#bashanosaurus

Factfiles:

Jakapil kaniukura

Artwork by @i-draws-dinosaurs, written by @zygodactylus

Name Meaning: Deep Jawed Shield Bearer 

Time: 99 to 97 million years ago (Cenomanian stage of the Late Cretaceous) 

Location: Candeleros Formation, Neuquen and Mendoza, Argentina 

Jakapil is to nonavian dinosaurs as Annakacygna is to birds. This may seem extreme - what could possibly top the cup zoomy swan of filter feeding death - but Jakapil is a weird little dude. It was a bipedal armored dinosaur, similar to the Early Jurassic basal form Scutellosaurus - except, you’ll note, it lived a hundred million years later. At about 1.5 meters long, it was a small dinosaur, again similar to its relative from so long ago. It had rows of osteoderms on its body, and a predentary - unlike other early thyreophorans. It may have diverged from the main thyreophoran group in the Sinemurian, representing a lost lineage of bipedal armored forms that persisted (presumably in South America). However, its classification is a major debate among researchers - many features of the jaw are more similar to Ceratopsians than to Thyreophorans, indicating it may be an armored variant of an early Ceratopsian (which, would be, to say the least, wild) or a completely new clade of Ornithischian altogether! The large amount of wear on its teeth indicates it chewed its food, rather than sheering or chopping it - something only found in a few Ornithischian groups. It lived in a large desert environment, peppered with oases, and filled with a variety of other animals - fish, frogs, tuatara, snakes, turtles, mammals, and other dinosaurs like Andesaurus, Ekrixinatosaurus, Giganotosaurus, Buitreraptor, Alnashetri, and Bicentenaria. 

Bashanosaurus primitivus

Artwork by @i-draws-dinosaurs, written by @zygodactylus

Name Meaning: Early bashan Reptile 

Time: 168 million years ago (Bathonian stage of the Middle Jurassic) 

Location: Lowermost Shaximiao Formation, Yunyang, Chongqing, China

Bashanosaurus is an interesting new stegosaur that is another specimen from the earliest part of the stegosaur family tree, helping to show even more clearly what the first members of this weird group were like. In fact, it had many features similar to both the early thyreophoran Scelidosaurus as well as features similar to the early stegosaur Chungkingosaurus. It grew to about 2.8 meters long, but the known fossils were probably from a subadult, and as such it may have grown larger - though it was still small compared to later stegosaur species. This also indicates that stegosaurs appeared and diversified very, very quickly, reaching very complex forms within twenty million years. It is the oldest known stegosaur as well, dating to just a million years older than the previous record holder. Living in a large floodplain not unlike other Jurassic environments such as the later Morrison, Bashanosaurus shared its home with the early macronarian Yuzhoulong, as well as wide variety of turtles (the more complex environment, famed for mamenchisaurids and weird theropods, would come later). 

Sauropelta - Sean Closson (twitter)

Apologies in advance if today's article is a bit more scatterbrained than some of my better blogposts in the past, but I've been procrastinating writing for a bit and need to get something out.

The larger group of Dinosauria is traditionally split into two main groups: The Saurischians (lizard hips) and Ornithischians (bird hips). The Saurischians include the Therapods (most meat eaters) and Sauropods (long necks), and have been the focus of a lot of my dinosaur discussion on this blog. So today, I wanna highlight a group from Ornithischia, the Thyreophorans.

Miragaia - TheDinosaurMann (twitter)

Thyreophora includes most of what the public would think of as "Armoured Dinosaurs", and much of the uniting anatomical traits are adapted for a thick set body, weight bearing limbs, powerful tails, and a general predator deterring lifestyle. The earliest and more primitive members of this group were more slender, and evolved from a bipedal common ancestor, but the most derived members were the heaviest, spikiest, and well armoured dinosaurs of their time.

Scutellosaurus, an early Thyreophoran

Gabriel Ugueto/Serpenillus (twitter)

One anatomical trait common to all Thyreophorans is the extensive covering of Osteoderms, bony skin protrusions that decorate and protect the backs, heads, and tails of many members. In the Ankylosaur division, this is mostly present as rounded studs and lumps all along the back and sides of the animal. In Stegosaurs, they present as spikes and plates along the back and tail of the animal. Before researching this topic, it never occurred to me that these were analogous structures, but it makes sense these features had ancestral roots.

To best demonstrate the diversity of Thyreophorans, I want to highlight three of the most recent discovered species from across the group.

Bashanosaurus

@ ttorrooo (on twitter)

This Stegosaur was recently found in China in 2015 and described in 2022. Its name means "Bashan-lizard" Bashan being an old name for Chongqing, where it was discovered. Current research places Bashanosaurus as a very primitive member of the Stegosaur clade, and it shares many traits common with Scelidosaurus, a Thyreophoran thought to have evolved before Stegosaurs and Ankylosaurs diverged.

In later Stegosaurs, the back spines had evolved into angular plates, thought to be primarily a display structure. But in Bashanosaurus, the back spines are still very spiky, and parts of its body still preserve rows of spikes on the side of the body, which were reduced to just one spike on the shoulder or lost altogether in later species. It still had the tail spikes, and this seems to be an ancestral trait. It represents a visual clue on how Stegosaurs evolved some of their more derived traits.

Stegouros

@adamworks (tumblr)

This dinosaur was a very derived Ankylosaur discovered in Chile in 2018, and described in 2021. It's name means "roofed tail". Ankylosaurs were traditionally split into two groups, Ankylosauridae, many of which had tail clubs, and Nodosauridae, which were often heavier built, and lacked tail clubs. These groups were mostly from northern continents, and Ankylosaurs from Australia and Antarctica were harder to classify.

The description of Stegouros prompted the creation of a new division within Ankylosauria; Parankylosauria, a group of Gondwana dinosaurs that diverged earlier, and Euankylosauria, which included the Nodosaurids and Ankylosaurids. While the Northern Continent Ankylosaurs were larger, and utilised clubs in their tail weaponry, Stegouros and its relatives were smaller, less bulky, and Stegouros had a sword on its tail. This tail was less mobile, the "sword" formed from several fused vertebrae, but it was still very dangerous.

Jakapil

Gabriel Diaz Yantén/ PaleoGDY (on twitter)

Video version linked here

This dinosaur was a basal Thyreophoran discovered in Argentina across the 2010s and described in 2022. Its name means "shield bearer" in the Puelchan language. Jakapil represents a lineage of dinosaurs that split off from the rest of Thyreophora before Stegosaurs and Ankylosaurs even split. But whereas most of the time you'd think "basal" or "primitive" means from an older time, Jakapil was from the Late Cretaceous, after most of the Stegosaur lineage had died out.

Thyreophorans were mostly heavy set animals, so quadrupeal locomotion was the norm, but Jakapil was an obligate biped; its arms were too small to walk on. It's well muscled jaw and unique skull shape has many palaeontologists theorising it was a basal Ceratopsian, but the advanced osteoderm armour/spikes on the neck, shoulders and down the back concluded it was a Thyreophoran. A very unique dinosaur indeed.

Thanks for Reading

Hi, if you haven't read any of my stuff before, thanks for reading this. This is sort of my dive into amateur journalism. This is not a dinosaur blog, but I do talk about dinosaurs a lot, so feel free to check out the links in my Pinned Post.

(Type specimen of Bashanosaurus primitivus, from Dai et al., 2022)

Meaning of name: Bashanosaurus = Bashan [ancient name for Chongqing] lizard [in Greek]; primitivus = primitive [in Latin]

Age: Middle Jurassic (Bajocian)

Where found: Shaximiao Formation, Chongqing, China

How much is known: Partial skeletons of two individuals (including vertebrae, limb bones, plates, and spikes) and an isolated back vertebra from a third.

Notes: Bashanosaurus was a stegosaur, and along with Isaberrysaura from Argentina, it is one of the oldest stegosaurs known. As might be expected of an early stegosaur, it retained some similarities with older non-stegosaurian armored dinosaurs, such as Scelidosaurus. Bashanosaurus was relatively small for a stegosaur, probably around 2.8 m long. However, it is difficult to assess whether the known specimens represent adult individuals.

Bashanosaurus

Bashanosaurus — рід птахотазових динозаврів з клади стегозаврів (Stegosauria), відомий по викопним решткам із середньоюрських відкладень формації Шаксимяо (Shaximiao Formation) у Китаї. Включає в себе єдиний вид – Bashanosaurus primitivus. Може бути найдавнішим відомим науці стегозавром, оскільки рештки іншого претендента на цей статус, Adratiklit з Марокко, мають приблизно такий же вік, або навіть дещо молодші.

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