How It Works-Book Of Dinosaurs

A Europasaurus

fossil is examined

be specifi c to the env ironmental conditions in which it lived – and
these in themselves are indicative of certain time periods in
Earth’s geological histor y. For example, certain species of trilobite
(an extinct marine arthropod) are only found in certain rock strata

(layers of sedimentar y and igneous rocks formed through mineral
deposition over millions of years), which itself is identifi able by its
materials and mineralogic composition. This allows
palaeontologists to extrapolate the environmental conditions (hot,

cold, dry, wet, etc) that the animal lived and died in and, in
partnership w ith radiometric dating, assign a date to the fossil
and/or the period.
Interestingly, however, by studying the strata and the contained

fossils over multiple layers, through a mi xture of this form of
palaeontolog y and phylogenetics (the study of evolutionar y
relatedness between organism groups), scientists can chart
the evolution of animals over geological time scales. A good

example of this process is the now know n transition of certain
species of dinosaur into birds. Here, by dating and analysing
specimens such as archaeopter y x – a famous dinosaur/bird
transition fossil – both by strata and by radiometric methods, as

well as recording their molecular and morphological data,
scientists can then chart its progress through strata layers to the
present day. In addition, by following the fossil record in this way,
palaeontologists can also attribute the geophysical/chemical

changes to the rise, fall or transition of any one animal/plant
group, reading the sediment’s composition and structural data. For
example, the Cretaceous-Tertiary extinction event is identifi ed in
sedimentar y strata by a sharp decline in species’ diversit y –

notably non-av ian dinosaurs – and increased calcium deposits
from dead plants and plankton.
Excavating any discovered fossil in order to date and analyse it is
a challenging, time-consuming process, which requires special

tools and equipment. These include picks and shovels, trowels,
whisks, hammers, dental drills and even explosives. There is also
an accepted academic method all professional palaeontologists
follow when preparing, removing and transporting any

discovered fossil. First, the fossil is partially freed from the
sedimentar y matrix it is encased in and labelled, photographed
and reported. Next, the overly ing rock (commonly referred to
as the ‘overburden’) is removed using large tools up to a

distance of two to three inches from the fossil, before it is
once again photographed. Then, depending on the
stabilit y of the fossil, it is coated w ith a thin glue v ia
brush or aerosol in order to strengthen its structure,

before being wrapped in a series of paper, bubble
w rap and Hessian cloth. Finally, it is transported to
the laboratory.

With its base set at major extinction event at

the end of the Ordov ician, the silurian fossils

found differ markedly from those that pre-date

the period. Notable life developments include

the first bony fish, and organisms with

moveable jaws.

10 | SILURIAN | 443.7-416 Ma

Boasting the highest sea levels on the Palaezoic era, the

Ordovician saw the proliferation of planktonics,

brachiopods and cephalopods. Nautiloids, suspension

feeders, are among the largest creatures from this

period to be discovered.

11 | ORDOVICIAN | 488.3-443.7 Ma

The first geological period of the Paleozoic era,

the Cambrian is unique in its high

proportion of sedimentar y layers and,

consequently, adpression fossils. The

Burgess Shale Formation, a notable

fossil field dating from the Cambrian,

has revealed many fossils including

the genus opabinia, a five-eyed

ocean crawler.

12 | CAMBRIAN | 542-488.3 Ma

By examining discovered fossils, it is

possible to piece together a rough

history of the development of life on

Earth over a geological timescale

© Wallace63

© Nils Knötschke

© Jlorenz1

DINOSAURS’ LEGACY

What are fossils?

The fossil

record

An incredibly important time for

the development of life, the

Devonian period has relinquished

fossils demonstrating the evolution

of the pectoral and pelvic fins of

fish into legs. The first land-based

creatures, tetrapods and

arthopods, become entrenched

and seed-bearing plants

spread across dr y lands. A

notable Devonian find is the

genus tiktaalik.

9 | DEVONIAN | 416-359.2 Ma