Enigmosaurus

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Enigmosaurus
Temporal range:
Ma
Skeletal diagram of the holotype
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: †Therizinosauria
Superfamily: †
Therizinosauroidea
Genus: †Enigmosaurus
Barsbold, 1983
Type species
†Enigmosaurus mongoliensis
Barsbold, 1983

Enigmosaurus (meaning "Enigma lizard" or "Enigmatic lizard") is a

monotypic
, including only the type species E. mongoliensis, known from a well preserved pelvis and other tentative body remains.

Discovery and naming

Fossil localities in Mongolia. Locality of Enigmosaurus in Khara Khutul, at Area D

The

Segnosauria. Nicknamed as the "Dinosaur from Khara Khutul", it was shortly described and included into the Segnosauria.[2]

Schematic reconstruction of the pelvis

Three years later, the

ribs; distal end of a humerus; a tentative radius and the proximal end of an ulna. The femur however, was not found in association with the holotype individual, therefore it should be assigned to Therizinosauria incertae sedis; the other remains might pertain to the holotype. A very large left femur, measuring 105 cm (1,050 mm) long, was labelled with the same specimen number too, however, it was not associated with the holotype due to its large size (larger than the pelvis itself). Nevertheless, it seems to approach the size of the closer Segnosaurus.[5]

Possible synonymy with Erlikosaurus

Some

junior synonym of Erlikosaurus.[6][7] However, the Enigmosaurus pelvis doesn't resemble that of Segnosaurus as would be expected for the connection with Erlikosaurus, and there is a huge size difference.[2][3][8] In addition, both genera are known from different strata (lower and upper),[3][9][10] and they are considered to be distinct animals by most authors.[11][12]

Description

Diagram of the sacrum, in A ventral and B dorsal views

Enigmosaurus was a relatively large-bodied therizinosaur, with an estimated length of 5 m (16 ft) and a weight between 454 to 907 kg (1,001 to 2,000 lb).[13] As noted by Barsbold in the original description of Enigmosaurus, it can recognised by the following characteristics: the pubis and ischium are short; elongated margin in the anterior presymphyseal region of the distal pubis.[3] However, in the revised diagnosis by Zanno et al. 2010, there are even more specific traits for Enigmosaurus that were not pointed out/analyzed before: prominent cranial and caudal processes on the dorsoventrally somewhat flattened pubic boot; the pubic feet are fused, being medially elongated, a medial expansion forms a V-shaped structure; the medial fusion of the obturator process and pubic body, forms a tetraradiate process.[5]

Life restoration

The holotype pelvis is in relatively good preservation, compromising the sacral vertebrae, partial ilium, right and left pubis and the left ischium. The pelvis is somewhat large as a whole and opisthopubic. The ilium is widely positioned and turned externally; it preserves a large cubic process in the posterodorsal area. Elongated pubic peduncles are present in the ilium; the ischial peduncles are more reduced though. The distal end of the pubis is elongated, recurved and stocky. The ischium, is slightly shorter than the pubis and parallel to it, with a narrow shaft. The obturator process on the front edge of the ischium is horizontally elongated and low. Open edges are appreciable on the large trochanteric fossa. Apparently, the sacrum preserves six vertebrae, with elongated transverse processes.[3] For instance, its pelvis is very particular compared to other therizinosaur relatives, featuring areas of bone resorption and bone remodeling on the ilium. These specific traits may indicate the advanced age of the individual, if true, the fusion of the obturator process and pubic body could be discarded as an authentic autapomorphy for the species. Zanno noted that more analyses are required to settle this enigma.[5]

Classification

Enigmosaurus was by the describers assigned to a separate

Therizinosauroidea.[5]

Hip variation among therizinosaur genera (Enigmosaurus in center)

Below are the results of the recently performed

phylogenetic analysis of the Therizinosauria by Hartman et al. 2019, in which Enigmosaurus is recovered as a derived therizinosauroid.[12]

Therizinosauria

Falcarius

Jianchangosaurus

Therizinosauroidea

Paleoecology

Dinosauria
from the Bayan Shireh Formation (Enigmosaurus in yellow, first from left)

The remains of Enigmosaurus were found in sediments that were deposited during the Late Cretaceous period on the Bayan Shireh Formation, Khara Khutul locality, about 95.9 ± 6.0 million to 89.6 ± 4.0 million years ago, Cenomanian-Santonian ages.[3][14] Being a therizinosaur, it was likely a slow herbivore and/or omnivore, as suggested by most authors all over the time.[15][16][17] The biodiversity across the formation was characterized by therizinosaurs, as seen on the remains of Enigmosaurus, Erlikosaurus and Segnosaurus.[18] The holotype location, Khara Khutul, has also yielded the contemporary Segnosaurus[2] and an unnamed velociraptorine.[19][20] Most of the remaining paleofauna from this formation is known from Upper strata, whereas Enigmosaurus is known from Lower strata.[10]

At the locality, diverse paleoflora has been discovered, such as

Abelmoschus esculentus, however, definitive taxonomic affinities are quite unclear.[22]

See also

References

  1. S2CID 4348297
    .
  2. ^ a b c Barsbold, R.; Perle, A. (1980). "Segnosauria, a new suborder of carnivorous dinosaurs" (PDF). Acta Palaeontologica Polonica. 25 (2): 190–192.
  3. ^ a b c d e f g Barsbold, R. (1983). "Хищные динозавры мела Монголии" [Carnivorous dinosaurs from the Cretaceous of Mongolia] (PDF). Transactions of the Joint Soviet-Mongolian Paleontological Expedition (in Russian). 19: 89. Translated paper
  4. doi:10.1006/cres.1993.1011
    .
  5. ^
    S2CID 53405097
    .
  6. ISBN 9780520242098
    .
  7. ISBN 978-0-6911-3720-9
    .
  8. ISBN 0-7853-0443-6
    .
  9. hdl:2246/3712
    .
  10. ^
    PMID 30995236
    .
  11. PMID 23284972
    .
  12. ^
    PMID 31333906
    .
  13. ^ Holtz, T. R.; Rey, L. V. (2007). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House. Genus List for Holtz 2012 Weight Information
  14. doi:10.1111/ter.12456
    .
  15. JSTOR 4523011
    .
  16. PMID 27069815
    .
  17. S2CID 133643430
    .
  18. S2CID 197584839
    .
  19. doi:10.1080/02724634.2007.10010458
    .
  20. S2CID 83572446
    .
  21. ISBN 9780444502766
    .
  22. S2CID 86032547
    .
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