#lavocatisaurus

Bajadasaurus pronuspinax

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

Name meaning: Downhill reptile with forward-bent spines

Time: 145 to 132.9 million years ago (Berriasian to Valanginian stages of the Early Cretaceous)

Location: Bajada Colorado Formation, Argentina

Initially published in 2019, Bajadasaurus became pretty much instantly popular because of its bizarre, forward-pointing double mohawk of spines on its neck. The only other dinosaur like it is Amargasaurus, a dicraeosaurid sauropod that was thought to be entirely unique in its neck spines. The initial hypothesis in the paper describing Bajadasaurus was that the front-facing spines would have been passive defense structures that could impale predators that tried to make a charge at the otherwise-vulnerable head. However, a recent paper on Amargasaurus in 2022 has potentially turned that idea on its spiny head, suggesting that based on the interior bone histology of the spines as well as the outer texture Amargasaurus’ multi-pronged neck actually supported some sort of fleshy sail instead! The study didn’t include Bajadasaurus in its analysis, but based on its similarities to Amargasaurus it’s reasonable to assume that this forward-swept spine was also more of a sail, turning a deadly defensive fortification into a showy display feature!

Lavocatisaurus agiroensis

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

Name meaning: Lavocat’s reptile from Agrio del Medio (in honour of French palaeontologist René Lavocat)

Time: ~120 to 113 million years ago (Aptian to Albian stages of the Early Cretaceous)

Location: Rayoso Formation, Argentina

Lavocatisaurus was a genus of rebbachisaurid, the clade of diplodocoids that saw everyone else doing the whole neck thing and were like “actually what if I didn’t”. We actually have a complete series of neck vertebrae from Lavocatisaurus, and while its neck wasn’t as short as some of its relatives it’s clear that reaching tall branches wasn’t the priority here. The skull is wide and flat at the front, so it may have been a low browser, preferring to take in as wide a selection of plants as possible. The well-preserved skull also makes obvious a weird and unique feature of Lavocatisaurus; it had a big extra hole in its skull! Some sauropod skulls have a small hole in the side of the snout called the preantorbital fenestra, and while it usually looks like a pinhole in species that have it Lavocatisaurus has a bizarrely huge one. It’s not super clear what the purpose of this was, but it might have been to further lighten the skull.

Factfiles:

Lavocatisaurus agrioensis

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

Name meaning: Lavocat’s reptile from Agrio del Medio (in honour of French palaeontologist René Lavocat)

Time: ~120 to 113 million years ago (Aptian to Albian stages of the Early Cretaceous)

Location: Rayoso Formation, Argentina

Lavocatisaurus was a genus of rebbachisaurid, the clade of diplodocoids that saw everyone else doing the whole neck thing and were like “actually what if I didn’t”. We actually have a complete series of neck vertebrae from Lavocatisaurus, and while its neck wasn’t as short as some of its relatives it’s clear that reaching tall branches wasn’t the priority here. The skull is wide and flat at the front, so it may have been a low browser, preferring to take in as wide a selection of plants as possible. The well-preserved skull also makes obvious a weird and unique feature of Lavocatisaurus; it had a big extra hole in its skull! Some sauropod skulls have a small hole in the side of the snout called the preantorbital fenestra, and while it usually looks like a pinhole in species that have it Lavocatisaurus has a bizarrely huge one. It’s not super clear what the purpose of this was, but it might have been to further lighten the skull.

Ruixinia zhangi

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

Name Meaning: Ruixin Zhang’s Titanosauriform 

Time: 125 million years ago (Barremian stage of the Early Cretaceous)

Location: Yixian Formation (unknown bed), Liaoning, China 

Ruixinia is a recently named genus of almost-titanosaur, and it was named so hastily that it wasn’t even fully excavated and prepared prior to publication! It is known from the most complete series of tail vertebrae of any titanosauriform in its region, and the last few were fused together like those of Mamenchisaurus or Shunosaurus, except in Ruixinia they formed a rodlike structure rather than the features seen in those other taxa. It also had a neck longer than four meters with similar numbers of vertebrae to other almost-titanosaurs known from the region. Overall, Ruixinia was about 12 meters long, making it mid sized (for a sauropod). It may or may not have been a titanosaur - it had a weird number of similarities to Mamenchisaurs, but that’s a whole other conversation, and it’s possible it could have fallen outside the group of titanosaurs proper. More research is needed to better understand its position in the titanosaur family tree. Living in the frequently disrupted environment of the Yixian, Ruixinia shared its habitat with a wide variety of other dinosaurs, though without information as to the specific part of the ecosystem it came from, we cannot be sure which specific ones.