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Nearly
complete 'chicken from hell,' from mysterious dinosaur group
Nearly
complete 'chicken from hell,' from mysterious dinosaur group
Date:
March 19,
2014
Source:
Carnegie Museum of Natural History
Summary:
Scientists have discovered a bizarre, bird-like
dinosaur, named Anzu wyliei, that provides paleontologists with their first
good look at a dinosaur group that has been shrouded in mystery for almost a
century. Anzu was described from three specimens that collectively preserve
almost the entire skeleton, giving scientists a remarkable opportunity to study
the anatomy and evolutionary relationships of Caenagnathidae -- the
long-mysterious group of theropod dinosaurs to which Anzu belongs.
...........................
A team of
researchers has announced the discovery of a bizarre, bird-like dinosaur, named
Anzu wyliei,
that provides paleontologists with their first good look at a dinosaur group
that has been shrouded in mystery for almost a century. Anzu was described from
three specimens that collectively preserve almost the entire skeleton, giving
scientists a remarkable opportunity to study the anatomy and evolutionary
relationships of Caenagnathidae (pronounced SEE-nuh-NAY-thih-DAY) -- the
long-mysterious group of theropod dinosaurs to which Anzu belongs.
The three
described fossil skeletons of Anzu were unearthed in North and South
Dakota, from roughly 66 million-year-old rocks of the Hell Creek Formation, a
rock unit celebrated for its abundant fossils of famous dinosaurs such as Tyrannosaurus
rex and Triceratops. The scientific paper describing the discovery
appears today in the freely-accessible journal PLOS ONE.
The team of
scientists who studied Anzu was led by Dr. Matthew Lamanna of Carnegie
Museum of Natural History in Pittsburgh. Dr. Lamanna's collaborators include
Dr. Hans-Dieter Sues and Dr. Tyler Lyson of the Smithsonian Institution's
National Museum of Natural History in Washington, DC, and Dr. Emma Schachner of
the University of Utah in Salt Lake City. According to Dr. Lamanna, "Anzu
is far and away the most complete caenagnathid that has ever been discovered. After
nearly a century of searching, we paleontologists finally have the fossils to
show what these creatures looked like from virtually head to toe. And in almost
every way, they're even weirder than we imagined."
Hell's
Chicken
At roughly
11 feet long and five feet tall at the hip, Anzu would have resembled a
gigantic flightless bird, more than a 'typical' theropod dinosaur such as T.
rex. Its jaws were tipped with a toothless beak, and its head sported a
tall, rounded crest similar to that of a cassowary (a large ground bird native
to Australia and New Guinea). The neck and hind legs were long and slender,
also comparable to a cassowary or ostrich. Although the Anzu specimens
preserve only bones, close relatives of this dinosaur have been found with
fossilized feathers, strongly suggesting that the new creature was feathered
too. The resemblance to birds ends there, however: the forelimbs of Anzu
were tipped with large, sharp claws, and the tail was long and robust. Says Dr.
Lamanna, "We jokingly call this thing the 'Chicken from Hell,' and I think
that's pretty appropriate. So we named it after Anzu, a bird-like demon
in ancient mythology."
The species
is named for a Carnegie Museums of Pittsburgh Trustee's grandson, Wylie.
Not only do
the fossils of Anzu wyliei paint a picture of this particular species,
they shed light on an entire group of dinosaurs, the first evidence of which
was discovered almost 100 years ago. In 1924, paleontologist Charles Whitney
Gilmore described the species Chirostenotes pergracilis from a pair of
fossil hands found a decade earlier in ~74 million-year-old rocks in Alberta,
Canada. Later, in 1940, Caenagnathus collinsi was named, based on a
peculiar lower jaw from the same beds. More recently, after studies of these
and other fragmentary fossils, Hans Sues and other paleontologists determined
that Chirostenotes and Caenagnathus belonged to the same dinosaur
group, Caenagnathidae, and that these animals were close cousins of Asian
oviraptorid theropods such as Oviraptor.
Asian relations
Oviraptor ('egg thief') is widely known because the first
fossil skeleton of this animal, described in 1924, was found atop a nest of
dinosaur eggs, suggesting that the creature had died in the act of raiding the
nest. This thinking prevailed until the 1990s, when the same type of egg was
found with a baby oviraptorid inside, demonstrating that, rather than a nest
plunderer, Oviraptor was a caring parent that perished while protecting
its eggs. More than a dozen oviraptorid species have been discovered, all in
Mongolia and China, and many are known from beautifully-preserved, complete or
nearly complete skeletons. Additionally, beginning in the 1990s, several small,
primitive relatives of oviraptorids were unearthed in much older, ~125
million-year-old rocks in northeastern China. Many of these are also
represented by complete skulls or skeletons, some of which preserve fossilized
feathers. Researchers have established that caenagnathids, oviraptorids, and
these more archaic Chinese species are closely related to one another, and have
united them as the theropod group Oviraptorosauria.
The occurrence of
oviraptorosaurs in both Asia and North America was not a surprise to
paleontologists, because these continents were frequently connected during the
Mesozoic Era (the 'Age of Dinosaurs'), allowing dinosaurs and other land
animals to roam between them. However, because their fossils were so
incomplete, caenagnathids remained the most poorly known members of
Oviraptorosauria, and indeed, one of the least understood of all major dinosaur
groups. "For many years, caenagnathids were known only from a few bits of
the skeleton, and their appearance remained a big mystery," says Dr. Sues.
More
fossils, more knowledge
The nearly
completely represented skeleton of Anzu opens a window into the anatomy
of this and other caenagnathid species. Armed with this wealth of new
information, Dr. Lamanna and his team were able to reconstruct the evolution of
these extraordinary animals in more detail than ever before. Analysis of the
relationships of Anzu reaffirmed that caenagnathids form a natural
grouping within Oviraptorosauria: Anzu, Caenagnathus, Chirostenotes,
and other North American oviraptorosaurs are more closely related to each other
than they are to most of their Asian cousins -- a finding that had been
disputed in recent years. Furthermore, the team's analysis confirmed the recent
hypothesis that the enormous (and aptly-named) Gigantoraptor -- at a
weight of at least 1.5 tons, the largest oviraptorosaur known to science -- is
an unusual member of Caenagnathidae as well, instead of an oviraptorid as had
initially been proposed. "We're finding that caenagnathids were an
amazingly diverse bunch of dinosaurs," says Dr. Lamanna. "Whereas
some were turkey-sized, others -- like Anzu and Gigantoraptor --
were the kind of thing you definitely wouldn't want to meet in a dark alley.
Apparently these oviraptorosaurs occupied a much wider range of body sizes and
ecologies than we previously thought."
The anatomy
and ancient environment of Anzu provide insight into the diet and
habitat preferences of caenagnathids as well. Although the preferred food of
these oviraptorosaurs remains something of a puzzle, Dr. Lamanna and
collaborators think that caenagnathids were probably omnivores -- like humans,
animals that could eat either meat or plants. Moreover, studies of the rocks in
which several of the most complete caenagnathid skeletons have been found show
that these strata were laid down in humid floodplain environments, suggesting
that these dinosaurs favored such habitats. In this way, caenagnathids appear
to have differed greatly from their oviraptorid cousins, all of which have been
found in rocks that were deposited under arid to semi-arid conditions .
"Over the years, we've noticed that Anzu and some other Hell Creek
Formation dinosaurs, such as Triceratops, are often found in mudstone rock that
was deposited on ancient floodplains. Other dinosaurs, like duckbills, are
found in sandstone deposited in or next to rivers," says Dr. Lyson, who
found his first Hell Creek fossil on his family's ranch in North Dakota when he
was only six years old.
Anzu led a life that was fraught with danger. In addition
to sharing its Cretaceous world with the most notorious carnivore of all time
-- T. rex -- this oviraptorosaur seems to have gotten hurt a lot as well. Two
of the three specimens show clear evidence of injuries: one has a broken and
healed rib, while the other has an arthritic toe bone that may have been caused
by an avulsion fracture (where a tendon ripped a piece off the bone to which it
was attached). Says Dr. Schachner, "These animals were clearly able to
survive quite a bit of trauma, as two of the specimens show signs of
semi-healed damage. Whether these injuries were the result of combat between
two individuals or an attack by a larger predator remains a mystery."
As much
insight as the Anzu skeletons provide, paleontologists still have much
to learn about North American oviraptorosaurs. Ongoing studies of these and
other important fossils promise to remove more of the mystery surrounding these
remarkable bird-like creatures. "For nearly a hundred years, we
paleontologists knew almost nothing about these dinosaurs," concludes Dr.
Lamanna. "Now, thanks to Anzu, we're finally starting to figure
them out."
A
fully-articulated cast of Anzu wyliei is on public view in Carnegie
Museum of Natural History's Dinosaurs in Their Time exhibition.
Story
Source:
Journal
Reference:
- Lamanna MC, Sues H-D, Schachner
ER, Lyson TR. A New Large-Bodied Oviraptorosaurian Theropod Dinosaur
from the Latest Cretaceous of Western North America. PLoS ONE,
2014 DOI: 10.1371/journal.pone.0092022
