Australian Science Illustrated — Issue 54 2017

scienceillustrated.com.au | 73

A fossilised face stares up through the

microscope lens. The bizarre fossil provides

scientists with extremely detailed insight

into the beginning of 540 million years

of human evolution.

BEHOLD THE

FACE OF YOUR

DISTANT

RELATIVE

A

tiny monster is wriggling
between the sand grains. With
a large mouth surrounded by
wrinkled skin folds, it consumes
everything that it can get hold of,
forcing the remains out through
blunt spikes on the side of its body.
The odd creature’s fossilised
remains, which only measure 1 mm,
have just been discovered by a team
of scientists. The animal has been
named Saccorhytus (wrinkled sack),
and the discovery sheds much
needed light on the first branches of
our family tree.
Genetic studies have long shown
that humans and all other
vertebrates are related to
echinoderms such as starfish, sea

urchins, and sea cucumbers, but the

fossil remains of the common

ancestor of humans and sea

cucumbers has so far escaped

palaeontologists' attention.

Saccorhytus fits into this very

important spot on the family tree,

and the tiny creature helps scientists

understand how the founda-tions of

the human body were laid.

Like us, Saccorhytus was charac-

terised by midline symmetry. Its

thin, flexible skin probably covered

muscles and a primitive nervous

system, which allowed the animal

to wriggle forward on the bed of a

shallow sea in what is now China.

Moreover, scientists believe that the

animal’s spikes could be an initial

stage of human branchial arches,

which play an important role in

embryonic development.

O

ver a course of 20 million years, our

ancestors went from wrinkled sacks to fast

swimmers with spines, brains, and most of the

organs we have today. Vertebrates’ way

towards world supremacy had begun. The

oldest representative of the new animal family

tree branch was excavated in 1999 on the

banks of a mountain lake in Southern China

and named Myllokunmingia.

Myllokunmingia was only about 3 cm long

and the spitting image of a fish with a long

dorsal fin and a smaller ventral fin and gills on

each side. However, the most remarkable thing

about the creature was a bony skull and a

primitive cartilage spine.

The spine was a brand new invention,

which provided a unique advantage. Along its

body, a series of muscles were attached to the

spine, and when the muscles contracted

rhythmically, the body wound from side to side

like a snake, providing the animal with such

momentum that it could probably swim faster

and for longer than all other animals.

Primitive vertebrate

sped up

Early

vertebrates

gave us:

Spine

Skull

Brain

Heart

Liver

Kidneys

Pancreas

So far, scientists have only found one single

fossil of the early Myllokunmingia vertebrate.

520 million years ago

540 million years ago

DEGAN SHU, NORTHWEST UNIVERSITY, XI'AN, CHINA, & SHUTTERSTOCK

DEGAN SHU,

NORTHWEST UNIVERSITY, XI'AN, CHINA

By Gorm Palmgren