We performed multiple analyses of Tyrannosaurus rex (specimen MOR 1125) fibrous cortical and medullary tissues remaining after demineralization. The results indicate that collagen I, the main organic component of bone, has been preserved in low concentrations in these tissues. The findings were independently confirmed by mass spectrometry. We propose a possible chemical pathway that may contribute to this preservation. The presence of endogenous protein in dinosaur bone may validate hypotheses about evolutionary relationships, rates, and patterns of molecular change and degradation, as well as the chemical stability of molecules over time.

Stable-isotope profiles through successive growth increments of Miocene bivalves from Western Amazonia reveal paleobiological characteristics, such as biotope preferences, longevity, and ontogenetic development. Two groups of bivalves, a fluvial and a lacustrine group, are recognized. The fluvial group is composed of pearly freshwater mussels whose isotope profiles are characterized by clearly recognizable cyclicity of considerable amplitude, similar to those from pearly freshwater mussels studied from the modern Amazon region. The lacustrine group, dominated by pachydontine bivalves, is characterized by very low amplitude and irregular isotope signals. Additional trace element analyses show seasonal variation in phase with stable isotope cycles. Seasonal stable isotope cycles show growth rates and longevity in bivalves from the fluvial group but are not clearly expressed in the lacustrine group. The Miocene Pebas ecosystem of Western Amazonia can be characterized as a wetland system of connected shallow lakes, swamps, and tributaries. The stable isotope signatures of fluvial bivalves are good recorders of prior seasonal climate changes, in contrast with those of lacustrine bivalves.