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First tyrannosaurid remains from the Upper Cretaceous “El Gallo” Formation of Baja California, Mexico

100%

Peecook B. R., Wilson J. A., Hernandez-Rivera R., Montellano-Ballesteros M., Wilson G. P.

Acta Palaeontologica Polonica

2014

tom 59

nr 1

We report a complete left fourth metatarsal collected from rocks of the Upper Cretaceous (Campanian) “El Gallo” Formation exposed along the Pacific Ocean near El Rosario, Baja California, México. The metatarsal IV was part of an arctometatarsalian metatarsus, as evidenced by a deep medial notch proximally and extensive articulation for metatarsal III. This condition, along with the U-shape of the proximal end, supports identification as tyrannosauroid. It is assigned to Tyrannosauridae based on features on the posterior surface of the shaft, but finer taxonomic resolution is not possible. Compared to other tyrannosauroids, the metatarsal is relatively short, closely resembling the proportions of the gracile Albertosaurus sarcophagus rather than the much more massive, robust metatarsals of Tyrannosaurus rex. The Baja tyrannosaurid metatarsal is shorter than almost all other tyrannosauroid fourth metatarsals, raising the possibility that it pertains to an immature individual. North American tyrannosauroids are best known from the northern coast of the Western Interior Seaway, as well as less frequently on the southern coast of the seaway in Utah and New Mexico. The new record in Baja marks the first unambiguous skeletal material of a tyrannosaurid both in México and along the Pacific coast.

Mud-trapped herd captures evidence of distinctive dinosaur sociality

86%

Varricchio D. J., Sereno P. C., Xijin Z., Lin T., Wilson J. A., Lyon G. H.

Acta Palaeontologica Polonica

2008

tom 53

nr 4

A unique dinosaur assemblage from the Cretaceous beds of western Inner Mongolia preserves geologic and paleontologic data that clearly delineate both the timing and mechanism of death. Over twenty individuals of the ornithomimid Sinornithomimus dongi perished while trapped in the mud of a drying lake or pond, the proximity and alignment of the mired skeletons indicating a catastrophic mass mortality of a social group. Histologic examination reveals the group to consist entirely of immature individuals between one and seven years of age, with no hatchlings or mature individuals. The Sinornithomimus locality supports the interpretation of other, more taphonomically ambiguous assemblages of immature dinosaurs as reflective of juvenile sociality. Adults of various nonavian dinosaurs are known to have engaged in prolonged nesting and post hatching parental care, a life history strategy that implies juveniles spent considerable time away from reproductively active adults. Herding of juveniles, here documented in a Cretaceous ornithomimid, may have been a common life history strategy among nonavian dinosaurs reflecting their oviparity, extensive parental care, and multi−year maturation.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Wilson J. A.

1 Hernandez-Rivera R.

1 Lin T.

1 Lyon G. H.

1 Montellano-Ballesteros M.

1 Peecook B. R.

1 Sereno P. C.

1 Varricchio D. J.

1 Wilson G. P.

1 Xijin Z.

1 2014

1 2008

Wyniki wyszukiwania

First tyrannosaurid remains from the Upper Cretaceous “El Gallo” Formation of Baja California, Mexico

Mud-trapped herd captures evidence of distinctive dinosaur sociality