ÐÓ°ÉÔ­´´

Stan Wood is a professional fossil collector who also referees amateur
football matches – a serendipitous combination as it turned out. Ten years
ago, as Wood patrolled the sidelines, attempting to keep peace between a
marauding Bathgate eleven and the local opposition, he made a discovery.
Wood noticed that the walls of the Bathgate football pitch (some 30 kilometres
west of Edinburgh) were made from a most unusual type of rock. It was limestone,
but striated with fine, alternating black and pale brown layers. Wood was
so certain it must contain fossils that he bought up some similar walls
from surrounding fields and began a systematic search.

His hunch was correct, and before long Wood had traced the rock to East
Kirkton, a local lime quarry. The rocks had been neglected by fossil collectors
since its closure in 1844. Today, however, that quarry is one of the most
important palaeontological sites in the world. Recent research shows that
the limestone there was laid down under unusual circumstances just at the
time when aquatic animals were evolving into terrestrial pioneers. These
origins mean that fossils and information from East Kirkton are transforming
our understanding of early land animals.

Cutting edge

Between 1984 and 1987, Wood made initial excavations. Most of his finds
were in the ‘float’ – loose rock left by quarrymen – making it impossible
to know exactly which part of the quarry they came from. Then the National
Museums of Scotland leased the site from West Lothian District Council in
1987 and a team of palaeontologists began collecting the fossils. By recording
their distribution bed by bed and studying the environment in which they
were deposited, the scientists were able to put the animals into their original
context. The East Kirkton Project, led by Ian Rolfe of the National Museums,
has now snowballed to involve almost 100 researchers, helpers and volunteers
from more than 30 institutions in eight countries. The resulting research
published this month in the Transactions of the Royal Society of Edinburgh
– Earth Sciences gives a remarkable insight into the East Kirkton limestone.
But it is not without its contradictions.

The East Kirkton story really began some 338 million years ago, during
Lower Carboniferous times. What is now Scotland was then near the equator,
and even wetter – though much warmer – than it is today. Luxuriant forests
covered the land. These were dominated by primitive trees – tall and graceful
with scaly trunks branching into feathery leaves. The area was volcanic.
(Today the eroded stumps from these volcanoes provide some of its most dramatic
scenery, such as Castle Rock and Arthur’s Seat in Edinburgh.) The East Kirkton
limestone was laid down in a tiny lake on the flanks of such volcanoes,
in a small crater or a lava-dammed valley. Recent searches with boreholes
and geophysical surveys show that it covered little more than the 250 by
50 metres now occupied by the quarry. This prehistoric lake probably existed
for just a few tens of thousands of years.

Given its origin, East Kirkton limestone might be expected to contain
fossilised aquatic life, but early excavations revealed nothing but the
odd aquatic bacterial and algal slime. However, closer scrutiny of the rocks
seemed to provide a clue. Their alternating brown and black layers contained
large amounts of carbonate and silica minerals respectively. These were
interspersed with layers of volcanic ash. As long ago as 1834, an amateur
geologist called Samuel Hibbert had suggested that the unusual layering
and mineral content in these rocks resulted from water percolating up through
fresh volcanic ash. Hibbert thought that the limestone had been deposited
in a volcanic spring. Perhaps, geologists believed, this spring was too
hot to sustain aquatic life.

Inhospitable waters

This theory is only now being questioned (and more of that later), but
whatever made the lake inhospitable 338 million years ago means that it
is now a unique site for the study of early land-living animals. Any creature
fossilised in East Kirkton limestone must have made its own way over land
to the lake, fallen in, become petrified and then rapidly buried beneath
the next cloud of volcanic ash – or so it seemed. What makes the finds so
important is that they seem to fill a gap in the evolutionary record.

Of particular interest are the amphibian remains. Older fossil amphibians
have been discovered at sites in Greenland, the former Soviet Union, and,
most recently, in Scotland. But these animals are so primitive that they
are arguably still fishy in their way of life. By contrast, the East Kirkton
finds are fully de-veloped land-living tetrapods, or four-footed ani-mals.
They are among the oldest known fully terrestrial vertebrates. In addition,
East Kirkton was inhabited by remarkable arthropods – animals with external
skeletons and jointed legs, such as scorpions and eurypterids (distant relatives
of today’s horse shoe crab). A tiny harvestman (opilionid ‘spider’) is also
preserved: the oldest known by some 27 million years, it is apparently indistinguishable
from modern forms. Several rare species of millipede are also among the
finds.

The scorpion remains are from the genus Pulmonoscorpius. These are
the earliest known air-breathing scorpions, and show the creature in its
heyday (see Andrew Jeram, ‘When scorpions ruled the world’, New ÐÓ°ÉÔ­´´,
16 June 1990). They also give vital information about how scorpions evolved
from sea-dwelling creatures to the land animals they are today. Complete
fossils of scorpions are rare, but East Kirkton provides a bonanza for scientists
studying their evolution. Specimens in good condition range from about 13
to 280 millimetres in length, but fragments hint at much larger individuals
– perhaps measuring more than half a metre from claw to sting.

Palaeontologists had previously assumed that Carboniferous scorpions
were aquatic, but Pulmonoscorpius at East Kirkton have book-lungs (gill-like
respiratory surfaces protected within abdominal pockets) and walking legs
– both indicators that they lived on land. A combination of large, lateral,
compound eyes and simple, forward-looking eyes gave them acute eyesight
for hunting prey by day. Today’s much smaller nocturnal scorpions, which
rely heavily on feel to catch small insects, are sorry remnants of a once
highly diverse group.

Of all the arthropod remains at East Kirkton, the eurypterids are among
the most impressive, resembling huge, streamlined lobsters. One fossil fragment
comes from a head that must have been 62 centimetres across – perhaps the
most massive arthropod ever. Three types have been found at East Kirkton,
but they form such a neat series of size and shape – from the small Hibbertopterus,
through Dunsopterus to the large Cyrtoctenus – that they may well be simply
a single species at different stages of growth. Their anatomy suggests that
they lived on land, or were at least amphibious, sieving small prey from
shallow pools with comb-like forelimbs. But as no remains of their young
have been found, it seems likely that they did not breed around the lake
at East Kirkton.

Wonderful life

Inevitably, though, our distant relatives, the East Kirkton vertebrates
get the most public attention. A lizard-like creature found in 1988 was
thought to be the oldest known reptile, but a second find has led to some
reassessment . Important amphibian remains at East Kirkton include members
of the temnospondyls, the main group of primitive amphibians. This group
contains the ancestors of today’s frogs and salamanders. Finds at East Kirkton
have changed our ideas about their evolution.

Most of the temnospondyl remains are from Balanerpeton woodi, which
grew to be no more than half a metre long. Clues provided by its head suggest
it lived largely on land. Aquatic species usually have lateral line canals
along the sides of their heads to sense water displacement, and bony bars
to support the gills, but Balanerpeton has neither. Also, its wrist and
ankle bones are fused – as they are in most terrestrial animals to give
extra strength. Most tellingly of all, Balanerpeton’s stapes bone – usually
a heavy brace for the jaw joint n fishes and primitive amphibians – s long
and slender to carry high- frequency airborne sound from the eardrum to
the inner ear. In fact, the fossils suggest that Balanerpeton looked very
like a modern terrestrial salamander, which lives its adult life away from
water, returning only to breed.

Balanerpeton is the oldest temnospondyl yet discovered – although species
that are more primitive in evolutionary terms have been found in younger
rocks, such as Dendrerpeton which was discovered in the US in rocks some
320 million years old. This indicates that temnospondyls had already started
to diversify long before East Kirkton times.

Beside temnospondyls, the other main group of early tetrapods found
at East Kirkton is the anthracosaurs. A more solid palate and an extra bone
on the fifth toe of their hind limb help to distinguish them from temnospondyls.
One example, the 30-centimetre long Eldeceeon rolfei, has yet to be studied
in detail, but also probably lived on land. The slightly smaller Silvanerpeton
miripedes may have been the most aquatic of East Kirkton’s tetrapods. These
fossils show lateral lines and poorly developed wrists, ankles and vertebrae.
But perhaps they were simply immature adults, still carrying the signs of
their aquatic larval life. Again, as with the temnospondyls, East Kirkton’s
anthracosaurs are the world’s oldest, but not the most primitive – highlighting
that the evolutionary history of this group also remains a mystery.

Humdrum existence

It has always been tempting to think of East Kirkton as a kind of prehistoric
Pompeii – Carboniferous life seemingly preserved as a cataclysmic snapshot,
first pickled in a boiling spring and then engulfed by falling ash from
highly active local volcanoes. But close study of the limestone layers
reveals that the ash did not fall from clouds but was instead washed off
the flanks of surrounding volcanoes by rainwater. And the discovery that
forests grew on the volcanoes’ slopes indicates that they were only intermittently
active. Life in prehistoric East Kirkton was rather more humdrum than we
previously imagined.

Recent research by members of the East Kirkton Project even provides
conflicting evidence for the hot spring itself. By measuring the exact ratios
of light and heavy isotopes of carbon, hydrogen and oxygen in minerals from
the limestone, scientists can predict the temperature at which these minerals
were deposited. If the minerals crystallise from rainwater that has been
heated, then the rock contains a higher proportion of heavy isotopes than
it would if the water was cold. Unfortunately, the results of analyses of
silica and of calcite from carbonate layers, contradict one another.

Last year, researchers studying the hydrogen and oxygen isotopes in
silica found evidence that the mineral formed at 60 degreeC. They concluded
that it must have precipitated from rainwater that had percolated through
hot volcanic deposits – supporting the hot spring theory. But a second team,
analysing calcite samples, found isotope ratios for carbon and oxygen that
suggested the mineral formed at around 20 degreeC, much as precipitates
form in modern tropical freshwater lakes, and contradicting the hot spring
theory. The two findings have yet to be reconciled. One possible explanation
is that the environment of the lake at East Kirkton may have oscillated
between two extremes, corresponding to the deposition of carbonate and silica
layers. Hopefully, further investigations will resolve the issue.

But, if East Kirkton turns out not to have been a hot spring, why was
the lake apparently so inhospitable to aquatic animals? Study of the limestone
suggests another possible reason: the lake water was unusually heavily contaminated
by a cocktail of mineral salts, because it originated from rainwater that
was percolated through fresh volcanic ash. It was probably highly toxic.

Research at East Kirkton is far from complete. Besides the need to
resolve the problem of the limestone’s origin, some of the fossils are not
fully described, and a few have not even been assessed. Furthermore, all
the finds have been discovered in only two small parts of the quarry face
or in the debris of the old quarry. The site is now protected by Scottish
Natural Heritage against uncontrolled collecting. In future the whole of
East Kirkton may be opened up for research. Already there are tentative
plans by West Lothian District Council and Scottish Natural Heritage to
increase access so that the public can see where these remarkable relics
come from.

Michael Taylor is curator of vertebrate palaeontology at the National
Museums of Scotland, Edinburgh. The East Kirkton Project is published this
month as a special double issue, Volume 84, joint Parts 2 and 3 of the
Transactions of the Royal Society of Edinburgh – Earth Sciences, available
at £39 from CABI, Wallingford, Oxfordshire, OX10 8DE (telephone 0491
832111)

* * *

The world’s first reptile?

‘Lizzie the Lizard’, as she was called by the world’s press, gained
fame in 1988 as the oldest known reptile. Further notoriety came when the
Staatliches Museum fur Naturkunde in Stuttgart offered £200 000 to
buy her. Following an appeal in 1990, the National Museums of Scotland managed
to prevent the export. But Lizzie’s reputation as the ‘first reptile’ was
not so easily saved. Painstaking study of the animal’s palate, and the discovery
of a second specimen by museum staff, have thrown doubt on the animal’s
reptilian pedigree.

Just 20 centimetres long, with a skink-like body and small teeth, Westlothiana
lizziae probably lived in leaf litter, earth or rocks, feeding on soft invertebrates.
Debate about the creature’s classification stems from conflicting evidence
as to whether or not it was an amniote – a tetrapod whose developing young
are surrounded by so-called amniotic membranes, allowing them to breathe
and excrete while inside an egg or while developing within their mother’s
body. This is crucial for classification because reptiles are defined as
any amniote that is not a bird or mammal.

The innovation of amniotic membranes, and hence shelled eggs, freed
tetrapods from having to lay eggs in water. But fossils do not preserve
these delicate membranes, so how do we know whether West-lothiana was an
amniote? Studies of fossils and living animals reveal certain skeletal characteristics
which the group has in common.

The original Westlothiana appeared to show several of these markers
– notably details of the skull roofing bones and the vertebrae, and the
presence of two, rather than three, bones in the ankle joint. But the second
and more complete specimen shows the primitive three ankle joint bones.
Moreover, the newly exposed palate of the first specimen turns out not
to bear the amniote marker of the pterygoid flange – a low tooth-covered
cross-ridge on each side of the palate.

Unfortunately, we do not know which amniote markers evolved before
the membrane itself and which after. So all we can say is that Westlothiana
falls into a grey area between undoubted non-amniotes and undoubted amniotes.
The creature is very closely related to the oldest common ancestor of amniotes
and remains a crucial link in the evolution of reptiles and, ultimately,
ourselves.

* * *

The name game

Etiquette has changed since Victorian times, but there are still courtesy
and charm to be found in the naming of new species. The traditional way
was to name the genus after some anatomical peculiarity and the species
name often identified the collector – not the finder if money had changed
hands. For example, the first finds of East Kirkton fossils from the genus
Eurypterus were called Eurypterus scouleri. ‘Eurypterus’ from the Greek
for ‘broad wing’, reflecting the width of their hindmost swimming paddles
and ‘scouleri’ after John Scouler, Professor of Natural History at the
Andersonian College, Glasgow, who bought the specimens in the 1830s. You’ll
note that the quarryman got no credit.

Today things are often different. Allusions are more varied, perhaps
because we have run out of the obvious permutations of the various Greek
or Latin names for anatomical peculiarities. Silvanerpeton is ‘amphibian
of the wood god’ – a double pun on Stan Wood and the wood in which East
Kirkton quarry lies. Its species name S. miripedes adds ‘wonderful feet’
– so beautifully preserved and displayed in the specimen. Balanerpeton woodi
is ‘Wood’s amphibian of the hot springs’ – of doubtful veracity in the light
of the new evidence about the origins of East Kirkton limestone, but now
irremovably fixed under the International Code of Zoological Nomenclature.

‘Lizzie the Lizard’ is Westlothiana lizziae, to honour the local authority,
West Lothian District Council, which first allowed Wood to excavate at East
Kirkton and then helped the National Museums of Scotland to purchase the
first specimen of Westlothiana. Equally courteous is Eldeceeon rolfei,
to thank both Livingston New Town’s Development Corporation – ‘LDC’ – which
supported the public appeal for the specimen’s purchase, and Ian Rolfe,
leader of the East Kirkton Project.