The Change in Tanystropheus Species Due to Resource Availability

Aquatic Habits and Niche Partitioning in the Extraordinarily Long-Necked Triassic Reptile Tanystropheus

By: Stephan N.F. Spiekman, James M. Neenan, Nicholas C. Fraser, Vincent Fernandez, Olivier Rieppel, Stefania Nosotti, Torsten M. Scheyer

Summarized by: Sarah Kreisle, a geology major at the University of South Florida minoring in GIS. She is a senior planning to graduate December 2020. Afterwards, she plans on staying local to further her knowledge in Florida geology and seek a job or internship offering experience in the field. In her free time, she enjoys hiking and kayaking.  

What data were used? Researchers used fossilized remains of Triassic reptiles Tanystropheus hydroides and Tanystropheus longobardicus, most of which were found at the Besano Formation of Monte San Giorgio, Switzerland. 

Methods: Using digital modeling, both T. hydroides and T. longobardicus were re-created virtually, using dislodged and deformed parts from the original skull. After virtual re-construction, these specimens were analyzed for similarities and differences. Additionally, records of stomach contents and skeletal were used to compare and reconstruct diet and environments.

Results: After examination, the two species were found to have similarities between the shapes of their skulls, but diverged in their dietary patterns, evidenced by slight morphological differences in the skull, and skeletal size. In T. hydroides and T.longobardicus they found that its jawbone curved and allowed for the nasal area to sit on the top side of the body. The snout was very flat and plate-like, which is a similar feature to the present-day crocodile. In T. longobardicus, the snout still sits on top of the skull, but is less prominent than T. hydroides. When looking at the shape of skulls in both T. hydroides and T.longobardicus, the snout was curved and flat with their breathing capability on top, in order to swim more efficiently. It was very likely that these creatures were shallow water dwellers since their nasal cavities were not built to endure pressure at great depths. Due to their lengthy necks, they were likely to pounce on food rather than chase after it. A long neck made it much harder to move around with ease. The long necks of the T. hydroides were able to give them an advantage when stalking prey and causing less obvious movements that might alarm the prey. Using the re-creation of the skull, it is observed that the teeth of T. hydroides were more likely to snap at food, rather than suck food from a shell. Scientists can tell from the fang-like teeth, that it was grabbing and holding its prey. In past specimens, there has been evidence of squid-like creatures and fish scales collected from the stomach contents. Conversely, T.longobardicus was more likely to use its shorter teeth for eating soft shelled invertebrates or plants. Their teeth are tricuspid teeth (i.e., teeth with three cusps), which are also present among animals that eat both plant and animal matter. Though T. hydroides is very similar to T. longobardicus, the biggest difference between them is their size. T. longobardicus was less than half the size of T. hydroides. Likely, these creatures were eating different resources available over time, changing the amount of energy they required to survive. It is possible that these two species lived together in the same aquatic environment and deviated from each other in order to survive on available food sources. 

Figure 1 Both species in this picture are depicted to be different structurally, which could mean different food source and possible early competition for food. The skull of T. hydroides shows long curved teeth that would have gripped prey, whereas the skull of T. longobardicus had the short, tricuspid teeth. The tricuspid teeth are much easier to grind food, in both plants and meat. The skeleton of T. hydroides shows a significant size difference from T. longobardicus. The picture in the bottom right corner depicts that the small skeleton of the T. lonobardicus was mature due to the growth lines seen.

Why is this study important? This study is important because it displays niche partitioning, or natural selection driven by resource use. In examining these two species’ tooth alteration, stomach contents, and size difference, we see how very closely related organisms have evolved in different paths due to resource needs. This shift in consumption patterns may also indicate a time period in which competition for food sources was high. We can therefore hypothesize that while these species could have been descended from a recent common ancestor, they have since changed physically and behaviorally due to their environments. 

The big picture: Many other species have been defined by the process of niche partitioning and will most likely continue in the future as our environment readily changes. These changes further cause increased competition in the food web. Change in size of the Tanystropheus could have been due to the amount of energy available to them in food. Teeth and other characteristics of the genus Tanystropheus can explain features of animals in existence today. Learning about Tanystropheus will help us learn more about creatures during the Triassic and surrounding periods. 

Citation: Spiekman, S. N. F., Neenan, J. M., Fraser, N. C., Fernandez, V., Rieppel, O., Nosotti, S., & Scheyer, T. M. (2020). Aquatic Habits and Niche Partitioning in the Extraordinarily Long-Necked Triassic Reptile Tanystropheus. Current Biology30(19), 3889.