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Panphagia, the Oldest-Known Sauropodomorph Dinosaur

For decades, South America has been regarded by paleontologists as the place where dinosaurs originated. It is here that we have our clearest record of what the oldest dinosaurs looked like. Specifically, Brazil and Argentina hold the record for the countries that possess the oldest-known dinosaur fossils. Based upon the fossils that have been uncovered in Brazil’s Santa Maria Formation and Argentina’s Ischigualasto Formation (in particular a locality known as “the Valley of the Moon”), dinosaurs are believed to have appeared during the middle of the Triassic Period about 235-230 million years ago.

Prior to the appearance of dinosaurs in the middle Triassic, smaller dinosaur-like animals scurried about within the jungles of South America. These proto-dinosaurs are known as “dinosauromorphs”. They first appeared during the early Triassic Period, and continued into the late Triassic, well after dinosaurs had appeared and established themselves. Probably the most well-known of these early dinosauromorphs is Lagosuchus, a small reptile about the size of a chicken. What made Lagosuchus and its kind different from the other reptiles which were around at the time was the fact that Lagosuchus and its close relatives ran around on two legs instead of four. This would be a major innovation which would be exploited by the earliest dinosaurs.

File:Marasuchus.JPG

The skeleton of Marasuchus, an advanced “dinosauromorph” from Argentina, dated to the middle Triassic Period about 235 MYA. It has been hypothesized that Marasuchus and Lagosuchus are in fact the same animal. Photograph by Michelle Reback (July 28, 2008). Public domain image, Wikimedia Commons.
https://commons.wikimedia.org/wiki/File:Marasuchus.JPG

For a long time, our idea of what the earliest dinosaurs looked like was shrouded in mystery. However, it seemed that the first dinosaurs were carnivores. From the 1950s until the very early 1990s, creatures like Staurikosaurus of Brazil and Herrerasaurus of Argentina were the oldest-known dinosaurs, and they were also believed to be the most evolutionarily primitive. Still, despite their supposedly archaic nature, these were fairly large animals – Staurikosaurus reached 6 to 8 feet long, and Herrerasaurus was even bigger, reaching 12 feet long. Both of these animals, and Herrerasaurus in particular, clearly would have been formidable competitors to the other carnivorous four-legged reptiles which were alive at the time. This was quite an upgrade from small chicken-sized creatures like Lagosuchus, which had existed only a short time earlier. Considering the very short time difference between the appearance of small creatures like Lagosuchus and the subsequent appearance of large meat-eating dinosaurs like Herrerasaurus, it appeared as though one of two options applied here: either dinosaurs managed to evolve into a large size within a very short length of time, or there was some intermediate species which hadn’t been discovered yet. Was it possible that there was another dinosaur, as yet undiscovered, which could fill the gap between the primitive dinosauromorphs and creatures like Herrerasaurus?

In 1991, the skeleton of a new dinosaur was discovered in Argentina by Dr. Ricardo Martinez, a paleontologist from the University of San Juan. This animal was far smaller, and it seemed more primitive, than Herrerasaurus. It measured only 3 feet long, and it appeared to have an anatomy which was less advanced than either Staurikosaurus or Herrerasaurus. In 1993, the animal was named Eoraptor, “the dawn thief”. For nearly two decades, this little animal held the title of being the oldest-known dinosaur.

However, complications arose. A closer examination of the skeletons of both Herrerasaurus and Eoraptor created doubts as to whether or not Eoraptor really was the oldest and most primitive dinosaur ever found. For example, the fewer sacral vertebrae an animal has, the more primitive it’s believed to be. Eoraptor possessed three sacral vertebrae, but Herrerasaurus had only two. This indicated that Herrerasaurus, despite being five times larger, was actually more primitive than Eoraptor. Another point of contention was the structure of the lower jaw. When Eoraptor was first discovered and described, it was believed that it possessed a less-evolved jaw structure than Herrerasaurus, but this turned out to be false. Gradually, concerns began to be raised that Eoraptor, despite its small size, was actually not as primitive as it first appeared to be. Special attention was given to the skull and the teeth. Eoraptor possessed different kinds of teeth in its mouth, indicating that it was an omnivore. A close examination of both the skull structure and the teeth made some wonder if Eoraptor was as primitive as we initially believed. In fact, there were some aspects of its anatomy that bore a bit of a resemblance to the sauropodomorph dinosaurs – the long-necked long-tailed creatures that we typically associate with the word “dinosaur” – rather than the fleet-footed meat-eating theropod dinosaurs.

In 2011, Dr. Ricardo Martinez (the same man who had found Eoraptor’s skeleton in 1991) re-classified Eoraptor as a primitive sauropodomorph. This claim was met with skepticism by the scientific community. In a subsequent study, Martinez changed his mind again and stated that Eoraptor was so archaic that it could not be placed into any definite group of saurischian dinosaurs and ought to be placed at the very base of Saurischia. However in 2013, Dr. Paul Sereno did his own evaluation of Eoraptor’s skeleton and concluded that indeed it was a primitive sauropodomorph, distantly related to other prosauropods like Plateosaurus and Anchisaurus. Even so, the overwhelming majority of the scientific community has refuted this claim. Numerous studies have been conducted on Eoraptor since it was discovered and named, and most of them state that Eoraptor is either a very primitive theropod dinosaur or else it is the earliest saurischian, appearing before the saurischians split into theropods and sauropodomorphs.

All of this raises an interesting question. If Eoraptor was not the earliest sauropodomorph, then what was?

In 2006, Dr. Ricardo Martinez was once again exploring the middle Triassic rock layers of the Ischigualasto Formation, dated to 228.3 million years ago, when he found another skeleton. It looked similar to Eoraptor, but it was noticeably larger, measuring 4.25 feet (1.3 meters) in length; Martinez thought that the skeleton was of a juvenile, and that the adult would be larger, say perhaps 6 feet long. The skeleton was incomplete, including only a partial skull. Teeth were only found in the lower jaw. The skull was clearly similar to Eoraptor’s, but it also showed some features which can be seen in very primitive sauropodomorphs like Plateosaurus. For example, the lower jaw curves downwards towards the front, which is a tell-tale feature of that group. The teeth were also very similar to those seen in prosauropods. Based upon the skull structure and the shape of the teeth, this animal seemed to be more closely related to sauropods than theropods. In 2009, the animal was named Panphagia, which is ancient Greek for “eats everything” in reference to its supposedly omnivorous diet.

Reconstruction of the skeleton of Panphagia protos. Photograph by Eva Kröcher (December 5, 2010). Creative Commons “Attribution Non-Commercial Non-Derivative 3.0 (US)”, GNU Free Documentation License (GFDL), and Free Art License. https://commons.wikimedia.org/wiki/File:Panphagia_fossil_DSC_6168.jpg.

A complete skull was not found with the skeleton, but we have enough of the bones to give us an idea of the skull’s outline. Below is an illustration that I made of what the complete skull of Panphagia might look like, based upon what was seen in the photograph that you see above. The drawing was made with a black Crayola marker.

Skull of Panphagia protos. © Jason R. Abdale (February 9, 2021).

Based upon this skeleton and the description that Ricardo Martinez and Oscar A. Alcober gave in their paper on this animal, I have reconstructed what the entire animal might look like. The creature bears a slight resemblance to prosauropods like Plateosaurus and Anchisaurus. No hands were found with the specimen. However, the illustration which accompanied Martinez and Alcober’s paper showed Panphagia sporting hands with four fingers, although the fourth digit was so small that it was probably incorporated into the wrist and wasn’t seen on the outside. The fingers themselves were longer the more distal they were to the body (in other words, the middle finger was longer than the thumb, and the pinky was even longer than the middle finger), and this was repeated in the skeletal reconstruction seen above. Since this was the reconstruction seen in both sources, I incorporated it into my own illustration.

I think that there are two issues with the illustrated reconstruction of Panphagia’s skeleton seen in the scientific paper and in the physical reconstruction seen in the photo above. Firstly, I think that the tail is too short. The animal looks conspicuously front-heavy, and the tail ought to be longer to give it better balance. Secondly, I believe that the hand structure is incorrect. Prosauropods like Plateosaurus, Massospondylus, and Anchisaurus had hands with five fingers and large thumb claws. However, it must be noted that all three of those species came from the late Triassic and early Jurassic Periods, nearly twenty to thirty million years after Panphagia’s appearance, and their hand structure may have been more evolved than that seen in archaic animals like Panphagia. However, until a more complete specimen of this animal is found, I think my reconstruction is going to remain as it is.

My drawing was made with No. 2 pencil on printer paper.

Panphagia protos. © Jason R. Abdale (February 14, 2021).

 

For more information, please read Martinez’ and Alcober’s paper on this animal, which you can see here:

Martínez, Ricardo N.; Alcober, Oscar A. (February 16, 2009). “A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha”. PLoS ONE, volume 4, issue 2. Pages 1-12. doi:10.1371/journal.pone.0004397.

https://storage.googleapis.com/plos-corpus-prod/10.1371/journal.pone.0004397/1/pone.0004397.pdf?X-Goog-Algorithm=GOOG4-RSA-SHA256&X-Goog-Credential=wombat-sa%40plos-prod.iam.gserviceaccount.com%2F20210301%2Fauto%2Fstorage%2Fgoog4_request&X-Goog-Date=20210301T093333Z&X-Goog-Expires=3600&X-Goog-SignedHeaders=host&X-Goog-Signature=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.

 

Keep your pencils sharp, everyone.