Me again. I have two questions: One: Do you plan on watching When Dinosaurs Roamed America tonight on the Disc. Channel at 8:00? Two: How much do we know about the Cretacious flying dinosaurs (i.e., the birds) such as Ibernisornis, Hespironis, and the other birds that lived with the non-avian dinosaurs?
from Samuel C., age ?, ?, ?, ?; July 15, 2001

TOM: One: yes, I did watch it. In fact, I was a consultant on the project, and wanted to see if any of the changes or suggestions I made were included in the final version (some of them were).

Two: We know a LOT more about Mesozoic birds today than we did only twenty years ago. Before the 1980s only a few Mesozoic birds were known to science, and only four of them (Archaeopteryx, Ichthyornis, Hesperornis and its close relative Baptornis) were known from good fossils. Since the 1980s many, many new skeletons have been found. Dr. Brett-Surman and Greg Paul described one (which they thought was a non-avian dinosaur) as Avisaurus; it is now known from more complete material. Argentina has produced many, many new species. In the Gobi of Mongolia one of the most complete bodies (unfortunately, the skull is mostly missing) of one of the most advanced Mesozoic birds has been found and called Asparavis. Iberomesornis and Concornis are both known from excellent fossils from the Cretaceous of Spain. The best place for Mesozoic birds, though, are the Early Cretaceous Yixian Formation rocks of China, which contain fossils of almost a dozen species of new bird, many of them based on complete fossils. One of these birds (Confuciusornis sanctus) is known from hundreds, and possibly thousands, or specimens.

What we know about Mesozoic birds show that they came in a variety of sizes, from sparrow to ostrich (Gargantuavis of the Late Cretaceous of Spain); that they had a wide variety of habits (many were fliers, but some were flightless swimmers and some were flightless runners) and diets (insects, plants, fish). We also have evidence of the many different steps in the evolution of birds: the various different features that make modern birds different from all other living creatures did not appear all at once, but instead showed up step by step.