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A pipiscid-like fossil from the Lower Cambrian of south China


Abstract and Figures

Exceptional fossil preservation is critical to our understanding of early metazoan evolution. A key source of information is the Burgess Shale-type faunas. Fossils from these deposits provide important insights into metazoan phylogeny, notably that of stem-group protostomes,,, and related topics such as trophic specialization. Metazoan relationships are also being significantly reappraised in terms of molecular-based phylogenies,, but integration of these data with palaeontological systematics is not straightforward,. Moreover, molecular phylogenies are silent concerning the anatomies of stem-groups and the functional transitions that underpin the origin of different body plans,. Some hitherto enigmatic fossils possess unique character-state combinations that, although they can be shoe-horned into extinct phyla, may be more profitably interpreted as defining major stem-groups,. Here we describe a possible pipiscid, a metazoan previously known only from the Upper Carboniferous,, from the Lower Cambrian of south China. Pipiscids are currently interpreted as being agnathan chordates, but this discovery from the Chengjiang fossil-Lagerstätte indicates that the assignment of pipiscids to the Agnatha deserves to be reconsidered.
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VOL 400
19 AUGUST 1999
particulates on the background concentration of CCN over the
ocean could also have an effect on regional and global radiative
budgets. To estimate this effect, we apply the fuel-based emission
factors for particulate matter reported by Lloyds26 to generate total
annual particulate-matter emissions for ships (0.85 Tg yr
). This is
then globally distributed according to the method of Corbett and
Fischbeck2,3 to give us the emission rate of particulate matter (E
for any grid cell (x,y). We can then estimate the change in the CCN
number, DCCN
, assuming steady state for the CCN concentration
and using
where v
is the average CCN removal velocity (wet and dry), f
the CCN mass fraction of the emitted particulate matter, Nis the
number density of CCN (number per mass larger than Dp
p) emitted
by ships, and Dp
pis minimum diameter at which these particles
activate to form cloud drops. Based on the particulate-matter size-
distribution measurements of Lyyranen et al.27, for large engines
operating at full power, and assuming a Dp
pof 0.1 mm, we estimate f
to be 0.6 (CCN per g particulate matter emitted) and Nto be 10
CCN per g of CCN. In addition, we assume a CCN lifetime of three
days (vdep 0:4cms21). Assuming as a ®rst-order approximation
that the change in cloud droplet number is equal to DCCN for the
low CCN concentrations of the marine environment (100 cm
), the
potential effect of ships on annual average cloud albedo and
radiative forcing can be estimated28. To avoid problems with the
nonlinear response of cloud droplet number to CCN concentration,
and to keep our radiative forcing estimate conservative, we only
consider ship particulate-matter emissions where continental in¯u-
ence is small. This is determined using our annual average model
predictions for NSS-sulphate (with ships) and a threshold of
0.2 p.p.b.v. NSS-sulphate.
Using this method, we estimate the change in global radiative
forcing due to cloud effects from ship particulate-matter emissions
to be -0.11 W m
. This value is 14% of the IPCC estimate for 1990
global indirect forcing from all anthropogenic sulphate29. The
predicted average change in radiative forcing due to ships for the
Northern Hemisphere is -0.16 W m
and for the Southern Hemi-
sphere is -0.06 W m
. The direct effect of ship sulphur emissions is
expected to be less dramatic28. The sensitivity of our estimate to
various uncertain input parameters is shown in Table 1. As can be
seen, reasonable variation in individual input parameters can affect
this ®rst-order global estimate by at least a factor of 2.
Our results suggest that the emissions of sulphur and particulate
matter from the international shipping industry need to be con-
sidered in the study of marine and coastal atmospheres. Because
ship emissions, as a source of background sulphur, have been
neglected in the past, many observational studies of the marine
atmosphere need to be re-evaluated, particularly those in the
remote oceans of the Northern Hemisphere. M
Received 19 February; accepted 5 July 1999.
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sulphur, cloud albedo, and climate. Nature 336, 655± 661 (1987).
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®eld measurement campaign in NW Scotland. Chemosphere 28, 543± 557 (1994).
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Atlantic air from the United Kingdom in Halley Bay. J. Geophys. Res. 101, 22855±22867 (1996).
11. De Bruyn, W. J., Bates, T. S., Cainey, J. M. & Saltzman, E. S. Shipboard measurements of dimethyls
sul®de and SO
southwest of Tasmaniaduring the ®rst Aerosol Characterization Experiment (ACE 1).
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13. Pio, C. A., Cerqueira, M. A., Castro, L. M. & Salgueiro, M. L. Sulphur and nitrogen compounds in
variable marine/continental air masses at the southwest European coast. Atmos. Environ. 30, 3115±
3127 (1996).
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the western Paci®c Ocean during February±March 1994: Results from PEM-West B. J. Geophys. Res.
102, 28255±28274 (1997).
15. Thornton, D. C. & Bandy, A. R. Sulfur dioxide and dimethylsul®de in the central Paci®c troposphere.
J. Atmos. Chem. 17, 1±13 (1993).
16. Bandy, A. R., Scott, D. L., Blomquist, B. W., Chen, S. M. & Thornton, D. C. Low yields of SO
dimethyl sul®de oxidation in the marine boundary layer. Geophys. Res. Lett. 19, 1125±1127 (1992).
17. Hertel, O., Christensen, J. & Hov, O.Modelling of the end products of the chemical decomposition of
DMS in the marine boundary layer. Atmos. Environ. 28, 2431±2449 (1994).
18. Saltelli, A. & Hjorth, J. Uncertainty and sensitivity analyses of OH-initiated dimethyl sulphide (DMS)
oxidation kinetics. J. Atmos. Chem. 21, 187±221 (1995).
19. Suhre, K. et al. Physico-chemical modeling of the ®rst Aerosol Characterization Experiment (ACE 1)
Lagrangian B1: A moving column approach. J. Geophys. Res. 103, 16433 ±16455 (1998).
20. Carlton, J. S., Wright, A. A. & Coker, R. J. Marine Exhaust EmissionsÐA Regional Survey of the English
Channel (Marine Management (Holdings) Ltd, London, 1994).
21. Port of Los Angeles, Port of Long Beach, Dames & Moore, Morrison and Foerster Control of Ship
Emission in the South Coast Air Basin: Assessment of the Proposed Federal Implementation Plan Ship Fee
Emission Fee Program (Port of Los Angeles, Los Angeles, California, 1994).
22. Nonroad Engine and Vehicle Emission Study (US Environmental Protection Agency, Washington DC,
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ships on clouds. Science 246, 1146± 1149 (1989).
24. King, M. D., Radke, L. F. & Hobbs, P. V. Optical properties of marine stratocumulus clouds modi®ed
by ships. J. Geophys. Res. 98, 2729± 2739 (1993).
25. Ferek, R. J., Hegg, D. A., Hobbs, P.V., Durkee,P. & Nielsen, K. Measurements of ship-induced tracksin
clouds off the Washington coast. J. Geophys. Res. 103, 23199±23206 (1998).
26. Carlton, J. S. et al.Marine Exhaust Emissions Research Programme (Lloyd's Register Engineering
Services, London, 1995).
27. Lyyranen, J., Jokiniemi, J., Kauppinen, E., Joutsensaari, J. & Auvinen,A. Particle formation in medium
speed diesel engines operating with heavy fuel oils. J. Aerosol Sci. 29, S1003± S1004 (1998).
28. Seinfeld, J. H. & Pandis,S. N. Atmospheric Chemistr y and Physics:From Air Pollution to Climate Change
(Wiley & Sons, New York, 1998).
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of the Intergovernmental Panel on Climate Change (IPCC) (Cambridge Univ. Press, 1995).
Acknowledgements. This work was supported by the US NSF and the NOAAOf®ce of Global Programs.
Correspondence and requests for materials should be addressed to S.N.P. (e-mail: spyros@andrew.
A pipiscid-like fossil
from the Lower Cambrian
of south China
D. Shu*, S. Conway Morris², X-L. Zhang*, L. Chen*,Y.Li*
& J. Han*
*Department of Geology, Northwest University, Xi'an, 710069,
People's Republic of China
²Department of Earth Sciences, University of Cambridge, Downing Street,
Cambridge CB2 3EQ, UK
Exceptional fossil preservation is critical to our understanding of
early metazoan evolution. A key source of information is the
Burgess Shale-type faunas1±5. Fossils from these deposits provide
important insights into metazoan phylogeny, notably that of
stem-group protostomes2,3,6, and related topics such as trophic
specialization7. Metazoan relationships are also being signi®-
cantly reappraised in terms of molecular-based phylogenies8,9,
but integration of these data with palaeontological systematics is
not straightforward10,11. Moreover, molecular phylogenies are
silent concerning the anatomies of stem-groups and the func-
tional transitions that underpin the origin of different body
plans2,6. Some hitherto enigmatic fossils possess unique charac-
ter± state combinations that, although they can be shoe-horned
into extinct phyla12, may be more pro®tably interpreted as de®n-
ing major stem-groups2,3. Here we describe a possible pipiscid, a
metazoan previously known only from the Upper Carboni-
ferous13,14, from the Lower Cambrian of south China. Pipiscids
© 1999 Macmillan Magazines Ltd
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VOL 400
19 AUGUST 1999
| 747
are currently interpreted as being agnathan chordates13± 15, but
this discovery from the Chengjiang fossil-Lagersta
Ètte indicates
that the assignment of pipiscids to the Agnatha deserves to be
Phylum Uncertain
Xidazoon Shu, Conway Morris & Zhang gen. nov.
Xidazoon stephanus Shu, Conway Morris & Zhang sp. nov.
Etymology. Genus name an abbreviation of Chinese name for
Northwest University at Xi'an. Species name stephanos (Greek)
for crown.
Holotype. Early Life Institute, Northwest University, Xi'an. ELI-
Stratigraphy and locality. Qiongzhusi (Chiungchussu) Formation,
Yu'anshan member (Eoredlichia Zone); Lower Cambrian. Specimen
collected from Haikou, Kunming, located about 50 km west of
Diagnosis. Body with two-fold division, reminiscent of Banf®a but
anterior section more in¯ated and possessing prominent mouth
circlet. Anterior section with faint transverse divisions towards
front, otherwise smooth. Mouth de®ned by circlet of about 25
plates, divided into inner and outer regions, otherwise unarmed.
Circlet similar to plated mouth of Pipiscius, although in the latter
taxon the plates are more cuticularized and inner circlet folded into
pharynx. Posterior section tapering towards front and back, seg-
mented with cuticularized region of about six segments succeeded
anteriorly by about three less well-de®ned segments. Posterior
section similar to arthropodan metameres, but lacking evidence
of appendages. Cuticular segments also reminiscent of posterior
region in Yunnanozoon, but in latter taxon segments are ventrally
incomplete. Short terminal spines at posterior tip. Alimentary canal
with terminal openings, anterior region possibly expanded and
rectum with ?dilator muscles.
Figure 1 The Cambrian fossil Xidazoon stephanus, new species and Carbonif-
erous ?agnathan Pipiscius zangerli.a, Entire specimen and (to lower left)
incomplete individual of Xidazoon (compare to Fig. 2); b, detail of posterior section
showing segmental divisions, gut trace, ?dilator muscles and posterior spines
(right-hand side); c, detail of feeding apparatus of complete specimen; d, detail
of anterior and incomplete feeding apparatus of second specimen. e, Entire
specimen of holotype of Pipiscius, part (PF 8345); f, detail of feeding apparatus of
part; g, detail of feeding apparatus of counterpart. Scale bars: 10mm (a,b,e),
5mm(c,d) and 2mm (f,g).
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19 AUGUST 1999
Description. Xidazoon stephanus, new genus and species, is known
from two, or possibly three, specimens on a single slab (Figs 1a, 2).
The most complete specimen is about 8.5 cm long and a second
individual shows details of the anterior (Fig. 1d). The body
comprises two main regions. The anterior section is moderately
in¯ated, and the prominent circlet of the presumed anterior is
interpreted as a feeding apparatus surrounding a voluminous
mouth (Fig. 1c). The apparatus itself consists of plate-like struc-
tures, transversely folded to de®ne inner and outer circlets. The
edges of the inner circlet of plates are ridged (Fig. 1c), but they do
not bear teeth or other extensions. In the second specimen (Fig. 1d)
the plates appear to be separated adorally by narrower recessed
areas. These may represent ¯exible inter-plate membranes. The
anterior of the second specimen is incomplete, and that of the ®rst is
too crushed to give more than an estimate of the total number of
plates. The better-preserved half-circumference displays about 13
plates, and an allocation of typical plate width around the circum-
ference (,45 mm) gives a total of about 25. The mouth is gaping,
but apart from the circlet of plates lacks evidence of jaws or other
associated structures. Behind the feeding apparatus the anterior
region bears faint, widely separated transverse divisions that may be
The posterior section tapers in either direction from an expanded
central zone. It consists of about six well-de®ned segments (Figs 1b,
2), and in the anterior direction there is a series of more faint
transverse annulations. The surface appears to have been lightly
cuticularized. The segment boundaries vary from tightly adpressed
to separated, indicating originally relatively wide and ¯exible inter-
segmental membranes. At the posterior tip there are two or three
spinose projections (Figs 1b, 2).
Little is known of the internal anatomy. A gut trace is present in
the mid and posterior sections, and near the terminal anus diver-
ging strands may represent dilator muscles (Figs 1a, b, 2). Towards
the anterior of the visible gut trace it appears to expand, and in the
anterior section it may have been voluminous.
Preservation. The style and quality of preservation is similar to
other Chengjiang taxa, such as Yunnanozoon16±19. Thus, the extent of
decay appears to be limited. Features, notably the circlet of plates
and the posterior segmentation, seem to be original rather than
post-mortem artefacts.
Ecology. The ecology of Xidazoon is problematic. It was presumably
benthic, with the anterior circlet periodically contracting to ingest
detritus. The in¯ated nature of the anterior section in the most
complete specimen might be because of sediment ingestion. An
alternative possibility is that the anterior organ acted as a sucker for
lodgement on prey or hard substrates.
Discussion. Comparisons between Xidazoon and various extant
metazoan groups, such as the sipunculans and the much smaller
cycliophorans, are not convincing. Similarly, among the diverse
Burgess Shale-type assemblages, no exact counterpart to Xidazoon
has been recognized. There are some similarities to the otherwise
enigmatic Banf®a confusa5, which consists of a segmented unit,
apparently posterior to an elongate and smooth section, but this
taxon lacks evidence for the prominent feeding apparatus of
Xidazoon. The better-known anomalocaridids20 have a prominent
circular feeding apparatus and a bipartite body with segmented
posterior section. There are, however, many differences. The feeding
apparatus occurs in a variety of forms3,5,20, but none is particularly
similar to Xidazoon. Other characteristic features of the anomalo-
caridids, notably the anterior giant appendages and lateral lobes,
have no parallel in this new fossil.
The anterior circlet of Xidazoon is, however, similar to the
otherwise unique feeding apparatus of the putative agnathan
Pipiscius zangerli (Fig. 1e), a rare species from the 300-Myr-old
Mazon Creek fossil-Lagersta
Ètte (Upper Carboniferous) of Illinois.
The original description13 is convoluted, but in essence the feeding
apparatus is composed of two circles of sclerotized plates. The inner
series (`collar lamellae' of ref. 13) total 23, a number with no
apparent parallel in other metazoan organ systems. The outer circlet
is also cited13 as consisting of 23 plates. There is, however, a hitherto
Figure 2 Camera-lucida drawing of slab containing the two (or possibly three) specimens of the Cambrian fossil Xidazoon stephanus, new species.
© 1999 Macmillan Magazines Ltd
letters to nature
VOL 400
19 AUGUST 1999
| 749
unrecognized duplication on the leading anterior plate, so that the
total number of plates is effectively 24. This duplication de®nes a
line of bilateral symmetry in the apparatus. The plates are separated
by narrow clefts (`vanes' of ref. 13) that presumably accommodated
shape changes associated with feeding. The principal similarities
between the anterior apparatus of Pipiscius and Xidazoon are the
double nature of the circlet with direct continuity between the inner
and outer plates, the similar number of plates and evidence for
articulatory zones (Fig. 1d) that seem to be comparable to the
`vanes' (Fig. 1f). The apparatus, however, are not identical. In
Pipiscius the outer plates have a more complex structure, housing
triangular insets. These latter units may have accommodated move-
ment of the apparatus, possibly necessitated by a more pronounced
sclerotization. Deep pits associated with the `vanes', and possibly
employed for muscle insertions13, are not evident in Xidazoon.
Finally, the inner circle (`collar') of Pipiscius is directed inwards,
whereas in Xidazoon it appears to be more rim-like.
Concerning the possible connection between Xidazoon and
Pipiscius, there seems to be three alternative evolutionary scenarios.
First, the annular feeding apparatus is simply an example of
convergence. Among the many suctorial and other biological
attachment structures similarities can be shown, for example,
with the attachment organ of the ectoparasitic ciliate Trichodina
pediculus21 and the arm suckers of the octopus22, although no
phylogenetic connection with Xidazoon can be seriously enter-
tained. Notwithstanding the bi-annular arrangement of about 25
plates, the few similarities that otherwise exist between Xidazoon
and Pipiscius make convergence a reasonable option. Second,
Xidazoon and Pipiscius are related, but the assignment of the latter
taxon to the agnathans13,14 is erroneous: together they would
represent a new major Palaeozoic clade of as yet unknown af®nities.
In this sense it would be comparable to such enigmatic groups as the
typhloesids23 and tullimonstrids24.
The third proposal is that Xidazoon is a precursor to the
agnathans, including Pipiscius. This presupposes the homology of
the circular feeding apparatus in the two taxa, and that certain
features (such as ®n-rays and possible myotomes) of Pipiscius are
indicative of a chordate relationship. In this scenario Xidazoon
would potentially provide new insights into the organization of
stem-group deuterostomes. A link may also exist with the coeval
Yunnanozoon16± 19. This Chengjiang taxon displays putative gill slits,
and the cuticular segmentation has some similarities with Xidazoon.
One reconstruction18 of Yunnanozoon also depicts a circum-oral set
of plates. The bipartite nature of Xidazoon is more strongly devel-
oped than in Yunnanozoon, but the almost arthropod-like segmen-
ted posterior section could provide an intriguing phylogenetic link
with the protostomes25. Continuing investigations of Lower Cam-
brian fossil-Lagersta
Ètten may yield relatives of Xidazoon that will
help to resolve the controversial status of these fossils in the context
of metazoan phylogeny. M
Received 19 November 1998; accepted 2 July 1999
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Press, Oxford, 1998).
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Taiwan 10, 257±273 (1997).
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Acknowledgements. We thank the National Foundation of Natural Sciences of China, Minister of Science
and Technologyof China, Royal Society, National Geographic Society, and St John's College, Cambridge
for support. Access to Pipiscius was facilitated by P. Crane (Field Museum, Chicago), and M. P. Smith and
P. Donoghue (University of Birmingham). Technical assistance by S. J. Last and D. R. Simons is
acknowledged, as are critical comments by P. Janvier, D. B. Norman and S. Jensen.
Correspondence and requests for materials should be addressed to D.S. (e-mail: dgshu@sein.sxgb.
Environmental controls on the
geographic distribution
of zooplankton diversity
Scott Rutherford*, Steven D'Hondt*& Warren Prell²
*Graduate School of Oceanography, University of Rhode Island, Narragansett,
Rhode Island 02882, USA
²Geological Sciences, Brown University, Providence, Rhode Island 02912, USA
Proposed explanations for the geographic distribution of zoo-
plankton diversity include control of diversity by geographic
variation in: physical and chemical properties of the near-surface
ocean1±3; the surface area of biotic provinces4; energy availability5;
rates of evolution and extinction6; and primary productivity7.
None of these explanations has been quantitatively tested on a
basin-wide scale. Here we used assemblages of planktic foraminifera
from surface sediments to test these hypotheses. Our analysis
shows that sea-surface temperature measured by satellite8
explains nearly 90% of the geographic variation in planktic
foraminiferal diversity throughout the Atlantic Ocean. Tempera-
tures at depths of 50, 100 and 150 m (ref. 9) are highly correlated to
sea-surface temperature and explain the diversity pattern nearly
as well. These ®ndings indicate that geographic variation in
zooplankton diversity may be directly controlled by the physical
structure of the near-surface ocean. Furthermore, our results
show that planktic foraminiferal diversity does not strictly
adhere to the model of continually decreasing diversity from
equator to pole. Instead, planktic foraminiferal diversity peaks
in the middle latitudes in all oceans.
We used the Brown University Foraminiferal Data Base (BFD, 33
species and 6 subspecies .150 mm; 1,252 samples) to document the
global pattern of planktic foraminiferal diversity and to evaluate the
long-standing hypothesis of a latitudinal diversity gradient. Weused
planktic foraminifera for this study because all of the living species
are known and are included in the BFD, unlike other plankton
groups (such as radiolaria or copepods), which have hundreds of
species and greater taxonomic uncertainty. Our results clearly show
that, throughout the world ocean, planktic foraminiferal diversity
peaks in middle latitudes, is lowest at high latitudes and is inter-
... Some Cambrian weird wonders have found their 'home' in the animal tree of life, such as conodonts as chordates (Sansom et al., 1992;Aldridge et al., 1994;Pridmore et al., 1996;Donoghue et al., 2000), cambroernids as stem ambulacrarian Li et al., 2023), halkieriids as molluscs (Vinther et al., 2017), camenellan tommotiids as stem lophophorate (Guo et al., 2022), radiodonts (anomalocaridids and their relatives) as a lower stem group of euarthropods (Budd and Telford, 2009;Daley et al., 2009;Edgecombe and Legg, 2014). While some other fossil taxa are turned into problematica with increasing, drastic debates concerning their morphology and affinities, such as yunnanozoans (Hou et al., 1991;Chen et al., 1995;Dzik, 1995;Shu et al., 1996;Chen et al., 1999;Mallatt et al., 2003;Shu, 2003;Cong et al., 2015;Tian et al., 2022), vetulicolians (Hou, 1987;Shu et al., 1999;Shu et al., 2001;Lacalli, 2002;Caron, 2005;Shu, 2005;Aldridge et al., 2007;Lieberman, 2008;Ou et al., 2012;García-Bellido et al., 2014) and nectocaridids (Simonetta, 1988;Chen et al., 2005;Smith and Caron, 2010;Mazurek and ZatoŃ, 2011;Smith and Caron, 2011;Smith, 2013) etc. A similar situation also occurred in extant problematic taxa (e.g., placozoans, xenoturbellids, aceolomorphs, chaetognaths), of which the progress has been constantly reviewed in the systematic phylogeny field (e.g., Jenner and Schram, 1999;Edgecombe et al., 2011;Dunn et al., 2014;Telford et al., 2015;Giribet, 2016;King and Rokas, 2017). ...
... The lack of recognizable evolutionary grades in the three great clades strongly impacts interpreting the problematic bilaterian fossils. For example, vetulicolians has been interpreted either as protostomes (Hou, 1987;Caron, 2005;Aldridge et al., 2007;Lieberman, 2008) or deuterostomes (Shu et al., 1999;Shu et al., 2001;Lacalli, 2002;Shu, 2005;Ou et al., 2012;García-Bellido et al., 2014). Characters used to support these two hypotheses is as equivocal to each other, making it impossible to constrain vetulicolians either within protostome grade or deuterostome grade with current evidence. ...
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Genic and genomic data have been reshaping our understanding of the earliest radiation event of metazoans, the well-known Cambrian Evolutionary Radiation, not only from the respects of reshuffling the phylogenetic topologies of some animal phyla but by deciphering the deep homologies of many morphological features. These advances, together with the continuing discoveries of the Ediacaran-Cambrian fossils, are unveiling the cladogenetic process of the early metazoans and the patterns of morphologic evolution during this biological radiation event. In this review, I focus on a small but challenging field, the problematic fossils from the early Cambrian fossil Lagerstätten, such as the Chengjiang biota, mainly on the controversies concerning their interpretation and the consequent impacts on understanding the early evolution of animals. The bizarre body plans of the early Cambrian problematica alone do not account for the difficulties in studying their biology and affinity. Instead, it is the combined action of the taphonomic artifacts and the uncertainty in homologizing the preserved characters that impede generating plausible interpretations. Despite all these issues, a testable and repeatable method for interpreting fossils has emerged and is becoming more practicable. The integration of an evolutionary-grade conceptual frame is beneficial to the interpretation of the Cambrian problematic fossils. Together with the focus on taphonomic alternation and homologic assessment, the Cambrian problematic fossils are becoming more informative nodes in the “parsing tree” of early animal evolution.
... Х‫ݩ‬ іƳ Ҳ $Ӎ , ɫ ݊( , M ̾ƣɮ [5] . ԉ η T, ǻʉ=і ʉɴ 6 [24,25] ӌӔ Ҳ [29] ; ʇ M. ...
... =, ɹؕƥ ғ [24,25] . ɵ Ƴԯ ƗҲɵιҲ ‫$̹ͫ܈‬ , 7і ֘Ҳ , ʰʚ ؕ (̓ 3(d), (e)). ...
... Jawless vertebrates are the most primitive vertebrates on earth and appeared 520 million years ago, as early as the Cambrian period. In 1999, a paper in Nature reported that fossils of Myllokunmingia and Halou:Chthys were found among the early Cambrian Chengjiang Fauna in China (Shu et al., 1999). These two fish have spindle-shaped bodies, W-shaped sarcomeres, and relatively complex bony skulls, gill arches, pericardial cavities, and fin bars. ...
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During the process of vertebrate evolution, many thermogenic organs and mechanisms have appeared. Mammalian brown adipose tissue (BAT) generates heat through the uncoupling oxidative phosphorylation of mitochondria, acts as a natural defense against hypothermia and inhibits the development of obesity. Although the existence, cellular origin and molecular identity of BAT in humans have been well studied, the genetic and functional characteristics of BAT from lampreys remain unknown. Here, we identified and characterized a novel, naturally existing brown-like adipocytes at the lamprey brain periphery. Similar to human BAT, the lamprey brain periphery contains brown-like adipocytes that maintain the same morphology as human brown adipocytes, containing multilocular lipid droplets and high mitochondrion numbers. Furthermore, we found that brown-like adipocytes in the periphery of lamprey brains responded to thermogenic reagent treatment and cold exposure and that lamprey UCP2 promoted precursor adipocyte differentiation. Molecular mapping by RNA-sequencing showed that inflammation in brown-like adipocytes treated with LPS and 25HC was enhanced compared to controls. The results of this study provide new evidence for human BAT research and demonstrate the multilocular adipose cell functions of lampreys, including: (1) providing material energy and protecting structure, (2) generating additional heat and contributing to adaptation to low-temperature environments, and (3) resisting external pathogens.
... Infestation of the interior area of the anterior section in V. rectangulata may have been encouraged by the wide anterior gape in its exoskeleton. Vetulicola cuneata also possesses extended liplike structures at its anterior opening 19 , allowing larval V. gregarius to enter, whilst other vetulicolians such as Didazoon haoae and Pomatrum ventralis-which have no reported infestationhave narrow anterior openings that may have helped prevent infestation [20][21][22] . ...
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Here, we report the earliest fossil record to our knowledge of surface fouling by aggregates of small vermiform, encrusting and annulated tubular organisms associated with a mobile, nektonic host, the enigmatic Cambrian animal Vetulicola. Our material is from the exceptionally preserved early Cambrian (Epoch 2, Age 3), Chengjiang biota of Yunnan Province, southwest China, a circa 518 million-year old marine deposit. Our data show that symbiotic fouling relationships between species formed a component of the diversification of animal-rich ecosystems near the beginning of the Phanerozoic Eon, suggesting an early escalation of intimate ecologies as part of the Cambrian animal radiation.
... Xidazoon [56] is a possible junior synonym of Pomatrum. ...
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Deuterostomes make a sudden appearance in the fossil record during the early Cambrian. Two bilaterian groups, the chordates and the vetulicolians, are of particular interest for understanding early deuterostome evolution, and the main objective of this review is to examine the Cambrian diversity of these two deuterostome groups. The subject is of particular interest because of the link to vertebrates, and because of the enigmatic nature of vetulicolians. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document part of the explosive radiation of deuterostomes at the base of the Cambrian. The advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and potentially a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections. A new vetulicolian (Shenzianyuloma yunnanense nov. gen. nov. sp.) with a laterally flattened, polygonal anterior section provides significant new data regarding vetulicolians. Its unsegmented posterior region (‘tail’) bears a notochord and a gut trace with diverticula, both surrounded by myotome cones.
... Xidazoon [56] is a possible junior synonym of Pomatrum. ...
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Deuterostomes make a sudden appearance in the fossil record during the Early Cambrian. Two deuterostome groups, the chordates and the vetulicolians, are of particular interest for understanding the evolutionary dynamics of the Cambrian evolutionary event. Lagerstätten in China and elsewhere have dramatically improved our understanding of the range of variation in these ancient animals. Cephalochordate and vertebrate body plans are well established at least by Cambrian Series 2. Taken together, roughly a dozen chordate genera and fifteen vetulicolian genera document an explosive radiation of deuterostomes at the base of the Cambrian. A new vetulicolian with a polygonal anterior section and a narrow, unsegmented posterior region (‘tail’) bearing possible myotomes provides new insight into the affinities of the various body plans that emerged during the Early Cambrian. It seems clear that the advent of deuterostomes near the Cambrian boundary involved both a reversal of gut polarity and a two-sided retinoic acid gradient, with a gradient discontinuity at the midpoint of the organism that is reflected in the sharp division of vetulicolians into anterior and posterior sections.
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Cambrian vetulicolians have mosaic characteristics of both deuterostomes and protostomes, which has important implications for the origin and early evolution of the Deuterostomia. They are intriguing in their bizarre body plan with a series of pharyngeal gill slits. The anterior section is characterized by five pairs of gill pouches, while the paddle‐like posterior part is composed of seven or more segments. Although the overall external morphology and some internal anatomies of vetulicolians, such as pharyngeal cavity, gill system and alimentary canal, have largely been clarified, mysteries remain regarding some other internal structures, and their functional interpretations are highly controversial. In this study we identify an important but hitherto unrecognized feature: a sub‐rounded, wrinkled structure located ventrally at the posterior section (or ‘tail’) of weakly sclerotized members of vetulicolians, including Xidazoon stephanus and Didazoon haoae , from the early Cambrian Chengjiang biota. The enigmatic structure consistently appears at or between the third and fourth segments of the posterior section. We show that the new structure is an internal organ in the body cavity of vetulicolians and infer that it might have functioned for reproduction, excretion or digestion. The finding of this enigmatic structure from X. stephanus and D . haoae enriches our understanding of vetulicolians and might facilitate further exploration of the anatomy and physiology of early deuterostomes.
The fossil record of non-biomineralizing, soft-bodied taxa is our only direct evidence of the early history of vertebrates. A robust reconstruction of the affinities of these taxa is critical to unlocking vertebrate origins and understanding the evolution of skeletal tissues, but these taxa invariably have unstable and poorly supported phylogenetic positions. At the cusp between mineralized bony vertebrates and entirely soft-bodied vertebrates is the enigmatic Lasanius, a purported anaspid from the Silurian of Scotland. Interpretations of its affinity and significance are conflicted, principally because of its poorly understood anatomy due to taphonomic distortion and loss of soft-tissues. Here we use an array of modern techniques to reassess the anatomy of Lasanius via a comprehensive study of 229 complete and partial specimens. A new reconstruction clarifies the identity and position of preserved features, including paired sensory organs, a notochord, and digestive tract, supporting the vertebrate affinities of this genus. SEM-EDS trace element mapping suggests a bone-like composition of mineralized parts, but finds no evidence for mineralized dermal armour. Phylogenetic analysis recovers Lasanius as an early stem-cyclostome, and subsequent analysis supports the rejection of alternative placements (such as stem-gnathostome). We highlight that while distinguishing between the early cyclostome and gnathostome condition is problematic, increasing confidence in the anatomy of key taxa, such as Lasanius, is vital for increased stability throughout the early vertebrate tree.
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THE Chengjiang fossil Lagerstätte is one of the earliest and most important palaeontological sites from the Phanerozoic era1,2, about 530 million years ago3. It yields extremely abundant and remarkably preserved soft-bodied fossils and shells with soft parts of various kinds, including bradoriids4–6, trilobites7,8, crustaceans9, brachiopods, worms, sponges, algae and many unknown forms10–13. One of these fossils is Yunnanozoon 14, which we reinterpret here as the earliest known hemichordate. Possessing half of the characteristic chordate features and providing an anatomical link between invertebrates and chordates15, Hemichor-data is a minor but important phylum in evolutionary biology. Hemichordates comprise two main groups: the enteropneusts, or 'acorn worms', and the pterobranchs. Apart from the presumable inclusion of graptolites in pterobranchs16–19, there are very few hemichordate fossils2,17,20. Although Yunnanozoon is superficially similar to the chordates21, its typical tripartite body plan is broadly consistent with that of living balanoglossid hemichor-dates (enteropneusts).
The remarkable “evolution” of the reconstructions of Anomalocaris , the extraordinary predator from the 515 million year old Middle Cambrian Burgess Shale of British Columbia, reflects the dramatic changes in our interpretation of early animal life on Earth over the past 100 years. Beginning in 1892 with a claw identified as the abdomen and tail of a phyllocarid crustacean, parts of Anomalocaris have been described variously as a jellyfish, a sea-cucumber, a polychaete worm, a composite of a jellyfish and sponge, or have been attached to other arthropods as appendages. Charles D. Walcott collected complete specimens of Anomalocaris nathorsti between 1911 and 1917, and a Geological Survey of Canada party collected an almost complete specimen of Anomalocaris canadensis in 1966 or 1967, but neither species was adequately described until 1985. At that time they were interpreted by Whittington and Briggs to be representatives of “a hitherto unknown phylum.” Here, using recently collected specimens, the two species are newly reconstructed and described in the genera Anomalocaris and Laggania , and interpreted to be members of an extinct arthropod class, Dinocarida, and order Radiodonta, new to science. The long history of inaccurate reconstruction and mistaken identification of Anomalocaris and Laggania exemplifies our great difficulty in visualizing and classifying, from fossil remains, the many Cambrian animals with no apparent living descendants.
Opabinia regalis Walcott is an enigmatic fossil from the Middle Cambrian Burgess Shale of uncertain affinities. Recent suggestions place it in a clade with Anomalacaris Whiteaves from the Burgess Shale and Kerygmachela Budd from the Greenlandic Sirius Passet Fauna; these taxa have been interpreted as 'lobopods'. Consideration of available Opabinia specimens demonstrates that reflective extensions from the axial region, previously thought to be either gut diverticula or musculature, can be accommodated in neither the trunk nor the lateral lobes that arise from it. They must therefore be external structures independent of the lateral lobes. On the basis of their sub-triangular appearance, size and taphonomy, they are considered here to represent lobopod limbs. Some evidence for the existence of terminal claws is also presented. The question of whether Kerygmachela, Opabinia and Anomalocaris constitute a monophyletic or paraphyletic grouping is considered. While they share several characters, most of these are plesiomorphies. Further, Opabinia and Anomalocaris share several arthropod-like characters not possessed by Kerygmachela. It is concluded that these three taxa probably form a paraphyletic grouping at the base of the arthropods. Retention of lobopod-like characters within the group provides important documentation of the lobopod-arthropod transition. A proper understanding of Opabinia and its close relatives, which may include the tardigrades, opens the way for a reconstruction of the arthropod stem-group. This in turn allows the construction of a speculative but satisfying scenario for the evolution of major arthropod features, including the origin of the biramous limb, tergites and arthropod segmentation. 'Arthropodization' may thus be seen not to be a single event but a series of adaptive innovations.
The oldest known chordate, Yunnanozoon lividum Hou et al. 1991, from the Chengjiang Lagerstatte of Yunnan shows several features in its anatomy that had not been expected to occur at this stage of evolution. These features are described. Monotypic Yunnanozoa classis n., Yunnanozoida ordo n., and Yunnanozoidae fam n. are proposed for this early chordate. -from Author
Molecular biology has re-opened the debate on metazoan diversification, including the vexing question of the origin of the major body plans (phyla). In particular, sequence analyses of rRNA have reconfigured significantly metazoan phylog€try, while homeobox genes suggest there could be an underlying similarity of developmental instructions in nominally disparate phyla. Despite this dramatic progress I argue that this renaissance of activity is lop-sided, but can be redressed by palaeontological data, especially from the Cambrian and immediately preceding Vendian. The fossil record complements and amplifies the conclusions derived from molecular biology, notably in the early radiation of cnidarians (Ediacaran faunas) and key steps in the diver-sification of the protostomes.