Write An Essay On Mesozoic Reptiles

One of the quintessential depictions of prehistoric times is that of an ancient, often volcano ridden, landscape full of animals bearing large showy sails of skin stretched over their backs. Sailbacked animals are rather rare in our modern day and age, but back in the Mesozoic and Paleozoic there were sails a plenty.

By far the most popular sailbacked taxa of all time would be the pelycosaurs in the genus Dimetrodon. These were some of the largest predators of the Permian (up to 4.6 meters [15 feet] long in the largest species). Dimetrodon lived alongside other sailbacked pelycosaurs including the genus Edaphosaurus. These were large herbivores (~3.5 m [11.5 ft] in length) that evolved their sails independently from Dimetrodon. The Permian saw many species of sphenacodontids and edaphosaurids, many of which sported these showy sails (Fig. 1. [1–8]).

However sails were hardly a pelycosaur novelty. The contemporaneous temnospondyl Platyhystrix rugosus (Fig. 1 [9]) also adorned a showy sail.

Fast forward 47 million years into the Triassic and we find the rauisuchians Arizonasaurus babbitti,Lotosaurus adentus, Xilousuchus sapingensis, and Ctenosauriscuskoeneniall bearing showing sails on their backs (Fig. 1 [10–13]). Much like in the Permian, many of these taxa were contemporaneous and, while related, many likely evolved their sails separately from one another.

There are currently no fossils of sailbacked tetrapods in the Jurassic (as far as I know. Feel free to chime in in the comments if you know of some examples). However the Early Cretaceous gave  us a preponderance of sailbacked dinosaurs (Fig. 1 [14–19]) including the cinematically famous theropod Spinosaurus aegyptiacus, the contemporaneous hadrosaur Ouranosaurus nigeriensis, the gharial-mimic Suchomimus tenerensis, the potentially dual sailed sauropod Amargasaurus cazaui, as well as the allosauroids Acrocanthosaurusatokensis, and Concavenator corcovatus. Lastly, the discovery announced last year (and just now coming to light in the news) of better remains for the giant ornithomimid Deinocheirusmirificus have revealed that it too may have sported a small sail along its back.

Once again we find a group of related, largely contemporaneous, animals, most of which probably evolved their sails separately.

Such a huge collection of sailbacked animals all living around the same time (and sometimes the same place) has begged for some type of functional explanation. The usual go-to for large, showy surfaces like these or the plates of Stegosaurus has been thermoregulation. The thinking being that blood pumped through a large surface area like this, when exposed to the sun, has the ability to warm up faster than other areas of the body. Conversely when the sail is placed crosswise to a wind stream, or parallel to the orientation of the sun, heat will radiate out into the environment faster than other areas of the body. That most sailbacked dinosaurs were “localized” to equatorial areas, coupled with the large sizes of all the taxa (1-10 tonnes depending in species) has favoured a cooling mechanism function for dinosaur sails. Whereas a heating function has been presumed to be the primary function for sails in Dimetrodon and Edaphosaurus. No real function has been ascribed to the sails in rauisuchians or Platyhystrix, though this is probably due to a lack of knowledge/interest in these groups.

Alternate functions proposed for these sails have included a self-righting mechanism for swimming, sexual signaling and other presumed display functions. In certain cases, namely Spinosaurus aegyptiacus and Ouranosaurus nigeriensis, it has even been argued that the enlarged spines did not support a sail, but rather were supports for a large, fatty hump akin to that of camels or bison (Bailey 1996, 1997).

Given the wealth of hypotheses for potential sail functions it would be beneficial to first understand what extant sailbacked taxa use their sails for. Unfortunately—though unsurprisingly—there are few if any scientific studies on sail use in extant sailbacked animals. This has lead to the apparent assumption that there are no extant vertebrates with sailbacks.

There are, in fact, quite a few sailbacked animals alive today. These include various fish, amphibians and even reptile species. Learning what these taxa use their sails for may offer us a glimpse at what extinct animals were doing with their sails.
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This entry was posted inCrurotarsiDinosaursExtant ReptilesExtinct ReptilesLacertiliaUncategorizedand taggedacrocanthosaurusbasiliscusbasiliskchamaeleochameleochameleondimetrodonedaphosaurusfinfinbackhydrosaurusouranosauruspelycosaursailsailbacksailbackssexual dimorphismsexual selectionspinosaurusthermoregulationtrioceros

Between 200 and 65 million years ago, fearsome marine reptiles reigned over the oceans. Were they warm-blooded like today's mammals and birds or cold-blooded like nowadays fish and reptiles? For the first time, a study has settled the debate: some large marine reptiles were warm-blooded (in other words, they were endothermic), giving them a considerable advantage to swim fast over long distances and to conquer cold regions.

This work, conducted by researchers from the Laboratoire PaléoEnvironnements et PaléobioSphère (PEPS, CNRS/Université de Lyon 1) in collaboration with scientists from the Muséum National d'Histoire Naturelle and the École Normale Supérieure, has been published in the journal Science on 11 June 2010.

During the Mesozoic era (between 200 and 65 million years ago), when dinosaurs roamed the continents, fearsome predatory reptiles such as ichthyosaurs, plesiosaurs and mosasaurs reigned over the oceans. How did these large marine reptiles regulate their temperature? This question, linked to body temperature and thermoregulation processes, is essential in deciphering the feeding, ecology and evolution strategies of these now disappeared vertebrates.

To determine the body temperature of certain marine reptiles, a French team of geochemists and paleontologists(1) used, for the first time, the compositions of stable oxygen isotopes (18O/16O) in the phosphate of their skeletons. The researchers analyzed the dental remains of three major groups of large marine reptiles: ichthyosaurs, plesiosaurs and mosasaurs. They compared the 18O/16O ratio present in the tooth enamel of these reptiles to that of fish remains from the same period, found at the same latitudes. Fish, which are cold-blooded animals (ectotherms), have an isotopic composition that reflects the temperature of the sea water in which they live. In fish, the 18O/16O ratio increases as the temperature of the ocean decreases. The differences in isotopic composition between marine reptiles and fish that lived in the same body of water reflect the differences in their body temperatures.

The researchers found that the body temperature of the studied reptiles was constant, whatever the water temperature. Thus, ichthyosaurs and plesiosaurs regulated their body temperature independently of sea water temperature within a temperature range from around 12 degrees (±2°C) to around 36 degrees (±2°C). In the case of the three large groups of reptiles studied, the body temperature estimations lie between 35 and 39°C (±2°C).

Some large marine reptiles, now extinct, were thus capable of maintaining a higher body temperature than that of their living environment, suggesting a high metabolism adapted to predation and fast swimming over long distances, even in cold water. These animals consequently had an "endothermic" metabolism (i.e. capable of producing heat), similar to that of present day Cetacea. How and from what point these warm-blooded animals produced such energy remains to be determined.

(1) Researchers from the Laboratoire PEPS (CNRS/Université de Lyon 1), the Centre de Recherche sur la Paléobiodiversité et les Paléoenvironnements (CNRS/MNHN/UPMC) and the Laboratoire de Géologie de l'École Normale Supérieure (CNRS/ENS)

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Materials provided by CNRS (Délégation Paris Michel-Ange). Note: Content may be edited for style and length.

Journal Reference:

  1. A. Bernard, C. Lecuyer, P. Vincent, R. Amiot, N. Bardet, E. Buffetaut, G. Cuny, F. Fourel, F. Martineau, J.-M. Mazin, A. Prieur. Regulation of Body Temperature by Some Mesozoic Marine Reptiles. Science, 2010; 328 (5984): 1379 DOI: 10.1126/science.1187443

Cite This Page:

CNRS (Délégation Paris Michel-Ange). "Warm-blooded marine reptiles at the time of the dinosaurs." ScienceDaily. ScienceDaily, 15 June 2010. <www.sciencedaily.com/releases/2010/06/100614093341.htm>.

CNRS (Délégation Paris Michel-Ange). (2010, June 15). Warm-blooded marine reptiles at the time of the dinosaurs. ScienceDaily. Retrieved March 10, 2018 from www.sciencedaily.com/releases/2010/06/100614093341.htm

CNRS (Délégation Paris Michel-Ange). "Warm-blooded marine reptiles at the time of the dinosaurs." ScienceDaily. www.sciencedaily.com/releases/2010/06/100614093341.htm (accessed March 10, 2018).


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