David Dunkle immigrated to the United States
in his youth and attended the University of Kansas studying paleontology and went on to
earn a doctoral degree from Harvard studying under the famous paleontologist Alfred Romer. After graduating he became the chief paleontologist
at the Cleveland Museum of Natural History where he worked on arthrodires, armored fish
from the Devonian Period. He is best known today as the Dunkle in the
gigantic armored fish named after him, Dunkleosteus. In 1942, during World War II, Dunkle traveled
to Carter County Montana to collect fossils from the Cretaceous Lance Formation of Montana
along Sand Creek. During the trip, Dunkle and his team excavated
a beautifully preserved dinosaur skull that would become one of the most controversial
dinosaur discoveries ever made. Welcome to the Natural History of Dinosaurs,
my name is Benjamin Burger, and in this video we are looking at the controversy over Nanotyrannus,
a possible T. rex youngster. The fossil collected by Dunkle was prepared
for exhibit at the museum in Cleveland Ohio and fully described in a paper by the Smithsonian
paleontologist Charles Gilmore in 1946. He named the new dinosaur Gorgosaurus lancensis. The genus Gorgosaurus had previously been
named for fossil dinosaurs found in Alberta Canada, which are believed to be closely related
to Albertosaurus. These large carnivorous theropod dinosaurs
are members of the same family as Tyrannosaurus rex, but from slightly older rock layers,
in the Campanian Age of the Late Cretaceous Gilmore notice that the skull bore many similarities
to Tyrannosaurus rex, and was likely from a similar stratigraphic position in the Maastrichtian
Age, latest Cretaceous. The best-known Tyrannosaurus rex of the time
was found in the Maastrichtian Age Hell Creek Formation about 250 miles north of the new
fossil dinosaur site. Yet, the skull was less than half the size
of the skull of Tyrannosaurus rex, and bore more similarities to a smaller specimen named
Gorgosaurus sternbergi from Canada housed at the American Museum in New York. The skulls of both Gorgosaurus sternbergi
and Gorgosaurus lancensis where long and slender, and lacked the big bulky appearance of Tyrannosaurus
rex, and Albertasaurus In 1988, the Canadian paleontologist Phil
Currie, with co-authors Bob Bakker and Michael. Williams published a paper naming the Dunkle
dinosaur specimen a new genus, named Nanotyrannus. Phil Currie was actively excavating fossils
from Alberta Canada, and had acquired some specimens of Gorgosaurus from different life-stages
and the Dunkle specimen from Montana had a number of differences from these juvenile
specimens of Gorgosaurus, so the authors erected a new genus named Nanotyrannus. In 1990, the famous Tyrannosaurus rex specimen,
Sue was discovered from the Hell Creek Formation on the Cheyenne River Indian Reservation of
South Dakota, about 250 miles east of the Dunkle specimen discovery site in Montana. Given the proximity of and similar stratigraphic
occurrence, many researchers speculated that Nanotyrannus was juvenile specimen of Tyrannosaurus
rex, rather than Gorgosaurus or a separate genus. Thomas Carr was the first to formally suggest
that Nanotyrannus was a just a juvenile Tyrannosaurus rex. In his classic revision of Tyrannosaurid systematics. In 2001, the Burpee Museum in Rockford Illinois
funded a trip to collect fossils from the same area as the Dunkle specimen, and found
a second dinosaur named Jane that closely resembled it, rather than identifying the
new Jane specimen as Nanotyrannus, the researchers suggested that both specimens discovered in
the area were juvenile specimens of Tyrannosaurus. In 2005 a science conference was held at the
Burpee Museum. And Phil Currie and Michael Williams, two
authors that named Nanotyrannus agreed that both specimens likely represent juvenile specimens
of Tyrannosaurus rex, but not all researchers present were convinced. Leading to a continuing controversy over the
status of Nanotyrannus that has been heavily debated, maybe more than it deserves on the
internet between camps on either side. Further discoveries of juvenile specimens
of Tarbosaurus bataar from Mongolia, like the named genus Raptorex,which was revaluated
as a young Tarbosaurus, highlighted some of the changes that occurs in large theropod
dinosaurs as they grow up. And a new recent research paper has begun
to chip away at Nanotyrannus, further supporting Nanotyrannus’s juvenile status, as a youngster,
rather than a different species. This brings me to talk a little with you today
about the science of ontogeny. Ontogeny is the study of an organism’s shape
or morphology from the time of fertilization from an egg, through the entirety of an organism’s
full lifespan, until death. Every organism undergoes changes as it matures
and grows. These changes are manifested in changes to
the portions and size of the various anatomical components of an animal, including the overall
shape and form of an animal’s skull as it grows and matures. Ontogeny is closely related to the study of
allometry [Like llama], the study of how things change as they get bigger or smaller. One of the earlier researchers on allometry
was D’arcy Thompson, who wrote a famous book on the subject, entitled On Growth and
Form in 1917. Thompson developed a keen understanding of
growth in organism. As a multicellular organism grows it adds
new tiny individual cells to its body, the growth of these individual cells dictates
the growth within each portion of an animal, which can change drastically overtime. If one part of the organism grows more cells,
than another part, the shape of the animal will change, enlarging one part over another. The timing of the cellular growth of different
parts of an animal results in distortions in the size and shape of an animal as it matures. This difference in timing is called Heterochrony,
meaning different timing. Some animals exhibit isometric growth, which
means that younger individuals have identical portions to older individuals, they are like
mini versions of the adult form. However, most animals exhibit heterochrony,
with non-isometric growth. For example, in humans, babies have large
heads compared to their body, such that if you enlarged a baby to adult size, it would
not look like a normal adult human in portions. This is because the brain grows slower after
birth, than the arms and legs. In Tyrannosaurids, younger individuals have
longer and slender skulls, then their adult forms. New research has looked at Lines of Arrested
Growth in the sectioned bones of these dinosaurs identified as Nanotyrannus, which allow researchers
to determine the age of individual specimens. Like tree rings these lines found in the compact
bone, are believed to be annual growth rings. Specimens of Nanotyrannus are estimated to
be between 13 to 15 years of age, by counting these rings, whereas adult specimens of Tyrannosaurus
likely lived up to 30 or more years. There are still a few people that still hold
out that Nanotyrannus was is a dwarfed version of Tyrannosaurus rex, and separate species. They point to some differences in the teeth
and jaw, and arm. They invoke other dwarf species, like the
Channel Island Mammoths, which are mini-versions of Mammoths that were isolated during the
last Ice Age on the Channel Islands off the coast of California, where they evolved into
miniature versions compared to mammoths on the continent. This type of dwarfism requires geographic
isolation from the rest of the population. So the question becomes, was Nanotyrannus
geographically isolated from the rest of the population of Tyrannosaurus rex? Maybe on an island in the retreating Western
Interior Seaway? Most specimens attributed to Nanotyrannus
come from Southeastern region of Montana, whereas the larger population of Tyrannosaurus
rex has a much broader geographic range with specimens found from Texas, Colorado, Utah,
Wyoming, northern Montana, and the Dakotas. There is one specimen of Nanotyrannus that
appears to break this idea. A mysterious specimen known as the dueling
dinosaurs, which is a pair of dinosaurs, one being Triceratops, and the other a Nanotyrannus
found together in Northern Montana, near where some of the best specimens of Tyrannosaurus
rex have been found along the Missouri River. This single specimen runs opposite to the
idea of Nanotyrannus was geographic isolated, and further supports the idea that specimens
of Nanotyrannus are just younger individual specimens of Tyrannosaurus rex. Now the dueling dinosaurs have not been fully
described in detail. The specimen was found on private land it
failed to sell at auction, and currently is in storage. Hopefully sometime in the future it will put
on display at a museum and fully described in a publication. I think is amazing that we have enough specimens
now, of Tyrannosaurus rex, that we can start to understand the grow and development of
this iconic dinosaur. And I don’t think this diminishes the importance
of these specimens, in fact I think that it makes them more special, in being examples
of juvenile individuals of Tyrannosaurus rex. This is my first video of 2020, and I want
to try something new this year for those of you who support me on Patreon. I’ve been trying to think of way to give
back to those of you who support me. So this year, I’m going to be giving away
an original art work that will appear in each video that you support. This week, I’ve giving away a pencil sketch
I did of the holotype specimen of Nanotyrannus that Dunkle discovered in Montana. I will draw a card from a deck, with the names
of those supporters who contribute to my Patreon page at a new $5 level or above that now appears
on my Patreon page, if you like a chance at some original artwork of dinosaurs and other
extinct creatures, click on the link in the distribution below, if you currently support
me on the $1 level maybe consider increasing it to 5. I’ll draw from the list after each video,
starting with the next video, when I will draw two names, two changes to win, as I return
this year to hopefully be making weekly or bi-weekly videos uploading 2 to 4 new videos
each month. For those of you who have supported me at
this level currently, log in and fill out your mailing address, so that that if your
name is draw, I can mail out this art work. This includes my Eohippus supporters, Fred
Olney, Marlowe Andreyko, Magnus Solvang, Paolo Luzzatto-Fegiz, Max McGregor, Niso, Shawn
Cromett, and Emmett Larson. I’ll be making more videos on dinosaurs,
paleontology and geology, and I am super excited to add more videos this coming year! And if you have not done so, please at the
very least just subscribe to my channel on YouTube.
Hi Dr. Burger, I just recently discovered your YouTube-Channel and I love it so far, especially since subtitles are also available for me as a deaf person. So thank you for that!
I watched your video about Nanotyrannus and one thing bugs me and maybe you can help me. I'm sorry in advance, if the answer is obvious (but not for me at the moment):
You mentioned at 9:33 the lines of arrested growth and specimens of Nanotyrannus are estimated to be between 13 to 15 years of age, whereas specimens of adult Tyrannosaurus up to 30 or more years. Let's say, all specimens of Nanotyrannus are T-Rex youngsters respectively juveniles and here's my question: It is just me or has the T-Rex a very odd growth-rate? Because if a specimen of Tyrannosaur is 15 years old and still considered a juvenile, when did they reached maturity? Do we know how big freshly hatched T-Rex babies were?
I searched for the growth rate of big animals, such as elephants and whales. Elephants can be considered adult around 15-17 years. Even the blue whale, the biggest animal ever, reach maturity at 10 years. But they don't grow anymore fast, only a little and/or slowly. I mean, blue whales who reached maturity are around 16m (52 feet) long and they need a lot more time to grow to 30m (100 feet). By the time they reach this length, they're about 50 to 80 years old. Compared to these big animals, Nanotyrannus and T-Rex however were growing fast (from 15 to 30 years). At least for me. Don't you find it odd too, that they were still growing fast at this rate? Maybe you can clean it up for me?
I hope you unterstand my question and I'm looking forward for your answer. Paleontology is just a hobby for me, so not everything is obvious for me. Thanks again for your amazing content!