Thomas R. Holtz Jr.

Thomas Richard Holtz Jr., Ph.D. (born September 13, 1965) is an American vertebrate palaeontologist, author, and principal lecturer at the University of Maryland's Department of Geology. He has published extensively on the phylogeny, morphology, ecomorphology, and locomotion of terrestrial predators, especially on tyrannosaurids and other theropod dinosaurs. He wrote the book "" and is the author or co-author of the chapters "Saurischia", "Basal Tetanurae", and "Tyrannosauroidea" in the second edition of "The Dinosauria". He has also been consulted as a scientific advisor for the "Walking With Dinosaurs" BBC series as well as the Discovery special "When Dinosaurs Roamed America", and has appeared in numerous documentaries focused on prehistoric life, such as "Jurassic Fight Club" on History and "Monsters Resurrected" on Discovery.
Holtz is also the director of the Science and Global Change Program within the College Park Scholars living-learning community at the University of Maryland, College Park.
Theories.
Holtz has come up with several new theories and hypotheses about the dinosaurs' classification. For example, he coined the terms Maniraptoriformes and Arctometatarsus. He also proposed two classification systems for theropods. The first is the clade Arctometatarsalia, made up of tyrannosauroids, ornithomimosaurs, and troodontids, because all of these coelurosaurs had pinched middle metatarsal bones in their feet. In this proposed classification system, the tyrannosauroids were supposedly basal to a clade known as Bullatosauria, which was made up of the Troodontidae and the Ornithomimosauria. These two groups were purported to form a clade, because they both shared a common characteristic; which was a skull capsule. However, later on, both of these classification systems were found to be paraphyletic, or "artificial", clades. For example, troodontids are now known to be deinonychosaurs, or "raptors", closely related to dromaeosaurids and birds. The discovery of basal tyrannosauroids, such as "Guanlong", which lacked an arctometatarsus, also helped to disprove this theory. And, eventually, the "skull capsule" in troodontids and ornithomimosaurs was found to be an example of convergent evolution, causing the clade Bullatosauria to be abandoned.
Holtz was also a key figure in the discovery that tyrannosauroids were not carnosaurs, as had been previously believed by most palaeontologists, but rather large coelurosaurs. One of the first scientists to theorise this, Holtz contributed greatly to the debunking of a monophyletic Carnosauria.