Poposaurus, closely related to crocodiles, is an archosaur of the Late Triassic. However, many authors refer to this animal as a dinosaur making the Poposaurus dinosaur or crocodile debate a rather dreary one. The reason behind this is the fact that Poposaurus was a biped, and hence, walked on its two hind legs. This has been supported by a number of anatomical features, including strong hindlimb muscles and short forelimbs.
The type species of this genus is Poposaurus gracilis. Though a complete Poposaurus gracilis skeleton is yet to be discovered, nearly complete skeletal remains have shed light on the physical attributes of this archosaur of the Triassic. The body length of Poposaurus was 13 ft (4 m). It had an exceptionally long tail. Earlier, it was thought that Poposaurus was a herbivore due to a related archosaur Effigia, also being a herbivore. However, further research established the carnivorous nature of Poposaurus. These archosaurs were found in the United States, where they occupied areas far away from the sea. The discovery of Poposaurus has shed some light on the evolution of alligators and crocodiles.
The name 'Poposaurus' is pronounced as 'Pop-o-sore-us'.
Poposaurus is better described as an archosaur than a dinosaur. This is because this creature is more closely related to crocodiles than dinosaurs. However, apart from archosaur, the term dinosaur is used by some authors to describe members of this group. Poposaurus is a part of the Archosauria clade, which is further divided into the group of Pseudosuchia. Hence, they are referred to as pseudosuchians, as well.
Poposaurus is an archosaur that existed 216 million years ago, during the Late Triassic period.
Poposaurus became extinct at the end of the Triassic, 200 million years ago. However, the reason behind its extinction remains to be a mystery.
The Poposaurus remains have been found in four locations of the southwestern United States. In 1904, the first remains of this archosaur were recovered from the Popo Agie Formation of Wyoming. In 1915, a more complete skeleton of Poposaurus was recovered from the same location, and M. G. Mehl named the genus based on that. Subsequently, remains have also been unearthed from Texas, Arizona, and Wyoming.
The Poposaurus habitat was terrestrial, even though these archosaurs were similar to crocodiles. They lived far away from the water bodies and probably inhabited forests and woodlands.
There are no fossil records to understand the social behavior of this species. However, since no aggregated skeletal remains have been excavated, it can be assumed that Poposaurus was solitary.
The lifespan of this dinosaur-mimic species has not been ascertained. However, crocodiles living today have a life span of nearly 70 years. So, it is possible that their early relative from the Triassic that walked on two legs had a similar lifespan as well.
The exact reproductive details of Poposaurus are still a mystery. However, it is known that these archosaurs reproduced by laying eggs, and hence, were oviparous. The embryo developed within the eggs, and the baby Poposarus archosaurs hatched out after a certain period of time.
Despite being closely related to crocodiles, the Poposaurus had physical characteristics similar to that of dinosaurs. Hence, the physical characteristics of this pseudosuchian are quite fascinating to study.
The body of Poposaurus was laterally compressed, and its skeleton showed evidence of the fact that this archosaur had a narrow and elongated hip region. Additionally, the ischium and pubis bones of the hip and pubic regions, respectively, were also quite narrow. The recovered bones of Poposaurus have also revealed that these animals had a short torso, but tall neural spines. Additionally, this crocodile-like archosaur had hind legs, which were considerably larger than the front limbs. Each of these legs had a total of five digits. The hind legs were also provided with very strong muscles. Another prominent character of Poposaurus was its long tail. The tail made up nearly half its total length. Based on the Poposaurus life restoration, the Poposaurus skin was scaly.
Since a complete skeleton of Poposaurus is yet to be described, the total number of bones possessed by this animal has not been ascertained. However, the Poposaurus skeleton remains found to date, belonging to different individuals, consisting of several bones of the post-cranial skeletal system. Unfortunately, an entire Poposaurus skull is yet to be discovered. Astonishingly, when Poposaurus ilium was discovered, the paleontologist J.H. Lees attributed the remain to a phytosaur by the name of Paleorhinus bransoni.
The exact methods of communication used by these dinosaurs have not been ascertained yet. However, research has shown that modern-day members of the clade Archosauria, to which the Poposaurus belongs, have retained the genetic traits of vocalizations from their extinct ancestors. So, it can be assumed that individuals belonging to the genus Poposaurus used different vocalizations to communicate with each other. So, just like the crocodiles living today use different sounds in order to communicate with their young ones or as a part of courtship, Poposaurus may have done the same.
Poposaurus was quite a large archosaur, with an estimated length of 13 ft (4 m). However, the length of Poposaurus was half the length of large theropod dinosaurs known as Allosaurus, which had a length of 28 ft (8.5 m).
Even though the classification of Poposaurus puts it closest to the group of crocodiles rather than dinosaurs, this archosaur was capable of walking on two legs, and hence, was an obligate biped. The muscular hind legs and short forelimbs were proof of the fact that Poposaurus was bipedal. Additionally, it has been ascertained that it was quite swift in its movements.
Most of the members of this genus are thought to have weighed between 132-165 lb (60-75 kg). However, the heaviest individuals had a weight of 198.4-220.4 lb (90-100 kg).
There are no separate names given to the male and female members of the genus Poposaurus.
Baby Poposaurus dinosaurs would be known as hatchling dinosaurs.
The diet of Poposaurus has been one of the most well-studied aspects of it. One of the close and early relatives of Poposaurus, also belonging to the Late Triassic, was Effigia, which had a toothless snout and was herbivorous in nature. This led researchers to believe that the Poposaurus diet may have been herbivorous, as well. However, subsequently, the careful examination of Poposaurus jaws revealed the presence of sharp and curved teeth, a characteristic feature of carnivores.
In fact, 'hypercarnivorous' is the best term to describe Poposaurus. Hypercarnivore means any animal whose diet is predominantly made up of meat, amounting to more than 70%. Poposaurus may have fed on smaller animals and dinosaurs in its habitat. One of the important deductions made from this was that bipedal movement among crocodile-like archosaurs came first, followed by the diet becoming carnivorous.
Poposaurus, hypercarnivorous in nature, was most likely quite aggressive in order to pursue and capture its prey. However, in turn, it was not preyed upon.
The anatomy of Poposaurus was such that it had a muscle from its pubis bone attached to its liver. This muscle aided the archosaur to pull back on its liver while respiring, which led to the inflation of lungs and successful breathing.
A scan of the Poposaurus fossil revealed significant information about this archosaur. For instance, even though Poposaurus had a total of five digits, the fifth digit was quite reduced and appeared as a small splint of bone. Additionally, the fourth metatarsal of its digits was smaller than the third. Also, its pubis bones ended in a hook-like structure, a feature that is unique to this species of the Triassic.
Interestingly, despite being closely related to crocodiles, this archosaur of the Late Triassic walked on its two legs, and hence, showed bipedal movement. This feature has led to a more detailed understanding of the evolution of bipedal mobility. Poposaurus developed this trait independently, and this stance was not related to the evolution of the dinosaurs of the Triassic age. However, since Poposaurus walked on its two legs, it was a competition to the bipedal dinosaurs of the time. Nevertheless, why Poposaurus became extinct despite being able to compete with large bipedal dinosaurs of the Triassic remains a mystery.
*The first image is by Petrified Forest from Petrified Forest, USA
*The second image is by Smokeybjb