Open Paleo

Eshanosaurus

Xu et al., 2001 uh-SHAH-no-SAWR-us

Named for Eshan County in Yunnan Province, China, where the fossil was found, combined with Greek 'sauros' meaning 'lizard'.

201.4–199.5 million years ago Hettangian, Early Jurassic
Early Jurassic stages

Eshanosaurus is a genus of a dinosaur from the early Jurassic Period. It is known only from a fossil partial lower jawbone, found in China. It may be a therizinosaurian, and if so the earliest known coelurosaur.

Under dispute

Both the affinities and the age of Eshanosaurus are contested. The original description (Xu and colleagues, 2001) and a dedicated reassessment (Barrett, 2009) interpret its partial dentary as therizinosaurian, which, given the Early Jurassic age reported for the type locality, would make it the oldest known coelurosaur and imply an extensive ghost lineage. Others read the same material as a basal sauropodomorph (Kirkland and Wolfe, 2001); Senter and colleagues (2012) noted that all but three of the cited therizinosaurian characters also occur in sauropodomorphs, and both Zanno (2010) and Sues and Averianov (2016) treat its therizinosaurian identity as problematic. It has never been included in a numerical phylogenetic analysis. Saurischia is the least-inclusive clade the therizinosaur (theropod) and sauropodomorph hypotheses share.

Diagnosis

  1. Round fenestra present in the posterior portion of the dentary, anterior to the posterior end of the dentary tooth row
  2. Tooth denticles smaller relative to those in other therizinosauroids (3.5 per mm anteriorly, 4.4 per mm posteriorly)
  3. Tooth denticles oriented almost perpendicular to the anterior and posterior edges of tooth crowns
  4. Posterodorsal process of the dentary present, absent in other therizinosauroids

Species

Eshanosaurus deguchiianus Xu et al., 2001

Type species

Named for Hikaru Deguchi, who convinced describer Xu Xing to study dinosaurs.

Holotype
IVPP V11579 , Institute of Vertebrate Paleontology and Paleoanthropology
Material
Partial lower jaw
Horizon
lower Lufeng Formation, Hettangian, Early Jurassic , 201.4–199.5 million years ago
Locality
Yunnan, China

References

  1. Xu, X.; Zhao, X.; Clark, J. M. (2001). A new therizinosaur from the Lower Jurassic lower Lufeng Formation of Yunnan, China. Journal of Vertebrate Paleontology 21(3): 477-483. Informa UK Limited. doi:10.1671/0272-4634(2001)021[0477:antftl]2.0.co;2 xu2001b
  2. Molina-Pérez, R.; Larramendi, A. (2019). Dinosaur Facts and Figures: The Theropods and Other Dinosauriformes. Princeton University Press.

    Source of the body length and mass estimates.

    molina-pérez2019a
  3. Kirkland, J. I.; Wolfe, D. G. (2001). First definitive therizinosaurid (Dinosauria; Theropoda) from North America. Journal of Vertebrate Paleontology 21(3): 410-414. Informa UK Limited. doi:10.1671/0272-4634(2001)021[0410:fdtdtf]2.0.co;2

    Interpreted Eshanosaurus material as representing a basal sauropodomorph.

    kirkland2001a
  4. Zanno, L. E. (2010). A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology 8(4): 503-543. doi:10.1080/14772019.2010.488045

    Therizinosauria revision; declined to score Eshanosaurus, treating its affinity as unlikely to be resolved.

    zanno2010a
  5. Barrett, P. M. (2009). The affinities of the enigmatic dinosaur Eshanosaurus deguchiianus from the Early Jurassic of Yunnan Province, People's Republic of China. Palaeontology 52(4): 681-688. doi:10.1111/j.1475-4983.2009.00887.x

    Reassessed the dentary and concluded it supports therizinosaurian rather than sauropodomorph affinities

    barrett2009a
  6. Senter, P.; Kirkland, J. I.; DeBlieux, D. D. (2012). Martharaptor greenriverensis, a New Theropod Dinosaur from the Lower Cretaceous of Utah. PLoS ONE 7(8): e43911. Public Library of Science (PLoS). doi:10.1371/journal.pone.0043911

    Noted that all but three of the putative therizinosaurian characters of Eshanosaurus also occur in sauropodomorphs, urging caution.

    senter2012a
  7. Sues, H. D.; Averianov, A. (2016). Therizinosauroidea (Dinosauria: Theropoda) from the Upper Cretaceous of Uzbekistan. Cretaceous Research 59: 155-178. doi:10.1016/j.cretres.2015.11.003

    Treated the therizinosaurian identity of Eshanosaurus as problematic.

    sues2016a