No abstract

No abstract

The mineralized soft tissue of a dinosaur, only the second discovery of its kind is reported from the Lower Cretaceous of Las Hoyas, Spam. Cellular details of mineralized skin and muscle of Pelecanimimus are replicated in an iron carbonate. The outline of this ornithomimosaur is preserved by a phosphatized microbial mat that enshrouded the carcass. It confirms the existence of either a throat pouch or dewlap, and soft occipital crest. This study confirms the importance of microbial mats hi the fossilization of soft tissues and emphasises the need for careful monitoring of vertebrate remains for mineralized soft tissues prior to acid preparation. The multitoothed ornithomimosaur dinosaur Pelecanimimus polyodon was recently described from the Lower Cretaceous lacustrine lithographic limestones of Las Hoyas (Cuenca, Spain) (Perez-Moreno et al. 1994). The only known specimen of this, the first ornithomimosaur theropod found in Europe, preserves what were originally described as 'integumentary impressions'. These occur in the throat region, flanking the more proximal neck vertebrae, in the vicinity of the ribs, and behind the elbow. In addition a small triangular area at the rear of the skull was interpreted as a possible occipital crest (Perez-Moreno et al. 1994). Analyses confirm that these features represent mineralized traces of soft tissues. They are preserved both as replicas of the original skin and muscle tissue, and as impressions on microbial mats or veils that grew over them. In addition to Pelecanimimus, the lacustrine limestones of Las Hoyas (Melendez 1995) have yielded a well preserved diverse biota of plants,

appearance of the curculionid cuticle from Enspel is similar to that of modern beetles (Fig. lB), although the organic rnatrix surrounding the fibers has partially degraded. The preservation of chitin in the beetles and not in the flies may reflect the greater thickness and degree of cross-linking in the cuticle of the former. This study demonstrates that the primary control on the preservation of these biomolecules in ancient rocks is not time but the nature of the depositional environment and the inhibition of diagenetic alteration. In the case of Enspel, the combination of high productivity (evidenced by the abundance of diatoms in the matrix) and strongly reducing bottorn conditions (23) played a key role in the enhanced preservation of the chitin-protein complex.