An Excerpt From An In-Prep Dinosaur Book (Patreon)

If you've been following me on Twitter, you might have seen me mention an in-prep dinosaur book I'm working on. I haven't said anything about it, so this is an exclusive. The book is provisionally titled Dinopedia (not to be confused with Don Lessem's book of the same name, which I was consultant on) and belongs to a new Princeton University Press series, the only part of which I'm familiar with is Lawrence Millman's Fungipedia: A Brief Compendium of Mushroom Lore. I've become a real fan of this book and love Millman's personal, anecdote-based way of discussing the many topics covered in the work; I also really like the focus on folklore and the pop culture take on fungi.  You can read more about the book here, I really recommend it: https://press.princeton.edu/books/hardcover/9780691194721/fungipedia 

There isn't really 'lore', 'folklore' or whatever on non-bird dinosaurs, but there is of course a vast area which we might term the 'pop-culture interface'... dinosaurs in art, cinema, popular books and so on. It's this I've focused on in the book - I haven't yet figured out a focused way to promote the angle I'm taking, but I'm essentially thinking of it as 'a dinonerd's guide to dinonerdom', and I feel that I know my audience ... no-one else is really doing this. The book has to be finished this year, so should appear in print in 2021.

Anyway - the book is encyclopedic in format and features as many separate entries as I can get in within the wordcount. For now, I'm sharing here - exclusively - an entry I finished over the weekend. The illustrations are added to make the text more interesting and won't be included in the final book. There will be illustrations in the final book (my drawings, new ones) but I haven't done them yet.

Therizinosaurs

Properly Therizinosauroidea or Therizinosauria, a mostly Cretaceous coelurosaurian group so unusual that they’ve been described as dinosaurs designed by committee. Today we know that therizinosaurs are maniraptorans, and likely one of the oldest lineages within the group. We also know – thanks to Beipiaosaurus from Liaoning – that they were extensively feathered (as expected for maniraptorans), perhaps with a shaggy plumage mostly formed of hair-like filaments. Spine-like structures were also scattered throughout the plumage. The small, leaf-shaped teeth and beaked tips to the jaws look suited for a diet of leaves, though it might be that fungi, insects and fruit were eaten too. Therizinosaur proportions are unusual: they mostly have a long, robust neck, broad pelvis, stocky hindlimbs with broad feet, and a short tail. These features indicate that they maintained a more erect posture than typical for dinosaurs. They were likely high-browsing herbivores which used their large hand claws in manipulating foliage, as well as in self-defence and perhaps display. 

Caption: Maleev's original, 1954 take on Therizinosaurus as a giant 'turtle lizard'.

This is our modern take on these animals. But it’s taken decades to get to this point, and the story describing how we got here is pretty interesting. Things began in the 1950s when Russian palaeontologist Evgenii Maleev described a Late Cretaceous reptile known from ribs, bones from the foot and some massively long hand claws, the longest of which are 70cm long. He named it Therizinosaurus cheloniformis, meaning ‘turtle-like scythe lizard’, and thought it was an aquatic, turtle-like animal. By 1970, Anatole Rozhdestvenskii – another Russian palaeontologist – had realised that Therizinosaurus was a theropod, perhaps an ant-eating form that used those giant claws to break open insect nests. This ant-eating idea continued to raise its proverbial head over the years but isn’t consistent with the bulk of data (among other things, specialised ant-eaters are way smaller than therizinosaurs and have a suite of cranial features not seen in this group).

Caption: the holotype Erlikosaurus skull, which I got to examine and handle when Perle Altengerel visited the UK in 2007 (those are my hands).

We then move to 1980, when Rinchen Barsbold and Altangerel Perle described a group of Late Cretaceous Mongolian dinosaurs which they called segnosaurs. The group included Erlikosaurus – named for a complete skull – and Segnosaurus, based on a lower jaw, limb bones, a pelvis and some vertebrae. Barsbold and Perle thought that the beaks, small teeth and broad feet of segnosaurs showed that they were amphibious predators of fish. By 1982, Perle argued that Therizinosaurus was a member of this segnosaur group, a consequence being that Therizinosauroidea – rather than Segnosauria – is the oldest name for this group.

Caption: this montage is from the 2013 All Your Yesterdays. I'll be doing a new version for Dinopedia.

The broad feet of therizinosaurs are unusual relative to those of other theropods and it was this fact above all others which, in 1984, led Greg Paul to contest the theropod hypothesis otherwise favoured at this point. Paul argued that therizinosaurs had much in common with sauropodomorphs like Plateosaurus, yet were ornithischian-like in jaw and ankle anatomy. He therefore proposed that therizinosaurs were late-surviving relicts of the sauropodomorph-ornithischian transition…. which only makes sense if you accept the Phytodinosauria model of dinosaur affinities. This idea didn’t win adherents and, furthermore, ran counter to the consensus emerging on dinosaur phylogeny at the time. Paul’s idea wasn’t influential, but his take on therizinosaur anatomy – it basically had them as modified plateosaurs, with beaked jaws and massive hand claws – appeared in several books of the time and was the ‘go to’ look on these animals for a few years.

Later in the 1980s, a few authors proposed sauropodomorph affinities for therizinosaurs. It was the theropod idea, however, which would win out. In their 1993 description of the Chinese therizinosaur Alxasaurus, Dale Russell and Zhi-Ming Dong supported a position for these dinosaurs deep within Theropoda, and – in a surprise move – close to maniraptorans. A maniraptoran position for therizinosaurs was supported by later studies and bolstered by later finds, among them Beipiaosaurus (published in 1999) and the more archaic Falcarius from the Early Cretaceous of Utah (published in 2005). Falcarius is especially interesting because it’s proportioned more like a standard coelurosaur than other therizinosaurs.

Russell might well have ‘got therizinosaurs right’ when it comes to phylogeny (approximately, at least), but another interesting diversion in thoughts on these dinosaurs came from his 1993 attempt to reconstruct therizinosaur life appearance and behaviour. Working with Donald Russell and artist Ely Kish, Russell argued that therizinosaurs were convergent with chalicotheres, a group of clawed, long-armed herbivorous mammals. By combining the skeletal parts known from various therizinosaurs and making extrapolations to account for size, the team proposed that Therizinosaurus had a massive, broad pelvis, a short body, short, stocky hindlimbs and a long, robust neck. They described how it was likely adapted for sitting while reaching into foliage with the neck, and that its hand claws were used as props. An interesting interpretation of therizinosaur appearance and biology, to be sure, but one best considered only roughly correct.

Little direct evidence exists on therizinosaur biology. Embryos and eggs are known, as are a few footprints. Alas, none of these things tell us much beyond what we’d guess already. A 2013 study of bite strength in Erlikosaurus concluded that the bite was weak and that jaw action mostly involved cropping and leaf-stripping more than chewing.

Caption: most recent phylogenetic studies find therizinosaurs to be one of the earliest-diverging maniraptoran lineages. This cladogram was produced for the textbook.

If therizinosaurs are one of the oldest lineages within Maniraptora, it follows that they must have been in existence from the Middle Jurassic at least (since we know of early members of the bird lineage which date to that time). As of the time of writing, Jurassic therizinosaurs are all but unknown. What might be an Early Jurassic therizinosaur is known: namely, Eshanosaurus from southwest China, based only on an incomplete lower jaw. The identity of this specimen is controversial and some experts have argued that it’s a sauropodomorph. If it is a therizinosaur, it shows that several major events in maniraptoran and coelurosaurian evolution had occurred during the first half of the Jurassic, which is earlier than otherwise thought. 

See also Coelurosauria, Maniraptora, Phytodinosauria