16 | New Scientist | 5 March 2022THE “tyrant lizard king” –
Tyrannosaurus rex – might
have belonged to a dynasty.
A research team has proposed
splitting the famous species
into three, with Tyrannosaurus
imperator (tyrant lizard
emperor) and Tyrannosaurus
regina (tyrant lizard queen)
taking their places next to
T. rex. But the proposal is
already proving unpopular
with other palaeontologists.
T. rex was an apex predator
that lived in North America
between about 68 and 66
million years ago. The first
T. rex fossils were discovered
more than a century ago, but
for decades very few skeletons
were known. More have come
to light since the 1990s, says
Scott Persons at the College
of Charleston, South Carolina,
which means it is now possible
to assess whether the animals
fall into a single species.
To explore this question,
Persons and his colleagues
looked at bones from 38 T. rex
fossils, focusing in particular
on two features: the number
of front teeth in the lower
jaw and the stoutness of
the thigh bones.They discovered variation in
both features, which they think
justifies splitting the dinosaurs
into three distinct species. The
oldest animals – which had four
distinctly small incisors at the
front of the lower jaw and the
stout thighs of a heavily built
dinosaur – are placed in the
new species T. imperator.The researchers believe this
then evolved into two younger
species, both of which had just
two small incisors at the front
of the lower jaw. One of these
younger species had slender
thigh bones and was lightly
built – it has been named
T. regina. The other had stout
thighs and was heavily built;
this species retains the name
T. rex (Evolutionary Biology,
doi.org/hjc4).
“There will be those who
say you’re naming them just
because it’s intrinsically fun
and cool to name a new
Tyrannosaurus,” says Persons,
but he argues that the decisionis justified. He says modern
ecosystems show us that apex
predators evolve and diversify
into distinct species – lions and
leopards, for example – and it is
very likely that Tyrannosaurus
did so too.
The conclusions have
implications for some of the
most famous Tyrannosaurus
fossils, he adds: Sue, a skeleton
at the Field Museum in Chicago,
is actually T. imperator, while
Stan – which was sold to a
private buyer for $32 million
in 2020 – should be reclassified
as T. regina.
Philip Currie at the University
of Alberta, Canada, expects the
proposal to stimulate debate.
“I think the authors have made
a case that there are anatomical
changes in the genus that
seem to [change] with time,”
he says. “That is pretty amazing
in itself.”
But others will take more
persuading. “I understand
the temptation to divide T. rex
into different species, because
there is some variation in the
fossil bones that we have,”
says Stephen Brusatte at the
University of Edinburgh, UK.
“But ultimately, to me, this
variation is very minor. Until
I see much stronger evidence,
these are all still T. rex to me.”
Thomas Carr at Carthage
College in Wisconsin also thinks
the evidence in the new paper is
weak. His own in-depth analysis
of T. rex looked to uncover
patterns in the data, but he
found nothing that made him
think there was more than a
single species. “I just think
they’re seeing what they want
to see,” he says. ❚PalaeontologyColin BarrasEQ
RO
Y/A
LA
MY
Was T. r e x actually three
separate species?
PET owners may have long
suspected it, but now a study has
found that nearly 90 per cent of
dogs that experienced the death of
a “companion” canine in the same
household showed behaviours that
seem to indicate suffering in the
months after. This included being
less playful, eating less, being more
fearful and seeking more attention.
While grief-like behaviour has
been seen in wild animals such as
elephants, orcas and chimpanzees,
it hasn’t been studied in pet dogs,
despite many reports of the
phenomenon from their owners.
Federica Pirrone at the University
of Milan, Italy, and her colleagues
surveyed 426 people who had at
least two dogs, one of which had
died, and asked about changes to
the behaviour of the surviving pets.
These dogs were more likely to
“mourn” a former companion if the
two had had a friendly relationship,
especially if they used to share food
(Scientific Reports, doi.org/hh4t).
The reactions were unaffected by
how long the two dogs had known
each other, but nearly all had lived
together for more than a year.
Dogs were also more likely to be
badly affected if their owner also
felt more grief. “Dogs have become
extremely sensitive to human
communicative gestures and
facial expressions,” says Pirrone.
“A caregiver and a dog develop
an emotional connection.” ❚Animal behaviourClare WilsonDogs show grief
when other dogs
they live with dieNews
Sue, the Tyrannosaurus
skeleton at the Field
Museum in ChicagoDogs that lose a canine
companion eat and play
less, and seek more attentionOSCAR^ WONG/GET
TY
IMAGES“ There are anatomical
changes that seem to
change with time. That is
pretty amazing in itself”