Therizinosauria

    Picture a dinosaur roughly four or five meters in length, with a stout, relatively short tail, a long, flexible neck, a short, beaked skull resembling that of a prosauropod, long arms bearing immense, sickle-like claws on their fingers, two short, stout legs with broad feet bearing four functional toes each, and a big belly given additional space from the backshifting of the pubis.  This is a rough sketch of a therizinosaurian. Is it any wonder they've been so hard to pin down taxonomically, when they display features from so many other groups plus so many unique characters of their own?  They are now known to be coelurosaurians, but it is uncertain as to which group they're closest.
    For many years, these animals were known as segnosaurids, but the discovery of Alxasaurus showed their close relationship to a bizarre theropod named Therizinosaurus, which is based on a partial arm with meter-long claws. In the past they have been classified as strange theropods, late-surviving prosauropods, descendants of a transition from prosauropods to ornithischians, and relatives of Sauropodomorpha. They were almost certainly herbivores, possibly equipped with "cheeks," although it was once suggested they ate fish. Sometimes they are classified (informally) with oviraptorosaurians, as "enigmosaurs".

<--Therizinosauria
      |--Falcarius
      `--+--Jianchangosaurus
           `--Therizinosauroidea
                |--Beipiaosaurus
                `--+--Alxasaurus
                     `--Therizinosauridae
                          |--Erlianosaurus
    
                     `--+--Neimongosaurus
                               `--+--Enigmosaurus
                                    |--Erlikosaurus
                                    |--Nanshuingosaurus
                                    |--Nothronychus
                                    |--Segnosaurus 
                                    |--Suzhousaurus
                                    `--Therizinosaurus

Therizinosauria:

Taxon or Taxa: Time/Place: Comments:
Falcarius utahensis Kirkland, Zanno, Sampson, Clark, and DeBlieux, 2005 ?Barremian (EK) of Utah From the Yellow Cat Member of the Cedar Mountain Formation comes this basalmost-known therizinosaurian. This is the one I saw at SVP in 2004 (then known as the "Crystal Geyser therizinosaurian") that convinced me that Eshanosaurus and Protognathosaurus could not be therizinosaurians (or at least not therizinosaurians as we know them). It is known from bonebed material representing possibly thousands of individuals. Unlike later therizinosaurians, this was a gracile animal, not too different in build from oviraptorosaurians; a cursory examination of the skeletal reconstruction puts me in mind of something like a long-tailed Ajancingenia. Its pubis did not point backward, and it lacked skull specializations like the downturning of the dentary tip or a lateral shelf on the dentary. In fact, this animal looks to have been in transition from a carnivorous diet to an herbivorous diet. Whatever its particular mode of feeding was, it must have been successful, given the amount of remains known for it.
Jianchangosaurus yixianensis Pu H., Kobayashi, Lü J., Xu L., Wu Y., Chang H., Zhang J., and Jia S., 2013 early Aptian (EK) of China Jianchangosaurus is based on most of a skeleton (mostly articulated) from a juvenile perhaps 2 m long. The pubis bones are close to vertical, the ilia are not flamboyantly weird like those of more derived therizinosaurians, and in general the skeleton looks not unlike a basal coelurosaurian/basal maniraptoran with a reasonable approximation of an Erlikosaurus skull (pointier in the snout, but after all I said reasonable). A small patch of feathers is preserved near the base of the neck. The lower jaw has a slight downcurve to the tip of the dentary, but the tip is unexpanded, and there are teeth almost to the tip. Unlike more derived therizinosaurians, the dentary teeth do not become larger nearer the tip, but they are inset from the outer surface of the jaw by a shelf, unlike more basal Falcarius. The premaxillae are toothless, giving at least a substantial upper "beak". The anatomy of the skull suggests herbivory, although the postcrania are not fully committed to the task, as in Falcarius. Like Beipiaosaurus, Jianchangosaurus was a Yixian Formation theropod, which probably fails to surprise you if you caught the species name already.

Therizinosauria i.s.:  Skull bones from the LK of Alberta appear to belong to a therizinosaurian.

Taxon or Taxa: Time/Place: Comments:
"Chilantaisaurus" zheziangensis (N.D.) Dong, 1979 Cenomanian-Turonian (LK) of China This is an indeterminate therizinosaurian based on partial hindlimb remains. It has sometimes been described as part of the holotype of Nanshiungosaurus brevispinus, but unless there's a location wrong, that is an unlikely possibility.
?Eshanosaurus deguchiianus Xu, Zhao, and Clark, 2001 ?Hettangian (?EJ) of China So what's this doing here, you who have read the entry for Falcarius ask. Well, it's here. Based on a partial jaw, this could be the earliest known therizinosaurian (and coelurosaurian), or it could be a prosauropod-type critter. From what is now known of basal therizinosaurians, I lean toward the latter interpretation, but then there we get a full redescription that puts it as a therizinosaur and certainly not a prosauropod, so go figure. Time-traveler? Misidentified rock unit?  Some heretofore-unsuspected early radiation that split from the therizinosaur line but isn't related to the later versions?  A member of some otherwise unknown group?
?Martharaptor greenriverensis Senter, Kirkland, and DeBlieux, 2012 ?early Aptian (EK) of Utah Martharaptor potentially represents a second Cedar Mountain Formation therizinosaur. Inconveniently, it did not follow in the footsteps of Falcarius, its predecessor (both geologically and scientifically), by being found in a massive bonebed. Instead, it is known from a somewhat scrappy partial postcranial skeleton; this circumstance, along with its basal characteristics, mean its taxonomic relationships aren't a lock.
"Nanshiungosaurus" bohlini Dong and Yu, 1997 ?Barremian-?Albian (EK) of China Originally referred to Nanshuingosaurus, this large therizinosaurian is currently difficult to place because of the paucity of therizinosaurian remains in general.

Therizinosauroidea:

Taxon or Taxa: Time/Place: Comments:
Beipiaosaurus inexpectus Xu, Tang, and Wang, 1999 early Aptian (EK) of China The largest feathered classic dinosaur known from the Yixian (and the largest animal known there period), this theropod is a basal therizinosaurian. It is known from a partial disarticulated skeleton including remains from most areas of the body.
Alxasaurus elesitaiensis Russell and Dong, 1993 Albian (EK) of Mongolia The discovery of several nearly complete postcranial skeletons pertaining to this beast allowed the "segnosaurids" to be classified better and showed that they were close relatives of Therizinosaurus.

Therizinosauridae:  Possible therizinosaurid embryos are known from the Santonian-Campanian (LK) of China.

Taxon or Taxa: Time/Place: Comments:
Enigmosaurus mongoliensis Barsbold and Perle, 1983 ?Santonian (LK) of Mongolia Based on a pelvis with the characteristic wideswept ilia and backwards-pointing pubis, this therizinosaurid may be synonymous with another (contemporaneous and pelvis-less Erlikosaurus has usually been the favorite speculation).
Erliansaurus bellamanus Xu, Zhang, Sereno, Zhao, Kuang, Han, and Tan, 2002 early Maastrichtian (LK) of China Based on a partial skeleton including a few verts, parts of both the hip and shoulder girdle, and much limb material, Erliansaurus is described as a transitional form between the basal and derived therizinosaurids. It is from the same area as Neimongosaurus, but is a different animal.
Erlikosaurus andrewsi Perle, 1980 ?Santonian (LK) of Mongolia This taxon is based on remains that include an excellently-preserved skull. Therizinosaurian eggs from China may have been laid by this dinosaur. The genus is fairly often misspelled as "Erlicosaurus".
Nanshiungosaurus brevispinus Dong, 1974 early Maastrichtian (LK) of China This genus was originally described as a small sauropod. It is based on a partial vertebral column and pelvis, which is opisthopubic (given that no sauropod has ever hinted at opisthopuby, this must have made for an interesting point of discussion in the original description).
Neimongosaurus yangi Zhang, Xu, Sereno, Kuang, and Tan, 2001 early Maastrichtian (LK) of China A long-necked therizinosaurian, Neimongosaurus preserves features like a short tail and long neck that could be shared with oviraptorosaurians. It is based on two partial skeletons, and includes both most of the vertebral column and limb bones from a single individual, a first for a therizinosaurian; only the skull and hands are conspicuous in their absence. The dentary is extremely deep, especially toward the front. It was described as more derived than Beipiaosaurus, but less derived than the therizinosaurids.
Nothronychus: Kirkland and Wolfe, 2001 N. mckinleyi (type) Kirkland and Wolfe, 2001 mid Turonian (LK) of New Mexico Based on about a third of a skeleton of a fairly large therizinosaurid (up to 6 m), including a partial skull, several cervicals, other verts, a good chunk of the fore and hindlimbs, and an ischium once thought to be the squamosal of Zuniceratops, Nothronychus is North America's first named therizinosaurian.
Second species N. graffami is known from a nearly complete skeleton except for the skull and neck. The specimen was found at some distance into what was a Cretaceous sea. Because it is more complete than N. mckinleyi, the holotype of this species has been used for skeletal restorations.
N. graffami Zanno, Gillette, Albright, and Titus, 2009 early Turonian (LK) of Utah
Segnosaurus galbinensis Perle, 1979 ?Santonian (LK) of Mongolia Segnosaurus was the first recognized member of Segnosauridae, remains one of the larger therizinosaurians, and displays many of their unique characteristics.
Suzhousaurus megatherioides Li D., Peng C., You H., Lamanna, Harris, Lacovata, and Zhang J., 2007 Albian of China A basal therizinosaurian described as more derived than Beipiaosaurus and Falcarius, but less derived than Alxasaurus, Suzhousaurus was an early large genus. It is known from a partial postcranial skeleton, and may be closest to Nothronychus. It may be a therizinosauroid.
Therizinosaurus cheloniformis Maleev, 1954 early Maastrichtian (LK) of Mongolia This taxon was originally thought to be a giant turtle. It has meter-long claws, and we can thus safely assume it was a large animal.

 

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