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Ordovician faunas of Burgess Shale type

May 2010
Nature 465(7295):215-8

DOI:10.1038/nature09038

Source
PubMed

Authors:

Patrick Orr

University College Dublin

Joseph Botting

Guest Scientist at Nanjing Institute of Geology and Palaeontology

Lucy Muir

National Museum Wales

Show all 8 authorsHide

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.

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).

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LETTERS

Ordovician faunas of Burgess Shale type

Peter Van Roy

1,2

, Patrick J. Orr

, Joseph P. Botting

, Lucy A. Muir

, Jakob Vinther

, Bertrand Lefebvre

Khadija el Hariri

& 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

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

. 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

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

. It was accompanied by a major

increase in ecological complexity

. Until now, however, no excep-

tionally preserved biotas recording the critical early stages of the

Ordovician radiation were known. Beecher’s Trilobite Bed

of New

York, and the Soom Shale of South Africa

, are late Ordovician

(Sandbian and latest Hirnantian to earliest Rhuddanian

, respec-

tively) in age. The former represents a low-oxygen environment with

a low diversity fauna including the olenid trilobite Triarthrus eatoni

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

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

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

. 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

. The preservation, andconsequently appearance, of

Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, Connecticut 06520, USA.

UCD School of Geological Sciences, University College Dublin,

Belfield, Dublin 4, Ireland.

Leeds Museum Discovery Centre, Carlisle Road, Leeds LS10 1LB, UK.

42 Birkhouse Lane, Moldgreen, Huddersfield HD5 8BE, UK.

UMR CNRS 5125 PEPS,

ˆt. Ge

´ode, Universite

´Lyon 1, Campus de la Doua, 2 Rue Dubois, F-69622 Villeurbanne cedex, France.

´partement Sciences de la Terre, Faculte

´des Sciences et Techniques-Gue

´liz,

Universite

´Cadi Ayyad, Avenue Abdelkrim el Khattabi BP 549, 40000 Marrakech, Morocco.

Yale Peabody Museum of Natural History, Yale University, New Haven, Connecticut

06520, USA.

Vol 465

13 May 2010

doi:10.1038/nature09038

215

the fossils is remarkably similar to that of the Early Cambrian

Chengjiang fauna from China

, 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

, 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

Vol 465

13 May 2010

216

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

; they are exceptional only in the high degree of articulation of

multi-element skeletons in trilobites and echinoderms. In contrast to

Chengjiang

, 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

, 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

, 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

, greater depth of bioturbation

21,22

and increased behavioural complexity and ecospace occupation by

burrowing organisms

. 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

, the Moroccan sites were situated very

close to the Ordovician South Pole; Burgess Shale-type biotas clearly

persisted globally in cold, deep marine settings

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

and some groups, for example, marrellomorphs

,great

appendage arthropods

and eldonioids

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

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

20 mm

5 mm

2 mm

10 mm

20 mm 5 mm

5 mm 2 mm 10 mm

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

Vol 465

13 May 2010 LETTERS

217

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

Vol 465

13 May 2010

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Oct 2024

The rapid early diversification of arthropods has made understanding internal relationships within the group fiendish. Particularly unresolved is the origin of Euchelicerata, a clade consisting of the Prosomapoda (comprising the extant Xiphosura and Arachnida and the extinct Chasmataspidida, Eurypterida and synziphosurines) and the extinct Offacolidae. Here we describe new material of the Silurian ‘synziphosurine’ Bunaia woodwardi Clarke, 1919 that reveals previously unknown features of its ventral anatomy: a pair of elongated chelicerae in the prosoma, followed posteriorly by five pairs of biramous appendages, a first pre-abdomen somite bearing a pair of paddle-like uniramous appendages (exopods) and a ventral pretelsonic process. Phylogenetic analyses retrieve B. woodwardi as a member of Offacolidae closely related to Setapedites abundantis from the Early Ordovician Fezouata Biota. An anatomical comparison of the pretelsonic process of B. woodwardi, also present in Setapedites, with the posterior trunk morphologies of other Offacolidae, Habeliida and Vicissicaudata, suggests a possible homologous appendicular origin. This proposed apomorphic character supports a monophyletic Arachnomorpha, formed of Vicissicaudata, Habeliida and Euchelicerata. The establishment of this new homology could help to clarify the highly enigmatic phylogeny at the base of the euchelicerates as well as the sequence of character acquisition during their early evolution.

A pyritized Ordovician leanchoiliid arthropod

Article

Full-text available

Oct 2024
CURR BIOL

Alternative Pathways in Astrobiology: Reviewing and Synthesizing Contingency and Non-Biomolecular Origins of Terrestrial and Extraterrestrial Life

Article

Full-text available

Aug 2024

The pursuit of understanding the origins of life (OoL) on and off Earth and the search for extraterrestrial life (ET) are central aspects of astrobiology. Despite the considerable efforts in both areas, more novel and multifaceted approaches are needed to address these profound questions with greater detail and with certainty. The complexity of the chemical milieu within ancient geological environments presents a diverse landscape where biomolecules and non-biomolecules interact. This interaction could lead to life as we know it, dominated by biomolecules, or to alternative forms of life where non-biomolecules could play a pivotal role. Such alternative forms of life could be found beyond Earth, i.e., on exoplanets and the moons of Jupiter and Saturn. Challenging the notion that all life, including ET life, must use the same building blocks as life on Earth, the concept of contingency—when expanded beyond its macroevolution interpretation—suggests that non-biomolecules may have played essential roles at the OoL. Here, we review the possible role of contingency and non-biomolecules at the OoL and synthesize a conceptual model formally linking contingency with non-biomolecular OoL theories. This model emphasizes the significance of considering the role of non-biomolecules both at the OoL on Earth or beyond, as well as their potential as agnostic biosignatures indicative of ET Life.

HORSESHOE CRAB (XIPHOSURA) TRACES CRESCENTICHNUS AND SELENICHNUS FROM THE LATE CRETACEOUS DAKOTA SANDSTONE AT DINOSAUR RIDGE, COLORADO, USA

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Full-text available

Aug 2024

Shifting tides: Anthropocene entanglements and unravellings in the Bay of Fundy

Chapter

Jul 2023

Aurora Fredriksen

The highest tides in the world flow in and out of the northern end of the Atlantic's Gulf of Maine, in the Bay of Fundy. At their highest point, in the Minas Basin (an inlet of the larger bay), a spring tide 1 can rise 16 metres vertically and spread 5 kilometres horizontally. At low tide boats at dock sit on sand, and water can only be seen far in the distance. Visiting a dock at low tide brings to mind images of boats in the desert where the Aral Sea once was. But the impression is fleeting, as the tides bring the sea back each day, twice a day, and the flood tide is fast, faster that you can walk in some places. We-myself and a film-maker friend-almost lost two Go-Pros to the flood tide on the day we set four of these little waterproof cameras out on the sandy shore to film the tide flowing in to submerge them in real time. The flow was too fast though and inrushing seawater submerged them quickly, washing them off the sandy bottom. We eventually found them swishing in some rocky shallows several feet from where they had been set. We grabbed them and headed back to the truck at a jog, wet almost to our waists with seawater. This wasn't the first or last time in the fieldwork that the extraordinary flow of the Bay of Fundy's tides changed our plans, spoiled our 'data', soaked our legs. I was in the Bay of Fundy, in the summers of 2017 and 2018, to research the controversy surrounding tidal energy development, and particularly the tensions between tidal energy proponents and independent and indigenous fishers. In both years a friend came up from New York to film as I researched, to make a visual record of movement, more-than-verbal encounters, flows. Throughout the research and after, the Bay of Fundy-its waves and tides and all the things and relations it involves-was more than the setting or container of the controversy over tidal energy, it was a central thread running through the entangled stories of living with continuity and change in a time of disorienting environmental shifts. In spending time there, talking to people, going out in trucks and boats, watching birds and getting alternately soaked and left high and dry by its tides, I came to appreciate the Bay of Fundy not as a body of water in the North Atlantic, but as a flowing meshwork of unfolding, entangled, more-than-human lifeways (Ingold 2010). And, indeed, perhaps to as something exceeding meshwork, stretching beyond its material entanglements to "permeate senses and imaginations, emoting the 'marine' and the 'maritime'" (Peters and Steinberg 2019: 294), drawing bodies and imaginaries into relations that unfold and flow within a wider affective ecology (Vannini and Vannini this volume). In the liminal zones of seacoasts, the Anthropocene comes 'down to earth' (cf. Latour 2018), making global environmental changes legible in the intensifying forms of coastal erosion and flooding caused by rising seas, in redrawing the edges of things at sometimes alarming rates. In stratigraphic terms the Anthropocene proposes a new geological epoch marked by human impacts on Earth systems, readable in the rocky strata of the deep future. Colloquially, the Anthropocene is increasingly 1 A 'spring' tide does not refer to the season, but the high tides that come with the full and new moon, which are the highest in the lunar tidal cycle, getting steadily lower as the moon waxes and wanes towards a 'neap' tide at the half moon.

The purported record of an epibiontic rhabdopleurid in the Early Ordovician Fezouata biota of Morocco, with a discussion about benthic pterobranchs (Hemichordata) in the Lagerstätte

Article

Nov 2024
Geobios

Jörg Maletz

FOSSILIZATION OF WELL-PRESERVED DEEP-SEA LANTERNFISH: A CASE STUDY FROM THE MIOCENE MOROZAKI GROUP, CHITA PENINSULA, SOUTHWEST JAPAN

Article

Nov 2024
PALAIOS

Several biological and chemical changes occur during fossilization of organisms. However, the nature and mechanism of fossilization are not yet completely understood. In this study we investigated the changes in chemical composition during fossilization of lanternfish from the lower Miocene Yamami Formation, Chita Peninsula, Japan compared to modern/living lanternfish. This comprised chemical mapping using X-ray microscopic analysis, mineral identification using Raman spectroscopy, and chemical analysis using inductively coupled plasma mass spectrometry and elemental analysis. Carbon and nitrogen were lost significantly during fossilization, whereas slight changes were observed in phosphorus and calcium concentrations, which are major elements of hard tissues. Iron and sulfur concentrations are high in fossil fish compared to modern/living fish due to pyrite formation during fossilization. In agreement with earlier studies, we conclude that in-situ pyrite formation mediated by sulfur-reducing bacteria played an important role in the preservation of soft tissue textures in the Yamami Formation. This includes the preservation in the fossils of delicate organs, such as eyes in the Yamami lanternfish. The oxidation of pyrite is also important for fossil preservation because of the low solubility of iron oxides.

Late Ordovician sponge spicules from the Yangtze Platform, South China: Biostratigraphical and palaeobiogeographical significance

Article

Oct 2024
J ASIAN EARTH SCI

Highly resolved taphonomic variations within the Early Ordovician Fezouata Biota

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Full-text available

Sep 2024

The Fezouata Biota (Morocco) is a Burgess Shale-type (BST) assemblage that provides a wealth of information on Early Ordovician ecosystems. Much work has been done to compare the preservation of the Fezouata Biota to other BSTs. However, studies investigating preservation variations within the Fezouata Biota are rare. Here, we use probabilities to investigate the preservation of various ecological categories of Fezouata eumetazoans. Complex taphonomic processes and phylum-specific constraints have led to the better preservation of predators/scavengers in this biota. However, no differences in preservation are observed between vagile and sessile taxa. Importantly, Tremadocian taxa are better preserved than Floian ones. As such, this study highlights the gradual closure of the BST window of preservation in the Zagora region of Morocco and constitutes a benchmark for future palaeoecological and evolutionary studies on the Fezouata Biota.

Chitinozoans and the age of the Soom Shale, an Ordovician black shale Lagerstätte, South Africa

Article

Full-text available

Jan 2009

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.

The Great Ordovician Biodiversification Event

Book

Full-text available

Jan 2004

A kinetic model of Phanerozoic taxonomic diversity II. Early Phanerozoic families and multiple equilibria

Article

Jun 1979

J. John Sepkoski

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.

A new Late Silurian (Pridolian) naraoiid (Euarthropoda: Nektaspida) from the Bertie Formation of southern Ontario, Canada—delayed fallout from the Cambrian explosion

Article

Nov 2004

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.

Morphology, Palaeobiology and Phylogenetic Position of Vachonisia rogeri (Arthropoda) from the Lower Devonian Hunsruck Slate (Germany)

Article

Dec 2008
Palaeontograph Abteilung

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.

Eldonia berbera n. sp., a new species of the enigmatic genus Eldonia Walcott, 1911 from the Rawtheyan (Upper Ordovician) of Anti-Atlas (Erfoud, Tafilalt, Morocco)

Article

Jan 2003

Morphology, paleobiology and phylogenetic position of vachonisia rogeri (arthropoda) from the lower Devonian hunsr??ck slate (Germany)

Article

Dec 2008

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.

Middle Cambrian Eldonia from the Siberian Platform

Article

Jan 2002

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.

Middle Cambrian Eldonia from the Siberian Platform

Article

Jan 2002

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.

Taphonomy of Nonmineralized Tissues

Chapter