the month in snapshots

 

Dino of the Week: Staurikosaurus

Type Species: Staurikosaurus pricei
Classification: Dinosauria - Saurischia - Theropoda - Herrerasauridae
Time Period: Late Triassic
Location: Brazil
Diet: Carnivore

Staurikosaurus was a small and agile predator that reached about seven and a half feet in length, about two and a half feet in height, and clocked in around sixty pounds. Staurikosaurus is based on fragmentary material, but enough has been found to know that it was a quick-running carnivore with serrated teeth that curved back towards the throat, enabling it to catch and hold onto prey; though this teeth feature would disappear in later theropods, it was common among those of the Upper Triassic. A sliding joint in its jaw allowed the jaw to move backwards and forwards, as well as up and down, so that smaller prey could be worked backwards towards the throat. It had a long tail that it held off the ground as it ran; the rear part of its tail was stiffened and acted as a dynamic stabilizer enabling the creature to run and leap with precise agility. It would’ve preyed on small and medium-sized animals.

Dino of the Week: Isanosaurus

Type Species: Isanosaurus attavipachi

Classification: Dinosauria - Saurischia - Sauropoda

Time Period: Late Triassic

Location: Thailand

Diet: Herbivore

Isanosaurus’ name means ‘Isan lizard,’ and Isan is the name used to refer to northeast Thailand where the specimen was found. Isanosaurus’ discovery caused quite a stir, because upon examination of the few bones preserved, it became apparent that this creature was a sauropod – and it was found in Late Triassic rocks! Up to that point, it was believed that sauropods didn’t come onto the scene until the Early Jurassic, with Vulcanodon being the first of its kind. Isanosaurus pushed sauropod evolution back into the Triassic, upsetting plenty of cherished beliefs. Though some paleontologists question Isanosaurus’ geographical placement, insisting that it actually lived in the Early Jurassic, this is done more for philosophical than scientific reasons. Isanosaurus’ identification of a sauropod doesn’t mean it rivaled the titanic-sized sauropods of the later Jurassic, but it would put the sauropod genesis far earlier than traditionally believed. 

Many supersized prosauropods existed in the Late Triassic – take, for example, Camelotia – but these creatures’ morphologies still place them in the prosauropod camp. Isanosaurus’ remains include a neck vertebra, a back vertebra, and part of a second, six tail vertebra, two chevrons (features of the tail), fragmentary ribs, the right sterna plate, the right shoulder blade, and the left thigh bone. Even these scant finds give us a wealth of information that sets Isanosaurus apart from its prosauropod contemporaries. Its dorsal neural spines were high like those of some later sauropods, unlike the low neural spines of prosauropods; and the lateral sides of the vertebrae were concave, though not deeply excavated as in later sauropods. 

The Isanosaurus specimen shows a quadrupedal locomotion, and the legs were column-like, as shown by the robust and straight thigh bone. The individual discovered likely measured around twenty feet head-to-tail when alive, but the fact that the vertebral neural arches were found separated from the vertebral centra indicates that these remains weren’t fused with each other; this implies that the animal probably wasn’t fully grown, so it’s only a guess as to how large Isanosaurus grew in real life. 

Dino of the Week: Procompsognathus

Type Species: Procompsognathus triassicus

Classification: Dinosauria - Saurischia - Theropoda - Coelophysoidea - Coelophysidae

Time Period: Late Triassic

Location: Germany

Diet: Carnivore

Procompsognathus lived 210 million years ago during the Norian stage of the Late Triassic. Its remains were found in Germany, and it lived in a dry, inland environment. Other dinosaur contemporaries included dubious coelophysoids and the prosauropods Plateosaurus and Efraasia. Procompsognathus was a chicken-sized, lightly-built, bipedal predator that likely fed on insects, lizards, and other small prey. It had long hind legs, short arms, large clawed hands, a stiff tail, and a long, slender snout filled with many small teeth. It grew between 2.5 to 3.5 feet in length and likely weighed just over two pounds. Its tibia was about twenty percent longer than its femur, indicating that it was a fast runner. 

The screenshot above is a cinematic representation of Procompsognathus from the movie The Lost World. In the novels from which the movie was adapted, Procompsognathus carried a sleep-inducing toxin in its saliva. This has no basis in reality, for we cannot uncover any such evidences in fossil remains. However, many reptiles had such weapons, so the hypothetical presence of such abilities isn't without merit in the natural world.

Procompsognathus shouldn’t be confused with Compsognathus: the former lived during the Late Triassic whereas the latter lived during the Late Jurassic. Though they were about the same size, a larger turkey-sized species of Compsognathus has been discovered. The similarity in their names may imply some sort of relationship - "Did the Triassic dinosaur eventually lead to the Jurassic dinosaur?" - but the similarities are symbolic. There's no evidence that Procompsognathus was the genetic forerunner of the later and larger-sized Compsognathus.

Dino of the Week: Antetonitrus

an artist's depiction of two Antetonitrus

Type Species: Antetonitrus ingenipes

Classification: Dinosauria - Saurischia - Sauropoda

Time Period: Late Triassic to Early Jurassic

Location: South Africa

Diet: Herbivore

Antetonitrus lived between the Late Triassic and Early Jurassic, one of the few dinosaurs to cross the Triassic-Jurassic boundary. It’s known by one specimen found in the Elliot Formation of South Africa, which records the Triassic-Jurassic boundary in southern Africa. Antetonitrus lived alongside the far more common Massospondylus, also found at the Elliot Formation. Other creatures from Antetonitrus’ habitat include several early ornithischians (bird-hipped dinosaurs) and lots of crocodylomorphs, along with crustaceans, fishes, and turtles. 

Antetonitrus is one of the oldest known sauropods, and it’s remarkable in that it possesses characteristics both of prosauropods and sauropods; because of this, scientists have poured over its remains to decipher clues about sauropod evolution in the Late Triassic. The specimen discovered measured up to thirty feet in length and stood six feet tall at the hips, but because the vertebral neural arches weren’t fused, the remains likely belong to a juvenile so that adults would’ve been much larger. Unlike prosauropods, Antetonitrus was primarily quadrupedal, and its forelimbs were much longer relative to its hind legs than seen with earlier sauropodomorphs. Yet Antetonitrus retained prosauropod characteristics: the first digit of its hand – the thumb – was twisted and flexible, enabling Antetonitrus to use it for grasping. Derived sauropods weren’t able to grasp, and their wrists had thick, robust wrist bones arranged in a manner that locked the hand into a permanent pronated position, which enabled the hands to bear the weight of the limbs. Antetonitrus’ wrist bones were broader and thicker than seen in prosauropods, but it had yet to reach the permanent pronated position of sauropods. Derived sauropods had a sickle-shaped claw on the first toe of their hind feet, and while Antetonitrus had a claw, it wasn’t sickle-shaped. Its femur was slightly S-curved (sigmoidal) in the lateral view, whereas saurppods had straight femurs. This ‘mixed bag’ puts Antetonitrus in the odd stage between strict prosauropods and sauropods. 

Dino of the Week: Lophostropheus

Type Species: Lophostropheus airelensis

Classification: Dinosauria - Saurischia - Theropoda

Time Period: Late Triassic to Early Jurassic

Location: France

Diet: Carnivore

Lophostropheus lived 200 million years ago at the boundary between the Rhaetian stage of the Late Triassic and the Hettangian stage of the Early Jurassic. As such it is one of the few Late Triassic creatures that survived into the burgeoning Jurassic Period. Lophostropheus was a medium-sized, moderately-built, bipedal carnivore. It could grow up to ten feet in length and likely weighed about 220-300 pounds. Its name means ‘crest lizard’ and is a reference to the predator’s skull crest. It likely preyed on small- to medium-sized prey.