ANKYLOS!

Strange Symmetries #11: Step Up To The Plate

Stegosaurs are some of the most popular and recognizable dinosaurs thanks to their unique appearances, with small heads, elaborate back plates, and spiky thagomizer tails.

Closely related to the ankylosaurs, they first appeared in the mid-Jurassic about 170 million years ago. While they lasted until at least the mid-Cretaceous (~100 milion years ago), their heyday was in the latter half of the Jurassic, ranging all across Asia, Europe, Africa, and North America – and the North American species like the eponymous Stegosaurus developed especially elaborate plates in a distinctive asymmetrical pattern, not arranged in pairs like most other stegosaurs but in alternating rows along each side of the midline of their backs.

Hesperosaurus mjosi lived around 156 million years ago during the late Jurassic, in what is now Wyoming and Montana in the Western United States. It was closely related to Stegosaurus but was a little older and a little smaller, about 5-6m long (~16-20').

Much like its more famous relative its plates seem to have alternated along its back, which may have been an adaptation to maximize visible surface area while minimizing the number of plates, saving on the energy needed to grow such large elaborate ornamentation.

Hesperosaurus might also represent a rare case of possible sexual dimorphism in non-avian dinosaurs, with wider more rounded plates potentially interpreted as belonging to males and taller pointed plates belonging to females.

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new thyreophoran!!!!! i love this guy so much

Skeletal reconstruction of Sauropelta edwardsorum, the nodosaurid dinosaur which lived 108.8 million years ago in the Early Cretaceous of what is now Wyoming, Montana, and Utah

Day 12: Miragaia longicollum

Scutellosaurus lawleri, one of the first thyreophoran ornithischian dinosaurs from early Jurassic Arizona

Results from todays flocking paleostream

First we had Altispinax, which I had to speed run eating to finish this little baby

Then, to the dismay of some, we did thyreosaurus which was my idea, whith some curious Spicomellus approaching. Also I would like to clarify that I am not a lazy bastard as I suffered with everyone

Then I did a newborn ornithoprion with zebra shark colors

Then we did mapusaurus and here he is cuddling with argentinosaurus as they are tired of fighting

Jakapil kaniukura Riguetti et al., 2022 (new genus and species)

(Select bones and schematic skeletal of Jakapil kaniukura, with preserved bones in white, from Riguetti et al., 2022)

Meaning of name: Jakapil = shield bearer [in Puelche]; kaniukura = crest stone [in Mapudungun, referring to the large ridge along the underside of its lower jaw]

Age: Late Cretaceous (Cenomanian), around 94–97 million years ago

Where found: Candeleros Formation, Río Negro, Argentina

How much is known: Partial skeleton of one individual, including parts of the skull, limbs, and over 40 armor plates.

Notes: Jakapil was a small thyreophoran (armored dinosaur), estimated as having been less than 1.5 m long and 4.5–7 kg in mass. Although it is not very completely known, it exhibits many features that are unusual for a thyreophoran, including a strong, deep lower jaw and very slender forelimbs, the latter of which suggests it walked on its hind legs. The only other thyreophoran previously thought to have been fully bipedal was the Early Jurassic Scutellosaurus.

The best known thyreophorans include the plated stegosaurs and the heavily armored ankylosaurs, but Jakapil may not have belonged to either group. If this is correct, then it is by far the latest-surviving thyreophoran currently known that was neither a stegosaur nor an ankylosaur.

Given the combination of limited remains and strange characteristics, it is perhaps not surprising that a few researchers have expressed skepticism of a thyreophoran identity for Jakapil, with one reviewer of the description paper noting that some of its features more closely resemble ceratopsians. Hopefully, more complete remains of this dinosaur will one day be found to shed further light on its anatomy and evolutionary relationships.

Reference: Riguetti, F.J., S. Apesteguía, and X. Pereda-Suberbiola. 2022. A new Cretaceous thyreophoran from Patagonia supports a South American lineage of armoured dinosaurs. Scientific Reports 12: 11621. doi: 10.1038/s41598-022-15535-6

Say hello to the latest thyreophoran dinosaur, Jakapil kaniukura! Bearing many traits that we would expect from the later Ankylosauria clade, such as an armored body.

March Madness Winner!

Drumroll please!

The winner for 2024's march madness wad Dunkleosteus!

Also, a new stegosaur paper dropped and I am so stoked for it. I did a little video on it so here's the link if you are interested in hearing more!

Ankylosaurus.

The thyreophorans were heavily armored ornithischian dinosaurs, with their most famous representatives being the stegosaurs and the ankylosaurs. Earlier members of the group were all small bipedal animals covered in rows of prickly osteoderms, and until now these "primitive" forms were known only from the early-to-mid Jurassic, around 200-165 million years ago.

But now the recent discovery of Jakapil kaniukura is suggesting a lineage of early thyreophorans actually survived for much much longer than previously thought – all the way into the Late Cretaceous, about 97-94 million years ago.

Just 1.5m long (5'), Jakapil lived in what is now southern Argentina, in an ancient desert with a braided river system. It was bipedal, with a short beak, small arms, and a body bristling with spiky armor, and its unusually deep lower jaw and heavily worn teeth indicate it fed on rather tough vegetation that required a lot of chewing to process.

It's currently only known from somewhat fragmentary remains, so reconstructions of its full appearance are rather speculative and there's already been some dispute about whether Jakapil actually was a thyreophoran. One proposal is that it shared a lot of anatomical features with early ceratopsians instead, which if true would make it an incredibly weird armored ceratopsian, and also the first definitive member of that group from South America. But the ceratopsian-like features could also just be due to convergent evolution – and a Jakapil-like dinosaur might actually help explain the only other known dubious South American "ceratopsian" Notoceratops, and the similarly-disputed Australian Serendipaceratops.

But whatever it was – late-surviving basal thyreophoran, southern armored ceratopsian, or even a previously unknown lineage of ornithishcians entirely new to science – it's an exciting and unexpected discovery.

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Jakapil

Jakapil — рід тиреофорових динозаврів із ранньокрейдової формації Канделерос в Аргентині. Типовим видом є Jakapil kaniukura.

Повний текст на сайті "Вимерлий світ":

https://extinctworld.in.ua/jakapil/

Skeletals of two Dacentrurid stegosaurs that both hail from the El Mers lll Formation of Morocco 168-160 million years ago and were both described within four years of each other, from bottom to top: Adratiklit boulahfa and Thyreosaurus atlasicus.

Day 30: Scutellosaurus lawleri

Aaaaaand done! I finally took a step out of my digital comfort zone and beat an art challenge with normal pens! (Somewhat, the shading was added digitally, I'm a coward)