68 Science & technology The EconomistMarch 21st 2020
2 task was to look for words associated with
success, such as “protect”, “support”,
“help”, “benefit” and “growth”, and also
words associated with failure, like “threat-
en”, “loss”, “kill”, “problem” and “risk”. Dif-
ferent words had different values attached
to them, depending on how positive or
negative they were felt to be by the original
model-makers. The result was that each ab-
stract could be assigned a sentiment score,
averaged from the five different inputs.
In total, the team analysed 1,030,558
words. They found that in papers pub-
lished in the 1980s, when conservation sci-
ence was in its infancy, terms from the neg-
ative list were much more common than
those from the positive one. During the
past decade, by contrast, terms associated
with success became more frequent. Aver-
age sentiment scores increased during the
study period by 140%.
That is clearly encouraging news for
conservationists. It suggests that their
methods are working in general, and are
improving with experience. But more de-
tailed analysis was also possible. Giant
pandas, which numbered 1,864 when cen-
sused in 2014 and had their status upgraded
from “endangered” to merely “vulnerable”
in September, have seen the sentiment of
the literature about them swing from nega-
tive to positive in a matching way. Papers
on the California condor (pictured on pre-
vious page), by contrast, remain littered
with negative sentiments even though its
numbers have risen, according to a census
in 2016, from an extinction-threatening 22
to 446. But only 276 of those birds were
wild, and so the condor is still listed as
“critically endangered”.
Given the numbers involved, it might
be argued that both of these results were
predictable. They seem, nevertheless, to be
evidence that the method works. And that
may be relevant in the context of the team’s
analysis of rat-clearance projects intended
to help species which have evolved in the
absence of those subsequently introduced
rodents, and also projects on small islands
intended to protect populations of such
autochthonous species (often these pro-
jects are the same thing). Sentiment analy-
sis sees no clear signal of success here.
Whether Dr Van Houtan’s method
might be generalised to other fields of sci-
ence is debatable. Conservation is, at bot-
tom, an emotion-driven activity. People
care about the results in a way that goes be-
yond professional amour propre. That re-
searchers’ sentiments show up in their
choice of words is therefore little surprise,
and might well not be true elsewhere. But
the fact that Dr Van Houtan has been able to
use natural-language processing to expand
the pool of papers which can be taken into a
review from the hundreds to the thousands
suggests that others might benefit from
having a look at his achievement. 7F
ossil by fossil, the story of the birds be-
comes clearer. It is now well established
that modern birds, the Neornithes, are ac-
tually a relict group of dinosaurs which
survived a cosmic collision, 66m years ago,
between Earth and an asteroid or comet.
This impact wiped out the rest of the Dino-
sauria, along with a lot of other creatures. A
paper published last week about a tiny di-
nosaur belonging to a related group, the
Enantiornithes, which was found pre-
served in amber in what is now Myanmar,
showed just how diverse flying dinosaurs
had become more than 30m years before
this collision. This week sees the release, in
a paper in Nature, of details of another fos-
sil, which those studying it believe is close
to the point of origin of the Neornithes
themselves.
The fossil in question is called Asterior-
nis maastrichtensis. As its name suggests,
the rock containing it was dug from depos-
its found near Maastricht—though actually
over the border from that Dutch city, in Bel-
gium. These deposits, which are between
66.8m and 66.7m years old, date from the
end of the Cretaceous period. Indeed, and
not coincidentally, the name of the last
stage of this period is the Maastrichtian, for
these are strata that originally defined it.
This particular rock interested palaeon-
tologists because it included visible leg
bones that looked as though they belonged
to a bird. Late Cretaceous bird fossils are
rare, so instead of chancing their arms by
using physical or chemical methods to ex-plore the rock for more remains, Daniel
Field of Cambridge University and his col-
leagues employed computerised tomogra-
phy, a process more familiar to most people
as a medical-scanning technique. The re-
sult, an image of the animal’s skull with
false colours added to clarify which bits are
which, can be seen in the picture.
A. maastrichtensisdoes indeed turn out
to be a member of the Neornithes. Specifi-
cally, it is part of the Galloanserae. This tax-
on includes both modern dry-land fowl
and their kin (chickens, quails and so on)
and modern waterfowl (ducks, geese and
the like). The skull of A. maastrichtensisex-
hibits features of both groups, so presum-
ably predates the split between them. Since
the Galloanserae are themselves reckoned
to have evolved shortly after the Neor-
nithes came into being, this puts A. maas-
trichtensisas having lived near to the origin
of the Neornithes.
As to what it looked like when alive, the
animal’s left femur, its best-preserved
bone besides those of its skull, suggest A.
maastrichtensiswas a long-legged creature
that strutted around. This, and evidence
that the rocks it was preserved in were orig-
inally part of a fossil shoreline, has led to
reconstructions that somewhat resemble a
modern wading bird.
As the example of A. maastrichtensis
shows, a single fossil can help to nail down
previously uncertain dates. Estimates of
the date of origin of the Neornithes, based
on so-called molecular clocks, which at-
tempt to use mutation rates to determine
when the most-recent common ancestors
of organisms now alive were themselves
alive, had suggested dates ranging from
139m to 89m years ago. Dates from fossils
are more accurate. Based on the discovery
of A. maastrichtensis, the smart money is
now on the Neornithes as a group being
only a little older than the dinosaur-killing
impact itself. 7Another ancient bird skull is a further
piece of avian history’s jigsawPalaeontologyFowl play
Who are you calling a chicken?