can grow to immense size and live for over a thousand years.

Today bald cypresses are found in parks and gardens, frequently as stand alone specimen trees, but such was not always the case:  ancient bald cypress forests, consisting of huge groves of thousand year old trees, once dominated the southern swamps of the United States. An old-growth stand of the trees can still be found near Naples, Florida–the grove is around 500 years of age and some of the trees exceed 40 m in height.  Unfortunately for the great trees, they were extensively overharvested for their water-resistant rot-proof lumber.  Nutria rats, which gnaw the seedlings to death, have prevented the forests from growing back. Furriers brought these large invasive rodents from the jungles of South America.  The voracious creatures escaped into the Louisiana marshlands and have defied all predators and control efforts and proliferated throughout the southern states.

Argh! Why, oh why are the nutria's teeth so red?

Bald cypresses are deciduous conifers–they shed their fine leafy needles during the winter (and are hence “bald”).  Coincidentally, “cypress” is a misnomer: the tree is not in the same genus as the funereal cypresses although it is in the same family (the Cupressaceae) along with some of the world’s most spectacular trees, the redwoods, the sequoia, the dawn redwoods, and the Japanese Sugi (Sequoia, Sequoiadendron, Metasequoia, and Cryptomeria respectively).

Another View of the Same Tree

The specimen in my grandparents’ yard lives in the mountains rather than the swamp, yet it is among the largest known.  I’ll let the placard speak for itself, but it was written in 2005 and the tree has had a good 5 years of warm wet summers (which it loves).

Taxodium is an ancient genus of tree and various taxodium species were widespread throughout much of the Mesozoic Era.  Fossil specimens date back to the Jurassic period so once these giant trees towered above the dinosaurs.

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