The Arizona Museum of Natural History and Virginia Tech announce the discovery and publication of a mid-Cretaceous Period tyrannosaur that significantly contributes to understanding tyrannosaur evolution. The find is important because of the scarcity of mid-Cretaceous deposits worldwide. Fossils from such rare deposits offer unique insights into the ancestors of the mighty dinosaurs of the end-Cretaceous.
The find is announced and described today in the journal Nature Ecology and Evolution. Co-discoverer and lead author of the paper, Mesa Arizona native Sterling Nesbitt, Department of Geosciences, Virginia Tech, states that the tyrannosaur "belongs to a dinosaurian fauna that just precedes the iconic dinosaurian faunas in the latest Cretaceous that include some of the most famous dinosaurs."
The tyrannosaur is named Suskityrannus hazelae. Suski means coyote in the Zuni language (used after consultation with Zuni Tribe). Tyrannus hazelae means tyrant (Latin) of Hazel, or Hazel's coyote tyrant, and is named after Hazel Wolfe, one of the field project's critical members.
Two tyrannosaurs of the same species were found within about 50 meters of each other in the Moreno Hill Formation in the Zuni Basin of western New Mexico. Field crews from the Arizona Museum of Natural History recovered the dinosaurs in 1996-1998. The fossils date to the early Middle Turonian, or 92 million years ago, thus predating the massive T. rex by 27 million years.
As the authors state, "This new species is phylogenetically intermediate between the grade of early-diverging, small to medium-sized tryannosauroids that originated in the Middle Jurassic and the enormous, bone-crunching apex predator tyrannosaurids of the final 20 million years of the Cretaceous."
These mid-Cretaceous gracile animals had a foot shaped for speed and recurved serrated teeth confirming their carnivorous status. Analyses of the skeletons suggest they had not yet completed their growth, i.e. they were juveniles. The dinosaur was about three meters (nine feet) long, stood 2-3 feet tall at the hip, and weighed 20-40 kilograms (about 45-90 pounds).
Dr. Steven Brusatte, University of Edinburgh, author of The Rise and Fall of the Dinosaurs and co-author of the Nature Ecology and Evolution paper, writes that "Suskityrannus is a key link between the enormous bone-crunching dinosaurs like T. rex and the smaller species they evolved from. The new species shows that tyrannosaurs developed many of their signature features like a muscular skull, broad mouth, and a shock-absorbing foot when they were still small, maybe as adaptations for living in the shadows."
These tyrannosaurs are also significant for our understanding of associated faunas from the Zuni Basin in similar timeframes: the ceratopsian Zuniceratops chistopheri, the hadrosaur Jeyawati rugoculus, the therizinosaur Nothronychus mckinleyi and ankylosaur fossils. In the late Cretaceous, ceratopsians such as Triceratops, numerous large hadrosaurs, ankylosaurs and, of course, the mighty tyrannosaurs roamed the landscapes, only to face the rapid extinction event about 66 million years ago.
Sterling Nesbitt, lead author of the Nature Ecology and Evolution paper, was a teen volunteer at the Arizona Museum of Natural History when he was part of the team that discovered Suskitryannus. Now an assistant professor at Virginia Tech, he writes that "My discovery of a partial skeleton of Suskityrannus put me onto a scientific journey that has framed my career."
The Arizona Museum of Natural History will permanently house the Suskityrannus fossils. Benjamin Paysnoe, Paleo-artist with the museum, has created a full-scale model of Suskityrannus that is on display at the museum along with a reproduction of the Suskityrannus skeleton. Also on view are Zuniceratops, therazinosaur remains, a partial skeleton and animatronic model of an early ankylosaur, as well as earlier and later dinosaurs.
Arizona Museum of Natural History
53 N Macdonald, Mesa, AZ 85201
Contact: Alison Stoltman
Tel. 480-644-4040
alison.stoltman@mesaaz.gov
FACT SHEET - A mid-Cretaceous tyrannosauroid and the origin of North American end-Cretaceous dinosaur assemblages
Sterling J. Nesbitt, Robert K. Denton Jr, Mark A. Loewen, Stephen L. Brusatte,
Nathan D. Smith, Alan H. Turner, James I. Kirkland, Andrew T. McDonald,
and Douglas G. Wolfe
Journal: Nature Ecology & Evolution
Paper: http://dx.doi.org/10.1038/s41559-019-0888-0
Summary
The origin and early evolution of tyrannosauroid dinosaurs has been a topic of great scientific interest since their discovery. Tyrannosauroid dinosaurs have a long history and the youngest members of the group, tyrannosaurids including the iconic Tyrannosaurus rex, reached incredible sizes. However, when they got big and which features were associated with reaching larger sizes is less understood. Additionally, few close relatives of the tyrannosaurids, (non tyrannosaurid tyrannosauroids) are known from North America and almost no dinosaurs are known from a time when sea levels were at their highest in the early part of the Late Cretaceous (Turonian stage about 92 million years ago).
In this paper, we present a small tyrannosauroid from the Turonian known from much of a skull and skeleton. We describe this as a new species (Suskityrannus hazelae) that links the small tyrannosauroids from North America and China with the much larger tyrannosaurids that lasted until the final days of the non-avian dinosaurs. Suskityrannus has a much more slender skull and foot than its later cousins. Furthermore, Suskityrannus is part of a unique dinosaurian fauna composed of smaller, close relatives of the classic members of Late Cretaceous faunas - large cetaposians like Triceratops, predators like Tyrannosaurus rex, and duckbill dinosaurs like Edmotosaurus.
Major Points
o The discovery of Suskityrannus fills in a critical gap in the fossil record of tyrannosauroid dinosaurs because there are few species between the Early Cretaceous species and the latest Cretaceous species (including Tyrannosaurus rex)
o Suskityrannus fills in a critical morphological gap between small tyrannosauroids and larger tyrannosaurids. For example, the foot of Suskityrannus is combination of the long foot of early tyrannosauroids with features (a pinched middle metatarsal) of later tyrannosauroids.
o Suskityrannus is one of the last smaller tyrannosauroids; soon after, tyrannosauroids reached their enormous sizes.
o Suskityrannus has one of the most complete skeletons of any non-tyrannosaurid tyrannosauroid from North America - all of the older occurences consist of teeth, isolated bones, or a partially associated skeleton.
o The fossil record of dinosaurs ~94-90 million years ago is one of the most poorly sampled, and least understood times of the Cretaceous Period, and Suskityrannus is from a dinosaur assemblage that documents this critical interval
o Suskityrannus and its associated dinosaurian assemblage (=fauna) (neoceratopsian Zuniceratops christopheri, the hadrosauromorph Jeyawati rugoculus, the therizinosaurid Nothronychus mckinleyi, and ankylosaur fossils) helps us understand the origin of the iconic dinosaur assemblages that lived in North America at the end of the Cretaceous.
o Just after this dinosaur assemblage, dinosaurs closely related to the Moreno Hill dinosaur assemblage increase in diversity and body-size in the Late Cretaceous.
? These include the ceratopsids (including Triceratops), hardosaurids (= duckbilled dinosaurs), and tyrannosaurids (including Tyrannosaurus rex).
Facts/Background
Name
'Suskityrannus' is derived from the Zuni 'Suski', which refers to 'coyote', the Latin 'tyrannus' meaning 'king', and 'hazelae' for Hazel Wolfe, whose tireless efforts, support, and sacrifices made possible much of the success at the Zuni sites.
We consulted with the Pueblo of Zuni Tribal Council for use of the Zuni word 'Suski' in the genus name.
Size
We estimate that Suskityrannus was 3.0 meters (~9 feet) long, and it 0.6-1.0 meters (~2-3 feet) tall at the hip.
20-40 kilograms in weight (45-90 pounds).
Relationships
Suskityrannus is a non-tyrannosaurid tyrannosauroid
Suskityrannus is more closely related to Tyrannosaurus rex (and other tyrannosaurids) than to all other Early Cretaceous tyrannosauroids.
All tyrannosaurids are tyrannosauroids, but not all tyrannosauroids are tyrannosaurids; the tyrannosaurid group is within the larger tyrannosauroid group
Tyrannosaurus rex and many other gigantic forms (e.g., Albertosaurus) are tyrannosaurids
Tyrannosauroids are theropod dinosaurs that ranged from the Middle Jurassic until the last days of the Cretaceous.
Tyrannosauroids are almost exclusively found in the northern hemisphere.
Anatomy
Suskityrannus was bipedal (stood on two legs) with its hindlimbs positioned directly underneath its body.
Suskityrannus had long feet, much longer than its larger cousins.
Suskityrannus had sharp, recurved, and serrated teeth, suggesting that it had a carnivorous diet.
Much of the skeleton of Suskityrannus is represented, but parts of the skull, hands, feet, and tail are still unknown.
We do not know if Suskityrannus had small arms (like Tyrannosaurus rex), and we do not know if Suskityrannus had two or three fingers.
The Suskityrannus specimens are all juveniles, but it is clear that Suskityrannus did not grow to the gigantic sizes of later tyrannosaurids.
Age & Geography
The Mesozoic Era includes the Triassic, Jurassic, and Cretaceous periods.
The Cretaceous Period lasted from 145-66 million years ago and dinosaurs were highly diverse during this time.
Suskityrannus is from the mid-Cretaceous (early Middle Turonian) about ~92 million years ago and predates Tyrannosaurus rex by ~27 million years.
Suskityrannus fossils were excavated from the Moreno Hill Formation, in the Zuni Basin of western New Mexico
During the mid-Cretaceous, sea level was at one of the highest levels it has ever been.
During the mid-Cretaceous, North America was bisected by the Western Interior Seaway so that it was not possible to get from today's west coast to the east coast of the United States.
The world was much warmer in the Cretaceous Period than it is today.
Discovery and history of the specimens
The locality "Two Rocks Balanced Basin" was discovered by Douglas Wolfe (Mesa Southwest Museum (MSM)now Arizona Museum Natural History) and his family on 11/11/96. Discoveries that day led to the formation of the Zuni Basin Paleontological Project (ZBPP) by Douglas Wolfe, Jim Kirkland and Robert Denton. Sterling Nesbitt was the first student to participate in ZBPP research with ZBPP scientists.
The first fossils of Suskityrannus, including the holotype with a partial skull were found in 1997 by Robert Denton and Brian Anderson, during the first ZBPP Expedition with citizen scientists from MSM's Southwest Paleontological Society (SPS).
The second more complete specimen was found by Sterling Nesbitt (lead author) and Doug Wolfe and was collected by Sterling, Doug Wolfe, and James Kirkland (among the author list), in 1998 during ZBPP & Dinamation International Society's Expedition
During the discovery, Sterling was a high school junior, today, he is an Assistant Professor in the Department of Geosciences at Virginia Tech.
This was the first new species of dinosaur he discovered, but not the first named by him
The Suskityrannus specimens all come from the same rock layer within 50 lateral meters of each other.
All specimens of Suskityrannus are from a rock unit called the Moreno Hill Formation, in the Zuni Basin of western New Mexico.
Suskityrannus was found with other dinosaurs including: the neoceratopsian Zuniceratops christopheri, the hadrosauromorph Jeyawati rugoculus, the therizinosaurid Nothronychus mckinleyi, and ankylosaur fossils. The remains of fish, turtles, mammals, lizards, and crocodylians were also found in the same area.
The Moreno Hill Dinosaur assemblage is reposited at the Arizona Museum of Natural History in Mesa Arizona.
Other
Before we understood that Suskityrannus was a tyrannosauroid, it was referred to as "Coelurosaur" and was animated in the Discovery Communications program "When Dinosaurs Roamed America" (2001) https://en.wikipedia.org/wiki/When_Dinosaurs_Roamed_America
A 3D model of the holotype skull of Suskityrannus is available through SketchFab: https://skfb.ly/6IZOW
The CT dataset of the holotype skull of Suskityrannus is available through Morphosource here: https://www.morphosource.org/Detail/SpecimenDetail/Show/specimen_id/19857
Quotes
Dr. Sterling J. Nesbitt, Virginia Tech:
"Suskityrannus gives us a glimpse into the evolution of tyrannosaurs just before they take over the planet".
"My discovery of a partial skeleton of Suskityrannus put me onto a scientific journey that has framed my career; I am now an Assistant Professor that gets to teach about Earth history".
"Suskityrannus belongs to a dinosaurian fauna that just proceeds the iconic dinosaurian faunas in the latest Cretaceous hat include some of the most famous dinosaurs".
Max Ofsa, Manager of 3D Design Studio (not an author on the paper, but helped 3D scan the skull of Suskityrannus), Virginia Tech:
"We are happy to use technology (3D surface scanners) to support ongoing research and outreach of our departments at Virginia Tech"
"Our combined efforts allows access to one-of-kind objects to as many people as possible."
Dr. Steven Brusatte, University of Edinburgh:
'Suskityrannus is a key link between the enormous bone-crunching dinosaurs like T. rex and the smaller species they evolved from. The new species shows that tyrannosaurs developed many of their signature features like a muscular skull, broad mouth, and a shock-absorbing foot when they were still small, maybe as adaptations for living in the shadows."
Dr. Mark Loewen, University of Utah and Natural History Museum of Utah:
"Suskityrannus and the other dinosaurs of the Moreno Hill fauna dinosaur give us a picture of the unique founders of the famous of the Late Cretaceous faunas of North America. These small, simple forms stranded on the "Gilligan's Island" of western North America eventually gave rise to the largest body sizes in each of their respective groups by the end of the Cretaceous."
Dr. James Kirkland, Utah Geological Survey:
"Helping facilitate the research in the Moreno Hill Formation during the 1990s, was one of my greatest accomplishments prior to becoming the State Paleontologist of Utah."
"Following Sterling out to see his dinosaur; I was amazed at how complete a skeleton was lying exposed at the site. Clearly the most complete individual skeleton we had found in the entire basin and we had not even started to collect it."
Dr. Andrew McDonald, Western Science Center:
"Until now, all the dinosaurs described from the Moreno Hill Formation are plant-eaters: the horned dinosaur Zuniceratops, the bipedal long necked Nothronychus, and the primitive duck-billed dinosaur Jeyawati. Suskityrannus, the first carnivorous dinosaur described from the Moreno Hill, adds an important new element to our view of this 92-million-year-old ecosystem."
Dr. Nathan Smith, Natural History Museum of Los Angeles County
"Suskityrannus is part of a fossil assemblage representing a poorly sampled time in vertebrate history that records a major transition in Cretaceous dinosaurs."
"Suskityrannus helps us flesh out the 'origins story' of Tyrannosaurus rex and its kin"
Douglas Wolfe, Zuni Dinosaur Institute for Geosciences (ZDIG)
"The discovery and description of Suskityrannus is one of the crowning achievements of the Zuni Basin Paleontological Project and a very successful example of collaboration between scientific professionals, students and volunteers working to narrow the "Cretaceous Dinosaur Gap".
"When I first met Sterling, he was a young student with extraordinary focus and passion. He was always going to be a paleontologist. Working with young scientists like Sterling and Andrew alongside experienced colleagues like Jim Kirkland, Bob Denton, Karen Chin and our co-authors has been superbly rewarding."
"90 million years ago, Earth was much warmer, oceans much higher; a Suskityrannus in New Mexico could walk to Mongolia but would have to swim to Kansas. The dinosaurs, crocodiles, trees, trackways and other fossils from the Moreno Hill Formation provide a glimpse of life in the Cretaceous Greenhouse and clues to Earth's changing future."
"I was very pleased when I learned our co-authors wanted to name the Zuni Basin tyrannosaur for Hazel. She is the light of my life and the glue that helps to hold our project together. I am very fortunate to have a partner who shares my fascination with the history and beauty of Life on Earth, and the spirit to explore some very remote country."
Our paper does NOT say that...:
- Suskityrannus is a direct ancestor of Tyrannosaurus rex.
- Suskityrannus grew into Tyrannosaurus rex.
Funding:
Discovery Channel
Department of Geosciences at Virginia Tech
American Museum of Natural History
Arizona Museum Natural History
Potential people to contact:
Dr. Robert McCord, Arizona Museum of Natural History Curator of Paleontology
Doug Wolfe CEO Zuni Dinosaur Institute of Geo Sciences Thomas Carr, Carthage College
Mark Norell, American Museum of Natural History
Eugenia Gold, Suffolk University
Thomas Holtz, University of Maryland
Lindsay Zanno, North Carolina Museum of Natural History
Xu Xing, Institute of Vertebrate Paleontology and Paleoanthropology