Large-scale
model of the 'Dudley bug'
trilobite Calymene blumenbachii (© Dr Karl Shuker)
One of the
best-known groups of fossil animal are the trilobites ('three-lobed'), this
name deriving from the distinctive three-lobed structure of their body, which
consists of the cephalon (head shield), the thorax, and the pygidium (tail
shield). Ranging in size from a dinner plate down to a pea, they are famed for
their segmented body form, numerous pairs of limbs, and extremely
well-developed compound eyes.
Global but
exclusively marine in distribution, this taxonomic class of arthropods was one
of the earliest, with the first-known representatives in the fossil record
dating back approximately 540-520 million years to the early Cambrian Period
(though it is suspected that there may well have been earlier forms as yet
unrepresented by documented fossils dating as far back as 700 million years, to
the pre-Cambrian).
Beautiful
illustration of trilobites from Système Silurien du Centre de la Bohême,
by Joachim Barrande, 1852 (public domain)
Bearing in mind
how zoologically familiar they are today and how their taxonomic identity as
arthropods is indisputable, it may come as something of a surprise to learn that
the first trilobite fossils to attract notable scientific attention, during the
1700s, incited considerable controversy as to what type of creature they
represented, resulting in some exceedingly bizarre notions being aired in all
seriousness.
They were
initially deemed to be ancient, three-lobed clam-like seashells (and were duly
dubbed Concha triloba), because these particular trilobite fossils
showed only the animals' dorsal side (thereby concealing the fact that
trilobites actually possessed legs – lots of legs, in fact!).
Sentimentally priceless - a diverse
selection of trilobite casts on a matrix slab bought for me by my late mother Mary Shuker during our first, very happy visit to Lyme Regis, Dorset (© Dr Karl Shuker)
Not everyone
agreed with this identification, however, and offered various alternative but
equally erroneous suggestions. The normally authoritative British zoologist Dr
George Shaw (1751-1813), for instance, proposed that trilobites were fossil
caterpillars, while some contemporaries opined that they were archaic
centipedes, or (less preposterous) crustaceans.
The matter
remained contentious until American palaeontologist Charles D. Walcott resolved
it in a very convincing manner – by skilfully and painstakingly using a hacksaw
to open up no fewer than 3,500 fossils of curled-up trilobites, thereby
revealing the presence of their jointed legs, and, in turn, these
hitherto-baffling beasts' true nature as arthropods.
Spectacular,
life-like model of Bristolia bristolensis, a notably long-spined species
of early Cambrian trilobite from the southwestern USA (©
Andrew 'Trilobite' Scott – click here
for a ShukerNature exclusive showcasing many other examples of Andrew's
stunning artwork)
During the
lengthy course of their evolution, the trilobites became exceedingly
successful, yielding a vast diversity of species (some 17,000 are currently
recognised) as well as body forms and lifestyles before decreasing markedly in
the Devonian, and finally dying out completely around 252 million years ago (in
the mass extinction that occurred at the end of the Permian) – or did they?
There is no well-established reason why they should have done.
As a zoologist
living in the West Midlands, England, I
am very aware that one particular trilobite species, Calymene blumenbachii from the Silurian Period, is so abundant in
the fossiliferous limestone quarries of Wren's Nest in the West Midlands town
of Dudley that it is popularly known as the Dudley bug or Dudley locust, and
even appears on the Dudley County Borough Council's official coat-of-arms.
Naturally, therefore, I've been a fan of trilobites ever since childhood, and
my fossil collection contains several specimens, but my interest in
cryptozoology would subsequently yield an additional reason for my being
fascinated by them.
Dudley
bug trilobite, from James Geikie's Outlines of Geology, 2nd rev. edit,
1883 (public domain)
In the
mid-1980s, I purchased veteran American cryptozoologist Prof. Roy P. Mackal's
classic book Searching For Hidden Animals (which had originally been
published in 1980 in the U.S.A., but
not until 1983 in the U.K.), and
was delighted to find that it documented a wide range of lesser-known cryptids.
However, one
chapter that obviously attracted my particular interest was tantalisingly entitled
'Living Trilobites?'. It included a discussion as to whether any representatives
of these archaic arthropods might have survived the Permian mega-death and
persisted in benthic anonymity on the ocean floor into the present day.
Prof.
Roy P. Mackal and the UK
hb 1st edition of his book Searching For Hidden Animals (©
Prof. Roy P. Mackal/Cadogan Books)
As Mackal noted,
many trilobites were shallow coastal dwellers (especially the later ones), yet
no living trilobites from such localities have ever been discovered.
Consequently, the only hope for modern-day survival is if "some forms
adapted to a deeper, more obscure environment and there found refuge" - or
if some that were already so adapted simply persisted. Should this scenario
have indeed taken place, it could explain why no Cenozoic trilobite fossils have
ever been found - because these would not be readily discovered or accessed on
the ocean floor. But what about obtaining living specimens there?
Until reading
Mackal's book, I hadn't been aware that the very first global marine research
expedition, the voyage of HMS Challenger from 21 December 1872 to 26
May 1876, seriously believed that living trilobites might be dredged up
from the ocean bottom. But although countless specimens that included
representatives of over 4,000 hitherto-unknown animal species were indeed
procured there, none of them were trilobites. Or, as worded in the
authoritative Encyclopaedia Britannica's eleventh edition, published in
1911, the "faint hope" of finding such creatures was not realised.
HMS
Challenger portrayed in an engraving from 1858 (pubic domain)
In reality,
however, a few years before this expedition had even set out on its epic
voyage of zoological discovery, a claim had been made that a living trilobite
had already been obtained, and from a depth of 1,200 fathoms (7,200 ft). Moreover, this claim was
actually believed for a time before the creature's true, non-trilobite identity
was revealed. Another veteran cryptozoological chronicler, Willy Ley, who
briefly reported the case in one of his many articles, didn't provide further
details, but as noted by Mackal the timing and morphological similarities
strongly suggests that the discovery in question was actually that of a certain
Antarctic species of isopod crustacean (the taxonomic group which includes
woodlice and sea slaters) that is astonishingly trilobite-like in outward
appearance.
Brought to
scientific attention in 1830, its first officially recorded specimen had
actually been found inside the gut of a marine fish examined by American
naturalist Dr James Eights while visiting the South Shetland Islands between
Patagonia and Antarctica during the so-called 'Expedition of 1830'. Emphasising
its remarkable morphological convergence, in 1833 Eights formally christened
this memorable new species Brongniartia [now Ceratoserolis] trilobitoides.
And it was indeed initially mistaken for one of these prehistoric arthropods by
some observers, but it sports two pairs of antennae (a crustacean
characteristic), whereas trilobites only had one.
Ceratoserolis
trilobitoides from James Eights's 1833 description paper
(public domain)
Other modern-day
creatures that have often been mistaken for living trilobites are chitons and
water pennies. Chitons (or polyplacophorans, to give them their formal
zoological name) constitute a taxonomic class of molluscs characterised by
their very distinctive shells, which are composed of eight separate but
slightly overlapping plates, and afford these animals a superficially segmented
appearance dorsally.
If a chiton is
turned over, however, its ventral body surface is seen to be non-segmented and
only possessing a single, typically-molluscan foot, in contrast to the many
limb pairs possessed by trilobites. As for water pennies, these trilobite
imposters are the larval stage of certain aquatic freshwater psephenid beetles,
belonging to the genus Mataeopsephus.
19th-Century
engraving of chitons (public domain)
Also
superficially trilobite-like in outward dorsal appearance are both the larvae
and the larval form-retaining adult females of lycid (net-winged) beetles
belonging to the genus Platerodrilus, and which are therefore known
colloquially as trilobite beetles (click here
for a ShukerNature article featuring these distinctive insects). Native
principally to tropical rainforests in India and
southeastern Asia, some of them are brightly coloured.
Finally, the
juvenile stage of those famous 'living fossils' known as xiphosurans or horseshoe
crabs is termed a trilobite larva, once again because of its superficial
similarity to genuine trilobites. Horseshoe crabs, incidentally, are the
closest living relatives of another taxonomic group of iconic fossil arthropods
– the eurypterids or sea scorpions.
Exquisite
illustration by Ernst Haeckel from 1904 featuring trilobites, horseshoe crabs,
and sea scorpions (© public domain)
Back in the
1980s, a bizarre story emanating from Australia briefly hit the
news headlines, claiming that some trilobites had been found inhabiting Perth's storm drains.
Not surprisingly, however, this was soon exposed as a hoax, featuring an old
tyre that had been cut into the shape of a trilobite.
A
fossil trilobite species of familiar, non-extreme morphology (public domain)
Numerous deepsea
collecting expeditions have been launched since Challenger, but none has
ever procured any living trilobites, and yet some tantalising indirect (or, to
be precise, ichnological) evidence for such creatures may have been
recorded, which Mackal described as follows:
...in 1967, I was invited by Ralph Buchsbaum, professor of
zoology at the University
of Pittsburgh,
to give a seminar on our researches at Loch Ness. During the social hour after
the presentation one of his colleagues told me about experimental photography
of the sea bottom that was in progress. He stated that photographs of fresh
tracks identical to the Cruciana [sic – Cruziana], the fossilized
trilobite tracks, had been obtained. He expressed the hope that traps could be
lowered to catch whatever was making these highly suggestive tracks. As far as
I know the nature of these tracks was never determined and nothing was ever
trapped, because of a subsequent loss of funding for the project. The business
of identifying sea-bottom trails and tracks is a tricky one and to infer living
trilobites from a track is even more tricky. A marvelous collection of sea-bottom
tracks and trails is presented in a book entitled The Face of the Deep
by B. C. Heezen and C. D. Hollister. Only a tiny fraction of aquatic animal
tracks have been identified, so that fertile ground for new discoveries is
indeed abundant...Underwater photography of the ocean floor...appears to be a
promising tool for future cryptozoological expeditions.
Cruziana
from Portugal
(public domain)
Cruziana is a famous
trace fossil taking the form of elongate, bilobed burrows that are roughly
bilaterally symmetrical. As noted in a 2010 Lethaia paper by Dr Stephen
Donovan, many examples are believed to be the tracks or trails yielded by
trilobites while deposit-feeding, but certain others are deemed not to be,
because they were present in freshwater environments (where no trilobite
fossils have so far been found) and/or were of Triassic date, by which time all
trilobites were supposed to have died out. But were these ostensibly
anachronistic tracks actually made by surviving post-Permian trilobites for
which direct fossil evidence has simply not been found as yet?
Incidentally,
two other types of trace fossil believed to have been created by trilobites are
Rusophycus and Diplichnites. The former fossils are excavations
featuring little or no forward movements, and have therefore been interpreted
as traces left by trilobites while resting or in defence/protection mode. In
contrast, the latter fossils are believed to be traces left by trilobites while
walking upon the sediment surface.
Rusophycus
trace fossil from Ordovician Period (public domain)
Mackal ended his
living trilobites chapter on a somewhat pessimistic note, concluding:
"While not impossible, it is most improbable that living trilobites still
exist". After that, this fascinating prospect appeared to have vanished
from the modern world just as surely, it would seem, as the trilobites
themselves – which is why I was so startled, but delighted, by a certain
comment allegedly made by a well-respected current scientist more recently.
On 24 June 2004,
Yahoo! News released online a report concerning the receipt of a $600,000 start-up grant from the private
Alfred Sloan foundation for a proposed 10-year international survey of the
oceans' depths, at an estimated total cost of US $1 billion, to be funded by
governments, companies and private donors, and officially dubbed the Census of
Marine Life (CoML). As part of this grand-scale project, scientists led by researchers
from the University of Alaska planned to use robot submarines and sonar to track down life
forms in the Arctic Ocean's chilling deepwater domain, and expectations were that by
the end of its decade-long course, the survey could easily have doubled the
number of species known from this particular ocean.
Three-dimensional reconstruction of Drotops armatus, a
very spiny species of Devonian trilobite from Morocco (public domain)
All very worthy indeed, but what caught my eye amid all of
these statements was one attributed in the news report to none other than Dr
Ron O'Dor, chief scientist of the multi-nation CoML. According to the report,
whose exact wording is quoted here as follows, Dr O'Dor "speculated that
Arctic waters might hide creatures known only from fossils, such as trilobites
that flourished 300 million years ago". It would seem, therefore, that the
notion of finding living trilobites has not been entirely discounted by
scientists after all.
Happily, the CoML did indeed take place, this very ambitious
project ultimately featuring scientists from more than 80 different nations,
and releasing the world's first-ever census in 2010 – but no living trilobites
were listed. Nevertheless, there is a notable precedent well worth mentioning
here.
Pilina, a fossil
monoplacophoran outwardly resembling modern-day Neopilina (public
domain)
The monoplacophorans are a primitive taxonomic class of
molluscs, whose youngest fossil species date from around 380 million years ago.
On 6 May 1952, however, trawling off Mexico's western coast
at a depth of almost 12,000 ft in dark, muddy
clay, the Danish research ship Galathea hauled up 10 complete specimens
and three empty shells of a small, seemingly unremarkable mollusc superficially
resembling a limpet but which proved
upon scientific examination to be a living monoplacophoran. This
hitherto-unknown species was formally named Neopilina galatheae, since
when further specimens of it, and of several additional modern-day species too,
have been obtained (see my Encyclopaedia of New and Rediscovered Animals, 2012, for full details).
Structurally, these living monoplacophorans are very
different internally from their archaic fossil ancestors, so if living
trilobites do exist, these too are likely to be highly evolved species.
Nevertheless, the discovery of Neopilina and kin readily demonstrates
that it is by no means impossible for invertebrates deemed by their fossil
record to have died out in very far-distant prehistoric ages to be represented,
in fact, by living species that have simply evaded scientific detection.
A classic late-1800s illustration of living trilobites by
Heinrich Harder (public domain)
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