Reconstruction of the abelisaurid Carnotaurus sastrei from the Late Cretaceous of Patagonia (Argentina). In this drawing, I practiced hatching with a ballpoint pen. Carnotaurus is one of the most famous theropods. He is known for his well-preserved skeleton, which is missing a significant part of the tail and legs below the knees. This dinosaur is easily recognizable by its short upturned muzzle and cone-shaped flattened supraorbital horns, as well as its heavily reduced forelimbs. Impressions of scaly skin have been preserved, on which large 4-5-centimeter tubercles stand out among the small scales. Carnotaurus has appeared in numerous books and films about dinosaurs, including M. Crichton's "The Lost World" and the Disney's "Dinosaur".

(This is posting several days late here because tumblr didn’t put in my queue properly. And also a little late for Halloween, but since this October saw the description of a new dinosaur species with a particularly spooky name, I couldn't resist putting it into the schedule anyway.)

Spectrovenator ragei was an early member of the abelisaurid lineage, living in southeastern Brazil during the Early Cretaceous, about 120 million years ago. It was one of the smallest known abelisaurids, measuring just 2m long (6'6"), and lacked a lot of the skull specializations seen in larger-bodied Late Cretaceous forms like Carnotaurus, suggesting it was more of a generalist predator.

Its genus name translates to "ghost hunter" due to it being found underneath the fossil remains of another dinosaur entirely – a "ghost" unexpectedly appearing when the specimen was being prepared – but it's extra appropriate since it also helps to fill in a rather sizeable ghost lineage in the fossil record of abelisaurids.

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For around 50 years some very unusual dinosaur tracks have been found in ancient desert sediments in South America: strange footprints showing the impression of only a single toe, a walking style never before seen in any reptiles.

And recently a fossil of what might be the track maker has actually been found.

Named Vespersaurus paranaensis, this new species lived during the Late Cretaceous of Brazil (~90 mya) and was a member of the noasaurid family of theropods, closely related to the weird-jawed Masiakasaurus from Madagascar.

Measuring about 1.5m long (~5′), Vespersaurus was fairly lightly built with legs proportioned for running -- and its feet were absolutely unique. Although it had the standard three main toes of a theropod, it bore its weight entirely on the middle toe and held the other digits off the ground. The two raised toes on each foot also had large knife-like claws which may have been used during hunting, vaguely similar to the sickle claws on the feet of dromaeosaurs. But unlike dromaeosaurs these claws weren’t highly curved or pointed, suggesting Vespersaurus used more of a scratching and slashing technique rather than the raptors’ puncture-and-restraint strategy.

Much like ancient horses, it may have developed its single-toed stance as an adaptation for more efficient fast running, possibly to avoid larger predators or to chase down small fast-moving prey like hopping desert mammals.

The known one-toed fossil footprints are actually slightly older than the Vespersaurus fossil, and similar tracks in Argentina have been found dating back to the Late Jurassic (~150mya), so there may have been a long lineage of “one-toed” desert-dwelling noasaurids in South America that haven’t been found yet.

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By José C. Cortés on @ryuukibart

Group: Neoceratosauria

Classification: Cellular Life, Archaea, Proteoarchaeota, Eukaryota, Unikota, Opisthokonta, Holozoa, Filozoa, Metazoa, Eumetazoa, Planulozoa, Bilatera, Nephrozoa, Deuterostomia, Chordata, Craniata, Vertebrata, Gnathostomata, Eugnathostomata, Teleostomi, Euteleostomi, Sarcopterygii, Rhipidistia, Tetrapodomorpha, Eotetrapodiforms, Elpistostegalia, Stegocephalia, Tetrapoda, Reptiliomorpha, Anthracosauria, Batrachosauria, Cotylosauria, Amniota, Sauropsida, Eureptilia, Romeriida, Diapsida, Neodiapsida, Sauria, Archosauromorpha, Archelosauria, Archosauriformes, Crurotarsi, Archosauria, Avemetatarsalia, Ornithodira, Dinosauromorpha, Dinosauriformes, Dinosauria, Saurischia, Eusaurischia, Theropoda, Neotheropoda, Averostra, Ceratosauria

Definition: The clade of the most recent common ancestor of Ceratosaurus and Carnotaurus, and all of that most recent common ancestor’s descendants. 

Organisms Within: The clades Ceratosauridae and Abelisauroidea

Time Range: Given this is another node-based clade, we can only guess at when the earliest member of this group evolved. Since earliest known Abelisauroids are from the earliest portion of the Middle Jurassic, it stands to reason that the earliest Neoceratosaur had to evolve before this; the best guess at such is shown below. 

Characteristics: This group contains all the more derived members of Ceratosauria, and they remained as weird and strangely diverse as their less derived relatives. The bulk of this group included the Abelisauroids, which ranged from the huge and tiny-armed Carnotaurus to the small and fast Noasaurids. 

From https://en.wikipedia.org/wiki/Ceratosauria

Neoceratosaurs were relatively medium-sized predators or smaller during the Jurassic; however, the later Abelisaurids that would inhabit mostly the Southern Hemisphere got very large and often were at the top of the food chain in their environments. 

By Jack Wood on @thewoodparable

The beginning members of this group would probably have had some feathers, though as Abelisauroids evolved, the derived Abelisaurids primarily lost their fluffy covering. Furthermore, Ceratosaurids probably had osteoderms along their back, though this says nothing about the Noasaurid group, which were primarily small and thus probably retained their feathers. 

From https://en.wikipedia.org/wiki/Eoabelisaurus

Biogeography: It is very uncertain where Neocreatosauria originated, given that Ceratosaurs were very widespread and Neoceratosaurs were also; early members of Abelisauroidea are not helpful, either, as they are fairly widespread. As such, it is unlikely it will ever be determined where this group first evolved. 

Posts about Ceratosauridae and Abelisauroidea to come soon.

Sources:

https://en.wikipedia.org/wiki/Abelisaur

https://en.wikipedia.org/wiki/Ceratosaurus

https://en.wikipedia.org/wiki/Ceratosauria