Azendohsaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Unclassified

Family: Azendohsauridae

Genus:Azendohsaurus

Species:Azendohsaurus laaroussii

Introduction

Originally thought to be one of the earliest dinosaurs, recent research has revealed that this species is not actually a dinosaur at all. In May 2010, a group of researchers from a collection of academic institutions, including the American Museum of Natural History, Columbia University, the University of Antananarivo, and the University of California, published their detailed research on new fossil finds of Azendohsaurus found in Madagascar, stating that this species was, in fact, not a primitive dinosaur but something even more interesting. Scientists now believe that this species was a basal archosauromorph, which is a diverse group of diapsid reptiles that lived from the late Permian (298–251 million years ago) to the Late Triassic (235–201 million years ago). It is believed that Azendohsaurus lived during the Late Triassic, although maybe as early as 230 million years ago.

Classification

All dinosaur species are classified based on their hip structure as either Ornithischia (bird-hipped) or Saurischia (lizard-hipped) dinosaurs. Despite the name, it is from the lizard-hipped dinosaurs that today's avian dinosaurs (birds) descend. While this may seem illogical, scientifically it is known as convergent evolution, whereby the backward pointing pubis seen in ornithischian dinosaurs and birds actually evolved separately.

For more than 30 years, Azendohsaurus was regarded as a primitive dinosaur based on dental and gnathic (jaw) characteristics. Originally, Azendohsaurus was described and classified as an ornithischian dinosaur based on the similarity of its teeth to Fabrosaurus and Lycorhinus, dinosaurs from the Late Jurassic in southern Africa. Palaeontologists later realized, however, that Azendohsaurus's teeth more closely resembled that of basal sauropodomorph dinosaurs. Although this classification remained for many years, a non-dinosaurian plylogenetic position was suggested as early as 2002. It was not until 2010 that Azendohsaurus was described and assigned to the Archosauromorph clade, which is a diverse group of diapsid reptiles that include the orders Rhynchosauria, Trilophosauridae, Prolacertiformes, and Archosauriformes. While it is from archosauromorphs that the lineages of crocodiles, dinosaurs, and birds descend, Azendohsaurus is now considered to be only distantly related to dinosaurs.

Anatomy

Fossil remains of Azendohsaurus collected so far are limited to a skull, several teeth, and mandible from Madagascar and a mandible from Morocco. It was initially thought that Azendohsaurus was a relative of the Bristol dinosaur Thecodontosaurus. However, as the latest research has demonstrated that Azendohsaurus is not a dinosaur but a more primitive diapsid reptile, definite ideas about its body form remain somewhat speculative. Like modern-day diapsid reptiles—which include all crocodiles, lizards, and snakes—extinct diapsid species were extremely diverse and were likely characterized by many different body forms. It is thought, however, that Azendohsaurus may have resembled another early lizard-like archosaur called Trilophosaurus.

Azendohsaurus was a relatively small animal, being only 1.8–2.0 meters (6–6.5 ft) long and weighing 35–55 kilograms (77–120 lbs). Current paleontologist theory states that this species was a quadrupedal herbivore, somewhat lizard-like in appearance, with its hind and forelimbs likely ending in four to five clawed digits.

Azendohsaurus had a strong skull, with leaf-shaped teeth not only found along its jaw, but also on the roof of its mouth. Like all diapsid reptiles, it possessed two temporal fenestrae, or openings, on either side of its skull.

Intelligence

With the exception of the troodontids (EQ of 5.8) and the dromaeosaurids (EQ of 5.8), all dinosaur species fall below 2.0. While this compares poorly with today's animals, new research on dinosaur cranial morphology has indicated that they may have been more intelligent than previously thought. Current EQ measures for Azendohsaurus have currently not been conducted. Fossil specimens are limited to just a skull and jaw, which makes it impossible to calculate a body-to-brain ratio. Azendohsaurus's recent reclassification from dinosaur to archosauromorph also means it is difficult to determine its intelligence. It is likely, however, that this primitive species possessed an EQ in the lower to middle range compared to dinosaur species, as evidence suggests that herbivore species were less intelligent than carnivore species.

Reproduction and Population

The paucity of fossils makes it very difficult for paleontologists to determine past populations. This is especially so for Azendohsaurus, as unearthed fossils are limited to finds of only a skull and several mandibles. From remains discovered so far, however, it appears that Azendohsaurus was at least distributed from what is now Morocco to Madagascar during the Late Triassic period, when Pangaea was still a supercontinent.

Like dinosaur species, it is assumed that extinct archosauromorph reptiles were oviparous and laid a number of eggs per clutch (number of eggs produced in a nest at a single time). Although it is considered unlikely that Azendohsaurus performed highly-developed or sophisticated parental care, to date, no eggs shell fossils of Azendohsaurus have been found, which limits current understanding of the reproductive behavior of these ancient reptiles. It is considered possible, however, that Azendohsaurus exhibited some form of brooding behavior, such as seen in modern-day crocodiles, which bury eggs underground to keep them warm.

Diet

Azendohsaurus was an herbivorous species that fed on the plants found within its frequently arid environment. Vegetation across the giant supercontinent of Pangaea demonstrated geographic variation, but primarily consisted of gymnosperms, including palm-like cycads, ferns, and conifers, as angiosperms, or flowering vascular seed plants, had not yet evolved. Azendohsaurus was a relatively small species, especially in comparison to many species of dinosaur, and it was likely restricted to feeding on low-lying vegetation such as ferns, horsetails, cycads, and mosses, for which its leaf-shaped teeth were well adapted.

The revelation that this species was a basal archosauromorph is again an example of convergent evolution, in which a number of features found in both Azendohsaurus and later herbivores, such the gigantic sauropods, evolved separately. This discovery is particularly meaningful, as it proves that plant-eating, particularly the craniodental characteristics connected with herbivory, evolved independently on at least six to eight different occasions, and was more common within archosauromorphs than previously thought.

Behavior

Given the scarcity of fossil remains, very little is known about the behavior of Azendohsaurus, particularly in regards to social and defensive behavior. Without the discovery of full skeletal specimens, paleontologists can only speculate on the activity of these extraordinarily ancient reptiles.

From dentition and jaw morphology, it is known that Azendohsaurus was an herbivore and was also likely a quadruped. While it is not known if they formed herds, many species of ancient and modern-day plant-eaters exhibit this behavior. The discovery of a second species of Azendohsaurus in Madagascar in a “red bed” (red-colored sedimentary layers of sandstone, siltstone, and shale), in which several individuals died together, does provide tentative evidence of herd behavior. Given the small stature of Azendohsaurus, herd-living would have offered a measure of protection to offspring.

Habitat and Other Life Forms

During the Triassic period, all land masses on earth were joined together in one supercontinent called Pangaea. At the end of the Triassic and the beginning of the Jurassic period, this super landmass began to develop rifts, and by the end of the Jurassic period 145 million years ago, it had separated into the two distinct continents of Gondwana and Laurasia.

The prevailing climate during the Late Triassic period was generally very hot and dry, although some regions experienced wet monsoonal climate phases, and was characterized by warm temperate conditions at the southern and northern poles, as there was no polar ice. The Late Triassic fauna in Africa, including what is now present-day Morocco and Madagascar, was similar to many regions of Pangaea. Dinosaur populations consisted primarily of carnivorous theropods and beaked, herbivorous ornithischians. The Late Triassic was also the time period in which the first primitive mammals appeared.

Research

Named for the Moroccan village of Azendoh, which is located close to the fossil deposit in the Atlas Mountains, Azendohsaurus laaroussi was unearthed in 1972 by paleontologist J. M. Dutuit in the Argana Formation, a geological formation found in continental Africa. Several other species have been located within this formation, which is dated to the Late Triassic. From this, it is estimated that Azendohsaurus lived between 228 and 222 million years ago.

Azendohsaurus laaroussi is known from very limited remains—to date from only two dentaries, a maxilla, and isolated teeth. In the late 1990s, however, a second species was discovered in the Makay Formation of Madagascar. The remains were a complete skull, mandible, and associated vertebrae. Although this species was described and named Azendohsaurus madagaskarensis more than a decade ago by a team of American and Malagasy scientists, it was only in 2010 that new research revealed that this species was not a dinosaur, but a basal archosauromorph. Such an interesting revelation highlights the difficulty of classifying animals from only a few fossilized remains.

Bibliography

Black, Riley. "Azendohsaurus, the Dinosaur That Wasn’t ." Smithsonian Magazine, 21 May 2010, www.smithsonianmag.com/science-nature/azendohsaurus-the-dinosaur-that-wasnt-71721082. Accessed 14 Apr. 2020.

Carpenter, Kenneth. Eggs, Nests, and Baby Dinosaurs: A Look at Dinosaur Reproduction. Indiana UP, 1999.

"Dinobase." University of Bristol, dinobase.gly.bris.ac.uk. Accessed 14 Apr. 2020.

Fastovsky, David E., and David B. Weishampel. Dinosaurs: A Concise Natural History. Cambridge UP, 2009.

Fastovsky, David E., and David B. Weishampel. Evolution and Extinction of the Dinosaurs. Cambridge UP, 2005.

Flynn, J. J. et al.. “A New Species of Azendohsaurus (Diapsida: Archosauromorpha) from the Triassic Isalo Group of Southwestern Madagascar: Cranium and Mandible.” Palaeontology, vol. 53, no. 3, 2010, pp. 669–88.

Gauffre, François-Xavier. "The Prosauropod Dinosaur Azendohsaurus laaroussii from the Upper Triassic of Morocco.' Palaeontology, vol. 36, no. 4, 1993, pp. 897–908. The Palaeontological Association, www.palass.org/publications/palaeontology-journal/archive/36/4/article‗pp897-908. Accessed 14 Apr. 2020.

Lucas, Spencer G. Dinosaurs: The Textbook. 4th ed., McGraw-Hill, 2004.

Martin, Anthony J. Introduction to the Study of Dinosaurs. 2nd ed. Malden, MA: Blackwell, 2006.

Norell, Mark, et al. Discovering Dinosaurs: Evolution, Extinction, and the Lessons of Prehistory. University of California Press, 1995.

Parker, Steve. Dinosaurus: The Complete Guide to Dinosaurs. Firefly Books, 2009.

Weishampel, David B., et al. Dinosauria. University of California Press, 2007.

Willis, K. J., and J. C. McElwain. Evolution of Plants. Oxford University Press, 2002.