Thomas R. Holtz Jr.

Last updated
Tom Holtz, Jr.
Born (1965-09-13) September 13, 1965 (age 58)
Education Johns Hopkins University, Yale University
Alma mater
Known forStudies of dinosaur phylogeny and Coelurosaurian Tyrannosauroids
Scientific career
Fields Paleontology
Author abbrev. (zoology) HOLTZ, T.R., JR

Thomas Richard Holtz Jr. (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. [1] He wrote the book Dinosaurs and is the author or co-author of the chapters "Saurischia", [2] "Basal Tetanurae", [3] and "Tyrannosauroidea" [4] 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 , Dinosaur Revolution and Clash of the Dinosaurs on Discovery. [5]


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.

Early life

Holtz was born in California. He has stated that he wanted to be a dinosaur as a child, but upon learning that it is impossible to turn into a dinosaur he shifted his goals to study them. He attended Johns Hopkins University, where he met his future wife. He then attended Yale, where he met John Ostrom, who served as his academic advisor. [6]


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.

Gallimimus, an example ornithomimosaurian theropod that Holtz assigned to the Bullatosauria Gallimimus mongoliensis mount.jpg
Gallimimus, an example ornithomimosaurian theropod that Holtz assigned to the Bullatosauria

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 theorize this, Holtz contributed greatly to the debunking of a monophyletic Carnosauria that contained Megalosauroidea, Allosauroidea and Tyrannosauroidea. However, fellow vertebrate paleontologist Oliver Rauhut is known to recover a monophyletic Carnosauria that contains both Megalosauroidea and Allosauroidea in many of his publications, although like most researcher he agrees that Tyrannosauroids are likely Coelurosaurians as based on the conclusions made by Holtz.

Selected publications


  1. Holtz, Thomas R. Holtz Jr..
  2. "Saurischia", pp. 21–23, with H. Osmólska
  3. "Basal Tetanurae", pp. 71–110, with R. E. Molnar, P. J. Currie
  4. "Tyrannosauroidea", pp. 111–136.
  5. Holtz, Thomas R. Jr. (September 8, 2011). Comment on "Coming soon to your screens: Dinosaur Hyperbole", weblog entry by Hone, Dave (September 7, 2011). Dave Hone's Archosaur Musings . Retrieved September 13, 2011.
  6. "Interview with Dr. Thomas R. Holtz, Jr". Buzzy Magazine.

Related Research Articles

<span class="mw-page-title-main">Theropoda</span> Clade of dinosaurs

Theropoda, whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally carnivorous, although a number of theropod groups evolved to become herbivores and omnivores. Theropods first appeared during the Carnian age of the late Triassic period 231.4 million years ago (Ma) and included the majority of large terrestrial carnivores from the Early Jurassic until at least the close of the Cretaceous, about 66 Ma. In the Jurassic, birds evolved from small specialized coelurosaurian theropods, and are today represented by about 10,500 living species.

<span class="mw-page-title-main">Coeluridae</span> Extinct family of dinosaurs

Coeluridae is a historically unnatural group of generally small, carnivorous dinosaurs from the late Jurassic Period. For many years, any small Jurassic or Cretaceous theropod that did not belong to one of the more specialized families recognized at the time was classified with the coelurids, creating a confusing array of 'coelurid' theropods that were not closely related. Although they have been traditionally included in this family, there is no evidence that any of these primitive coelurosaurs form a natural group with Coelurus, the namesake of Coeluridae, to the exclusion of other traditional coelurosaur groups.

<span class="mw-page-title-main">Coelurosauria</span> Clade of dinosaurs

Coelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs.

<span class="mw-page-title-main">Carnosauria</span> Extinct Infraorder of theropod dinosaurs

Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as Giganotosaurus, Mapusaurus, Carcharodontosaurus and Tyrannotitan which are among the largest known predatory dinosaurs.

<span class="mw-page-title-main">Tetanurae</span> Clade containing most theropod dinosaurs

Tetanurae is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans. Tetanurans are defined as all theropods more closely related to modern birds than to Ceratosaurus and contain the majority of predatory dinosaur diversity. Tetanurae likely diverged from its sister group, Ceratosauria, during the late Triassic. Tetanurae first appeared in the fossil record by the Early Jurassic about 190 mya and by the Middle Jurassic had become globally distributed.

<span class="mw-page-title-main">Ornithomimosauria</span> Extinct clade of theropod dinosaurs

Ornithomimosauria are theropod dinosaurs which bore a superficial resemblance to the modern-day ostrich. They were fast, omnivorous or herbivorous dinosaurs from the Cretaceous Period of Laurasia, as well as Africa and possibly Australia. The group first appeared in the Early Cretaceous and persisted until the Late Cretaceous. Primitive members of the group include Nqwebasaurus, Pelecanimimus, Shenzhousaurus, Hexing and Deinocheirus, the arms of which reached 2.4 m (8 feet) in length. More advanced species, members of the family Ornithomimidae, include Gallimimus, Struthiomimus, and Ornithomimus. Some paleontologists, like Paul Sereno, consider the enigmatic alvarezsaurids to be close relatives of the ornithomimosaurs and place them together in the superfamily Ornithomimoidea.

<i>Afrovenator</i> Extinct genus of dinosaurs

Afrovenator is a genus of megalosaurid theropod dinosaur from the Middle or Late Jurassic Period on the Tiourarén Formation and maybe the Irhazer II Formation of the Niger Sahara region in northern Africa. Afrovenator represents the only properly identified Gondwanan megalosaur, with proposed material of the group present in the Late Jurassic on Tacuarembó Formation of Uruguay and the Tendaguru Formation of Tanzania.

<i>Proceratosaurus</i> Extinct genus of dinosaurs

Proceratosaurus is a genus of carnivorous theropod dinosaur from the Middle Jurassic (Bathonian) of England. It contains a single species. P. bradleyi, known from a mostly complete skull and lower jaws. Proceratosaurus was a small dinosaur, estimated to measure around 3 m (9.8 ft) in length. Its name refers to how it was originally thought to be an ancestor of Ceratosaurus, due to the partially preserved portion of the crest of Proceratosaurus superficially resembling the small crest of Ceratosaurus. Now, however, it is considered a coelurosaur, specifically a member of the family Proceratosauridae, and amongst the earliest known members of the clade Tyrannosauroidea.

<i>Megaraptor</i> Extinct genus of dinosaurs

Megaraptor is a genus of large theropod dinosaur that lived in the ages of the Late Cretaceous. Its fossils have been discovered in the Patagonian Portezuelo Formation of Argentina, South America. Initially thought to have been a giant dromaeosaur-like coelurosaur, it was classified as a neovenatorid allosauroid in previous phylogenies, but more recent phylogeny and discoveries of related megaraptoran genera has placed it as either a basal tyrannosauroid or a basal coelurosaur with some studies still considering it a neovenatorid.

<i>Monolophosaurus</i> Extinct genus of dinosaurs

Monolophosaurus is an extinct genus of tetanuran theropod dinosaur from the Middle Jurassic Shishugou Formation in what is now Xinjiang, China. It was named for the single crest on top of its skull. Monolophosaurus was a mid-sized theropod at about 5–5.5 metres (16–18 ft) long and weighed 475 kilograms (1,047 lb).

<span class="mw-page-title-main">Megalosauroidea</span> Extinct superfamily of Dinosaurs

Megalosauroidea is a superfamily of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as Megalosaurus bucklandii and all taxa sharing a more recent common ancestor with it than with Allosaurus fragilis or Passer domesticus. Members of the group include Spinosaurus, Megalosaurus, and Torvosaurus. They are possibly paraphyletic in nature with respect to Allosauroidea.

<span class="mw-page-title-main">Tyrannosauroidea</span> Extinct superfamily of dinosaurs

Tyrannosauroidea is a superfamily of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent beginning in the Jurassic Period. By the end of the Cretaceous Period, tyrannosauroids were the dominant large predators in the Northern Hemisphere, culminating in the gigantic Tyrannosaurus. Fossils of tyrannosauroids have been recovered on what are now the continents of North America, Europe and Asia, with fragmentary remains possibly attributable to tyrannosaurs also known from South America and Australia.

<i>Dryptosaurus</i> Extinct genus of reptiles

Dryptosaurus is a genus of basal eotyrannosaurian theropod dinosaur that lived on the island continent of Appalachia approximately 67 million years ago during the end of the Maastrichtian age of the Late Cretaceous period. Dryptosaurus was a large, bipedal, ground-dwelling carnivore that could grow up to 7.5 metres (25 ft) long and weigh up to 1.5 metric tons. Although it is now largely unknown outside of academic circles, the famous 1897 painting of the genus by Charles R. Knight made Dryptosaurus one of the more widely known dinosaurs of its time, in spite of its poor fossil record. First described by Edward Drinker Cope in 1866 and later renamed by Othniel Charles Marsh in 1877, Dryptosaurus is among the very first theropod dinosaurs ever known to science.

Chuandongocoelurus is a genus of carnivorous tetanuran theropod dinosaur from the Jurassic of China.

<span class="mw-page-title-main">Allosauroidea</span> Extinct superfamily of Dinosaurs

Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among the apex predators that were active during the Middle Jurassic to Late Cretaceous periods. The most famous and best understood allosauroid is the North American genus Allosaurus.

<span class="mw-page-title-main">Maniraptoriformes</span> Clade of dinosaurs

Maniraptoriformes is a clade of dinosaurs with pennaceous feathers and wings that contains ornithomimosaurs and maniraptorans. This group was named by Thomas Holtz, who defined it as "the most recent common ancestor of Ornithomimus and birds, and all descendants of that common ancestor."

<span class="mw-page-title-main">Tyrannoraptora</span> Clade of dinosaurs

Tyrannoraptora is a clade defined as "all descendants of the last common ancestor of Tyrannosaurus rex and Passer domesticus ". The clade was named in 1999 by the American paleontologist Paul Sereno, though in his original concept had Tyrannosauroidea being the sister taxon to Pennaraptora. Phylogenetic analyses have since, however, found the group also encompasses Compsognathidae, Ornithomimosauria, Alvarezsauroidea, and Therizinosauria. Thus tyrannoraptorans are divided into tyrannosauroids and maniraptoromorphs.

<span class="mw-page-title-main">Megaraptora</span> Extinct clade of dinosaurs

Megaraptora is a clade of carnivorous tetanuran theropod dinosaurs with controversial relations to other theropods. Its derived members, the Megaraptoridae are noted for their large hand claws and robust forelimbs, which are usually reduced in size in other large theropods.

<span class="mw-page-title-main">Orionides</span> Clade of dinosaurs

Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.

<span class="mw-page-title-main">Timeline of tyrannosaur research</span>

This timeline of tyrannosaur research is a chronological listing of events in the history of paleontology focused on the tyrannosaurs, a group of predatory theropod dinosaurs that began as small, long-armed bird-like creatures with elaborate cranial ornamentation but achieved apex predator status during the Late Cretaceous as their arms shrank and body size expanded. Although formally trained scientists did not begin to study tyrannosaur fossils until the mid-19th century, these remains may have been discovered by Native Americans and interpreted through a mythological lens. The Montana Crow tradition about thunder birds with two claws on their feet may have been inspired by isolated tyrannosaurid forelimbs found locally. Other legends possibly inspired by tyrannosaur remains include Cheyenne stories about a mythical creature called the Ahke, and Delaware stories about smoking the bones of ancient monsters to have wishes granted.