AUTHOR'S NOTE: Apologies for the late release of this article. Between my day job, moving into new lodgings, and preparing my first book for the publishers, I didn't have time to complete this article before the end of 2019.
In light of the spread of coronavirus and the fact that millions of people are now spending most of their days at home, I thought I'd finally complete and share this article in the hope that it will offer a clear and pleasant distraction in a time of great uncertainty.
(Morocco, 168 million BCE -- "before the common era"; same dating as "BC")
Other than Stegosaurus, stegosaurs rarely attract much public or even scientific attention. These plated and armored herbivores lived from the middle of the Jurassic Period (201 to 145 million BCE) to the Early Cretaceous Period (145 to 100 million BCE) and their fossilized bones and tracks are known from every continent. But while scores of new ceratopsians, sauropods, and feathered dinosaurs have been described (i.e. named and announced to the general public) in the past twenty years, only five new confirmed stegosaurs have been named since 2001.
Discovered in Morocco's Atlas Mountains, Adratiklit ("mountain lizard" in Berber) is the fifth of these new stegosaurs and oldest one known to science. It is also the only third to be discovered in Africa and the first one to be described from North Africa (the other two African stegosaurs, Kentrosaurus and Paranthodon, are from Tanzania and South Africa, respectively).
As of writing, Adratiklit's remains aren't complete enough to show us how its plates were shaped or how many spikes sprouted from its tail. Enough of the skeleton has been unearthed, though, to determine that this animal was more closely related to Dacentrurus and Miragaia -- two later Jurassic stegosaurs from England and Portugal, respectively -- than either of the other two African stegosaurs. This herbivore also seems to have had more in common with these European stegosaurs than with Huayangosaurus, the second-oldest confirmed stegosaur and the most primitive member of the group.
If accurate, then Adratiklit may have shared its European relatives' exceptionally long neck and multi-spiked tail (in contrast to Stegosaurus, which had a proportionately short neck and only four tail spikes) and lacked teeth in the front of its jaws (like most later stegosaurs and unlike Huayangosaurus, whose beak was lined with peg-like front teeth).
More importantly, Adratiklit hails from a time and place in the fossil record that few other dinosaurs are known from and demonstrates that the stegosaurs were already diversifying by the middle of the Jurassic Period.
(Argentina, 140-134 million BCE)
A serious contender for the strangest dinosaur of all time, Bajadasaurus ("lizard from the Bajada [Colorada]") lived in Argentina about 30 million years after Adratiklit roamed Morocco.
Like Brachiosaurus and Diplodocus, this dinosaur was a sauropod, and while the sheer size of these long-necked, multi-ton herbivores would have discouraged most predators, Bajadasaurus may have relied on another defense. The scientists who discovered the dinosaur not only found to a complete partial skull (an impressive discovery in itself since sauropods skulls are so fragile that they're often destroyed during fossilization), but also a single neck vertebrae. Instead a single blunt spine leaning backward, the Bajadasaurus vertebra had a pair of pointed spines, each nearly two feet long and curving forwards.
Based on Amargasaurus, a later Argentinian sauropod with a double row of backward-curving spines running down its neck, Bajadasaurus' discoverers believe that similar spines sprouting from its other neck vertebrae. The spines themselves were rather fragile, but if covered in a keratinous sheath like the horns of cattle and other horned mammals, these structures would have been an impressive defense (or least deterrent) against predators.
Both Amargasaurus and Bajadasaurus were members of the dicraeosaurids ("bifurcated lizards"), a family of sauropods distantly related to Diplodocus. These herbivores were small by sauropod standards (generally less than fifty feet long and weighing only a few tons) and developed comparatively short necks, confining their diet to low-lying plants like ferns and cycads. Yet all dicraeosaurids shared high vertebral spines along the neck and back, an adaptation that would have exaggerated their size from a distance. The neck spines of Amargasaurus and Bajadasaurus would have amplified this effect, potentially deterring local predators or attracting individuals of the same species during the breeding season.
Like Adratiklit, Bajadasaurus also sheds light on a murky chapter in the history of the dinosaurs, in this case the first fifteen million years of the Cretaceous Period.
Moros and Suskityrannus
(Utah and New Mexico, 96 and 92 million BCE)
Over the past twenty-odd years, fossil discoveries in Asia, Europe, and North America have slowly revealed the origins of the tyrannosaurs: They emerged around that same time that Adratiklit did, and from the mid-Jurassic to the mid-Cretaceous, they were lower-to-middle-tier predators rarely more than ten feet long and usually dwarfed by larger predators in their habitat. It was only during the last fifteen million years of the Cretaceous (81-66 million BCE) that tyrannosaurs became the largest predatory dinosaurs in North America, climaxing with T. rex during the last two million of those years.
Announced to the general public in February of 2019, the wolf-sized Moros ("impending doom" in Latin) roamed Utah about thirty million years before T. rex. Suskityrannus ("coyote tyrant", a combination of Zuni and ancient Greek) was unveiled in May and inhabited western New Mexico a few million years after Moros. Together, they are the two oldest Cretaceous tyrannosaurs known from North America and, in the words of Moros' discoverer paleontologist Lindsey Zanno, they offer glimpses of the tyrannosaurs' transition "from wallflower to prom king".
Neither of these tyrannosaurs is yet known from adult individuals: Though nearly full-grown, the original specimen of Moros is estimated to have been about six years old and weighed about 170 lbs when it died, while the more complete of the two Suskityrannus individuals was about half that age and size. Yet as the paleontologists that named these tyrannosaurs point out, both already had the hallmarks of their later, larger descendants.
Zanno characterized Moros as "exceptionally fast and lightweight" and that it "could easily have run down prey while avoiding confrontation with the predators of the day". Paleontologist Stephen Brusatte, meanwhile, stated that Suskityrannus "[showed] that tyrannosaurs developed many of their signature features like a muscular skull, broad mouth, and shock-absorbing foot when they were still small, maybe as adaptations for living in the shadows."
While probably similar in size and shape upon reaching adulthood, Moros and Suskityrannus inhabited different worlds: Moros' fossils hail from the highest and youngest layer of Utah's Cedar Mountain Formation. In life, it was dwarfed not only by larger theropods (probably along the lines of the earlier Acrocanthosaurus or Siats), but also by the main herbivores of its habitat -- long-necked sauropods as big as whales and spiky-thumbed iguanodonts the size of rhinos.
Suskityrannus, meanwhile, was discovered the slightly younger Moreno Hill Formation and it inhabited a niche closer that those of later tyrannosaurs to that of Moros. It might still not have been the region's largest predator but Suskityrannus was close in size to its main large herbivores, the cow-sized ceratopsian Zuniceratops and the horse-sized hadrosaur ancestor Jeyawati. While the large herbivores contemporary with Moros became scarce in North America as the Cretaceous progressed, ceratopsians and hadrosaurs became only more common, growing progressively larger and more specialized alongside the tyrannosaurs.
(Brazil, 90 million BCE)
If stegosaurs receive surprisingly little press among dinosaurs, the noasaurs ("Northern Argentinian lizards") usually get none at all. These dinosaurs were bipedal theropods like the tyrannosaurs and emerged around the same time. But while tyrannosaurs are known mostly from the northern continents, reached huge sizes at the end of the Cretaceous, and were exclusively carnivorous, noasaurs are known mostly from South America and Africa, were rarely more than six feet long, and ranged from toothless, ostrich-like herbivores to the snaggled-toothed, lower-tier predators that may have specialized in hunting fish.
Vespersaurus ("evening lizard") was closer to the latter kind of noasaur than the former, though fish may have been rare in its environment. It measured between three and five feet long and inhabited southern Brazil during the mid-Cretaceous, when the region was a vast desert. Instead of gutting small fish, Vespersaurus' jaws may have snatched lizards and other small animals that inhabited the same harsh environment.
More important than Vespersaurus' jaws, though, its three toes: Only the middle and longest of the three touched the ground and bore most of the animals weight as it walked. Until 2019, this was an adaptation not seen in feet of non-avian dinosaurs but paralleled in modern desert-dwelling birds: Both roadrunners and ostriches have feet in which two elongated toes bear the bird's weight as it stands or walks and helps them run fast across uneven terrain (though roadrunners have the extra two digits that most bird feet have while ostriches have lost them altogether).
And, like both Adratiklit and Bajadasaurus, Vespersaurus' fossils shed light on one of the more obscure times and places in dinosaur history: This small predator is the first dinosaur described from its bone bed and hails from a country better known for the fossils of its pterosaurs than those of its dinosaurs.
"It is a rich but little explored area that would surely bring great news to the world of paleontology," says Neurides de Oliveira Martins, one of the paleontologists involved in Vespersaurus' discovery and naming.
Ambopteryx- A scansoriopterygid theropod from mid-Jurassic China and the second known one with bat-like wings (after Yi, described in 2015).
Aquilarhinus- Primitive hadrosaur from Late Cretaceous Texas with a distinctive, shovel-like bill.
Asfaltovenator- Early large theropod from mid-Jurassic Argentina with evolutionary ties to both Allosaurus and Megalosaurus, two later Jurassic theropods thought to be distantly related to each other.
Fostoria- Medium-sized iguanodont preserved in opal from mid-Cretaceous Australia.
Hesperornithoides- An extremely early troodontid from Late Jurassic Wyoming.
Imperobator- The large bird-like theropod from Late Cretaceous Antarctica and the fifth non-avian dinosaur described from the continent.
Kamuysaurus- Saurolophine hadrosaur from Late Cretaceous Japan and one of the most complete discovered in this country so far. Until 2019, it was informally called "Mukawaryu" ("dragon from Mukawaryu").
Mnyamawamtuka- A comparatively small titanosaur from mid-Cretaceous Tanzania with heart-shaped tail vertebrae.
Notatesseraeraptor- Early theropod with affinities to both coelophysids and dilophosaurs from Late Triassic Switzerland.
Phuwiangvenator- A megaraptoran from Early Cretaceous Thailand. It is the oldest-known megaraptoran to date.
Siamraptor- Mid-sized carcharodontosaur from Early Cretaceous Thailand.
Vallibonavenatrix- Low-spined spinosaur from Early Cretaceous Spain.
Wamweracaudia- A mamenchisaurid sauropod from Late Jurassic Tanzania and the first mamenchisaurid known from outside of China.
Ngwevu- A short-snouted sauropodomorph from Early Jurassic South Africa, previously regarded as a specimen of Massospondylus.
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https://www.museumfuernaturkunde.berlin/en/presse/pressemitteilungen/discovery-new-dinosaur-genus (news article about Wamweracaudia on the Museum für Naturkunde website)
https://nhmu.utah.edu/blog/2019/03/11/tiny-tyrant-stalked-utah-t-rex (Blog post about Moros on the Natural History Museum of Utah's website by Riley Black)