SVP abstracts 27: Plesiosaur breathing

Wintrich and Vanoefer 2020
bring us a look at plesiosaur breathing, but do not consider the vertical feeding configuration (Fig. 1) and bubble-net blowing hypothesis.

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.

From the Wintrich and Vanoefer 2020 abstract:
“Plesiosaurs are enigmatic marine reptiles known from the Late Triassic to the Late Cretaceous and represent the most derived group of sauropterygians.

Why ‘enigmatic’? Plesiosaurs are readily identified without argument.

“Among plesiosaurs, there are several lineages showing an extremely long neck, which raises different biomechanical questions dealing with use and function, up to the breathing mechanism. Furthermore, for aquatic tetrapods, buoyancy control is an important adaptation to support the body in the water column. The respiratory system and its influence on buoyancy control have been discussed only briefly, and no mathematical approach has been taken so far. However, the breathing mechanism and therefore the respiratory system of highly aquatic tetrapods has to be specialized in different ways to enable life in a pelagic environment.”

“Here, we follow different mathematical approaches based on the metabolism (work of breathing), the trachea, and the morphology of the skull and trunk, in order to reconstruct the breathing mechanism, respiratory system, and lung volume in plesiosaurs, and then discuss the most plausible respiratory anatomy.”

“Furthermore, we find support for the hypothesis of a functional secondary palate from the reconstructed respiratory system as well as for the use of gastroliths, especially in the Elasmosauridae.”

“In addition to this, we calculated the center of mass to reconstruct buoyancy control in plesiosaurs.”

“In general, we studied four different long-necked plesiosaurs (Cryptoclidus, Albertonectes, Rhaeticosaurus, Rhomaleosaurus) and included Augustasaurus as the most derived pistosaur for which the entire neck is known.”

“Our results demonstrate that the lung volume was larger than suspected for an aquatic tetrapod. However, plesiosaurs showed an adaption similar to that of marine turtles, which have shifted the lung to the dorsal side of the trunk. The influence of the long trachea on breathing is not as great as suggested before. However, especially in the elasmosaurid, the long neck influences the center of mass. This supports the hypothesis of gastroliths functioning in buoyancy control in elasmosaurs. Furthermore, based on an ancestral state reconstruction, we show that the specialized plesiosaurian respiratory systems probably evolved in early sauropterygians.”

‘Influences’. ‘Supports’. ‘Probably’. Conclusions?
I didn’t see any here. Did I miss something? Seems like this is all old news. Earlier we looked at the possibility that plesiosaurs were vertical hunters (Fig. 1), expressing bubble nets as they rose beneath fish schools, as in modern mysticetes. Let’s see that ‘specialized’ hypothesis tested in the 2021 abstracts.


References
Wintrich T and Vanhoefer J 2020. A specialized respiratory system in plesiosaurs (Sauropterygia): breathing with the long neck. SVP abstracts.

Plesiosaur necks: not so flexible after all

With a neck WAAAYYY longer than half the total length
elasmosaurs, like Albertonectes (Figs. 1, 2), have been traditionally referred to as ‘a snake threaded through a sea turtle’ (going back to the Buckland lectures 1832, full story online here). Snakes have no trouble swimming, but so far, paleontologists have not considered the long, minimally flexible neck of elasmosaurs a propulsive organ, as in sea snakes. That might change a little today.

Figure 1. A weak attempt at making sine waves in the neck of Albertonectes.

Figure 1. A weak attempt at making sea snake-like sine waves in the neck of Albertonectes. Note the minimum of bending through effort. Relaxation realigned the neck.

Earlier a vertical configuration was suggested
to explain the weird and extreme morphology of elasmosaurs, entering fish and squid schools from below, distinct from all other oceanic predators. While the flippers were powerful propulsive organs for long distance, when it came to fine tuning while hovering, perhaps the increasingly longer (Fig. 2), snake-like necks helped some. It also moved the bulky flapping torso further from the mouth, so the school of fish would be less and less  likely to notice the intruder in the middle.

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 2. 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.

By contrast, Noe, Taylor and Gomez-Perez 2017 reported,
Based on the anatomy of the articular faces of contiguous cervical vertebral centra, neural arches, and cervical ribs, the plesiosaur neck was mainly adapted for ventral bending, with dorsal, lateral and rotational movements all relatively restricted. A new model is proposed for the plesiosaur bauplan, comprising the head as a filter, straining, sieve feeding or sediment raking apparatus, mounted on a neck which acted as a stiff but ventrally flexible feeding tube, attached to the body which acted as a highly mobile feeding platform.”

“The neck increased drag due to its form and large surface area, but was also potentially part of an integrated locomotor system, for instance affecting steering (as it lies in front of the locomotor apparatus) and because the rear of the neck acted as anchorage for musculature from the anterior limb girdles. Hence, any explanation of neck function should consider both slow speed locomotion and more rapid movement during respiration, feeding and predator avoidance.”

Their study looked at
Muraenosaurus (Figs. 3, 4), Cryptoclidus and Tricleidus (none if these yet in the LRT) as exemplars of long-necked plesiosaurians. All are related to one another, not to elasmosaurs. Noe, Taylor and Gomez-Perez presented a history of plesiosaur neck interpretation and presented their own interpretation (ventral flexion, Fig. 5). Given that comprehensive review, apparently no prior workers envisioned a sea-snake analog for the long neck of elasmosaurs, nor have any envisioned a vertical feeding orientation.

Figure 2. Muraenosaurus in dorsal and lateral views. Compare to figure 1.

Figure 2. Muraenosaurus in dorsal and lateral views. Compare to figure 1.

Rather than a flexible ball-and-socket joint
between cervicals, each plesiosaur vertebra consisted of a spool-shaped centrum with flat or slightly concave articular surfaces (Fig. 4). Most cervical centra are wider than deep. according to Noe, Taylor and Gomez-Perez, but that is largely due to a dorsal indentation for the neural spine. Cervicals preserved in situ indicate no intervening cartilage between centra. So, think of plesiosaur centra as Incan wall stones. There are no spaces between either. This compaction between vertebrae greatly restricts movement between individual cervicals and restricts cervical movement overall. Even so, even half a degree per centrum magnified by 76 cervicals can add up (Fig. 1) permitting some movement. Short, L-shaped cervical ribs are fused to each centrum.Their distal processes do not articulate with one another, but hypothetical ligaments extending from anteroposteriorly-oriented distal tips may have done so.

Figure 5. Muraenosaurus cervical sections from Noe et al. 2017 alongside a ghosted diagram of a complete Muraenosaurus neck.

Figure 4. Muraenosaurus cervical sections from Noe et al. 2017 alongside a ghosted diagram of a complete Muraenosaurus neck. The space between centra can be compared to the space between Incan wall stones. In other words: none. That is not shown in the ghosted reconstruction.

Noe, Taylor and Gomez-Perez conclude,
The consistent presence of numerous cervical segments that lack bony stiffening adaptations, however, is also strong evidence that flexibility was an important functional element in plesiosaur necks (Evans 1993), and gives the potential for a considerable range of movement in the living animal (cf. Zarnik 1925–1926).” The authors compare plesiosaurs to stiff-necked tanystropheids (with only 12 cervicals) to emphasize their point. They overlooked the tight articulations of each centrum with its neighbors. 

From a historical perspective, Noe, Taylor and Gomez-Perez report, 
“Previous workers have considered the degree of neck flexibility in plesiosaurs to range from: extreme mobility (Hawkins 1840; Zarnik 1925–1926; Welles 1943; Welles and Bump 1949), including the ability to arch the neck like a swan (Conybeare 1824; Andrews 1910; Brown 1981b); through relative inflexibility (Hutchinson 1897; Williston 1914; North 1933; Shuler 1950; Storrs 1997); to almost complete rigidity (Buckland 1836; Watson 1924, 1951; Cruickshank and Fordyce 2002; Figs. 3, 9); although some of this variation in interpretation may be due to differences between the species studied (Watson 1924, 1951).”

Clearly some of these workers were right and others were wrong.
But which ones? Zoe, Taylor and Gomez-Perez conclude, to their credit, “Overall, the range of movement available to the plesiosaur neck was strictly limited.”

Figure 7. Illustration from Noe, Taylor and Perez-Gomez showing their view of plesiosaur feeding and escape configurations.

Figure 5. Illustration from Noe, Taylor and Perez-Gomez showing their view of plesiosaur feeding and escape configurations. Usually paleo illustrations are more anatomically accurate than this.

Elasmosaurs were morphologically different than anything else in the sea. 
And they became more and more different as time went by (Fig. 2). So, something was working better and better as evolution selected for more extreme neck lengths.

Once again, let’s broaden our scope and look at the environs,
including coeval predators. All of these were robust, fast, streamlined, short-neck predators that swam horizontally preceding an attack from outside in. All of this is the opposite of elasmosaurs who hypothetically loitered below schools of fish unobtrusively rising to slip only their head in from below with minimum turbulence in order to remove fish or squid at leisure from the inside out.

Plesiosaur respiration at the surface
had to take place horizontally due to air pressure constraints. Alternatively, elasmosaurs could have gulped air, then assumed a horizontal or diving orientation to let the air bubble travel back through their long neck back or up to their lungs. With such tiny nostrils, gulping air seems more reasonable than narial inhalation.

Exhalation could have been more leisurely
and might have involved producing a ‘bubble net’ from stale air stored in the long trachea and released through the tiny nares. Extant baleen whales sometimes produce a bubble net to herd fish and plankton as they rise to feed on them. Perhaps elasmosaurs did the same, again based on their vertical orientation.

Fins at all four corners
Noe, Taylor and Gomez-Perez report, “With limbs at the four corners of the body, plesiosaurs could potentially produce vectored thrust from different limbs, to provide fine control of movement in all directions, and around all axes. This is more useful in slow swimming or hovering animals than simple shark-like control fins, which require movement in order to generate a current over the control surfaces.” Exactly. Unfortunately, these authors did not consider plesiosaurs to have a vertical orientation. Instead they focused on the ability of the neck to flex ventrally from a horizontal orientation.

Stomach stones
Noe, Taylor and Gomez-Perez report, “Swimming efficiency was further impaired by the mass of the neck, and the stomach stones commonly preserved in plesiosaurs. This stone ballast was probably needed to establish trim control and longitudinal stability to enable the animal to swim slowly horizontally and to hover, especially when diving in shallow water when the animal was positively buoyant.” The other explanation is that stomach stones helped weight the body below the more buoyant neck (filled with stagnant air), again supporting a vertical orientation when not swimming to other locations.


References
Noe LF, Taylor MA and Gomez-Perez M 2017. An integrated approach to understanding the role of the long neck in plesiosaurs. Acta Palaeontologica Polonica 62 (1): 137–162.

The many faces of Styxosaurus

Styxosaurus snowii (Originally Cimoliasaurus snowii, Williston 1890, KUVP 1301; Welles 1943; Late Cretaceous, Campanian, 80mya; SDSMT 451; Figs. 1, 2) is another giant elasmosaurid with dog-like fangs related to Simolestes in the large reptile tree (LRT, 1438 taxa).

Figure 1. Skull of Styxosaurus (KUVP 1301) from Sachs, Lindgren and Kear 2018, colorized using DGS methods.

Figure 1. Skull of Styxosaurus (KUVP 1301) from Sachs, Lindgren and Kear 2018, colorized using DGS methods. Broken teeth on this side of the skull repaired based on the dimensions of unbroken teeth on the other side of the skull.

Several new papers
(refs below) have taken another look at the skull of Styxosaurus, now known for about 130 years. Prior freehand drawings of the skull (Fig. 2) seem to overlook certain interesting details, many of which are critical for accurate scoring.

Figure 2. The changing face of Styxosaurus from Welles 1890, Otero 2016 and colorized here.

Figure 2. The changing face of Styxosaurus from Welles 1890, Otero 2016 and colorized here. Maybe a little easier to see each bone when colored? 

Overall,
a skeletal reconstruction of Styxosaurus required just a little updating (Fig. 3).

Figure 3. Styxosaurus skeleton as originally drawn and revised here.

Figure 3. Styxosaurus skeleton as originally drawn and revised here.

A biting animation
(Fig. 4) of Styxosaurus shows the interweaving of the oversized teeth. Note the elongate posterior dentary teeth. As in Tricleidus, these would have made effective foot traps when water was being expelled whenever the jaw closed.

Figure 6. Styxosaurus mandible animated.

Figure 4. Styxosaurus mandible animated.


References
Otero RA 2016. Taxonomic reassessment of Hydralmosaurus as Styxosaurus: new insights on the elasmosaurid neck evolution throughout the Cretaceous. PeerJ Figure 3. Styxosaurus skeleton as originally drawn and revised here.
Sachs S, Lindgren J and Kear B 2018. Reassessment of the Styxosaurus snowii (Williston, 1890) holotype specimen and its implications for elasmosaurid plesiosaurian interrelationships. Alcheringa: An Australasian Journal of Palaeontology, DOI: 10.1080/03115518.2018.1508613
Welles SP 1943. Elasmosaurid plesiosaurs with a description of the new material from California and Colorado. University of California Memoirs 13:125-254. figs.1-37., pls.12-29.
Welles SP and Bump J 1949. Alzadasaurus pembertoni, a new elasmosaur from the Upper Cretaceous of South Dakota. Journal of Paleontology 23(5): 521-535.
Williston SW 1890a. Structure of the Plesiosaurian Skull. Science. 16 (405): 262.
Williston SW 1890b. A New Plesiosaur from the Niobrara Cretaceous of Kansas. Transactions of the Annual Meetings of the Kansas Academy of Science. 12: 174–178.

wiki/Styxosaurus

Simolestes enters the LRT as an elasmosaur

Traditionally considered a short-snouted pliosaur,
due to its rosette anterior dentary, Simolestes borax (Lydekker 1877; Mid-Late Jurassic; BMNH R 3319; Fig. 1) nests in the large reptile tree (LRT, 1435 taxa; subset Fig. 2) with the elasmosaurs, Albertonectes and Libonectes.

Figure 1. Simolestes in several views and colorized using DGS methods compared to the elasmosaur, Libonectes.

Figure 1. Simolestes in several views and colorized using DGS methods compared to the elasmosaur, Libonectes.

I have looked for,
but not seen any post-crania for Simolestes, despite reports that post-crania exists. And I’m willing to let the data decide.

Given that the two elasmosaur skulls are the same size
(Fig. 1) lends weight to the hypothesis that Simolestes is an elasmosaur, not a pliosaur. Distinct from Libonectes, Simolestes has a single upper and lower fang, like a dog, with smaller teeth elsewhere.

Figure 4. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).

Figure 2. Subset of the LRT focusing on Eusauropterygians (pachypleurosaurs, nothosaurs, plesiosaurs and kin).

And another eusauropterygian,
Peloneustes (Fig. 3) also enters the LRT, nesting, with no surprise, close to Dolichorhynchops.

Figure 3. Peloneustes fossil on display.

Figure 3. Peloneustes fossil on display.


References
Godefroit P 1994.  Simolestes keileni sp. nov., un Pliosaure (Plesiosauria, Reptilia) du Bajocien supérieur de Lorraine (France). Bulletin des Académie et Société Lorraines des sciences, ISSN 0567-6576, 1994, tome 33, n°2, p. 77-95. 33. .
Lydekker  R 1877. Notices of new and other Vertebrata from Indian Tertiary and Secondary rocks. Records of the Geological Survey of India 10(1):30-43

 

 

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

Build Your Own Paper Elasmosaur, Thalassomedon!

Click to access 2 page Thalassomedon model pdf file

Click to download a two-page Thalassomedon paper model pdf file

Download the pdf. Print out on 8.5×11 “cover stock” paper.
Cut out the pieces. Fold them as instructed. Glue them together.
Tape piano wire along the neck if you don’t want it to curl and droop.
Hang on thread.

Enjoy!

From your friend at The Pterosaur Heresies.

Thanks for coming back.