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Ordovician faunas of Burgess Shale type

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Ordovician faunas of Burgess Shale type

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The renowned soft-bodied faunas of the Cambrian period, which include the Burgess Shale, disappear from the fossil record in the late Middle Cambrian, after which the Palaeozoic fauna dominates. The disappearance of faunas of Burgess Shale type curtails the stratigraphic record of a number of iconic Cambrian taxa. One possible explanation for this loss is a major extinction, but more probably it reflects the absence of preservation of similar soft-bodied faunas in later periods. Here we report the discovery of numerous diverse soft-bodied assemblages in the Lower and Upper Fezouata Formations (Lower Ordovician) of Morocco, which include a range of remarkable stem-group morphologies normally considered characteristic of the Cambrian. It is clear that biotas of Burgess Shale type persisted after the Cambrian and are preserved where suitable facies occur. The Fezouata biota provides a link between the Burgess Shale communities and the early stages of the Great Ordovician Biodiversification Event.
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LETTERS
Ordovician faunas of Burgess Shale type
Peter Van Roy
1,2
, Patrick J. Orr
2
, Joseph P. Botting
3
, Lucy A. Muir
4
, Jakob Vinther
1
, Bertrand Lefebvre
5
,
Khadija el Hariri
6
& Derek E. G. Briggs
1,7
The renowned soft-bodied faunas of the Cambrian period, which
include the Burgess Shale, disappear from the fossil record in the
late Middle Cambrian, after which the Palaeozoic fauna
1
domi-
nates. The disappearance of faunas of Burgess Shale type curtails
the stratigraphic record of a number of iconic Cambrian taxa. One
possible explanation for this loss is a major extinction
2,3
, but more
probably it reflects the absence of preservation of similar soft-
bodied faunas in later periods
4
. Here we report the discovery of
numerous diverse soft-bodied assemblages in the Lower and
Upper Fezouata Formations (Lower Ordovician) of Morocco,
which include a range of remarkable stem-group morphologies
normally considered characteristic of the Cambrian. It is clear that
biotas of Burgess Shale type persisted after the Cambrian and are
preserved where suitable facies occur. The Fezouata biota provides
a link between the Burgess Shale communities and the early stages
of the Great Ordovician Biodiversification Event.
The large number of Burgess Shale-type occurrences in the
Cambrian
2
provide a remarkable record of the results of the initial
radiation of metazoan marine life. In contrast, exceptional preser-
vation is rare in Ordovician strata: the few previously reported
examples
5–8
are low diversity assemblages from environmentally
restricted settings and do not represent a normal, open marine eco-
system. Consequently our understanding of the Great Ordovician
Biodiversification Event, which is one of the most dramatic episodes
in the history of marine life
9–12
, is based almost exclusively on the
shelly fossil record.
During this event, most marine higher taxa diversified at a faster
rate than at any other time in the Phanerozoic. Biodiversity increased
twofold at the ordinal level, about three times at the family level, and
nearly four times at the levelof genus
9–11
. This major radiation resulted
in the replacement of the Cambrian Evolutionary Fauna by the
Palaeozoic EvolutionaryFauna that dominated the marine realm until
the end-Permian mass extinction
1
. It was accompanied by a major
increase in ecological complexity
12
. Until now, however, no excep-
tionally preserved biotas recording the critical early stages of the
Ordovician radiation were known. Beecher’s Trilobite Bed
5
of New
York, and the Soom Shale of South Africa
6
, are late Ordovician
(Sandbian and latest Hirnantian to earliest Rhuddanian
13
, respec-
tively) in age. The former represents a low-oxygen environment with
a low diversity fauna including the olenid trilobite Triarthrus eatoni
5
,
and the latter is dominated by nektonic organisms and probably
accumulated in an euxinic environment. Other examples from the
Middle and Upper Ordovician
7,8
are low diversity assemblages from
near-shore marginal environments.
A complex of recently discovered exceptionally preserved faunal
assemblages occurs in muddy bottom open marine settings in the
Lower Ordovician of southeastern Morocco. These assemblages record
considerable diversity, including a number of taxa characteristic of
Early to Middle Cambrian Burgess Shale-type faunas, previously
thought to have become extinct during the Cambrian, which occur
here in association with elements typical of later biotas. About 1,500
soft-bodied fossil specimens representing at least 50 different taxa have
been collected to date from approximately 40 excavations spread out
over an area of about 500 km
2
in the Draa Valley, north of Zagora in
southeastern Morocco (Supplementary Fig. 1). All these localities fall
in the Lower Fezouata Formation (Tremadocian) or the conformably
overlyingUpper Fezouata Formation (Floian)which reach a combined
thickness of 1,100 m (ref. 14) in the area north of Zagora. The largely
transgressive sequence crops out over a wide area in the Anti-Atlas and
consists mainly of mudstone and siltstone. Although sediments
become coarser near the top of the sequence, implying slightly shal-
lower and more energetic conditions, our observations indicate that
the depositional setting for all localities is a deeper-water, low-energy
environment. Although generally below storm wave base, the infrequent
occurrence of thin, laterally discontinuous hummocky cross-stratified
sandstones and shell pavements shows that occasional heavy storms
influenced deposition in the area. The majority of fossiliferous horizons
represent sediment mobilized by storms or other events that was re-
deposited rapidly, entombing locally transported and in situ elements
within and below event beds.
Horizons of exceptional preservation range from the top of the
Lower Fezouata Formation through to the top of the Upper
Fezouata Formation. The fossils are distributed in distinct lenses or
as more laterally continuous horizons. The strata containing excep-
tionally preserved specimens vary from greenish silty mudstones to
sandy siltstones rich in detrital mica. Bioturbation associated with
the soft-bodied fossils is dominated by low diversity, small diameter
(1–3 mm) burrows parallel or inclined to bedding. Although high
sedimentation rates may have limited the infauna, the low diversity
and consistently small diameter of burrows suggest that low-oxygen
conditions may have prevailed. The simplicity, small size and occur-
rence of the burrows is reminiscent of bioturbation reported from the
exceptionally preserved Cambrian faunas of Sirius Passet, Chengjiang
and Kaili
15
.
The exceptionally preserved fossils are usually flattened. Various
worms, presumed to be annelids, however, are preserved with some
three-dimensionality. Most non-biomineralized arthropods and
some of the trilobites preserve evidence of their appendages.
Preserved soft tissues are typically bright reddish-brown to yellow
in colour, resulting from the oxidation of pyrite that precipitated on
the surface
16
. Framboidal and polyhedral pyrite morphologies, now
iron oxide pseudomorphs, vary consistently between different tissues,
the form of pyrite probably reflecting the decay-susceptibility of the
original material
17
. The preservation, andconsequently appearance, of
1
Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520, USA.
2
UCD School of Geological Sciences, University College Dublin,
Belfield, Dublin 4, Ireland.
3
Leeds Museum Discovery Centre, Carlisle Road, Leeds LS10 1LB, UK.
4
42 Birkhouse Lane, Moldgreen, Huddersfield HD5 8BE, UK.
5
UMR CNRS 5125 PEPS,
ba
ˆt. Ge
´ode, Universite
´Lyon 1, Campus de la Doua, 2 Rue Dubois, F-69622 Villeurbanne cedex, France.
6
De
´partement Sciences de la Terre, Faculte
´des Sciences et Techniques-Gue
´liz,
Universite
´Cadi Ayyad, Avenue Abdelkrim el Khattabi BP 549, 40000 Marrakech, Morocco.
7
Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut
06520, USA.
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the fossils is remarkably similar to that of the Early Cambrian
Chengjiang fauna from China
17
, reflecting similar sedimentation
and diagenetic pathways.
The Fezouata assemblages are dominated by benthic organisms.
There is pronounced spatial and stratigraphic variation in taxonomic
composition and relative abundance, suggesting ecological variation
and/or evolutionary change between assemblages at different stra-
tigraphic levels. The shelly fossils include conulariids, a diversity of
trilobites (asaphids, harpetids, odontopleurids, phacopids, proetids,
ptychopariids and agnostids), articulated hyolithoids and other mol-
luscs (helcionelloids, bivalves, gastropods, nautiloids), brachiopods,
occasional bryozoans, and echinoderms (homalozoans, asterozoans,
Figure 1
|
Exceptionally preserved Burgess Shale-type organisms from the
Early Ordovician Fezouata biota. a, Demosponge Pirania auraeum
19
, top of
Lower Fezouata Formation (CAMSM X 50156.1a). b, Choiid demosponge,
top of Lower Fezouata Formation (YPM 226567). c, Annelid worm, top of
Lower Fezouata Formation (YPM 226538). d, Organism showing possible
similarities to halkieriids, Upper Fezouata Formation (YPM 227515).
e, Possible armoured lobopod, Upper Fezouata Formation (YPM 227516).
f,Thelxiope-like arthropod, Upper Fezouata Formation (YPM 226544).
g, Marrellomorph arthropod, probably belonging to the genus Furca, Upper
Fezouata Formation (MHNT.PAL.2007.39.80.1). h, Skaniid arthropod,
Upper Fezouata Formation (YPM 226539). i, Spinose arthropod appendage
apparatus consisting of six overlapping elements, top of Lower Fezouata
Formation (YPM 226559).
LETTERS NATURE
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various eocrinoids, cystoids, rare crinoids); planktic and benthic
graptolites are also present (Supplementary Fig. 2). Most of these
elements are typical of normal open-marine shelly Ordovician
faunas, with many taxa representative of the Palaeozoic Evolutionary
Fauna
1
; they are exceptional only in the high degree of articulation of
multi-element skeletons in trilobites and echinoderms. In contrast to
Chengjiang
18
, a diverse echinoderm faunais present, indicating normal
salinities. The consistently high faunal diversity and comparable sedi-
mentology indicate that the environmental setting, which was not
subject to large variations in temperature or salinity, was similar at
all Moroccan sites.
The shelly taxa are supplemented by at least 50 non-biomineralized
taxa, which dominate the biota, representing at least two-thirds of all
specimens collected. Many of these non-biomineralized forms are
recorded from the Ordovician for the first time. A striking feature is
the high number of organisms archetypal of Cambrian Burgess Shale-
type faunas, including various demosponges (Pirania,Hamptonia,
Choia
19
, wapkiids, and other undescribed forms; Fig. 1a, b), annelid
worms (Fig. 1c, Supplementary Fig. 3a–c), an organism with possible
similarities to halkieriids (Fig. 1d, Supplementary Fig. 3d, e), palaeos-
colecids, possible armoured lobopods and other stem arthropods
(Fig. 1e, Supplementary Fig. 3f), a Thelxiope-like arthropod (Fig. 1f),
marrellomorphs (Fig. 1g), skaniids (Fig. 1h), a naraoiid, and arthro-
pods of uncertain affinity (Fig. 1i). The Burgess Shale-type organisms
co-occur with several taxa characteristic of later biotas, such as
machaeridians
16
, other worms including tube-dwelling forms,
Tremaglaspis (Fig. 2a), a cheloniellid (Fig. 2b, Supplementary Fig. 3g),
a possible stalked barnacle (Fig. 2c, Supplementary Fig. 3h) and two
new xiphosuran genera (Fig. 2d, e, Supplementary Fig. 3i). The chelo-
niellids and horseshoe crab fossils mark the oldest unequivocal
examples of these groups, pushing their likely origins back into the
Cambrian. The horseshoe crabs are the most abundant arthropods;
several hundreds of specimens of the two taxa are known. One of these
new xiphosurans is a small, basal form retaining a fully segmented
opisthosoma (Fig. 2d). The other, in contrast, is highly derived, with
a fused preabdomen and appendages very similar to those of extant
horseshoe crabs (Fig. 2e, Supplementary Fig. 3i). The horseshoe crabs,
and several other arthropods, are represented by successive instars.
Some 20 to 30 other exceptionally preserved invertebrates await study,
mainly arthropods, but also problematica; no chordates have been dis-
covered to date. Two different algae are also represented.
These Moroccan discoveries show that Burgess Shale-type faunas
flourished at least until the Floian. The rarity of Burgess Shale-type
taxa in post-Middle Cambrian rocks elsewhere probably results from
a lack of preservation
2,4
rather than the extinction and replacement of
these faunas during the later Cambrian. A number of explanations
have been offered for the closure of this taphonomic window, includ-
ing a change in clay chemistry
20
, greater depth of bioturbation
21,22
,
and increased behavioural complexity and ecospace occupation by
burrowing organisms
23
. The scarcity of bioturbation at most localities
in the Fezouata formations implies that direct scavenging was limited;
more importantly, it shows that environmental conditions hostile to
an infauna, for example, low-oxygen conditions, as indicated by con-
sistently small burrow diameters and low ichnological diversity, pre-
vailed. Whereas Cambrian Burgess Shale-type faunas occur at
relatively low palaeolatitudes
24
, the Moroccan sites were situated very
close to the Ordovician South Pole; Burgess Shale-type biotas clearly
persisted globally in cold, deep marine settings
2
.
The new discoveries in theFezouata formationsindicate that Burgess
Shale-type taxa continued to have an important role in the diversity
and ecological structure of deeper marine communities well after the
Middle Cambrian, and prompt a reassessment of the structure of post-
Cambrian Palaeozoic communities. Several typical Burgess Shale taxa
were present in the early Ordovician, while naraoiids extend to the
Silurian
25
and some groups, for example, marrellomorphs
26
,great
appendage arthropods
27
and eldonioids
28
survived at least into the
Devonian (eldonioids have also been recorded from the Upper
Ordovician of Morocco
29,30
). The continued importance of Burgess
Shale-type organisms through the Lower Palaeozoic reduces the dis-
tinction between Cambrian and subsequent faunas and warrants re-
investigation of the dramatic turnover between the Cambrian and
Palaeozoic evolutionary faunas in the light of new discoveries of soft-
bodied fossils. At the same time, the presence of post-Cambrian taxa
(for example, machaeridian
16
and tube-dwelling annelids, horseshoe
crabs, cheloniellids, phacopids, asterozoans and crinoids) alongside
Burgess Shale-type elements in the Fezouata biota indicates that sig-
nificant diversification occurred before the Tremadocian.
METHODS SUMMARY
All figured specimens are housed in the collections of the Yale Peabody Museum
of Natural History, Lyon 1 University, the Natural History Museum of Lyon, the
Natural History Museum of Marseille, the Natural History Museum of
a
c
20 mm
20 mm
5 mm
5 mm
5 mm
5 mm
e
2 mm
2 mm
d
10 mm
10 mm
20 mm 5 mm
5 mm 2 mm 10 mm
b
Figure 2
|
Exceptionally preserved post-Cambrian elements of the
Fezouata biota. a, Aglaspidid arthropod Tremaglaspis, Upper Fezouata
Formation (MHNT.PAL.2007.39.92.1). b, Cheloniellid arthropod, Upper
Fezouata Formation (NMS G 2004.2.1). c, Possible stalked barnacle, Upper
Fezouata Formation (YPM 227519). d, Xiphosuran with fully segmented
opisthosoma, top of Lower Fezouata Formation
(MHNT.PAL.2007.39.43.2). e, Xiphosurid with fused preabdomen, Upper
Fezouata Formation (YPM 227586).
NATURE
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Toulouse, the National Museums of Scotland and the Sedgwick Museum, as
indicated by their accession numbers. Locality details for all specimens are kept
at these institutions, and can be provided by the authors upon request.
Specimens were prepared with scalpels and fine needles under high magnifica-
tion using Nikon SMZ800 and 1500 stereomicroscopes and, when necessary,
repaired using cyanoacrylate glue. Interpretative drawings were made with a
camera lucida attached to Leica MZ6, Nikon SMZ1500 and Wild M5 stereo-
microscopes. Photographs were made with Canon EOS 350D, Nikon D80 and
Nikon D200 digital reflex cameras, Leica MZ16 and MZ6 stereomicroscopes
with a Leica DFC 425 digital camera, and a Leica MZ16FA with an Olympus
ColourView III digital camera. With the exception of the images in Fig. 1a, e,
Fig. 2c, Supplementary Figs 2c–i and 3d, photographs were taken with crossed
polarizers. Digital photographs were processed in Adobe Photoshop CS2 and CS3,
and composite images (Fig. 1b, c, f, h, i; Fig. 2c, e; Supplementary Figs 2a, b, 3a)
were stitched together using Adobe Photoshop CS3 and Microsoft ICE.
Received 22 January; accepted 22 March 2010.
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Supplementary Information is linked to the online version of the paper at
www.nature.com/nature.
Acknowledgements S. Butts (Yale Peabody Museum of Natural History), A. Prieur
(Lyon1 University),D. Berthet (Natural HistoryMuseum of Lyon), A. Me
´dard-Blondel
and S. Pichard (Natural History Museum of Marseille), G. Fleury (Natural History
Museum of Toulouse), the National Museums of Scotland and the Sedgwick
Museum provided access to specimens. M. Ben Said Ben Moula, W. and D. De
Winter, B. MacGabhann, R. and V. Reboul-Baron, C. Upton, B. Van Bocxlaer, and
D. and K. Van Damme assisted with fieldwork, and B. Tahiri arranged logistical
support. E. Champion helped with the preparation of figures. J. De Grave and B. Van
Bocxlaer (Ghent University) provided photographic equipment, and the
Palaeontology and PetrologyResearch Units of Ghent University allowed use of their
imaging facilities. P. and O. Van Roy-Lassaut financially aided fieldwork. This
research was fundedby an Agency for Innovation by Science and Technology(IWT)
doctoral fellowship and by an Irish Research Council for Science, Engineering and
Technology (IRCSET)
EMPOWER postdoctoral fellowship awarded to P.V.R.
Fieldworkwas supported by a NationalGeographic SocietyResearch and Exploration
grant.
Author Contributions All authors carried out field work and contributed to the
interpretation of the fossils. P.V.R., P.J.O., J.P.B. and D.E.G.B. wrote the paper with
input from the other authors.
Author Information Reprints and permissions information is available at
www.nature.com/reprints. The authors declare no competing financial interests.
Correspondence and requests for materials should be addressed to P.V.R.
(peter.vanroy@yale.edu) or D.E.G.B. (derek.briggs@yale.edu).
LETTERS NATURE
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... Cheloniellida is a major clade of generally rare (nekto-)benthic vicissicaudate euarthropods ranging from the Early Ordovician (Van Roy, 2006b;Van Roy et al. 2010, 2015 to the Early Devonian (Broili, 1932(Broili, , 1933Stürmer & Bergström, 1978;Bartels & Brassel, 1990;Bartels et al. 1998;Van Roy, 2006b;Kühl et al. 2011Kühl et al. , 2012. They have a dorsoventrally flattened body and are characterized by the possession of a cephalic shield with sharply procurved posterior margins and a trunk with broad, radially arranged tergopleura, followed by a single posterior cylindrical sclerite bearing a pair of furcal appendages dorsolaterally and terminated by a small, cap-shaped telson. ...
... Duslia and other cheloniellids. Triopus also has a more elongate shape than most other cheloniellid taxa, although in this respect it can be compared to Paraduslia talimaae Dunlop, 2002, which has a similar ovoid outline, and to a lesser extent to the undescribed cheloniellid from the Fezouata Biota, which is also quite elongate, but tapers posteriorly, giving it more of drop shape (Van Roy, 2006b;Van Roy et al. 2010, 2015. ...
... ). Included taxa. Cheloniellon calmani Broili, 1932, Drabovaspis complexa (Barrande, 1872), Duslia insignis Jahn, 1893, Duslia sp. from the Tafilalt Biota (Alessandrello & Bracchi, 2006; Van Roy, 2006b; Lefebvre et al. 2022), Neostrabops martini Caster and Macke, 1952, Paraduslia talimaae Dunlop, 2002, Pseudarthron whittingtoni Selden and White, 1983, Triopus draboviensis Barrande, 1872, Triopus sp. from the Tafilalt Biota (Van Roy, 2006b; Lefebvre et al. 2022), undescribed cheloniellid from the Fezouata Biota(Van Roy, 2006b;Van Roy et al. 2010, 2015, specimen UWGM 2345 from the Waukesha exceptionally preserved fauna(Wendruff et al. 2018(Wendruff et al. , 2020bAnderson et al. 2021). ...
Article
Cheloniellida is a rare but significant clade of artiopod euarthropods, and a major component of Vicissicaudata alongside aglaspidids. The first cheloniellid to be described was Triopus draboviensis , based on a single specimen from the Upper Ordovician Letná Formation in Bohemia. Because this specimen was believed to be missing its anterior, Triopus draboviensis has been the subject of considerable speculation regarding its affinities, with several authors combining various isolated cephalic shields with its trunk. Notwithstanding, Triopus draboviensis has eluded detailed restudy in the 150 years since its first description. Here we provide a redescription of the holotype and hitherto only known specimen of Triopus draboviensis , and describe a recently discovered second partial specimen as Triopus sp. It is shown that the holotype of Triopus draboviensis preserves the complete cephalic shield, while the trunk reveals a likely articulating device, which may represent an apomorphy for Cheloniellida. Further information on the trunk morphology provided by the new specimen has allowed a complete reconstruction of the dorsal exoskeleton of Triopus . An assessment is made of fossils previously suggested to represent the cephalic shield of Triopus draboviensis ; while it is shown that none of those fossils can be attributed to Triopus , it is reaffirmed that Drabovaspis complexa likely does belong to Cheloniellida, making Drabovaspis the third cheloniellid genus known from the Letná Formation, after Triopus and Duslia . A revised diagnosis for Cheloniellida is provided, and the recently described problematic euarthropod Parioscorpio venator from the Silurian of Wisconsin is firmly rejected from this clade.
... Konservat-Lagerstätten should be supposed to play a critical role in understanding the onset and continuity of GOBE, specifically because they preserve exceptionally diverse biotic groups including some soft-bodied organisms, providing more information than otherwise attainable on life macroevolution. Over recent decades, several Early Ordovician Lagerstätten have been reported from different continents [2][3][4] that have significantly updated our understanding of biodiversity in various environments, with fresh discoveries indicating new biotic adaptations and interactions. However, the rarity of Ordovician soft-bodied biotas and the commonly poor preservation of faunas hinder the development of a complete evolutionary picture of the GOBE, e.g. in South China [5][6][7]. ...
... In contrast with some other [33][34][35], the Liexi fauna occurs in a marine geological setting with muddy substrate, and its burial and preservation probably resulted from a sudden muddy flood moving from the shelf edge to the upper slope, similar to the burial Fezouata biota [36,37]. Most of the documented fossiliferous Early Ordovician Lagerstätten globally are interpreted to occur in high-latitude regions, such as the Fezouata biota near the South Pole [2,3] and the Afon Gam biota from North Wales at a palaeolatitude of 60°S [4]. During the Early Ordovician, South China was thought to be a typical tropical palaeogeographical setting, e.g. ...
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The Ordovician Lagerstätten record substantial amounts of excellent preservation and soft-bodied fossils during the Great Ordovician Biodiversification Event (GOBE). However, few Lagerstätten are known from the Lower Ordovician, most of which are preserved in restricted environments and high-latitude regions. Here, we report on a new tropical Lagerstätte, Liexi fauna, which has been recently discovered from a carbonate succession within the Lower Ordovician Madaoyu Formation in western Hunan, South China. It contains a variety of soft tissues, as well as rich shelly fossils, including palaeoscolecidan worms, possible Ottoia , trilobites, echinoderms, sponges, graptolites, polychaetes, bryozoans, conodonts and other fossils. The fauna includes taxa that are not only Cambrian relics, but also taxa originated during the Ordovician, constituting a complex and complete marine ecosystem. The coexistence of the Cambrian relics and Ordovician taxa reveals the critical transition between the Cambrian and Palaeozoic Evolutionary faunas. The unusual Liexi fauna provides new evidence for understanding Ordovician macroevolution and the onset of the GOBE.
... The horseshoe crab is known as a living fossil because it has survived nearly 500 million years and is called a stabilomorph because it has a highly stable morphology (Eldredge and Stanley 1984;Kin and Błażejowski 2014). Ancient horseshoe crab fossils have been found since Ordovician times (Rudkin et al. 2008;Van Roy et al. 2010), and the existence of horseshoe crabs with the same form emerged in the Jurassic period (Sekiguchi and Sugita 1980;Briggs et al. 2005). At present, there are four species of horseshoe crab spread on the coasts of North America and Asia (Sekiguchi and Shuster 2009). ...
... Large collections of Euproops danae from the Mazon Creek Konservat Lagerstätte in the YPM IP (>500 specimens) (Haug and Rötzer 2018), or the Field Museum, Chicago (>500 specimens) (Fisher 1977) are other avenues worth exploring for abnormalities. Finally, xiphosurans from the Lower and Upper Fezouata formations, Morocco (Lower Ordovician), could be explored as hundreds of specimens are known from these deposits (Van Roy et al. 2010), despite the uncertain taxonomic affinities of these forms. ...
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Xiphosurids are marine chelicerates that have been subject to extensive biological and palaeontological scrutiny over the past two centuries. This research effort is fuelled by the unique anatomical and physiological characteristics of the group, a long fossil record with conserved morphology, and use as modern analogues for understanding extinct arthropod groups. Despite this extensive literature, abnormal xiphosurid specimens are somewhat understudied. Recent studies have documented malformed specimens, the majority of which are attributed to injuries and developmental complications. To augment this recent research, we present records of Limulus polyphemus and Tachypleus tridentatus with malformed with malformed appendages, cephalothoraces, thoracetrons, and telsons. Causes of abnormalities are discussed and attributed to moulting issues and injuries. Three new examples of abnormal fossil xiphosurids are also presented: Euproops danae and Mesolimulus walchi specimens with cephalothoracic injuries and one specimen of M. walchi displaying a curved telson. We conclude that documenting abnormalities within populations may aid identification of spawning areas that require conservation attention. These oddities represent a potential avenue to minimize the population threats currently facing these unique chelicerates.
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The calcareous siltstones within the Ordovician section of the Takche Formation near Takche, Spiti region of Tethyan Himalaya, India, contain numerous specimens of non-calcified marine macroalgae in association with brachiopods, gastropods, tentaculitoids, and few trace fossils. The algal remains, representing five genera, are preserved as black or dark brown carbonaceous compression fossils, interpreted as warm-water marine macroalgae, namely, Inocladus sp., Callisphenus? sp., Algites sp. (siphonous algae), Fisherites sp., and Mastopora sp. (non-siphonous). Callisphenus is characterised by a radially symmetrical short pyriform thallus, with a central axis surrounded by short laterals whereas Inocladus sp. is characterised by an unsegmented simple thallus with internal parallel medullary siphons and cortical tubes. These algal remains, probably transported from a more near-shore living niche, co-occur with Cyclocrinitids, Tentaculitoids tube worms, trace fossils and brachiopods, suggesting that deposition of the studied units took place in low energy hydrodynamic conditions influenced by intermittent storm events. The study represents the first diversified macroalgal records from the Ordovician strata in the Tethyan realm of Indian subcontinent.
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Palmichnium gallowayi (Sharpe, 1932) new combination from the Middle Ordovician Martinsburg Formation (proximal deltaic facies) of Rondout, near Kingston, New York State, is redescribed. It consists of opposing series of five tracks, the outer two large and pear-shaped, the inner three smaller and elliptical, arranged in a chevron converging in the direction of travel, on either side of a wide medial impression. It is attributed to a medium-sized stylonurid eurypterid using a decapodous gait, crawling onto the shoreline, traversing the intertidal zone, a behavior interpreted as part of its reproductive life cycle. This provides the earliest ichnological evidence for the ‘mass-molt-mate’ hypothesis, which proposes that eurypterids migrated en masse into nearshore environments to molt and mate.
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Recent transcriptomic studies of myriapod phylogeny have been based on relatively small datasets with fewer than 40 myriapod terminals and variably supported or contradicted the traditional morphological groupings of Progoneata and Dignatha. Here we amassed a large dataset of 104 myriapod terminals, including multiple species for each of the four myriapod classes. Across the tree, most nodes are stable and well supported. Most analyses across a range of gene occupancy levels provide moderate to strong support for a deep split of Myriapoda into Symphyla + Pauropoda (=Edafopoda) and an uncontradicted grouping of Chilopoda + Diplopoda (=Pectinopoda nov.), as in other recent transcriptome-based analyses; no analysis recovers Progoneata or Dignatha as clades. As in all recent multi-locus and phylogenomic studies, chilopod interrelationships resolve with Craterostigmus excluded from Amalpighiata rather than uniting with other centipedes with maternal brood care in Phylactometria. Diplopod ordinal interrelationships are largely congruent with morphology-based classifications. Chilognathan clades that are not invariably advocated by morphologists include Glomerida + Glomeridesmida, such that the volvation-related characters of pill millipedes may be convergent, and Stemmiulida + Polydesmida more closely allied to Juliformia than to Callipodida + Chordeumatida. The latter relationship implies homoplasy in spinnerets and contradicts Nematophora. A time-tree with nodes calibrated by 25 myriapod and six outgroup fossil terminals recovers Cambrian–Ordovician divergences for the deepest splits in Myriapoda, Edafopoda and Pectinopoda, predating the terrestrial fossil record of myriapods as in other published chronograms, whereas age estimates within Chilopoda and Diplopoda overlap with or do not appreciably predate the calibration fossils. The grouping of Chilopoda and Diplopoda is recovered in all our analyses and is formalized as Pectinopoda nov., named for the shared presence of mandibular comb lamellae. New taxonomic proposals for Chilopoda based on uncontradicted clades are Tykhepoda nov. for the three blind families of Scolopendromorpha that share a “sieve-type” gizzard, and Taktikospina nov. for Scolopendromorpha to the exclusion of Mimopidae.
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Known antennae of trilobites are all flagelliform, in marked contrast to the varied first antennae of marine pancrustaceans. An exceptionally preserved specimen of the Early Ordovician (late Tremadocian) asaphid Asaphellus tataensis Vidal, 1998, from the Fezouata Shale in Morocco, exhibits both antennae in situ; they are relatively short, widen distally, and bear a series of round, dome-shaped organs along both their dorsal and ventral surfaces. These organs are vastly larger than chemo- or mechanosensory sensilla on the antennae of other arthropods, rendering their homology and function uncertain. The clavate antennae of Asaphellus reveal the furthest deviation from the inferred ancestral state of the trilobite antenna known to date. This could be an adaptation for detection of prey, because most Asaphidae have been claimed as predators and scavengers on the basis of specialized features of the calcified exoskeleton.
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Over one hundred of arthropod fossil species have been described from the famous Chengjiang Lagerstätte (South China, Cambrian Stage 3, ca. 518 Ma) including a diverse assemblage of radiodonts – a group containing Anomalocaris and its relatives. These iconic stem-group euarthropods include some of the largest animals of the time, and some are known from hundreds of specimens. A longstanding conundrum has been the rarity or absence of hurdiids from Cambrian Series 2 Lagerstätten like Chengjiang. This is because radiodonts are generally common in such deposits and the oldest radiodont ever discovered is a hurdiid. Furthermore, this family displays the widest geographic and temporal ranges of all radiodont families, and the highest diversity. Here we document the first hurdiid frontal appendages from Chengjiang, which display unique features within the family and may provide insights for understanding the character evolution of hurdiid appendages. The palaeoenvironmental distribution of hurdiids suggests that the rarity of hurdiids in Chengjiang may be due to a preference for deeper water environments, and the later success of this family from the Wuliuan onwards may relate to their ability to tolerate cooler water temperatures than other radiodont families. The palaeogeographical, palaeoenvironmental, and stratigraphical patterns observed in hurdiids maybe caused in part by the limited distributions of Konservat-Lagerstätten in the Cambrian as well.
Chapter
Given the overexploitation of horseshoe crabs everywhere in the world, and due to the insufficient data on their inhabitants, it is very decisive that genomic distinction analysis are done to evaluate their patterns and levels of genetic dissimilarity for constant monitoring and managing of their inhabitants. Phylogenetic studies are significant for addressing diverse biological relationships amongst species, their origin, the demographic changes, and their migration patterns. In spite of the low diversity rate in the cluster, the phylogenetic relations amongst the mangrove horseshoe crabs are still a resolute. For the investigation of molecular phylogenetics and the evolutionary relationship amongst the Indian horseshoe crabs, a set of molecular inherent information is required. Partial sequencing (~658 bp) of mitochondrial cytochrome c oxidase subunit I gene (COI) from five individual horseshoe crabs using Universal DNA primers were adopted for DNA barcoding. Phylogenetic and BLAST analyses revealed that all species collected in this study were Tachypleus gigas. DNA barcode sequences can be accessed at GenBank using accession numbers: KU880543, KU880544, KT380891, KT380892, and KT380893. Molecular phylogenetics analysis will be helpful in understanding divergence of evolution of T.gigas. Evaluating the genetic variability of horseshoe crab is significant as it is beneficial for the management and conservation of wild inhabitants.
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Isolated chitinozoans from the Scorn Shale Member of the Cedarberg Formation, SW South Africa are described and provide,I date of the latest Hirnantian-earliest Rhuddanian. The recovered chitinozoans are typical of the latest Ordovician Spinachitina oulebsiri Biozone, although an earliest Silurian age is possible. They indicate a very short time span (less than 1 Ma) across the Ordovician-Silurian boundary. This is currently the highest biostratigraphical resolution attainable for the Scorn Shale Lagerstatte. Correlation of the Soom Shale chitinozoans with identical assemblages in post-glacial, transgressive deposits of Northern Africa is possible; both faunas occur in shales that overlie glacial diamictites of the Hirnantian glaciation. A new species, Spinachitina verniersi n. sp. is described. lJ. Micropalaeontol. 28(1): 53-66, May 2009.
Article
The kinetic model of taxonomic diversity predicts that the long-term diversification of taxa within any large and essentially closed ecological system should approximate a logistic process controlled by changes in origination and extinction rates with changing numbers of taxa. This model is tested with a new compilation of numbers of metazoan families known from Paleozoic stages (including stage-level subdivisions of the Cambrian). These data indicate the occurrence of two intervals of logistic diversification within the Paleozoic. The first interval, spanning the Vendian and Cambrian, includes an approximately exponential increase in families across the Precambrian-Cambrian Boundary and a “pseudo-equilibrium” through the Middle and Late Cambrian, caused by diversity-dependent decrease in origination rate and increase in extinction rate. The second interval begins with a rapid re-diversification in the Ordovician, which leads to a tripling of familial diversity during a span of 50 Myr; by the end of the Ordovician diversity attains a new dynamic equilibrium that is maintained, except for several extinction events, for nearly 200 Myr until near the end of the Paleozoic. A “two-phase” kinetic model is constructed to describe this heterogeneous pattern of early Phanerozoic diversification. The model adequately describes the “multiple equilibria,” the asymmetrical history of the “Cambrian fauna,” the extremely slow initial diversification of the later “Paleozoic fauna,” and the combined patterns of origination and extinction in both faunas. It is suggested that this entire pattern of diversification reflects the early success of ecologically generalized taxa and their later replacement by more specialized taxa.
Article
The discovery of a new naraoiid nektaspid in the Upper Silurian (Pridolian) of southeastern Ontario significantly extends the range of this unusual group. Nektaspids are nonmineralized arthropods typical of Early and Middle Cambrian soft-bottom communities, but were thought to have become extinct in the Late Ordovician. The unique holotype specimen of Naraoia bertiensis n. sp. comes from a Konservat–Lagerstätte deposit renowned for its eurypterid fauna (the Williamsville Member of the Bertie Formation). Naraoia bertiensis lacks thoracic segments and is morphologically similar to Naraoia compacta from the Middle Cambrian Burgess Shale, save for the presence of a long ventral cephalic doublure and a subtly pointed posterior shield. To examine the phylogenetic relationships of the new naraoiid, we coded characters of the holotype specimen and of nine previously described nektaspids. The results confirm a sister taxon relationship between Naraoia compacta and Naraoia bertiensis and the monophyly of nektaspid forms lacking thoracic segments (family Naraoiidae). This latter group may have arisen from an ancestral segment-bearing form through heterochronic loss of thoracic segments early in the Cambrian. The disjunct occurrence of a naraoiid nektaspid in the Late Silurian resembles the reappearance of other “Lazarus taxa” that were thought to have been eliminated during mass extinction events. The naraoiid lineage survived the Late Ordovician biotic crisis, but in this case the “Lazarus effect” seems likely to be taphonomic in origin.
Vachonisia rogeri LEHMANN, 1955, is redescribed on the basis of 5 previously known and 15 new specimens. V rogeri exhibits a dorsal shield, which covers the full length of the body. In cross section, the shield is shaped like a broad and low "V", probably with a very obtuse angle. Characteristics of the dorsal shield are a median ridge, which ends in a small anterior projection, an anterior indention of the shield, postero-lateral edges, and a ventral cavity that accommodates the appendages. The outer margin and the inner margin of the ventral shelf are strengthened. The limbs of V rogeri are arranged in two tagmata: a head and a trunk region. The head region possesses a hypostome, one pair of short and stout antennae (A1) and four additional limb pairs. Each of the first three post-antennal pairs of appendages has an endopod and an exopod. The exopods are walking leg-like and vary considerably in length and in the position and number of spines. The endopods of A2 and A3 bear a terminal chela. The endopod of the third post-antennal appendage (A4) is short and walking leg-like. A5 is a thin, extended, multi-segmented limb. The second branch (endopod?) was not found, but probably exists. Mature individuals developed between 50 and 80 biramous trunk appendages. The exopods consist of numerous short podomeres, each carrying a flattened seta with strengthened margins. The endopod podomeres (up to six) are fairly short, each bearing an endite. There is evidence from CT scans that endites occur on only the most anterior endopods (presumably the first to the fifth). The chelate condition of some appendages in the head, the notable increase in size in the exopods from A2 to A4, and the development of a flat ventral shelf on the ventral shield parallel the morphology of xiphosuran chelicerates. These characters are taken as indicators of a similar mode of life. V. rogeri was able to capture and comminute larger food particles. The trunk appendages and the shape of the shield of V rogeri indicate some swimming capability. The new material includes three ontogenetic stages. It is probable that V rogeri developed a stable number of head appendages early while the number of trunk appendages increased during ontogeny. The outline of the dorsal shield of the earliest ontogenetic stage is rounded in contrast to that in later stages. A close phylogenetic relationship of V rogeri with the recently described Silurian Xylokorys chledophilia (SIVETER et al. 2007) is proposed. Both taxa share a dorsal shield covering the full body. Additionally, they have the same number of head appendages and a very similar structure of the appendages in the head and trunk region. Both form the sister group of a taxon including Marrella splendens from the Cambrian, Mimetaster hexagonalis from the Devonian and presumably species of Furca so far described from the Ordovician. The monophyly of the often debated Marrellomorpha is confirmed based on several synapomorphies. The Marrellomorpha are interpreted as early stem lineage representatives of the Euarthropoda. The low degree of cephalisation of the Marrellomorpha is comparable to other early, stem Euarthropoda.
Article
Vachonisia rogeri Lehmann, 1955, is redescribed on the basis of 5 previously known and 15 new specimens. V. rogeri exhibits a dorsal shield, which covers the full length of the body. In cross section, the shield is shaped like a broad and low "V", probably with a very obtuse angle. Characteristics of the dorsal shield are a median ridge, which ends in a small anterior projection, an anterior indention of the shield, postero-lateral edges, and a ventral cavity that accommodates the appendages. The outer margin and the inner margin of the ventral shelf are strengthened. The limbs of V. rogeri are arranged in two tagmata: a head and a trunk region. The head region possesses a hypostome, one pair of short and stout antennae (A1) and four additional limb pairs. Each of the first three post-antennal pairs of appendages has an endopod and an exopod. The exopods are walking leg-like and vary considerably in length and in the position and number of spines. The endopods of A2 and A3 bear a terminal chela. The endopod of the third post-antennal appendage (A4) is short and walking leg-like. A5 is a thin, extended, multi-segmented limb. The second branch (endopod?) was not found, but probably exists. Mature individuals developed between 50 and 80 biramous trunk appendages. The exopods consist of numerous short podomeres, each carrying a flattened seta with strengthened margins. The endopod podomeres (up to six) are fairly short, each bearing an endite. There is evidence from CT scans that endites occur on only the most anterior endopods (presumably the first to the fifth). The chelate condition of some appendages in the head, the notable increase in size in the exopods from A2 to A4, and the development of a flat ventral shelf on the ventral shield parallel the morphology of xiphosuran chelicerates. These characters are taken as indicators of a similar mode of life. V. rogeri was able to capture and comminute larger food particles. The trunk appendages and the shape of the shield of V. rogeri indicate some swimming capability. The new material includes three ontogenetic stages. It is probable that V. rogeri developed a stable number of head appendages early while the number of trunk appendages increased during ontogeny. The outline of the dorsal shield of the earliest ontogenetic stage is rounded in contrast to that in later stages. A close phylogenetic relationship of V. rogeri with the recently described Silurian Xylokorys chledophilia (Siveter et al. 2007) is proposed. Both taxa share a dorsal shield covering the full body. Additionally, they have the same number of head appendages and a very similar structure of the appendages in the head and trunk region. Both form the sister group of a taxon including Marrella splendens from the Cambrian, Mimetaster hexagonalis from the Devonian and presumably species of Furca so far described from the Ordovician. The monophyly of the often debated Marrellomorpha is confirmed based on several synapomorphies. The Marrellomorpha are interpreted as early stem lineage representatives of the Euarthropoda. The low degree of cephalisation of the Marrellomorpha is comparable to other early stem Euarthropoda.
Article
The problematic fossil Eldonia ludwigi Walcott, 1911 is recorded first time on the Siberian Platform. It is discovered in the upper Middle Cambrian (Mayan Stage) of the southeastern slope of the Anabar Massif, The peculiarities of preservation allow us lo reveal features in common wilh Ordovician-Devonian paropsonemids.
Article
The problematic fossil Eldonia ludwigi Walcott, 1911 is recorded first time in the Siberian Platform. It is discovered in the upper Middle Cambrian (Mayan Stage) of the southeastern slope of the Anabar Massif. The peculiarities of preservation allow us to reveal features in common with Ordovician-Devonian paropsonemids.