Pelecanimimus findings announced

Jeff Poling

Several years ago, paleontologists announced the discovery of a non-avian dinosaur they named Pelecanimimus polyodon, "pelican mimic with many teeth." It caused quite a buzz in the paleontological community as the fossil included the mineralized soft tissue of the animal. The scientists announced at the time that the skin impressions showed what might have been an integument of hairlike structures, but more study was needed. Earlier this year paleontologists announced their findings.

Pelicanimimus was discovered in the Lower Cretaceous lacustrine lithographic limestone deposit of Las Hoyas, Cuenca, Spain. These limestones have yielded well preserved fossils of plants, crustaceans, insects and fishes. Three birds have been found, some with feather impressions. Mineralized muscle tissue was found with some of the fishes.

Pelicanimimus was determined to be an ornithomimosaur, the first discovered in Europe. The fossil sports approximately 220 teeth, remarkable not only in that this count is the highest of all theropods, but also in that it occurs in an animal where most other known specimens have toothless beaks (indeed, the only known fossil with evidence of a keratin covered beak is of another ornithomimosaur). Pelicanimimus and the other toothed ornithomimids may represent the primitive condition of ornithomimosaurs.

Parts of the skin and musculature of the dinosaur was preserved both as an impression on a microbial mat that covered the decaying animal, and as a mineralized replica made up of an iron carbonate. The skin impressions in the microbial mat form a well defined outline of the animal. This outline shows the animal had a throat pouch or dewlap (a loose fold of skin hanging from the throat, as in certain types of cattle), and a soft occipital crest (a crest formed of skin on the back of the head). Iron carbonate in the preservational environment preserved the muscle tissue in remarkable detail, in some cases in all three dimensions (only one other dinosaur fossil, from Brazil, shows this degree of preservation of muscle tissue).

These muscle fibers, along with preserved wrinkling of the skin, is what scientists originally thought might be a preserved integumentary covering of hairlike structures. The skin impressions indicate Pelicanimimus had a smooth, naked skin without any dermal structures such as feathers, scales or hair. As with its teeth, this aspect of Pelicanimimus is also remarkable in that all other dinosaur skin impressions show some sort of dermal structure, most often feathers (Archaeopteryx and other birds) or scutes and osteoderms (tyrannosaurs, ankylosaurs, stegosaurs and hadrosaurs).