Open Paleo

Bagaraatan

Osmólska, 1996 BAH-gah-RAH-tan Disputed

From Mongolian 'baga' (small) and 'araatan' (carnivorous animal, beast of prey); meaning 'small predator'.

72.2–66.0 million years ago Maastrichtian, Late Cretaceous
Late Cretaceous stages

Bagaraatan is a genus of theropod dinosaur from the Late Cretaceous period of what is now the Nemegt Formation of Mongolia. It may have been a small predatory dinosaur measuring around 3 to 4 meters (9.8 to 13.1 ft) in length.

Under dispute

Bagaraatan ostromi was named by Osmólska (1996) on an incomplete Nemegt Formation skeleton that Osmólska placed within Tetanurae but could refer only tentatively to Avetheropoda given the incomplete material. Słowiak and colleagues (2024) found the holotype to be a chimera of a caenagnathid oviraptorosaur and a juvenile tyrannosaurid, restricted the holotype to the tyrannosaurid elements, and reinterpreted it as an indeterminate juvenile tyrannosaurid (possibly a juvenile Tarbosaurus) without formally sinking the name, leaving its validity as a distinct genus unresolved.

Diagnosis

  1. Mandible with two surangular foramina separated by a flat, ventrally descending process
  2. Caudal vertebrae with hollow, very thin-walled centra filled with crystallized matrix
  3. Hyposphene-hypantrum articulation stout and present in at least sixteen proximal caudals
  4. Prezygapophyses in proximal caudals with ridges on lateral surfaces, subvertically oriented
  5. Ilium with two deep depressions on lateral surface of postacetabular process separated by a crest-like projection
  6. Femur with anterior crest below lesser trochanter (absent in all other known archosaurs)
  7. Tibia and fibula fused distally with each other and with coalesced astragalocalcaneum
  8. Double surangular foramina (anterior and posterior)
  9. Horizontal ridge on lateral surface of postacetabular process of ilium

Species

Bagaraatan ostromi Osmólska, 1996 Disputed

Type species

Named in honor of John H. Ostrom, the American paleontologist whose work on Deinonychus revived interest in the bird-dinosaur connection.

Holotype
ZPAL MgD-I/108 , Institute of Paleobiology, Polish Academy of Sciences
Material
Incomplete skeleton including left mandible, 25 caudal vertebrae, fragmentary pelvis, left hind limb lacking most of the pes
Horizon
lower Nemegt Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
Northern Sayr, Nemegt, Ömnögovi, Mongolia Osmólska (1996) places the holotype "in the sand layer of the lower portion of the Nemegt Formation, in the eastern part of the Northern Sayr". Gradziński and Jerzykiewicz (1972) map two sites with coeluroid postcranial fragments, 13 and 26; neither is tied to this specimen.

References

  1. Osmólska, H. (1996). An unusual theropod dinosaur from the Late Cretaceous Nemegt Formation of Mongolia. Acta Palaeontologica Polonica 41: 1-38. osmólska1996a
  2. Gradziński, R.; Jerzykiewicz, T. (1972). Additional geographical and geological data from the Polish-Mongolian Palaeontological Expeditions. Palaeontologia Polonica 27: 17-30.

    Maps the expedition's numbered Nemegt sites, two of them, 13 and 26, captioned as yielding coeluroid postcranial fragments.

    gradziński1972a
  3. Słowiak, J.; Brusatte, S. L.; Szczygielski, T. (2024). Reassessment of the enigmatic Late Cretaceous theropod dinosaur, Bagaraatan ostromi. Zoological Journal of the Linnean Society 202(3). Oxford University Press. doi:10.1093/zoolinnean/zlad169

    Reassessment that disentangled the chimeric holotype: mandibular and pelvic material reinterpreted as juvenile tyrannosaurid; femur and hindlimb elements reassigned to Caenagnathidae indet.

    słowiak2024a