Alxasaurus

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title: "Alxasaurus" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["therizinosauria", "dinosaur-genera", "albian-dinosaurs", "dinosaurs-of-china", "fossil-taxa-described-in-1993", "taxa-named-by-dong-zhiming", "taxa-named-by-dale-russell"] description: "Therizinosauroid dinosaur genus from the Early Cretaceous" topic_path: "geography/china" source: "https://en.wikipedia.org/wiki/Alxasaurus" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Therizinosauroid dinosaur genus from the Early Cretaceous ::

| fossil_range = Albian, ~ | image = Alxasaurus_FukuiJH.jpg | image_caption = Skeletal mount at the Fukui Prefectural Dinosaur Museum | display_parents = 2 | taxon = Alxasaurus | authority = Russell & Dong, 1993 | type_species = Alxasaurus elesitaiensis | type_species_authority = Russell & Dong, 1993

Alxasaurus (; meaning "Alxa lizard") is a genus of therizinosauroid theropod dinosaurs from the Early Cretaceous (Albian age) Bayin-Gobi Formation of Inner Mongolia. It is known from five specimens, recovered from the Bayin-Gobi in 1988, as part of the China-Canada Dinosaur Project. During their preparation, palaeontologists Dong Zhiming and Dale Russell noted strong similarities to Segnosaurus. In 1993, they described Alxasaurus and named its type species, A. elesitaiensis. While therizinosaurs had previously been tentatively seen as late-surviving basal sauropodomorphs, the description of Alxasaurus lent credence to the idea that they were instead highly derived coelurosaurs.

While outside of Therizinosauridae itself, Alxasaurus had many of the traits characteristic of derived therizinosaurs, such as an abbreviated tail, shortened metatarsals and broad feet convergent with those of basal sauropodomorphs, and fairly long, recurved hand claws. Like related genera, it likely would have had a beak and a large gut, both adaptations for a herbivorous diet.

History of discovery

::figure[src="https://upload.wikimedia.org/wikipedia/commons/a/ad/Alxasaurus_elesitaiensis.jpg" caption="paratypes]]. Together, they represent most of the species [[hypodigm]], aside from the skull."] ::

Description

::figure[src="https://upload.wikimedia.org/wikipedia/commons/5/58/Alxasaurus_Scale.svg" caption="isbn=978-1-4008-3615-4}}"] ::

Mandible and lower dentition

::figure[src="https://upload.wikimedia.org/wikipedia/commons/c/c4/Therizinosaurian_mandibular_morphology_(Alxasaurus_jaw).png" caption="interdental plates]] appear to have been present. While not preserved in ''Alxasaurus'', its presence in other therizinosaurs suggests that a beak likely would have been present."] ::

Postcranial skeleton

The cervical (neck) vertebrae of Alxasaurus' holotype are badly crushed, though as far as can be gathered, their centra were amphiplatyan, meaning that their surfaces were relatively flat at both ends. Their neural spines were small and narrow. The zygapophyses, the articular processes of the vertebrae, were broad, and curved anteroventrally (forward and downward). From either side of the anterior (front) portion of the vertebral centra, alar processes extended, bearing capitular facets. The smaller IVPP 88402 specimen preserves three articulated vertebrae, two from the base of the neck, and one being the first dorsal (back) vertebra. The latter had a more robust neural spine than any of the preceding vertebrae, intermediate morphologically between the cervical and dorsal vertebrae. The zygapophyses of the dorsal vertebrae had planes of articulation that sloped medially, and the prezygapophyses were buttressed by the roof of the neural canal. The sacrum is very crushed. The sacral vertebrae have centra that are relatively flat ventrally (at the bottom), diminishing in size the more posterior they were. As in Segnosaurus, the sacral spines did not extend above the highest point of the ilium. Alxasaurus' caudal (tail) series is fairly well-preserved, though some of the distal (far) vertebrae are absent. From what can be gathered, the vertebral count was decreased. Like other therizinosaurs, the tail was short, relative to that of other theropods.[[File:Therizinosauria unguals comparison.png|thumb|Comparison of therizinosaur manual unguals, including Alxasaurus|left]]The scapula of Alxasaurus was long and slender, and its blade was only slightly extended distally. The anteroproximal (front, near the body axis) margin is not preserved. The posterior part of the coronoid was subcircular, tapering to a blunt point. The acrocoracoid process was situated close to the ventral margin of the glenoid articulation. The arm bones were crushed, and so details of the humerus, radius and ulna are difficult to discern. The manus (hand), on the other hand, is preserved in detail, though the manual phalanges (digit bones; in this case, finger bones) are disarticulated and have incomplete shafts. The distal carpals, the bones of the wrist closest to the hand itself, were similar to those of Therizinosaurus, though the second distal carpal had an additional articular lobe on its posterior surface. The metacarpals, the bones of the manus itself, were also very similar to those of Therizinosaurus, though less powerfully constructed. The phalanges bore ligament pits which extended to the medial surfaces, unlike in that genus. Overall, the phalanges were very similar to those of Segnosaurus. The unguals (claws) were badly crushed, partly because they were hollow proximally. They were similar in shape to those of Deinocheirus, but were narrower. In comparison to taxa like Therizinosaurus, they were small, and likely served a more generalised function.

The anterior portion of the ilium is unpreserved, as is the pubis. Dorsal to the posterodistal end of the ilium was a large crest, probably homologous to a rugose area found in the same position in Segnosaurus. Two flattened, strap-like elements are preserved, tentatively interpreted as ischia. The shaft of Alxasaurus' femur was slightly bowed laterally, unlike in Segnosaurus, where it was straight. The femoral head is inclined dorsomedially. The bones of the tarsus (ankle) are unknown. Many pedal (foot) elements are known, though identifications are largely dubious. The proximal end of the third metatarsal was probably broad, as in Segnosaurus. The metatarsus overall was abbreviated, converging on basal sauropodomorphs. The foot overall was likely quite broad.

Classification

::figure[src="https://upload.wikimedia.org/wikipedia/commons/7/7c/Alxasaurus_TD.png" caption="Life reconstruction"] ::

While exhibiting many typical therizinosaur features in overall body shape and in the teeth, the skeleton of Alxasaurus also shows several features present in more typical theropods, and the discovery of this animal provided significant evidence that therizinosaurs were aberrant theropods. Specifically, the semilunate carpal bone of the wrist is found only in maniraptoran theropods, which also include oviraptorosaurs, dromaeosaurs, troodontids, and birds. Alxasaurus is now thought to occupy a position between the early Beipiaosaurus and later therizinosaurids such as Erlikosaurus, Segnosaurus, or Therizinosaurus.

Although Rusell and Dong coined the Alxasauridae to contain Alxasaurus, the family has not been widely corroborated in most analyses. In 2010, Lindsay E. Zanno noted that, while technically still valid, the group currently consists of only a single species and is thus of dubious utility.

The following cladogram is based on the phylogenetic analysis conducted by Hartman et al., 2019:

|label1=Therizinosauria |1={{clade |1=Falcarius [[File:Falcarius Restoration.png|75px]] |2={{clade |1=Jianchangosaurus [[File:Jianchangosaurus Restoration.png|75px]] |label2=Therizinosauroidea |2={{clade |1=Beipiaosaurus [[File:Beipiaosaurus Restoration.png|75px]] |2={{clade |1="Chilantaisaurus" zheziangensis |2=Enigmosaurus [[File:Enigmosaurus Restoration.jpg|75px]] |3=Alxasaurus [[File:Alxasaurus TD.png|75px]] |4=Therizinosauridae [[File:Therizinosaurus Restoration.png|75px]] }} }} }} }} }}

References

References

1. (1993). "The affinities of a new theropod from the Alxa Desert, Inner Mongolia, People's Republic of China". Canadian Journal of Earth Sciences.
2. Olshevsky, George. (1991). "A Revision of the Parainfraclass Archosauria Cope, 1869, Excluding the Advanced Crocodylia". G. Olshevsky.
3. (1984). "The segnosaurian dinosaurs: relics of the prosauropod-ornithischian transition?". Journal of Vertebrate Paleontology.
4. Paul, Gregory S.. (2010). "The Princeton Field Guide to Dinosaurs". Princeton: Princeton University Press.
5. Lautenschlager, Stephan. (22 June 2014). "Morphological and functional diversity in therizinosaur claws and the implications for theropod claw evolution". Proceedings of the Royal Society B: Biological Sciences.
6. (1999). "A therizinosauroid dinosaur with integumentary structures from China". Nature.
7. (2005). "A primitive therizinosauroid dinosaur from the Early Cretaceous of Utah". Nature.
8. (2010). "A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora)". Journal of Systematic Palaeontology.
9. (2019). "A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight". PeerJ.

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