TROODON NO MORE?
I'm clearly behind the times, because it look like Troodon, a well known and beloved genus of theropod, has been declared an invalid genus. And this was deduced back in 2017, apparently! Still, it only seems to be making its way into public consciousness now. While it's a stinger, it's not really too surprising. Troodon has been a mess since it was first named in 1856, based on nothing but a serrated tooth. Originally classified as a lizard, then a megalosaurid (like almost every predatory dinosaur at one time or another), in 1924 it was considered that Troodon was a carnivorous pachycephalosaurid. I'm old enough to remember books still calling it a unique meat-eating ornithischian, even though this was pretty much thrown out by 1945 (books on dinosaurs tended to take a long time to bring themselves up to date). Of course, now omnivorous ornithischians are accepted in the early development of the order.
Stenonychosaurus was a quite well known theropod in the 80s and 90s, before being considered a junior synonym of Troodon (the same thing happened with the family Saurornithoididae and Troodontidae). In 2017 it was suggested that the original specimen of Troodon being just a tooth, was undiagnostic, and referred all species back to Stenonychosaurus, although since, some have been pulled to a new genus, Latenivenatrix. This has been challenged, though, by others stating that Troodon formosus, the type specimen, should be the valid name, considering that Stenonychosaurus went unused for so many years. In either case, it seems that the family Troodontidae, and even the subfamily Troodontinae, are going to remain the favoured names.
Edmontosaurus (formerly also Anatosaurus and Anatotitan) is one of the best-known ornithopods from the late Cretaceous, known from two species: the earlier E. regalis and the end-of-Cretaceous E. annectens. Now, an international team has concluded that the Alaskan genus Ugrunaaluk is a third species, E. kuukpikensis. Edmontosaurus was already known to have ranged far and wide across North America, but this pushes it further north than generally supposed, into what was already the Arctic north. While it wasn't as cold in the Arctic in the late Cretaceous as it is now, it still shows that Edmontosaurus was able to adapt to a variety of different habitats. The Japanese genus Kamuysaurus is a closely-related hadrosaur that spread into Asia on similar latitudes, showing that Edmontosaurus and its closest relatives were a hugely successful group of herbivores and among the most common dinosaurs of the period. "The caribou of the Cretaceous" at SciTech Daily
Two transitional genera of chasmosaurine ceratopsids have been identified from fossils in New Mexico, bringing light to the evolution of this branch of late Cretaceous dinosaur diversity. The two new genera show a clear pattern of development from the well-known Pentaceratops known from 75.3 million years ago, which had notably tall frill with a distinct, deep notch in its centre. An as-yet-unnamed example from 100,000 years later shows the frill notch deepening, while 100,000 years later still the new Navajoceratops sees the frill close up over the notch. By 74.6 mya, Terminocavus sees the frill begin to close up fully, and it finally heals over in Anchiceratops at 71.5 mya.
The precision of dating the genera is remarkable and illustrates a clear lineage. I wonder, though, it the new genera will be folded into Pentaceratops and Anchiceratops following further analysis. Sci-News.com
RUNNING IN CROCS
South Korea, the prehistoric tracker's heaven, has revealed an array of fossil tracks over the years, but a recent discovery has upturned established facts about crocodylomorphs. A group of tracks that clearly show bipedal locomotion - and were originally hypothesised to be from a large pterosaur - have been re-identified as the ichnogenus Batrachopus, a genus reserved for crocodile-related tracks. While there are many bipedal genera of croc relatives known from the fossil record, they all date back to the Triassic period, dying out in the mid-to-late Triassic in a major extinction event. Before this, crocodylomorphs were the dominant reptile group, with a huge variety of forms, but after the max extinction most were replaced in their niches by dinosaurs.
These tracks however date back 113 million years to the early Cretaceous, over 100 million years after we'd expect to find them. While the exact genus of croc that left the tracks isn't known, it shows that more diverse crocs survived in some regions far later than originally thought. Scientific American Nature (for more detail)
Back in 2011, Chilean scientists discovered a strange, ovoid fossil in the Antarctic rocks. It was nicknamed The Thing, but after years of analysis, it has been conclusively identified as the egg of a marine reptile. Julia Clarke of the University of Texas was the one who finally deduced it was a soft-shelled egg, of the type lain by lizards and snakes. At 11.4 by 7.9 inches it's absolutely huge and the first fossil egg to be unearthed in Antarctica. It's larger than any dinosaur egg save for that of the elephant bird, and even that was only slightly larger and much thicker-shelled. Clarke and her fellow palaeontologists has deduced it's egg of a mosasaur, a gigantic marine lizard, which explains the similarity to modern lizard and snake eggs, but it's far larger than nay soft-shelled egg ever seen before. It's also a surprise since it was hypothesised that mosasaurs gave birth to live young, an idea now thrown into doubt. The formations where the egg was found have previously turned up fossilised mosasaurs and plesiosaurs of various stages of development, so it seems it may have been a sort of marine reptile birthing ground and nursery.
The mosasaur egg has been given the taxonomic name Antarcticoolithis bradyi. Syfy Wire