So the researchers divvied up the task of traveling around the world to visit the fossils included
in the original paper and to reassess all 457 characters described — in person. “It was essentially a
replication study,” Brusatte says.
The team went in expecting to cast doubt on the
tree created by Baron, Norman and Barrett — or
possibly to completely debunk it. But that didn’t
Langer, Brusatte and their coauthors reported
last November in Nature that their analyses
showed that the original, 130-year-old evolutionary tree was still the best fit to the dinosaur
dataset used by Baron’s team.
But, they found, the original tree wasn’t that
much more likely to be correct than the newly
described tree. “This is the thing that really blew
us away: It wasn’t actually a statistically significant result,” Brusatte says. In fact, the often-accepted tree wasn’t even that much more likely
than an older, third arrangement of the tree that
grouped ornithischians closer to the other herbivores in the family, the long-necked sauropods,
and left the fierce theropods as the outliers.
“There is currently great uncertainty about
early dinosaur relationships and the basic
structure of the dinosaur family tree,” the researchers concluded. “It seems that the flood of new
discoveries over the past decades has revealed
Brusatte adds: “We shouldn’t rewrite the textbooks just yet. But we’ve taken what we thought
was a certainty and turned it into a mystery — and
a big mystery, at that.”
How the different dinosaur groups are related
to one another may seem like insider baseball,
Nesbitt says. But the evolutionary tree is the
common ground, the framework within which
researchers can discuss dinosaur evolution, dinosaur origins and what binds all dinosaurs together.
“It makes it difficult to ask questions about how
features are evolving if we can’t have some agreed-upon taxonomy,” he adds.
Similarly, without an agreed-upon evolutionary
tree, it’s hard to know which anatomical features
to follow through the tree — such as any that might
have helped dinosaurs survive the end-Triassic
extinction. Each arrangement of the evolutionary
tree seems to highlight different features as being
particularly important, Langer says. “If you don’t
know how the tree is arranged, you can’t say which
feature characterizes [dinosaurs].”
The thorny problem revolves around which to
tackle first: How to define a dinosaur or how to
redraw the dinosaur family tree?
But Langer suggests the answer, as always, is to
return to the fossils. In the paper by Langer and
his coauthors, they make a plea for researchers
to do the mundane work. “We proposed that we
need more … anatomical descriptions and definition of characters,” Langer says. “It’s boring to do,
but people have to do more of this.”
As Nesbitt cradles the Teleocrater pelvic bone,
he turns to a tall cabinet of wide, shallow drawers. He slides open a drawer filled with dozens of
carefully labeled boxes, each holding one or more
bones from Teleocrater, collected during a 2015
expedition to Tanzania’s Ruhuhu Basin.
The first known fossils of Teleocrater rhadinus,
to date the only species of the genus Teleocrater,
He hit pay dirt: His team found a bone bed
containing at least three Teleocrater individuals,
including a braincase and jawbone. The skull was
a particularly exciting find, because it showed
the team that Teleocrater, clearly a nondinosaur
from other features, had the skull depression,
just like a true dinosaur.
Paleontologists tend to say that finding more
fossils from early dinosaurs and their close relatives is the surest way to fill in the gaps on how the
creatures evolved and to tidy up the family tree.
Nesbitt laughs. “Now we have way more fossils,”
he says, “and it’s way messier.” s
s Kevin Padian. “Palaeontology: Dividing the
dinosaurs.” Nature. March 23, 2017.
A March 2017 analysis of a
longer list of ornithischian
species concluded that
ornithischians and theropods
are closely related.
Based on hip shape, sauropods
and theropods were thought to
be more closely related to each
other than to ornithischians.
A November 2017 analysis
upheld the traditional view but
found that other arrangements
are almost equally likely —
including a view that clusters
herbivorous ornithischians and
The dinosaur family tree
has three main branches:
long-necked sauropods and
fierce theropods. Their relationships may be shifting.
BARON ET AL HYPOTHESIS
SOURCE: M.C. LANGER ET AL /NATURE 2017