Roundup on Thunderstorm Ridge: keeping up with Petrified Forest NP

Last week's publication of the stem-caecilian Funcusvermis reminded me that I really ought to show off Petrified Forest National Park (PEFO) more often. Since the last spotlight, on the "biloph" trilophosaur Trilophosaurus phasmalophus in spring 2020, four more species of Triassic vertebrates have been described from fossils found in the park, to go along with a bushel of reports on anatomy, identifications of rare forms, vertebrate trace fossils, stratigraphy and geochronology, and other topics, to say nothing of conference abstracts and papers that mention PEFO fossils in wider contexts. (SVP conferences are usually good for a handful of PEFO topics.) Because we're talking the Late Triassic, the taxonomic diversity is wide. There's a little bit of almost everything.*

*Interestingly enough, that includes Paleozoic marine invertebrates: reworked fossiliferous cobbles of the Permian Kaibab Formation have been found in the park's Chinle Formation outcrops, particularly the Sonsela Member. There are also limited Neogene deposits with Hemphillian vertebrates.

Classically, as with most places that have produced vertebrate fossils for more than a century, big singular fossils were long the focus (e.g., skulls of phytosaurs). Although there is still interest in those kinds of fossils, increasingly study has focused on bonebeds and microvertebrates, with much more care given to stratigraphic placement. It turns out that PEFO holds a whole weird and wonderful landscape of everything that gave it a go in the Late Triassic, before a couple of groups of archosaurs took over land management for the rest of the Mesozoic. (And if you don't like vertebrates, the plants are just about as wild in their own way, and there are freshwater and terrestrial invertebrates as well.) It practically begs for a book like those on Florissant, Fossil Lake, the Morrison, and the White River Badlands.

Here's a strat column to help keep the geologic units straight, borrowed from the park website.

With all of that in mind, here are a few quick hits from the past few years of research at PEFO:

On the concept of "100 Dinosaurs from A to Z"

Back in the 1980s, there were books aimed at the kid market that promised 100 (or 101) alphabetical dinosaurs. This was about the last time in dinosaurological history when a book with that premise could still boast a fairly comprehensive selection of reasonably well-known dinosaurs. To be honest, it's a little unclear in hindsight why books with 100 dinosaurs would be compelling when there were competing books on the market that gave the reader more dinosaurs and were not significantly more difficult reading. Maybe they were seen as more kid-friendly, but then again, someone who's up for "100 Dinosaurs" is probably going to age out of it and go for "A Field Guide To Dinosaurs" pretty quickly. The market seemed to agree, because the books turned into just "Dinosaurs A-Z" by the end of the decade and then disappeared.

Most of them were not actually complete alphabets, simply because the dinosaur alphabet wasn't completed until 1983 (Quaesitosaurus and Xiaosaurus), and for several other letters, the choices were pretty dismal. F would always be Fabrosaurus, which may well have helped it hang around after taxonomic obsolescence by lodging in the brains of impressionable children. (Otherwise there was Fulgurotherium, but it was poorly known, space was limited, and Muttaburrasaurus and perhaps Rhoetosaurus were already there to represent Australia.) U would be "Ultrasaurus", because it was huge and in the news and the only other option was Unquillosaurus. J? It's a choice between the two immortals Jaxartosaurus or Jubbulpuria, or just skipping it. (In related news, I've had a soft spot for Jubbulpuria for decades. Us "J"s have to stick together!)

With a minimal knowledge of 1980s dinosaurs, it's easy enough to figure out most of the genera that would be in these books.

• First you have the superstars: Tyrannosaurus, Triceratops, Stegosaurus, Apatosaurus (with obligatory comments about Brontosaurus). Today, that inner ring would include Spinosaurus and Velociraptor (even if Deinonychus did the heavy lifting), and Brontosaurus would swap for Apatosaurus.
  
• Then there's the B-listers, names like Allosaurus, Parasaurolophus, Styracosaurus, Brachiosaurus, and Iguanodon, and lots of entries from the Morrison and Late Cretaceous of North America.
• Then you descend into a grab-bag of C-listers, geographic and stratigraphic tokens and oddities, and flavors-of-the-month, some of which would go on to better things, while others didn't. (Yaverlandia! "Ultrasaurus"!)
• Finally, there's Geranosaurus and Altispinax. (Altispinax never had it so good as it did in the 1980s.)
  

Today, with more than 1600 formally described species of non-avian dinosaur that a reasonable person (i.e., me) would recognize (with some sleeping dubious dogs being left to lie to avoid inconvenient issues of priority), promising "100 dinosaurs" is not impressive. At the moment, one could write "100 dinosaur" books just on specific countries. Argentina, China, Mongolia, the United Kingdom, and the United States of America all qualify (granted, the UK edition would have a distinctly scrappy and Victorian flavor), with Canada almost there. In fact, with China and the US both well over 300 species, "100 dinosaur" books for them would be omitting more than 2 out of 3 species. Surprisingly, complete alphabets of dinosaurs from these prolific countries are not possible at this time; Argentina (missing "Y") and China (missing "U") get the closest, with the U.S. a distant third with no "Q", "W", or "X".

It is also possible to have entire "100" books on certain groups. Maniraptors? No sweat, at just over 200 (which gives some wiggle room for reclassification of entire lineages). Old-timey prosauropods? Yep, they just make it. Titanosaurs? Room to spare (as we observed in great detail). Ankylosaurs just make it, too (you can throw in stegosaurs for more thyreophoran charm and bump some of the underachievers). Ceratopsians cross easily, and while hadrosaurids by themselves don't quite make it, going down to Hadrosauromorpha to pick up traditional basal hadrosaurs also crosses the threshold. Complete alphabets are still a problem, though. (You can do it with titanosaurs if you make Wintonotitan an honorary member.) Why someone should *want* to write a book on 100 dinosaurs of a country or a specific group, I'm not sure (if you were going to go to the trouble, you might as well cover *all* of them and not just an arbitrary number), but someone certainly *could*.

When I started drafting this post, I thought about coming up with my own list of 100 dinosaurs, for the fun of it. Then I realized I would basically pick 100 dinosaurs I remembered as important from the 1980s. While classics are classics for a reason, it isn't any fun to come up with the same old list that any of us could have picked. Nor was the idea of consciously selecting some kind of quota (geographic, stratigraphic, taxonomic, year of description, etc.). So, I decided to leave it up to fate. I copied the genera and species from The Compact Thescelosaurus, then took some pity and eliminated every nomen dubium, which removed 315 entries. (Before I did this, I tried it once and got all three entries for Cionodon. Yay?) The remaining 1,313 were run through the Google Sheets random sort function and the first 100+ entries were grabbed to produce the following lightly curated list (the entries were at the species level but the books always worked at the genus level, so I scratched multiple entries from the same genera). If you don't like Dravidosaurus or would rather have 101, the genus on deck is Tyrannotitan. If both conditions apply, then Rugocaudia is up next.

Behold, 100 Random Dinosaurs From A To Z:

Acristavus	Dracovenator	Leptorhynchos	Scutellosaurus
Acrotholus	Dravidosaurus	Lirainosaurus	Shidaisaurus
Adamantisaurus	Ekrixinatosaurus	Lufengosaurus	Similicaudipteyx
Adasaurus	Eomamenchisaurus	"Mamenchisaurus" sinocanadorum	Soriatitan
Adelolophus	Epachthosaurus	Mendozasaurus	Spinosaurus
Afrovenator	Eucnemesaurus	Miragaia	Stenopelix
Albertonykus	Euhelopus	Monolophosaurus	"Syntarsus" kayentakatae
Alioramus	Euoplocephalus	Nambalia	Tendaguria
Altirhinus	Europasaurus	Nanosaurus	Timimus
Anhuilong	Ferganocephale	Nanuqsaurus	Torosaurus
Antetonitrus	Graciliceratops	Neuquenraptor	Torvosaurus
Aviatyrannis	Hesperornithoides	Nigersaurus	Tototlmimus
Bahariasaurus	Hypselospinus	Notatesseraeraptor	Tsintaosaurus
Beipiaognathus	Hypsilophodon	Ouranosaurus	Unenlagia
Caenagnathasia	Iguanacolossus	Patagonykus	Utahceratops
Camarillasaurus	Incisivosaurus	Patagosaurus	Valdosaurus
Camposaurus	Isanosaurus	Piveteausaurus	Vouivria
Camptosaurus	Iyuku	Plateosaurus	Wuerhosaurus
Carcharodontosaurus	Jeyawati	Plesiohadros	Xenoceratops
Ceratosaurus	Jingshanosaurus	Polacanthus	Xiaosaurus
Chaoyangsaurus	Juravenator	Regaliceratops	Yandusaurus
Chirostenotes	Kaatedocus	Ruehleia	Yangchuanosaurus
Citipes	Klamelisaurus	Saichania	Yehuecauhceratops
Dongbeititan	Leaellynasaura	Saltriovenator	Yixianosaurus
Dracoraptor	Leptoceratops	Sanxiasaurus	Zhongjianosaurus

You know what? I feel pretty good about this list. It's got an interesting spread in time, space, lineage, and fame. It gets 25 out of 26 letters, too (no Q, which didn't show up until 257 with the much-beloved Qinlingosaurus, but that's randomness for you).