Elasmosaurs: bottom feeders?

Added September 21, 2020:
Think about a bubble net, as in humpback whales, coming form the long, dead=air storage vessel that is that elongate trachea. That long neck rotating like an inverted cone to surround confused fish just above the jaws.

No, not restricted to the bottom. They did have to breathe.
Did elasmosaurs cruise sea floors and coral reefs looking for fish? Or did they cruise open waters staring up at traveling schools? We may never know for sure, but you have to wonder given their flat bellies and very long snaky necks.

Here’s the pros and the cons:

Elasmosaur on the rug.

Figure 1. Elasmosaur (Thalassomedon) model on the rug. Note how all the elements hug the floor, including the neck. Imagine the real thing just above the seafloor, taking nips and bites from fish and other sea life hiding wherever they can among the corals and sea detritus. The distal end of the long neck is quite flexible, as opposed to the rest of the neck and torso. Please ignore the supporting straw. It was used to support this model as a hanging ornament. Note how the hind fins have a posterior, rather than lateral orientation, to support a vertical configuration.

BTW
This is a paper elasmosaur model (Fig. 1) you can build yourself. Download the printout for free here.

Traditional hypotheses say:
Elasmosaurus was a slow swimmer. The neck would have been held quite straight when resting with sideward‭ ‬movements only occurring when necessary. All Elasmosaurus would have to do was swim up to a shoal of fish,‭ ‬possibly from below so that it could hide its body in the slightly darker depths,‭ ‬and use its neck to dart its head in and pluck out a mouthful of fish.”

Zammit et al. (2008) found that the necks of elasmosaurs were capable of 75˚ to 177˚ of ventral movement, 87˚ to 155° of dorsal movement, and 94˚ to 176° of lateral movement (quite a range!), depending on the amount of tissue between each vertebrae. Here’s a reconstruction preserved largely like this.

Figure 3. Click to enlarge. Albertonectes reconstructed. This 11 m elasmosaur is the longest thusfar recorded. This may be the breathing pose, swallowing air, then submerging the neck. When horizontal the air could be passed back to the lungs, as hypothesized for Dinocephalosaurus.

Figure 3. Click to enlarge. Albertonectes reconstructed. This 11 m elasmosaur is the longest thusfar recorded. This may be the breathing pose, swallowing air, then submerging the neck. When horizontal the air could be passed back to the lungs, as hypothesized for Dinocephalosaurus.

Let’s try this on for size:
Given:

  1. Elasmosaur teeth were efficient fish traps.
  2. Elasmosaurs were large enough to require a lot of fish.
  3. Lots of fish travel in schools, but also congregate among coral reefs.
  4. Elasmosaurs were relatively slow.
  5. There were faster, more efficient predators in the sea.
  6. long neck would have made a tempting target and an easy kill.
  7. Big elasmosaurs grew from small babies.
  8. Elasmosaurs below the flippers were essentially flat.
  9. Elasomosaur necks were snaky (“a snake drawn through the shell of a turtle”) distally and stiff proximally. And finally,
  10. Pressure differential on an underwater vertical body of 11 meters would have provided enough compressive force for the air within the lungs to rise within the body (through the long neck principally, inspiring notions of  bubble nets or inappropriate underwater burps). This problem goes away with a largely horizontal body.
  11. Added September 21, 2020:
    Think about a bubble net, as in humpback whales, coming form the long, dead=air storage vessel that is that elongate trachea. That long neck rotating like an inverted cone to surround confused fish just above the jaws.
Coral reef surrounded by dozens of unsuspecting fish ready to be gobbled up by one or several elasmosaurs.

Coral reef surrounded by dozens of unsuspecting fish ready to be gobbled up by one or several elasmosaurs. Linked from Wikipedia.

The coral reef diner model
The horizontal and slow-moving elasmosaur, no matter what size (baby or adult) can find slow-moving small and large items to eat among the corals without having to compete with the fast-moving prey and predators further toward the surface. Today, swordfish and marlins are the best adapted hunters of the open sea and back then, ichthyosaurs and mosasaurs would have been elasmosaur competitors and/or predators in that niche. Best to stay camouflaged near the bottom, feeding on octopus, fish, crab, what have you, with giant bellies 9 meters out, moving to the next reef whenever it was largely depleted or the belly was full.

Breathing could have taken place like Dinocephalosaurus, swallowing air at the surface, then passing it back to the lungs when the head was level or lower than the lungs.

References
Noé LF, Taylor MA and Gómez-Pérez M 2017. An integrated approach to understanding the role of the long neck in plesiosaurs. Acta Palaeontologica Polonica 62 (1): 137–162.
Zammit M, Daniels CB and Kear BP 2008. Elasmosaur (Reptilia: Sauropterygia) neck flexibility: Implications for feeding strategies. Comparative Biochemistry and Physiology – Part A: Molecular & Integrative Physiology 150(2):124-130.

wiki/Elasmosaurus

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