A Second Specimen ofCitipati OsmolskaeAssociated With a Nest of Eggs from Ukhaa Tolgod, Omnogov Aimag, Mongolia

Abstract

Adult dinosaurs preserved attending their nests in brooding positions are among the rarest vertebrate fossils. By far the most common occurrences are members of the dinosaur group Oviraptorosauria. The first finds of these were specimens recovered from the Djadokhta Formation at the Mongolian locality of Ukhaa Tolgod and the Chinese locality of Bayan Mandahu. Since the initial discovery of these specimens, a few more occurrences of nesting oviraptors have been found at other Asian localities.Here we report on a second nesting oviraptorid specimen (IGM 100/1004) sitting in a brooding position atop a nest of eggs from Ukhaa Tolgod, Omnogov, Mongolia. This is a large specimen of the ubiquitous Ukhaa Tolgod taxon Citipati osmolskae. It is approximately 11% larger based on humeral length than the original Ukhaa Tolgod nesting Citipati osmolskae specimen (IGM 100/979), yet eggshell structure and egg arrangement are identical. No evidence for colonial breeding of these animals has been recovered.Reexamination of another "nesting" oviraptorosaur, the holotype of Oviraptor philoceratops (AMNH FARB 6517) indicates that in addition to the numerous partial eggs associated with the original skeleton that originally led to its referral as a protoceratopsian predator, there are the remains of a tiny theropod. This hind limb can be provisionally assigned to Oviraptoridae. It is thus at least possible that some of the eggs associated with the holotype had hatched and the perinates had not left the nest.

A new baby oviraptorid dinosaur (Dinosauria: Theropoda) from the Upper Cretaceous Nemegt Formation of Mongolia

“…The pubic apron is thin and narrow. The caudally concave ischium (Fig 3I) is similar in morphology to other oviraptorids [4, 40, 72]. The medial surface of the ischium is flat in contrast to the lateral surface that has a concavity due to the obturator process.…”

“…Interestingly, oviraptorids are restricted to Asia although they are more diverse than caenagnathids which are reported from both Asia and North America [8, 10]. However, most of the caenagnathids are represented by fragmentary materials [12, 21–34] with only a few exceptions [8, 9, 35, 36] compared with the numerous nearly complete skeletons of oviraptorids [4, 19, 20, 37–40].…”

“…Although the Nanxiong Formation is the most productive formation with regard to the number of oviraptorid taxa [20], the Gobi Desert of Mongolia, including the classic Nemegt locality (Fig 1), has also yielded abundant oviraptorids [1, 2, 4, 37, 40–49]. Despite this high diversity, oviraptorid occurrences have been relatively rare in the Altan Uul area [10, 50].…”

A new two-fingered dinosaur sheds light on the radiation of Oviraptorosauria

“…The crouched posture of the individuals differs from the opisthotonic 'death pose' commonly seen in theropod dinosaurs [62], in which the body lies on one side and the head, neck and tail are arched dorsally. Instead, the feet and belly of each individual are parallel to the bedding plane and the arms and legs are tucked underneath the body-a pose that resembles the resting poses inferred for other non-avian theropods [6,30,31,[63][64][65][66]. This posture is unlikely to be the result of taphonomy, especially considering that it is consistent in at least three individuals oriented in different directions.…”

“…Individual A, the holotype, is the most complete, whereas only the right side of individual B and the pelvic region of individual C are preserved. Individuals A and B are crouched in positions that resemble inferred resting poses of other oviraptorids [6,7,30,31], facing opposite directions, with their legs beneath their bodies, arms folded, and heads tucked towards their right arms. Another juvenile skeleton (MPC-D 102/11, 31 kg) was confiscated at the same time, and is preserved in the same crouched posture.…”