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In order to attain the awe-inspiring diversity of life on
this planet, nature had to overcome numerous obstacles over billions of
years of evolution. New environments had to be conquered; new forms had
be created to exploit newly available resources. Since man first began
to look back through the long history of the natural world via
paleontology and geology, we’ve uncovered some of the turning points in
the development of life on Earth.
10The Earliest Humans
The Omo Remains
Of course, you can trace humanity’s family tree back a long way. But
who were the earliest modern humans, like you and the people you know?
Well, Omo I and II might just hold the answers. The two partial skulls,
discovered in Ethiopia around 1967, were recently confirmed to be an
astonishing
195,000 years old,
making them the earliest known anatomically modern humans. (There
actually is some debate around Omo II, but Omo I is agreed to be a fully
modern human.) In fact, scientists now think that
Homo sapiens only evolved around
200,000 years ago, making it likely that the Omo pair were among the first true humans ever to walk the Earth.
So what are the implications of the two skulls? Well, aside from
confirming humanity’s emergence in Africa, they’ve deepened one of the
great mysteries of human evolution. Evidence of
cultural traits—like
musical instruments, needles, and ornaments—only dates back to around
50,000 years ago. Complex tools like harpoons also appear after that
date, although crude stone implements date back much further. So, if
entirely modern humans were roaming the land 200,000 years ago, why did
it take them 150,000 years to develop anything resembling culture?
9The Earliest Bird
Protoavis
We now know that birds evolved from dinosaurs, and that many dinosaurs were actually
covered in feathers.
As a result, the question “Which was the earliest bird” can seem more
like “When do we stop considering a creature a dinosaur and start
calling it a bird?” For a long time, paleontologists drew the line at
creatures like
Archaeopteryx (pictured) and
Confuciusornis, small animals covered in feathers and capable of flying, as well as climbing trees and running. We also know that
Confuciusornis had a genuine beak, which gives it an advantage over its rivals for the position of earliest true bird.
However, there is an even older candidate for the title of first bird.
Protoavis
lived around 220 million years ago, at least 80 million years before
its nearest rival. The fossil was found in Texas by paleontologist
Sankar Chatterjee, who argues that it is even closer to modern birds
than
Archaeopteryx. If this is true, and
Protoavis is
the oldest known bird, it would potentially rewrite our entire
understanding of avian evolution. Currently, the consensus is that birds
evolved from coelurosaurian dinosaurs. But
Protoavis is easily as old as the first coelurosaurians, making such a scenario impossible. If
Protoavis is a bird, then birds must have come from somewhere else.
Don’t rewrite the textbooks just yet, though, because the identification of
Protoavis as a bird has proven
enormously controversial.
The fossil was not in good condition when Chatterjee found it, leading
many paleontologists to suggest it’s actually a mixture of bone
fragments from two or more species, which an overeager Chatterjee pieced
together into a plausible skeleton. Others simply point out that
there’s no reason to believe
Protoavis is the ancestor of
today’s birds. Instead, convergent evolution might simply have resulted
in two unrelated species sharing a similar design.
8The First Species To Walk On Land
Tiktaalik And Pneumodesmus
Part fish, part frog, and part alligator,
Tiktaalik
was the platypus of the Devonian, splashing in the shallows some 375
million years ago. Discovered in Canada in 2004, the species is
considered to be an important transitional link between aquatic
vertebrates and the very first land animals. Among other adaptations,
Tiktaalik boasted ribs capable of supporting its body, lungs, a movable neck, and eyes on the top of its head like a crocodile. It also
boasted proto-legs, halfway evolved from fins, that would have allowed it to push itself along riverbeds. However,
Tiktaalik‘s
“legs” probably didn’t have the range of motion required to truly walk
on land. At best, it might have been able to briefly scramble around on
mud flats. Otherwise, it probably remained in the shallows.
But while vertebrates like
Tiktaalik struggled to make the transfer to land, they had actually been beaten to the punch by a species of millipede known as
Pneumodesmus,
which lived some 428 million years ago. At just 1 centimeter (0.4 in)
in length, the tiny myriapod wasn’t much to look at, but
Pneumodesmus
was the first creature we know of to actually live on land. That also
makes it the oldest air-breathing creature we know of, boasting tiny
breathing openings known as spiracles on the outside of its body. As
such,
Pneumodesmus must be considered one of nature’s most successful experiments, paving the way for all the land animals to come.
7The Earliest True Reptile
Hylonomus Lyelli
Reptiles were the first vertebrates to become completely capable of
living on land, even reproducing outside of the water. That makes them
pretty awesome, and the tiny critter known as
Hylonomus lyelli
might just be the most awesome of them all. The lizard-like creature,
which measured just 20 centimeters (8 in) in length, is currently the
oldest undisputed species of reptile, dating back at least 310 million
years. Probably an insectivore,
Hylonomus lyelli was discovered in 1860, preserved
inside a tree trunk in Nova Scotia.
Of course, 1860 was a long time ago and two challengers to the first reptile title have emerged since then.
Westlothiana and
Casineria are both slightly older than
Hylonomus lyelli (338 million years for
Westlothiana and 335 million years for
Casineria). However, the scientific community is still debating whether either was indeed a fully evolved reptile, since they share
some amphibian traits, meaning that they were probably dependent on a stable water source to live and reproduce. For the time being,
Hylonomus lyelli can keep its title.
6The Oldest Creature Capable Of Flight
Rhyniognatha Hirsti
As a means of locomotion, flight requires a complex design (low body
weight, but a sturdy frame) and a lot of effort by powerful wing
muscles. The first creature capable of flight was actually the
oldest known insect,
Rhyniognatha hirsti.
The tiny insect lived some 400 million years ago, meaning that flight
is by no means a recent development from an evolutionary perspective.
Rhyniognatha hirsti was discovered in 1928, in rocks dating
back to the Devonian. The fossil was promptly ignored for almost 75
years, until biologist Michael Engel accidentally rediscovered it
in a drawer
in London’s Natural History Museum. Engel gasped out loud on spotting
the incredible specimen—and that was before he even knew how old it was.
Since then, experts have
studied its remains
thoroughly, confirming that the tiny insect had wings and was very
likely capable of using them to fly. However, they are still not
completely certain which family of insects it belonged to. Nevertheless,
the fossil is a fascinating find and further study should reveal more
about the earliest known pioneer of flight.
5The First Flowering Plants
Potomacapnos And Amborella
People tend to associate plants with flowers, but flowers are
actually a very recent development, at least on the evolutionary
timescale. Before they showed up, plants reproduced via spores for
hundreds of millions of years. In fact, scientists aren’t even sure why
flowers evolved in the first place, since they are delicate and require
huge amounts of energy, which many plants might put to better use
growing seeds or increasing in height. Additionally, non-flowering
plants have nothing that really corresponds to flowers, making it
something of a puzzle where they came from in the first place. These
loose ends led Darwin to famously describe the rise of flowers as “an
abominable mystery.”
The oldest known flowering plant fossils date to the Cretaceous, between 115 and 125 million years ago. Among the oldest is
Potomacapnos,
a surprisingly complex plant resembling a modern poppy. Such complexity
in early fossils indicates that flowers probably evolved very rapidly
to something approaching their modern form, rather than slowly
developing over a lengthy period. But it’s hard to draw any firm
conclusions, since flowers are fragile and rarely survive to be
fossilized.
However, some answers might lie with a rare shrub found only on the Pacific island of New Caledonia.
Amborella trichopoda
(pictured) is the only surviving member of the Amborellales. At the
start of the Cretaceous, the Amborellales split from the non-flowering
plants dominating the landscape, becoming the oldest order of flowering
plants to survive into the present. Later, two other surviving orders
emerged: the Nymphaeales, which became modern water lilies, and the
Austrobaileyales, from which all other flowering plants developed. Since
the Amborellales emerged first,
Amborella trichopoda remains closest to the
original flowering plants.
By comparing it with the Austrobaileyales, we can get some idea of
which traits flowering plants originally boasted and which simply
evolved further down the line.
4The Earliest Mammal
Hadrocodium Wui
The oldest known mammal resembled a small mouse or modern-day shrew.
Hadrocodium wui,
identified in China in 2001, was some 3.5 centimeters (1.4 in) long,
weighed 2 grams, and probably had a lifestyle and diet similar to modern
shrews, since its teeth consisted of specialized fangs for
chopping up insects.
So how do we know that
Hadrocodium was a mammal and not a
therapsid (a type of mammal-like reptile that flourished in the
Mesozoic)? Well, as well as a notably large brain for its size,
Hadrocodium boasted middle-ear bones separate from its jaw, which is
considered a notable point of evolutionary divergence between mammals
and reptiles. In fact, Hadrocodium could be considered quite modern in
its design, especially when it comes to its
sense of smell.
However, what makes
Hadrocodium wui truly impressive is its
age. At 195 million years old, Hadrocodium lived long before some of the
best-known dinosaurs, including the stegosaurus, diplodocus, and
tyrannosaurus. In fact, the mighty tyrannosaurus lived closer to us in
time than it did to
Hadrocodium wui.
3The First Tree
Wattieza
Trees played (and still play) a crucial role in the formation of the
Earth’s atmosphere. Without their power to convert carbon dioxide
into oxygen,
the planet would quickly become inhospitable to life, at least as we
know it. In fact, the first forests drastically changed our ecosystem,
causing the planet to cool and directly creating the conditions we take
for granted today. As such, the appearance of the tree can be considered
one of the most important evolutionary breakthroughs of all time.
Currently, the oldest known tree is a 397-million-year-old species known as
Wattieza, which resembled a modern palm and probably reached a height of around 10 meters (30 ft).
Wattieza
preceded the dinosaurs by some 140 million years, spreading across the
planet long before the first vertebrates took to the land. It reproduced
using spores,
similar to those used by ferns and fungi today. The species is
currently extinct, but a 180-kilogram (400 lb) fossil (pictured above)
was discovered in New York in 2004, solving many unanswered questions
about how forests came to dominate the land.
2The Earliest True Dinosaur
Nyasasaurus Parringtoni
The reign of the dinosaurs began after the dreadful
Permian extinction,
which took place some 250 million years ago and wiped out around 90
percent of all species on Earth, including 95 percent of marine life and
most of the planet’s trees. Afterward, the dinosaurs emerged.
The oldest true dinosaur currently known is
Nyasasaurus parringtoni,
which was discovered in Tanzania in the 1930s, but only conclusively
dated in 2011. Only a few bones from the species have been identified so
far—scientists still have no clue whether it was a carnivore or a
herbivore, nor are they completely certain whether it walked on two legs
or not.
Nevertheless, we can say that
Nyasasaurus parringtoni was
less-than-imposing,
standing just 1 meter (3 ft) tall and weighing 18–60 kilograms (40–135
lb). In fact, it’s barely even a dinosaur by most standards, but
analysis of its bones has revealed that it was a fast-growing animal,
indicating that it was warm-blooded, an
essential trait
of dinosaurs. For now, the scientific community hopes to discover more
fossils, since we haven’t even been able to identify the family of
dinosaurs it belongs to yet.
1The Oldest Life-Form
What is the oldest life-form known to science? Well, it’s a
surprisingly tricky question to answer, since early life-forms were so
basic its often hard to identify them accurately. For example, rocks
discovered near Pilbara in Australia were initially thought to contain
traces of a purple, ocean-dwelling microbial community almost 3.5
billion years old. This would have been the oldest evidence of life on
Earth and everyone got very excited—until earlier this year, when new
testing conclusively proved that the “microfossils” were actually just
strangely shaped mineral deposits created by hydrothermal events. In
other words, they were
never alive at all.
The same thing happened in South Africa, where tiny tubes found in
rocks were taken as evidence of 3.4-billion-year-old bacteria, only for a
subsequent study to identify them as
natural formations
created by volcanic activity. Fortunately, these revelations haven’t
set the hunt for the oldest fossil back too far, since Australia’s
Strelley Pool Formation
contains carbon-rich “bag-shaped bodies” that are considered to be
convincing evidence of ancient microbial life. At 3.43 billion years
old, the Strelley Pool deposits are only about 20 million years younger
than the Pilbara “microfossils” were thought to be.
Intriguingly, there’s some evidence that the Strelley Pool organisms
were photosynthetic, surviving by converting light to energy. Although
no fossil record of them has been found, it’s generally agreed that the
earliest bacteria were rock-eaters known as
chemolithotrophs,
with photosynthetic bacteria emerging later. So we can be pretty sure
that the earliest bacteria predate even the Strelley Pool deposits by a
long, long time.
