Won't somebody please think of the champsosaurs?

Every so often, you may stumble across a crocodile-like thing lurking at the edge of your typical "two-page spread of all kinds of prehistoric critters" found in popular dinosaur books. If the book is of any quality, it includes a legend identifying the denizens, and the crocodile-like thing will be tagged "Champsosaurus" (if there isn't an error in the legend, of course). Unless you're intrigued by the name, or something else tickles your fancy, you'll probably continue along. There are a lot of crocodiles and crocodile-like things to keep track of, after all. What makes this one unusual?

Snails (and not-snails?)

I am posting this on May 24, 2015, which also happens to be Bob Dylan's 74th birthday. I considered titling this "A Hard Shell's A-Gonna Crawl", but even I have standards. "Shell" doesn't sound a bit like "rain".

Hash slabs

It is common for fossils in the wild to be found in beds of uncountable fragments, some identifiable to species, others only barely recognizable as fossils. These assemblages are often called "fossil hash", for obvious reasons. Although you can have conceivably make a hash out of just about any kind of body fossil and some kinds of more discrete trace fossils (it takes a bit of creativity here), the term is usually applied to invertebrate fossils. This leads to the phenomenon of "hash slabs" or "hash plates", a more portable portion of a bed of fossil hash. Hash slabs can make great display or educational pieces, and a good slab rewards continued study; you can never find everything the first time, and as you learn more, you are able to find more. [2017/05/08: why have I been using "hash slab" as opposed to "hash plate"? I don't know, except I seem to be the kind of person who just has to reinvent the wheel.]

Chilesaurus

Well, sic transit gloria mundi to Chilesaurus, I guess. A couple of days on top of the world, and then hustled off the stage for a tiny-maniraptoran-slash-Batman-cosplayer. Could be worse; at least it's Batman. 'Round here, though, I've never really had much interest in the origins of flight, early bird evolution, or so on, so nuts to Yi. Let's bring Chilesaurus back on the stage for a few more minutes.

The Ballad of Atlantosaurus

"Come gather 'round me, people, and listen to the tale

Of Marsh's first big sauropod, its bones now rest at Yale

Atlantosaurus montanus, from Morrison, C-O,

Known from but a sacrum, it was famous long ago"

The majestic Atlantosaurus, next to an elephant that strangely seems to have arrived via 19th century Photoshop. Shamelessly appropriated from Wikipedia, appropriated in turn from De Wereld vóór de schepping van den mensch, Nicolas Camille Flammarion (1886), original title "Le Monde avant la création de l’homme" (1886).

Concerning Brontosaurus

"And I've found/It's all up to what you value" — G. Harrison

By now, the paleontological world has weighed in on the news that Brontosaurus may in fact be a valid genus after all (Tschopp et al. 2015). If you've got some time (befitting its subject matter, it's not what you'd call a short document), the publication is well worth reading. Alternately, if you are strapped for time or just break out in hives when confronted with anatomical terminology, there are many shorter and less technical explorations of the topic. The concise description is that Tschopp et al. ran a number of diplodocid and putative diplodocid specimens through a phylogenetic analysis and then attempted to apply more objective measures than the classic eye test to determine which species should be in which genera. Among the results was the absorption of Dinheirosaurus by Supersaurus, which would make the latter the newest member of the exclusive Morrison–Lourinhã club; the designation of the new genus Galeamopus for longtime problem "Diplodocus" hayi; and the headline finding, that Brontosaurus was distinct from Apatosaurus.

Nautiloids: cephalopod overlords of the Ordovician

The cephalopods include a wide variety of tentacled friends. Today, they are represented by a few species of Nautilus and Allonautilus, and an array of squids, octopuses, and cuttlefish grouped under the subclass Coleoidea. Aside from the nautiloids, with their chambered shells, the modern cephalopods are not great for making fossils. The external shell fell out of cephalopod fashion coincidentally not long after the Cretaceous–Paleocene extinction event eliminated almost all of the practitioners, and although there is a history of internal shells in coleoids, those have been reduced or lost altogether by the smart modern coleoid. They still have more resistant beaks, feeding organs (the radula), and tentacle hooks, with some preservation potential, but otherwise you're looking at a lot of soft tissue. What this means is that most of the groups of cephalopods we see today have wimpy fossil records. On the other hand, we know of a great diversity of extinct shelled cephalopods, from three major lineages. The most famous are the ammonites, best known for coiled forms. They appeared by the middle Paleozoic and left the scene at the end of the Cretaceous. Going extinct at the same time, but apparently only extending back to the Triassic, are the belemnites, a subgroup of the coleoids represented by their bullet-shaped internal shells. Finally, there are abundant extinct forms, primarily from the Paleozoic, lumped together as "nautiloids". These early nautiloids had the run of things from the Ordovician to the Devonian, following which they declined until the lineage that includes modern nautilids was the last branch remaining unpruned at the end of the Mesozoic.