Friday, December 21, 2012

It Came From the Depths...

Gnarly, bitey stuff from the depths is something we will never get sick of here at da' salad and I hope you feel the same way- if you do there is much of interest to you in this post. Hollywood, myth and legend are replete with stories of beasts from the depths rising to engage  us in mortal battle. Indeed it seems that modern stories of shark and croc attacks tap an especially visceral nerve in our primal subconscious. Our dependence on the water's edge for food, recreation and water coupled with our knowledge (and imagination) of the critters that occasionally seek us out here as prey means that the waters edge has always occupied a special type of nightmare realm for us. It is truly a meeting place of life and death. And since it seems we are making it through this Maya thing ok so far, hominins meeting a grisly fate at the waters edge at the hands (fins) of large predators will continue. It also appears that death-stalking water bound predation of land-lubbers has been ongoing for some time...

Pannoniasaurus is the name of the new freshwater mosasaur from the Santonian mid-Late Cretaceous of Hungary. Here is the full paper of this spectacular discovery via PLOS ONE. It appears, based on geochemical testing and the preservation of multiple growth stages of this squamate, that it is the first full time "freshie" mosasaur known. Inhabiting an environment replete with amphibians, turtles, crocs, pterosaurs, fish, birds, and dinosaurs Pannoniasaurus appears to have grown 6 meters long and was the largest predator in its habitat. Although the legs have not been recovered that has not stopped artists and the authors from speculating that Pannoniasaurus may have never lost, or even re-evolved, somewhat functional legs.

The discovery of fully freshwater mosasaurs should come at no surprise to those familiar with the diversity of freshwater seals and toothed whales that exist today. Arctic ringed seals gave rise to no less than three types of inland seals after the retreat of the ice sheets of the last ice age. And there are at least four species of river dolphins in addition to many populations of marine mammals that occasionally enter fresh or brackish waters to feed.

Boto, Amazon River Dolphin. (c) Kevin Schafer
But of the marine mammals who have moved into freshwater habitats it is the river dolphins that have committed most fully to this realm. This paraphyletic group differ from their fully marine cousins in having flexible necks, reduced vision, more flexible pectoral fins and reduced dorsal fins- all adaptations to their relatively more turbid and convoluted haunts.

While river dolphins may offer some context into imagining Pannoniasaurus, mosasaurs were definitely not dolphins and many types likely engaged in predation beyond simple piscivory. Toothed whales are actually descended from mammals related to deers- not really arch-predator material there. Even killer whales, technically dolphins, are very picky about what they will eat. Mosasaurs are closely allied with monitor lizards, notoriously opportunistic predators and capable macropredators. Even if Pannoniasaurus was not capable of land movement there is no reason it was not capable of the hunting method observed in killer whales, bottlenose dolphins and most recently the Wels catfish- strand hunting- in which either to snatch terrestrial prey or corral aquatic prey the aquatic hunter temporarily strands itself.

River Tarn, France. pigeon-hunting catfish
So now we can imagine during this interval of the Cretaceous, in this corner of the world- mosasaurs regularly striking at and making a meal of unwary dinosaurs. Cool.


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