#sanjuansaurus

[ildarotyrannus]

Reconstruction of the early dinosaur Herrerasaurus ischigualastensis from the Late Triassic (Carnian stage) Argentina. This genus was described by Osvaldo Reig back in 1963, but due to the fragmentary nature of the bones, the classification of the animal was controversial (opinions were expressed that it was a prosauropod or even a dinosaur outside the two main groups). Only in 1988 was a complete skeleton with a skull found, which allowed reconstructing the dinosaur and its approximate kinship. However, it is still unclear whether Herrerasaurus was an early theropod or whether it was closer to sauropodomorphs. The remains, named Ischisaurus cattoi and Frenguellisaurus ischigualastensis, were later assigned to Herrerasaurus.

Herrerasaurus is interesting for its rather large size for an early predatory dinosaur: some specimens of "Frenguellisaurus" reached 6 m. The skull was relatively small, but the jaws carried sharp saw-toothed teeth, including "fangs". There was also a shock-absorbing joint in the middle of the jaw, which allowed holding large prey. The hands were armed with three grasping fingers, and the longest of them was the third. The rudimentary fourth and fifth fingers were hidden by soft tissues. The pelvis of a Herrerasaurus is unusual. Only two sacral vertebrae fused with it (at least 3 in other dinosaurs), and the acetabulum was not completely open. At the same time, the pubic bone was directed not forward, but backward, as in maniraptorans, and carried a massive "boot". At one time, this served as the basis for Gregory Paul to designate the herrerasaurs as an early group in which bird-like features arose, and even to bring them closer to the "protoavis".

In this work, I tried out a style with shading using a black pencil, not a pen. It is much easier to apply shadows with a pencil, and I liked the result. It shows an extensive cover of filaments inspired by a possible "fluffy" ancestral state for ornithodirans (dinosaurs, pterosaurs and small groups close to them).

Black ballpoint pen and black colored pencils, 2023.

[dankusner]

Dinosaurs displayed fast growth from the beginning 

WASHINGTON – One of the traits that helped make the dinosaurs such an evolutionary success story -– thriving for 165 million years – was their fast growth rate, from massive meat-eaters like Tyrannosaurus to immense planteaters like Argentinosaurus.

But when did this characteristic first appear?

A new study indicates it was present in the earliest dinosaurs, as revealed by microscopic features in bone fossils from Argentina that showed that they exhibited growth rates on par with those of today’s mammals and birds.

Rapid growth offers numerous advantages.

“Growing quickly allows organisms to escape the risky business of being small for a long part of their life history. It also allows them more time to reproduce throughout their lifespan, which imparts a measure of evolutionary fitness, generation by generation,” said paleontologist Kristi Curry Rogers of Macalester College in Minnesota, lead author of the study published this month in the journal PLOS ONE.

The researchers examined patterns preserved within the bones of dinosaurs and some of their cousins that inhabited northwestern Argentina between about 231 and 229 million years ago.

“The organization of minute bone mineral crystals and proteins, along with blood vessels and cellular organization, all reflect relative speed of growth,” Curry Rogers said. “Of course, all these soft squishy parts have long since decayed, millions of years ago, when these bones were becoming fossils. But all the hard parts that persist through time record the spaces where these soft parts once were. This allows us to reconstruct and compare growth patterns among animals.”

The researchers studied five early dinosaurs – all bipedal, fleet-footed, and with clawed, grasping hands and sharp teeth.

Three were meat-eaters, forerunners of massive predators such as T. rex and Giganotosaurus.

Herrerasaurus and Sanjuansaurus were around 10-15 feet long, while Eodromaeus was about the size of a turkey.

The other two – similarly turkeysized Eoraptor and Chromogisaurus – were forerunners of long-necked, fourlegged giants such as Argentinosaurus and Dreadnoughtus.

All five showed signs of exceptionally fast growth.

But the researchers also got a bit of a surprise when they discovered that some of the non-dinosaur reptiles in these ancient Argentine ecosystems were keeping pace, having their own speedy growth rates.

“Dinosaurs arose from humble origins, starting off as small, bipedal carnivores, who were themselves dominated by a diverse array of other ruling reptiles,” Curry Rogers said.

Quick growth was detected in fearsome four-legged crocodile-like Saurosuchus, the dominant terrestrial predator of its time at about 23 feet long, as well as crocodile relatives Proterochampsa and Trialestes.

Other animals including tusked plant-eating reptile Hyperodapedon and mammal-like reptile Exaeretodon also grew quickly, but regularly paused their growth throughout life – a pattern distinctive from the continuous fast growth of dinosaurs.

The first dinosaurs and these other animals evolved during the Triassic Period.

This was in the aftermath of Earth’s worst mass extinction 252 million years ago at the end of the Permian Period.

About 95% of species were lost amid severe climate change apparently caused by massive Siberian volcanic activity

[artbyconnorross]

Here’s the finished product from yesterday! Saurosuchus isn’t ready to hand off the title of apex predator to the dinosaurs yet, and devours a Sanjuansaurus

[1dinodaily]

9/20/22 Sanjuansaurus

[stavrosskundromichalis]

And now, time for an all dinosaurian Triassic fauna. From left to right: Coelophysis bauri, Blikanasaurus cromptoni, Ingentia prima, Lessemsaurus sauropoides, Unaysaurus tolentinoi, Chindesaurus bryansmalli, Efraasia minor, Coloradisaurus brevis, Camposaurus arizonensis, Eucnemesaurus fortis, Guaibasaurus candelariensis, Gnathovorax cabreirai, Sanjuansaurus gordilloi, Pampadromaeus barberenai, Herrerasaurus ischigualastensis, Staurikosaurus pricei, Eodromaeus murphi, Bagualosaurus agudoensis, Alwalkeria maleriensis, Panphagia protos, Chromogisaurus novasi, Eoraptor lunensis, Saturnalia tupiniquim and Buriolestes schultzi.

[theafenogaster]

Sanjuansaurus

[a-dinosaur-a-day]

Pisanosaurus mertii

By José Carlos Cortés 

Etymology: Pisano’s Reptile

First Described By: Casamiquela, 1967

Classification: Dinosauromorpha, Dinosauriformes, Dracohors, Silesauridae?

Status: Extinct

Time and Place: 231.4 million years ago, in the Carnian of the Late Triassic 

Pisanosaurus is known from the Cancha de Bochas Member of the Ischigualasto Formation in San Juan Argentina. 

Physical Description: If a Silesaurid - as is currently thought - Pisanosaurus would have been a small, slender, and quadrupedal animal, only about 1 meter in length. It had an open hip socket, like dinosaurs, which may point to a very interesting phylogenetic position (see the Other section below). It had very elongated bones in its hands, and its upper hips were weirdly wide as well. Beyond that, we don’t know much about with Pisanosaurus may have looked like. It seems logical to suppose it would have had a small head with a little beak in the front of the mouth - as both Silesaurids and early Ornithischians (the other hypothesis for the type of creature Pisanosaurus was) have such structures for snipping off plant material. Given its small size, Pisanosaurus - like all other early members of the group of reptiles that would later include birds (Avemetatarsalia) - would have been covered with fluff all over its body. If Pisanosaurus was an early Ornithischian and not a Silesaurid, it would have been bipedal, with short forelimbs not used in locomotion.

Diet: Either way, Pisanosaurus would have been an herbivore, eating low-lying vegetation in its densely forested home.

Behavior: As a small, lithe herbivore, Pisanosaurus would have been very skittish - running at the slightest sign of danger, making sure to avoid the many large predators it shared a home with. It probably wouldn’t have been very social - given it wasn’t very abundant! - but it may have foraged in large groups of mixed herbivores, sticking together to rely on each other in the event of danger. This reliance would have allowed bulkier herbivores to notice and react to danger quicker (since the small lithe ones like Pisanosaurus would have already been running away) - and the smaller ones would have had large, bulky roadblocks to stop the approach of predators. As an early dinosaur, it most likely partook in some sort of care of its young, though of course, we do not know what. 

(As an Ornithischian) by Michael B. H., CC BY-SA 3.0 

Ecosystem: The Ischigualasto Environment is one of the more famous ecosystems of the Late Triassic - due to it being a hotbed of early dinosaur discoveries, including some of the earliest potential members of the group. In fact, it is such an important environment that today the rock formation is considered a UNESCO World Heritage Site. It was an extensive series of rivers channeling through a large floodplain, erring towards the wetter side of the scale - mud was the name of the game, and there was a wide variety of plant material present, including a dense conifer forest, ferns, and horsetails. It did experience seasonal rainfall, with possible times of extremely heavy precipitation. Occasionally, everything would be buried in volcanic ash - leading to the beautiful preservation of the environment.

Pisanosaurus wasn’t the only Silesaurid here - there was also Ignotosaurus, the slender and small Silesaurid. There were also famous early dinosaurs such as Eoraptor - the small, bipedal early Saurischian(?), Herrerasaurus and Sanjuansaurus, the large taxonomically-confusing predators, and Chromogisaurus, one of the earliest known “prosauropods.” Of course, this being the Triassic, dinosaurs were only a small part of the ecosystem. The Ischigualasto - like most places of the time period - was absolutely lousy with other archosauriformes! Non-Dinosaurian Archosauriformes were extensively diverse at this time, making up a large chunk of the “large charismatic land animal” roles. There was Aetosauroides, an Aetosaur (sort of like a cross between an ankylosaur, an ant-eater, and a crocodile), Proterochampsa and Pseudochampsa - crocodilian-like creatures that were actually equally closely related to crocodiles and dinosaurs - both frequented the rivers of the environment. Saurosuchus, a large and bulky stem-croc, would have been a huge pain in the rear for herbivores like Pisanosaurus. Sillosuchus was a weird stem-croc, bipedal and strangely dinosaur like - with even, potentially, a beak - but utterly scaly, and bulky in stature! There was also Venaticosuchus, an Ornithosuchid (one of the most basal groups of stem-crocs), and Trialestes - a fast moving stem-croc, and one of the earliest Crocodylomorphs (the group of crocodilians and their closest relatives). 

(Without Feathers) by Nobu Tamura, CC BY-SA 4.0 

It being the Triassic, this wasn’t an environment free of non-reptiles! Temnospondyls - large carnivorous amphibians - were crawling about; as were a variety of Synapsids. Small, carnivorous dog-shaped cynodonts like Chiniquodon would have directly competed with the local dinosaurs; they even grew to be quite large and fast, like in Diegocanis and Ecteninion. They also came in large, bulky herbivorous forms, like Exaeretodon. Dicynodonts were present too, with their strange pig-like appearance: Ischigualastia was a common synapsid on the floodplains of Pisanosaurus’ home. In short, Pisanosaurus was surrounded with a cast of characters showcasing some - but certainly not all - of the weirdness that the Triassic  had to offer.

Other: What Is Pisanosaurus? Back in the day, Pisanosaurus was a famous creature for being one of the earliest “Ornithischian” dinosaurs - one of two major groups of dinosaurs, famous for including such later iconic members as Stegosaurus and Triceratops. In fact, for the longest time, Pisanosaurus was… the only Ornithischian known from the Triassic. This is odd, to say the least - there are dozens of Triassic dinosaurs known, they’re just all from the other group, the Saurischians (containing such iconic later forms as Apatosaurus, Tyrannosaurus, and… all birds). So, for the longest time, Pisanosaurus stood as a focal point of dinosaur research - an important piece of the puzzle of the origin of this elusive, but important group. 

By Nix 

Except it isn’t an Ornithischian. Lately, studies have shown time and time again that Pisanosaurus actually more closely resembles the Silesaurids - a group of almost dinosaurs that were quadrupedal, active herbivores living around the world at the time of the Triassic, before going extinct at the end-Triassic extinction. This would make its appearance much different than what a “basal Ornithischian” would suggest - and, of course, the fact that Pisanosaurus is known from only a single fragmented skeleton does not make solving this problem much easier. Weirdly enough, there are some hypotheses which suggest that Silesaurids are… the earliest Ornithischians, (as per Pisanosaurus having an open hip-socket), representing a weird side-branch of the group from the Triassic. As this hypothesis gains traction, it may become increasingly true that Pisanosaurus was a Silesaurid - it was just also an early Ornithischian. Only time will tell in the solving of this mystery - for now, we must wait for more evidence.

~ By Meig Dickson

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[stavrosskundromichalis]

More improved versions of older illustrations.. From top to bottom (left to right): Panphagia protos, Eoraptor lunensis, Guaibasaurus candelariensis, Eucnemesaurus fortis, Alwalkeria maleriensis, Sanjuansaurus gordilloi, Saturnalia tupiniquim and Unaysaurus tolentinoi.

For prints, check: https://www.stavrosillustration.se

[stavrosskundromichalis]

Sanjuansaurus gordilloi was an herrerasaurid dinosaur. It lived during the Late Triassic (Carnian) period in northwestern Argentina. It was a lightly built, bipedal carnivore, about 3 metres in length.

The Ischigualasto Formation in northwestern Argentina was a volcanically active floodplain covered by forests, with a warm and humid climate. It was subject to seasonal variations including strong rainfalls. Vegetation consisted of ferns, horsetails, and giant conifers, which formed highland forests along the banks of rivers.

This is a speculative restoration based on the likelihood that proto-feathers were present in basal dinosaurs, and perhaps even a more ancestral animal, in light of the pycnofibers of pterosaurs.

For prints, check: https://www.stavrosillustration.se

[a-dinosaur-a-day]

Ignotosaurus fragilis

By Jack Wood on @thewoodparable

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Name: Ignotosaurus fragilis

Name Meaning: Unknown Reptile

First Described: 2013

Described By: Martínez et al. 

Classification: Avemetatarsalia, Ornithodira, Dinosauromorpha, Dinosauriformes, Silesauridae

Ignotosaurus is a Silesaurid from the Ischigualasto Formation of Argentina, living about 231.4 million years ago, in the Carnian age of the Late Triassic. It is known from part of the leg bone, which indicates it was a small Silesaurid. This difference in leg bone probably indicates that it differed from other Silesaurids mainly in its method or needs during locomotion. It was closely related to Eucoelophysis, Silesaurus, and Sacisaurus, making it a fairly derived member of the Silesaurid group. Ignotosaurus lived in a complex community with many other species of reptiles, including early dinosaurs and other Archosauromorphs, such as Scaphonyx, Herrerasaurus, Proterochampsa, Chanaresuchus, Saurosuchus, Sillosuchus, Trialestes, Aetosauroides, Panphagia, Eoraptor, Chromogisaurus, Eodromaeus, and Sanjuansaurus. However, compared to, say, Herrerasaurus and Scaphonyx, or really, many others in this formation, it was relatively rare - indicating it was not a very common component of this ecology. 

Source:

Martínez, R. N.m C. Apaldetti, O. A. Alcober, C. E. Colombi, P. C. Sereno, E. Fernandez, P. S. Malnis, G. A. Correa, D. Abelin. 2013. Vertebrate succession in the Ischigualasto Formation. Journal of Vertebrate Paleontology 32 (sup1): 10-30. 

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[a-dinosaur-a-day]

Sanjuansaurus gordilloi

Source: https://en.wikipedia.org/wiki/Sanjuansaurus

Name: Sanjuansaurus gordilloi 

Name Meaning: Raul Gordillo's San Juan lizard 

First Described: 2010 

Described by: Alcober & Martinez 

Classification: Dinosauria, Saurischia, Eusaurischia, Theropoda, Herrerasauridae 

Sanjuansaurus is a recently discovered early basal theropod, determined to be in the Herrerasauridae family due to its similar structure to Herrerasaurus. It was discovered in the Ischigualasto Formation in Argentina, in the same formation that Herrerasuarus was found in. It was from the Carnian Stage of the Late Triassic, about 231.4 million years ago. It was an early theropod, living amongst the other dinosaurs described in this blog, still outsized and outnumbered by the archosaurs and other reptiles in the area. It was a similar shape to the other Herrerasaurids, suggesting that the body type was an important part of the local ecosystem in the area. 

Sources: 

http://www.prehistoric-wildlife.com/species/s/sanjuansaurus.html

http://en.wikipedia.org/wiki/Sanjuansaurus