Bowdler-Hicks, Alison (2002)

279 Pages·2011·32.81 MB·English

Bowdler-Hicks, Alison (2002) The taxonomy, phylogeny and
biogeography of the Marrolithinae (Trinucleidae, Trilobita). PhD thesis.

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THE
PHYLOGENY AND BIOGEOGRAPHY
TAXONOMY,
OF THE MARROLITHINAE
(TRINUCLEIDAE, Trilobita)
By
Alison Bowdler-Hicks
(PhD Thesis)
Division
Earth Sciences
of
University
Glasgow
of
December
2002
Abstract
Trinucleid trilobites are characterised by their pitted fringes on the cephalon. The
Marrolithinae is Trinucleidae in innermost is
the the
a subfamily of which arc of pits
truncated by the next arc and flange pits are present along the posterior to posterolateral edge
lobe. The Marrolithinae ten 60
of the genal currently comprise genera and some species and
had its the Gondwana during
subspecies and origins on margin of the rifling and northward
during
drift the Ordovician. The history Marrolithinae
of numerous microplates mid of the
but
back forth
reflects a complex, currently unresolved, pattern of migration and across the
the Rheic Ocean from
gulf of the Llanvirn Ashgill
widening early until the mid such that
found in
species are now the Anglo-Welsh France, Iberia, Bohemia, Turkey, Central
area,
Asia, N. Africa
and part of S. America. The Marrolithinae for European,
are widely used
North African Turkish
and indicators for Anglo-Welsh
correlation
and are zonal several
biozones.
An detailed is
extensive and overhaul of the the Marrolithinae
present classification of
to taxonomic framework from
undertaken produce a clear to the phylogeny
which understand
biogeographical history have been
the Historically,
and of subfamily.
marrolithine species
defined
typological has increasingly
using a strongly approach which proved unworkable as
in in
species show ranges of variation morphology that have led to the
uncertainty
identification
has
of specimens and therefore lowered The
their
stratigraphical usefulness.
lack
of appreciation of morphological has in
variation resulted the naming of a great many
than
more species are probably actually present in the fossil Extensive museum
record.
have been
analysed supplemented by field Wales Shropshire
collections
sampling within and
field locations horizons.
of and A large 2000
and comparison collection of over specimens of
Moroccan Marrolithinae
Llanvirn to Ashgill for first This has
was studied the time. material
been important in the reclassification of the Marrolithinae. These the earliest
samples contain
have therefore thrown light Onnia lineage
Onnia Deanaspis
and on the as
specimens and
The Moroccan
the
samples also contain the of
presently understood. earliest representatives
The Moroccan in
Hammannaspis. important the
new genus species played an role
distribution Marrolithinae
the around proto-Tethys.
of
The re-evaluation of the classification of marrolithine genera and species has included the first
in fringe
trinucleid detailed
cladistic subfamily, pit
analysis of a analysis of variation
development
taxa the
within samples and and consideration of palaeogeographical
relationships between the marrolithine taxa in space and time. These differing approaches
have led
to the production of a more constrained and easier to use classification which will
Marrolithinae.
enhance the stratigraphical usefulness of the
The Marrolithinae herein 30
as revised comprises species and subspecies within the genera
Marrolithus [within Costonia is Protolloydolithus, Reuscholithus,
which synonymized],
Whittardolithus, Lloydolithus,
Beltonolithus, Marrolithoides, Deanaspis, Onnia
and
Hammannaspis
gen. nov.
Rrotolloydolithus
The is
ancestor of Hanchungolithinae, Hanchungolithus.
undoubtedly the
Bettonolithus
probably gave rise to three Whittardolithus Lloydolithus
stocks:
and as one
Marrolithus
Hammannaspis
stock and
and
Reuscholithus
gen. nov. as another. was probably
derivative
the
a one of the youngest Marrolithus Marrolithoides likely the
species. was most
Anglo-Welsh
Hammannaspis
representative in
of did
that
gen. nov., a genus not appear
Avalonia. Deanaspis Onnia
in
and coexisted the Caradoc the third
early and make up
Bettonolithus
stock.
Recognition between
has
of variation
samples of what are now recognised as the same species
important implications
the
on previous typological
approach to the taxonomic classification of
Marrolithinae.
the These include
variations in
the temporal the
and spatial changes extent and
fringe inflations in Marrolithus
elevation of favus favus, M. (s. 1. ) M. (s. 1. )
elegans and
Using
the
arenarius. revised taxonomy the history
palaeogeographical of the subfamily
becomes The
directions
clearer. main migration for be
the to
marrolithines appears contrary
Arenig
the
to ocean currents of as presently understood. The the
complex migration around
light
peri-Gondwanan margin also sheds on the relative positions of the Perunican, Armorican
Iberian
and microplates.
Acknowledgements
I like to thank two Alan Owen Keith Ingham for
would my supervisors and their guidance and
I institutions
thank the
unending patience. also curatorial staff at all the museums and other
Steve
thanks to Bob Owens, Derek Siveter, Andy Ross, Mike Dorling
visited, with special
Tunicliffe Euan Clarkson Mike Jewkes. Thanks Pete Sheldon Adrian Rushton
and to
also and
for
their NERC husband, Simon, for financial
words of encouragement. support.
and my
Mum Dad family friends for help.
and and all my and the
kindness
To the loving patience and of my son, Calum, this is for
you.
iv
Declaration
The in
material presented this thesis summarises the results of three years of research carried
out in the Division of Earth Sciences of Glasgow University the supervision of Drs A.
under
W. Owen J. K. Ingham. This is based independent
and study research and any
on my own
have been
in
previously published or unpublished results of other researchers used this thesis
full in
the text.
given acknowledgement
A.
kl
c-i-cXar
(r
2
ýý 2c:
PO
V
LIST OF CONTENTS:
ABSTRACT ii
ACKNOWLEDGEMENTS iv
DECLARATION
CHAPTER ONE
INTRODUCTION
1
CHAPTER TWO
MORPHOLOGY
(,
CHAPTER THREE
CLADISTIC ANALYSIS
21
CHAPTER FOUR
SYSTEMATICS
59
CHAPTER FIVE
ORDOVICIAN PALAEOGEOGRAPHY STRATIGRAPHY
and 200
CHAPTER SIX
HISTORY MARROLTHINAB
PALAEOGRAPHICAL the
of 217
REFERENCES
251
APPENDIX
271
vi
I INTRODUCTION
by fringes The
Trinucleid trilobites are characterised their pitted on the cephalon.
is Trinucleidae in innermost is
Marrolithinae the the
a subfamily of which arc of pits
by flange
truncated the next arc and pits are present along the posterior to posterolateral edge
lobe. The Marrolithinae 60
of the genal currently comprises ten genera and some species and
had its
subspecies and origins on the margin of Gondwana during the rifling and northward
drift
of numerous microplates during the Ordovician. The history the Marrolithinae
mid of
but back forth the
reflects a complex, currently unresolved, pattern of migration and across
the Rheic Ocean from Llanvirn Ashgill that
widening gulf of the early until the mid such
found in the Anglo-Welsh France, Iberia, Bohemia, Turkey, Central
species are now
area,
Asia, N. Africa S. America.
and part of
1.1 Aims
The aims of this project are to produce an extensive and detailed overhaul of the present
classification of the Marrolithinae to establish a clear taxonomic framework from which to
the biogeographical history Historically,
understand phylogeny and of the subfamily.
have been defined has
marrolithine species using a strongly typological approach which
have
increasingly proved unworkable as species show ranges of variation in morphology that
in identification
led the has lowered their
to of specimens therefore
uncertainty and
The lack has in
of appreciation resulted
stratigraphical usefulness. of morphological variation
fossil
in
the naming of a great many more species than are probably actually present the
have has been
but
record. Some previous workers revised and synonymised species this not
for
for
attempted comprehensively the whole subfamily. The Marrolithinae are widely used
Anglo-
European, North African and Turkish- correlation and are zonal indicators for several
Welsh biozones.
I
1.2 Historical
review
The literature the Trinucleidae began in the the
extensive on early nineteenth century;
descriptions in instances by
systematic of new species some was also accompanied
discussions distribution Trinucleus Sternberg, 1833
on morphology, and ontogeny. ornalus
description Subfamily Marrolithinae.
was the earliest of a species now assigned to the
Murchison followed his description Trinucleus Lloydi in 1839. Barrande few
with of a years
later (1846) described Trinucleus The following 1847, Salter, Rouault
goldfussti.
year, and
Hawle Corda described the Trinucleus favus, Trinucleus
and species
pongerardi and
Trinucleus
senflenbergii respectively with Hawle and Corda erecting the Family Trinucleidae.
Salter (1848) began
to between his
see very close similarities some trinucleids with species
designation Trinucleus
of ornatus favus. Barrande in 1852, Hicks in 1875 Bergeron
var. and
in 1894 described Trinucleus
Trinucleus Trinucleus In 1895
ullima,
ramsayi and grenieri.
Oehlert described both Trinucleus bureaui Trirrucleus Kerforne in 1900
and maladai with
introducing Trinucleus
suenesi.
Bancroft (1929) the first to detail importance fringes for
was the trinucleid
of using pitted
He the Marrolithus Reuscholithus described R.
classification. erected genera reuschi,
and and
Cryptolithus C.
C.
cobboldi, gracilis, and detailing fringe and
Superbus; and pit morphology
distribution. By 1940
other workers were beginning to the importance of the pitted
see
fringes built Bancroft's
(1948),
and on original work. Over the 20 Williams
next years,
Whittington Williams (1955)
and and Whittington (1966) in Wales, Whittard (1956,1958)
all
in the Shelve Inlier and Dean (1960) in South Shropshire
the
most prolific
were some of
namers of new species of marrolithines. By 1960 the Marrolithus Bancroft, 1929b,
genera
Reuscholithus Bancroft, 1929b, Onnia Bancroft, 1933, Lloydolithus Bancroft, 1933, Bettonia
Whittard, 1956, Marrolithoides Williams, 1948, Costonia Protolloydolithus
Dean, 1960
and
Classification
Williams, 1948
were established. was still very typological with strict
definitions based leading
on pit numbers and patterns, to many workers showing uncertainty
in
to
their of specimens species.
assignment
Hughes fringe
(1970) the for
reviewed notation and methods of presentation trinucleid pit
data. he
A later the Marrolithinae to
erected subfamily for
year genera closely related
Marrolithus
but in Marrolithus,
which were previously placed the Cryptolithinae,
namely
Marrolithoides, Protolloydolithus, Reuscholithus left
Hughes
Costonia. However,
and
2
Bettoma the Cryptolithinae. An important discussed by Hughes that
within point was pit
distribution dependant individual.
the the the
and number of pits per arc are not on size of
The fringe its final in development (see
assumes characteristics very early on meraspid stage
Whittington, 1941 1959).
also and
A distribution in led Hughes,
the trinucleid
greater appreciation of role of pit classification
Ingham Addison to the Trinucleidae in 1975. They
and produce a review of entire
framework for
the
summarised, and partly established, modern morphological and taxonomic
including
Trinucleidae
the the Marrolithinae Deanaspis
establishment of genera and
Whittardolithus.
Morris (1988)
produced a summary of all British trilobite species and reallocated the species
formerly in Bettoma
placed to Bettonolithus former
a new genus as the name was
Owen
preoccupied. and Ingham (1988) detailed distribution data for
gave pit and statistical
successive population samples of Onnia from the Onnian of Shropshire where three
biozones based
successive on species or subspecies of the genus are recognised.
Shaw (1995) discussed the Bohemian Marrolithinae including Deanaspis. He
species of
the difficulties distinguishing between Onnia Deanaspis;
raised concern over of and closely
distinguished by differences in fringe development.
related genera
girder and pseudogirder
Hammann Leone (1997) described from Sardinia described two
and
specimens southern and
distinct
morphological groups with what they interpreted Deanaspis, distinguished by their
as
lobes,
glabella shape, convexity of genal steepness fringe
of and girder and pit characters.
(2001)
Bettley
et al. used marrolithine species amongst other faunal elements to revise the
British biozones through the Llandeilian-Caradoc interval.
standard
1.3
Material
The Marrolithinae
from History
extensive museum collections of the Hunterian, Natural and
Sedgwick National Museum
Wales,
Oxford
museums, of Birmingham and
and universities
British Geological Survey have been information
analysed, with up to 50 items of
separate
3