46 | New Scientist | 3 August 2019
This illustrates just how much progress has
been made in uncovering lost dinosaurs in
recent years. Even so, the dinosaur record may
be richer than the predictions say. “I think the
estimate of total richness for the dinosauria
we made is an underestimate,” says Starrfelt.
Not only are there likely to be updates to the
models used to estimate dinosaur diversity,
but new discoveries in familiar formations
will alter dinosaur counts and bump up the
numbers of those yet to be found.
In 2010, for example, Richard Butler at
the University of Birmingham, UK, and his
colleagues described one of the smallest
dinosaurs yet found. Named Fruitadens
haagarorum, this omnivorous biped with
prominent teeth was found in the Morrison
Formation, a rich and well-studied source
of dinosaur fossils dating from near the
end of the Jurassic. And last month another
small dinosaur, an early raptor named
Hesperornithoides miessleri was described
from the same formation.
It is the search for small dinosaurs like
these that is filling in our understanding of
even well-examined places. “New research
has shown that small dinosaurs are strongly
underrepresented in the fossil record because
their delicate bones are more susceptible to
destruction by scavengers and the elements
before they can become fossils,” says David245 225 205 185 165PERMIAN PERIOD TRIASSIC PERIOD
MILLION YEARS AGOJURASSIC PERIOD252 mya231 mya
201 mya 160 myaPermian-Triassic
mass extinction245 mya
Dinosaurs emerge
Nyasasaurus
Plateosaurus214 mya
Some dinosaurs start
to become large 193 myaDilophosaurus
Eoraptor
Mass extinction removes Ambopteryx
most of the dinosaurs’
reptilian competitorsLarge carnivorous
dinosaurs evolveThe reign of the dinosaurs
Dinsosaurs first emerged a quarter of the way through the Triassic period. By the beginning of the Jurassic, they were the dominant land animals and it stayed that way until
an asteroid hit Earth at the end of the Cretaceous. Some of these dinosaurs are depicted here, at the time when they first appear in the fossil recordOne of the worst days in the history of
the planet transpired 66 million years
ago. An enormous asteroid struck
what is now the Yucatan peninsula
in Central America, sparking a mass
extinction. It eradicated every
non-avian dinosaur, 93 per cent of
all mammals, as well as many other
forms of life. But were the likes of
Tyrannosaurus and Triceratops going
strong until the end, or had they
already begun to fade away?
At first glance, it appears that the
dinosaurs might have been waning.
Diversity counts seem to show that
there were more species 75 million
years ago compared with when the
asteroid struck, with especially high
numbers recorded in western North
America. But it now seems that
apparent boom is partly down to a
fluke of preservation. At that time,
a shallow inland sea created a broad
swath of floodplain environments
where dinosaur bodies were more
likely to get buried quickly and so be
preserved. By 66 million years ago,
this had largely drained away, leaving
fewer places for fossilisation to occur.
When this bias is taken into
account, it seems that dinosaurs
were not only doing fine just before
the asteroid hit, but that there may be
many more to discover from the last
days of the Cretaceous. Many of the
places where we know they lived and
where they might be preserved are
relatively unexplored, in particular
the eastern side of the US. The story
of the last days of the dinosaurs isn’t
yet complete.GOING OUT WITH A
BANG OR A WHIMPER?new find bring up questions about how that
discovery connects to others, and where to
look to fill the remaining gaps.
Another way to predict the missing dinosaurs
is to turn to maths. In biology, organisms are
categorised by their species and the genus that
the species belongs to, and researchers have
devised models to estimate the numbers of
dinosaur genera and species that once existed.
In 2006, for example, statistician Steve Wang
of Swarthmore College, Pennsylvania, and
Peter Dodson, a palaeontologist at the
University of Pennsylvania, estimated that
there were about 1850 genera of non-avian
dinosaurs that palaeontologists had some
hope of discovering, based on published
records of dinosaur discoveries and a
mathematical formula that links observed
data to unseen types. At that time, about
500 had been named, indicating that more
than 70 per cent were yet to be found.
More recently, in 2016, ecologists Jostein
Starrfelt and Lee Hsiang Liow at the University
of Oslo, Norway, accounted for both the
incompleteness of the fossil record and
biases in how the fossil record is studied – for
example, by the different research interests
of academics – to come up with an estimate
of 1536 discoverable dinosaur genera. At that
time, 974 had been identified, meaning that
37 per cent were yet to be found.Diminutive Moros
intrepidus wasn’t
such a tyrannical
tyrannosaurJORGE GONZALEZ