Pleistocene Paddlefish (Polyodon spathula)

A large population of 7 foot long, 150 pound paddlefishes lived in the primeval waters of the Mississippi River Drainage System  from well before the Pleistocene until the 19th century when humans began overexploiting this species.  An even larger population of smaller individuals also swam these waters for eons.  Millions upon millions of paddlefishes existed for tens of thousands of generations, yet, as far as I can determine from the scientific literature, not a single fossil specimen of Pleistocene Age has ever been found.  The paddlefish is a primitive species with a body structure supported by cartilage rather than bone.  There is nothing on their body that is hard and durable, therefore, evidence of their past existence is very unlikely to survive the ravages of time.  Sharks are also primitive fishes supported by cartilage, but at least they have hard teeth that do resist decomposition.  There isn’t even much evidence of paddlefish in the archaeological record, though Indians certainly utilized this species.  The remains of a paddlefish were excavated from a Native-American midden located in Wisconsin.

Scientists do know the paddlefish is an ancient species, possibly originating before the dinosaurs.  William Bemis, a paleontologist, described a Cretaceous Age fossil of a paddlefish found in Montana as “remarkably like (the 2) living species of polyodon.”  The only other extant species of paddlefish in the world occurs in Chinese rivers, and its scientific name is Polyodon gladius.  The 2 living species probably diverged during the Miocene between 25 million-5 million years BP, when climatic changes led to an environmental barrier that divided the American population from the Asian gene pool.  Genetic evidence suggests the American paddlefish has been uniform for a long time.  They travel great distances throughout the Mississippi River Drainage System and interbreed freely and do not live in isolated populations.  One tagged specimen caught in Moon Lake, Mississippi was captured later 870 miles away in Illinois.

American Paddlefish (Polyodon spathula).

The American paddlefish filter-feeding. No Pleistocene aged specimens of this species have ever been found because they are made of cartilage.  The adults have no teeth.

Paddlefish range map.  Paddlefish are now extinct on the periphery of their northeastern range and their populations are in decline elsewhere.

Paddlefish live in large rivers, braided channels, and oxbow lakes.  All of these habitats existed during the Pleistocene.  Braided channels more commonly formed during cold arid phases of Ice Ages.  The lower water table resulted in channels cut off and choked with sandbars.  Warmer wetter climate phases caused an increase in the formation of oxbow lakes as overflowing waters meandered more.  Paddlefish thrived in both habitats wherever there was an abundance of zooplankton.  Paddlefish use their unusual paddle-like structures to locate the tiny crustaceans and insects upon which they filter feed.  Their diet of mini-crustaceans probably explains why their flesh reportedly tastes like lobster.  They are still referred to as “poor man’s lobster,” even though this endangered fish is now rarer in fish markets than actual lobster.

Moon Lake, Mississippi still supports a commercial fishery for paddlefish.  They were so abundant during the early 20th century here that 100 could be caught in a single purse-seine haul.  The catch is much reduced today.

Moon Lake, Mississippi, an oxbow adjacent to the Mississippi River, still has a viable population of endangered paddlefish.

Oxbow lake formation fascinates me.  An oxbow lake is the remains of a meander that gets cut off from the main flow of the river, following a period of high water when the river surges over land to connect the shortest distance between 2 points.  These natural formations provided the only lake habitats over much of the south until man began building reservoirs.  Eventually, sediment builds in oxbow lakes until they evolve into marshes and then dry land.  Old oxbows that dry out are known as meander scars.

References:

Hoover, Jeffrey; et. al.

“Age and Reproductive Condition of an Unusually Large Bighead Carp from the Lower Mississippi River Basin”

Southeastern Naturalist 14 (4) 2015

Theler, James

“Animal Remains from Native American Archaeological Sites in Western Wisconsin”

Transactions of the Wisconsin Academy of Science, Art, and Letters 2010

 

 

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