CONTENT - International Society of Zoological Sciences

S5 ICZ2008 - Abstracts
S6 - Paleozoology and comparative anatomy:exceptional conservations
Non-bilaterians in the early fossil record
Stefan Bengtson
Swedish Museum of Natural History, Stockholm, Sweden
Given their basal positions in the metazoan phylogenetic bush,
sponges, ctenophores and cnidarians should be expected to have
played a major role in the first grand diversification of animals, during
the Neoproterozoic–Cambrian transition, some 570–530 million
years ago. The fossil record is far from clear with regard to these
events, however, partly because preserved characters in nonbilaterian
fossils are often too few and ambiguous for meaningful
phylogenetic analysis. The Neoproterozoic–Cambrian record of
exquisitely preserved embryos, body fossils and skeletal
components of non-bilaterians is growing in extent and quality,
shedding light on the early diversification of metazoans. The fossils
may share primitive characters that have been lost in living
representatives of the major groups, which helps us identify
relationships within the early branches of the metazoan bush,
including extinct lineages. A very early ctenophore-like fossil,
sponge-like fossils with cnidarian features, and embryos of strong
cnidarian aspect will be used to illustrate these points.
Remarkably preserved marine invertebrates from the Silurian of
Herefordshire, England
Derek E.G. Briggs 1 , Derek J. Siveter 2, 3 , David J. Siveter 4 and Mark D.
Sutton 5
1 Department of Geology & Geophysics, Yale University, PO Box
208109, New Haven, CT 06520-8109, USA
2 Geological Collections, University Museum of Natural History,
Oxford OX1 3PW, UK
3 Department of Earth Sciences, University of Oxford, Parks Road,
Oxford OX1 3PR, UK
4 Department of Geology, University of Leicester, Leicester LE1 7RH,
UK
5 Department of Earth Sciences and Engineering, Imperial College,
London SW7 2BP, UK
A remarkable assemblage of marine animals is currently emerging
from study of a 425 million-year-old (Silurian) volcanic ash in
Herefordshire, England. Tiny animals, most just a few mm in
dimension, are preserved in carbonate concretions. The fossils
cannot be extracted by mechanical or chemical means – nor are they
visible to x-radiography or scanning methods. The specimens must
be ‘prepared’ by grinding them away microns at a time to produce
high resolution 3-D reconstructions that can be manipulated on a
computer. The fidelity of preservation of even soft-part anatomy
allows the morphology of these animals to be investigated at a
comparable level of detail to their modern counterparts. The rare and
spectacular fossils include many animals that are very poorly
represented in the fossil record, as they lack any biomineralized
skeleton. The Herefordshire deposit represents one of very few
exceptionally preserved fossil biotas (Lagerstätten) known from the
~70 Ma period between the Cambrian and Devonian; it provides a
unique and important window on Palaeozoic marine life. The biota
includes a diverse suite of arthropods: a stem-group chelicerate and
crustacean, a phyllocarid, ostracods, a larval barnacle, a pycnogonid
and a marrellomorph. It also includes radiolarians, a diversity of
sponges, a polychaete worm, an aplacophoran-like mollusc, a
platyceratid gastropod, a brachiopod with pedicle, several
echinoderms including an asteroid with preserved tube-feet, and
many other organisms of uncertain affinity. These fossils are yielding
critical information on the evolutionary history and relationships of
living invertebrate taxa.
- 24 -
Bone growth marks suggest protracted growth in Apteryx (Aves,
Neornithes, Ratitae)
Jacques Castanet, Estelle Bourdon, Jorge Cubo and Armand de
Ricqlès
Equipe « Squelette des Vertébrés », UMR CNRS 7179. UPMC, 2, pl.
Jussieu, case 19,75005 Paris, France
Skeletochronology is a broadly used method that utilizes bone
growth marks (BGMs) to infer life history traits in tetrapods. In
modern birds, however, the presence of BGMs and their use for
individual aging remains controversial. Because most living birds
achieve their complete skeletal development in less than one year,
BGMs are either absent or scarce and restricted to the outer part of
bone cortices. A BGM pattern similar to that of non avian reptiles is
known in some non-neornithine birds and in extinct New Zealand
moas (Dinornithiformes). Till recently, BGMs were regarded as
unknown in living ratites (Turvey et al. Nature, 2005: 435). This is
now contradicted by the discovery of BGMs in the long bones of
Apteryx australis (Apterygidae). The occurrence of 7 or 8 wellmarked
lines of arrested growth (LAGs) in hindlimb bone cortices of
an adult suggests that this individual was at least 7 or 8 years old. In
the femur, the first 3 or 4 LAGs are separated by layers of parallelfibered
bone, weakly vascularized by primary vascular canals. In the
tibiotarsus and tarsometatarsus, these inner LAGS are locally erased
by bone remodelling. The 4 outer LAGs are closer to each other and
located in bone periphery. This LAG pattern and the decrease of
vascular density towards the periosteum suggests that Apteryx, in
contrast to other living birds, does not reach its adult body size until
up to 4 years of age and subsequently shows a prolonged periostic
osteogenesis during at least 4 more years.
Cambrian representatives of the tongue worms: ontogeny and
taxonomy
Christopher Castellani, Dieter Waloszek and Andreas Maas
1Workgroup Biosystematic Documentation, Helmholtzstr. 20,
University of Ulm, 89081 Ulm, Germany
During the last twenty years, several authors have tried to solve the
problem related to the systematic position of an enigmatic group of
parasites, the Pentastomida (tongue worms), but without convincing
success. Two major assumptions result from this controversy. The
first, supported mainly by investigations of sperm morphology and
nucleic acids, assumes close alliance to the eucrustacean in-group
Branchiura (fish lice). The second, founded on morphological,
embryological, anatomical and fossil data, points to a derivation from
even before the Arthropoda s. str. level, i.e. before achievement of
arthropod characteristics such as sclerotised body tergites,
compound eyes, or segmented limbs with exopods. In 2004, new
material of 3D-preserved (‘Orsten’-type-preserved) Cambrian
representatives of the tongue worms was obtained from a piece of
limestone rock collected in Västergötland, Sweden. In the framework
of the EU programme Molmorph we study more than 60 specimens
of different sizes, using two major techniques, SEM with
standardised views and biometry combined with statistical tools.
Preliminary measurements suggest that the new material might
represent not only different instars, at least three, but also contains
different species, at least two. The large material permits to
investigate all major external features of the fossils in detail. These
will be used in a re-evaluation of the taxonomy status of all Cambrian
fossil taxa described so far. In the light of the new data, we expect to
contribute further to a solution of the unclear systematic position of
Pentastomida.