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Dynamoterror dynastes
Dynamoterror dynastes

[Image: Dynamoterror_dynastes-novataxa_2018-McDo...Center.jpg]
Dynamoterror was about 30 feet long, hunting prey during the Late Cretaceous. (Western Science Center)

Temporal range: Late Cretaceous, 78 Ma 

Scientific classification
Kingdom:  Animalia
Phylum:  Chordata
Clade:  Dinosauria
Order:  Saurischia
Suborder:  Theropoda
Family:  †Tyrannosauridae
Subfamily:  †Tyrannosaurinae
Genus:  †Dynamoterror  McDonald et al., 2018
Type Species:  Dynamoterror dynastes  McDonald et al., 2018

Dynamoterror is a genus of tyrannosaurid theropod dinosaur that lived in what is now New Mexico during the Late Cretaceous Period, approximately 78 million years ago. The generic name is derived from the Greek word dynamis meaning "power" and the Latin word terror.

McDonald et al. found Dynamoterror to belong to the Tyrannosaurinae. In their phylogenetic analysis, the genus formed a polytomy with other large bodied derived tyrannosaurines. This polytomy was likely caused by the genus' fragmentary nature.

The holotype specimen of Dynamoterror, UMNH VP 28348, originates from the lower Campanian of the Allison Member of the Menefee Formation, New Mexico. Other fauna known from the formation include the nodosaurid Invictarx, the alligatoroid Brachychampsa sealeyi, and an unnamed centrosaurine ceratopsid.

Newly Discovered Tyrant Dinosaur Stalked Ancient New Mexico

The Dynamoterror, a relative of Tyrannosaurs rex, lived millions of years before other known species of tyrannosaur

By Brian Switek
OCTOBER 9, 2018 8:00AM

Tyrannosaurs often bear fierce names. Aside from the “tyrant lizard” Tyrannosaurus itself, there’s the “monstrous murderer” Teratophoneus, the “frightful lizard” Daspletosaurus, and the “gore king” Lythronax. But a new set of tyrannosaur bones extracted from the 80-million-year-old rock of New Mexico may have one of the most imposing names of all—Dynamoterror dynastes, the “powerful terror ruler.”

The remains of Dynamoterror were found in New Mexico’s Menefee Formation in 2012 during an expedition led by Western Science Center paleontologist Andrew McDonald and CEO of the Zuni Dinosaur Institute for Geosciences, Douglas Wolfe. During that year’s field season, expedition volunteer Eric Gutierrez found fragmented bones spilling out of the sandstone.* Dinosaurs are hard to find in this part of the San Juan Basin, making almost any find worth noting, but initial clues indicated that this find was something special.

“We could tell that it was a large theropod from the large fragments of hollow limb bones,” McDonald says, referring to the broader family that tyrannosaurs, ostrich mimic dinosaurs, raptors, birds and others belong to.

Time had not been kind to the bones of Dynamoterror, breaking and scattering the bones. It took years of puzzling together the recovered shards before the critical fragments—a pair of telltale skull bones called frontals—were pieced together, revealing the fossil’s identity as a previously-unknown tyrannosaur. The dinosaur is described in a paper published today in PeerJ.

Although the fossil is scrappy, it still adds context to the broader picture of the roughly 25 distinct tyrannosaurs known so far. Not only is Dynamoterror new, but it falls in a specific tyrannosaur subgroup that contains some of the last and largest of the species, like T. rex itself.
T. rex lived between 68 and 66 million years ago, and many of its famous relatives—like Gorgosaurus and Albertosaurus—lived about 75 million years ago. Dynamoterror and its relative Lythronax from Utah are more ancient still, about 80 million years old. “This indicates that derived tyrannosaurs must have arisen at an even earlier date” than previously expected, New Mexico Museum of Natural History and Science paleontologist Thomas Williamson says. The find points to an older, as-yet-unknown diversification of these famous carnivores.

[Image: Dynamoterror_dynastes-novataxa_2018-McDo...oley--.jpg]
A scan of the Dynamoterror skull frontal bones, used to identify the species. (Western Science Center)

n life, McDonald and colleagues hypothesize, Dynamoterror would have been about 30 feet long. Far larger than the earliest tyrannosaurs, though not quite as big as the celebrity T. rex, Dynamoterror is comparable in size to a few other tyrannosaurs of similar age—large enough to earn top predator status in its ancient realm.
Back in this tyrannosaur’s heyday, McDonald says, “the Menefee would have been much like the swamps and forest of the southeastern U.S.—hot, humid, and lush.” Shovel-beaked hadrosaurs, armored dinosaurs, and horned dinosaurs were some of the neighbors Dynamoterror rubbed shoulders with and likely preyed upon.

What makes Dynamoterror stand out, however, is that it’s another piece in an emerging picture of dinosaur evolution running riot between 80 and 75 million years ago. Back in the Late Cretaceous, North America was split in two by the Western Interior Seaway, a warm stretch of water that washed over the middle of the continent, with the western half known to experts as Laramidia. From the stony records of this subcontinent, paleontologists have been finding a slew of unexpected dinosaurs.
Historic finds in the northern parts of Laramidia, such as modernday Alberta and Montana, revealed rich communities of dinosaurs such as tyrannosaurs, horned dinosaurs, armored dinosaurs and more. Fossils found in southern rocks of the same age were often given the same names as the northern species. But in the past three decades, paleontologists have started to put together a very different picture. New discoveries and fossil revisions have shown that the dinosaurs found in Utah, New Mexico, Texas and Mexico were not the same as those found in the north. If you were to walk from Mexico to Alaska 80 million years ago, you’d find a gradient of different dinosaurs as you hiked along.
Dynamoterror is part of this story, and an important one as it’s from an area with few known fossils. No dinosaurs had been named from the Menefee Formation until earlier this year, when an armored dinosaur called Invictarx was identified. Dynamoterror is now the second, and the fact that it differs from other known tyrannosaurs of a similar age indicates that there were distinct evolutionary pockets along the length of the ancient subcontinent.

The new tyrannosaur also points to what may yet be found. Both Dynamoterror and Lythronax are from southern North America and are about 80 million years old. There seems to be a bias against the preservation of dinosaurs in rocks of this age, Williamson says, but the few and often scrappy fossils that have turned up have indicated that dinosaur diversity was just as rich as it was in the 75-million-year-old rocks where preservation is better.The search is taxing, but it means there are more dinosaurs to dig up.
Some of them will likely be tyrannosaurs. To the north, McDonald says, “roughly contemporaneous rocks have yet to produce diagnostic tyrannosaurid material.” It could very well be that there were other unusual tyrant lizards in northern Laramidia, now entombed in the rocks, waiting to be uncovered and help fill in the picture of how these tyrants came to rule North America.

Journal Reference:
Andrew T. McDonald, Douglas G. Wolfe and Alton C. Dooley Jr. 2018. A New Tyrannosaurid (Dinosauria: Theropoda) from the Upper Cretaceous Menefee Formation of New Mexico. PeerJ. 6:e5749.  DOI:  10.7717/peerj.5749

The giant tyrannosaurids were the apex predators of western North America and Asia during the close of the Cretaceous Period. Although many tyrannosaurid species are known from numerous skeletons representing multiple growth stages, the early evolution of Tyrannosauridae remains poorly known, with the well-known species temporally restricted to the middle Campanian-latest Maastrichtian (∼77–66 Ma). The recent discovery of a new tyrannosaurid, Lythronax argestes, from the Wahweap Formation of Utah provided new data on early Campanian (∼80 Ma) tyrannosaurids. Nevertheless, the early evolution of Tyrannosauridae is still largely unsampled. We report a new tyrannosaurid represented by an associated skeleton from the lower Campanian Allison Member of the Menefee Formation of New Mexico. Despite fragmentation of much of the axial and appendicular skeleton prior to discovery, the frontals, a metacarpal, and two pedal phalanges are well-preserved. The frontals exhibit an unambiguous autapomorphy and a second potential autapomorphy that distinguish this specimen from all other tyrannosaurids. Therefore, the specimen is made the holotype of the new genus and species Dynamoterror dynastes. A phylogenetic analysis places Dynamoterror dynastes in the tyrannosaurid subclade Tyrannosaurinae. Laser-scanning the frontals and creation of a composite 3-D digital model allows the frontal region of the skull roof of Dynamoterror to be reconstructed.

Holotype: UMNH VP 28348, incomplete associated skeleton including the left and right frontals, four fragmentary vertebral centra, fragments of dorsal ribs, right metacarpal II, supraacetabular crest of the right ilium, unidentifiable fragments of long bones, phalanx 2 of left pedal digit IV, and phalanx 4 of left pedal digit IV.

Etymology: Dynamoterror is derived from the transliterated Greek word dynamis (“power”) and the Latin word terror. The specific name, dynastes, is a Latin word meaning “ruler.” The intended meaning of the binomen is “powerful terror ruler.” The name also honors the binomen “Dynamosaurus imperiosus” (Osborn, 1905), a junior synonym of Tyrannosaurus rex (Osborn, 1905, 1906), but a particular childhood favorite of the lead author.

Locality: UMNH VP 28348 was collected in San Juan County, New Mexico, on land administered by the US BLM. Precise locality data are on file at UMNH and the BLM.

Horizon: UMNH VP 28348 was collected from outcrops of the Juans Lake Beds (Miller, Carey & Thompson-Rizer, 1991), upper part of the Allison Member, Menefee Formation; lower Campanian, Upper Cretaceous. Lucas et al. (2005) produced a radioisotopic date of 78.22 ± 0.26 Ma from a bentonite layer near the top of the Menefee Formation in the Gallina hogback in the eastern part of the San Juan Basin. In the part of the San Juan Basin where UMNH VP 28348 was collected, the overlying Cliff House Sandstone contains fossils of the ammonoid Baculites perplexus (Siemers & King, 1974), corresponding to between 78.0 and 78.5 Ma (Molenaar et al., 2002). According to the regional stratigraphic correlation chart of Molenaar et al. (2002), the Menefee Formation spans approximately 84.0–78.5 Ma, based upon correlations with marine biostratigraphic zones. This age range corresponds to uppermost Santonian—middle Campanian (Cohen et al., 2013).

Specific diagnosis (as for genus by monotypy): tyrannosaurine tyrannosaurid distinguished by two autapomorphies on the frontals: (1) prefrontonasal and prefrontolacrimal processes are in close proximity, separated only by a shallow notch; and (2) subrectangular, concave, laterally projecting caudal part of the postorbital suture, separated from the rostral part by a deep groove. The second autapomorphy should be treated as provisional, given the ontogenetic variation observed in this region of the frontal in other tyrannosaurids (Carr & Williamson, 2004) (see description of the lateral surface of the frontal below). In the context of the phylogenetic analysis of Carr et al. (2017), which is used herein, UMNH VP 28348 exhibits a feature that supports its affinities among derived tyrannosauroids (1561, “frontal, dorsotemporal fossa, medial extension, dorsal view: meets opposing fossa at the midline”; also present in Timurlengia euoticaXiongguanlong baimoensisB. sealeyi, and Tyrannosauridae), and a feature identified by Carr et al. (2017) as an unambiguous synapomorphy of “derived tyrannosaurines” (1571, “frontal, sagittal crest, form, dorsal and lateral views: present and pronounced (dorsoventrally tall), single structure”).

The description of Dynamoterror dynastes from the lower Campanian Allison Member of the Menefee Formation provides additional data on the morphology and diversity of early tyrannosaurines in Laramidia. However, additional discoveries are needed to elucidate the paleobiogeographic history of tyrannosaurines.
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