Vittatusivermis annularius: A Worm-like animal from the Early Cambrian of Yunnan Province, China.

While the earliest fossil animals appear in deposits over 750 million years old, animals do not become abundant until 541 million years ago, when a wide range of shelly fossils appear suddenly an event called the Cambrian Explosion  These shelly fossils were accompanied by the earliest unequivocal trace fossils, burrows presumed to have been produced by unknown Worm-like animals, implying that animals without hard parts also underwent a significant radiation at this time, and a several later Cambrian Lagerstätte preserve a range of soft bodied fossils, though soft bodied fossils from the earliest Cambrian are very rare, and nothing likely to have produced the burrows seen in these deposits has been seen to date.

In a paper published in the journal Scientific Reports on 6 November 2017, Xingliang Zhang and Wei Liu of the State Key Laboratory of the Continental Dynamics at Northwest University, and Yukio Isozaki and Tomohiko Sato of the Department of Earth Science and Astronomy at the University of Tokyo, describe a new species of Worm-like animal from the Early Cambrian Yuhucun Formation at the Tianning Phosphorite Mine in Anning County, Yunnan Province.

The new animal is named Vittatusivermis annularius, where 'Vittatusivermis' means 'ribbon-shaped Worm' and 'annularius' refers to the visible annuli (rings) on the surface of the animal. The species is described from a total of 66 specimens found on a single surface thought to be about 535 million years old. The largest specimens reach about 26 cm in length and 1 cm in width, they are flattened and show ring-like pattern, similar to that seen in  modern Annelids (though this does not imply a direct relationship, as such annuli are seen in other groups).

(a)–(c) Vittatusivermis annularius from the lowest Cambrian of the Baideng section, Anning, Yunnan, South China, with transverse annulations specifically emphasised. (a) specimen coated with MgO film and illuminated in a low angle light, showing cross annulations. (b) specimen folded lengthwise, showing a folded edge and both sides of the flattened body undifferentiated. (c) the same specimen as (b), coated with MgO film and illuminated in a low angle light, showing cross annulations. (d) Wutubus annularis from the late Ediacaran of South China. Zhang et al. (2017).

Vittatusivermis annularius cannot confidently be assigned to any modern group; its annuli are similar to those of Annelid Worms, but these are not usually flattened. Flatworms and Nemarteans are flattened, but do not usually have annuli. In the absence of any obvious preserved organs, it cannot be confidently assumed that the fossils represent entire creatures, they may be the shed skins of something like an Ecdysozoan. They do, however, resemble a number of other late Ediacaran and early Cambrian soft-bodied fossils and traces, including Onuphionella, a tubular fossil from the Early Cambrian interpreted as a Worm-tube, and Sabellidites, Shaanxilithes and Wutubus, worm-like soft-bodied animals from the Ediacaran Biota.

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Siphusauctum lloydguntheri: An enigmatic filter-feeding animal from the Middle Cambrian Spence Shale of Utah.

Fossil Lagerstätte such as the Burgess Shale and Chengjiang Biota provide information on the earliest animal assemblages on Earth, including the oldest known members of most animal phyla. These assemblages preserve a number of filter-feeding animals, some of which can be assigned to modern groups, while others remain enigmatic. One of these is Siphusauctum gregarium, which is known only from the Tulip Beds of the Cliff Shale Member of the Burgess Shale Formation, where it forms large colonies.

In a paper published in the Journal of Paleontology on 2 June 2017, Julien Kimmig of the Biodiversity Institute at the University of Kansas, and Luke Strotz and Bruce Lieberman, of the Biodiversity Institute and Department of Ecology & Evolutionary Biology at the University of Kansas, describe a second species of Siphusauctum from the Spence Shale of Utah.

The Middle Cambrian Spence Shale of northern Utah, which is slightly older than the Burgess Shale and has produced a wide variety of Algae, Sponges, Brachiopods, Eldoniids (soft-bodies animals of uncertain affinities), stem-Molluscs (animals of apparent Moluscan affinities, but which lived or split off from the other Molluscs before the common ancestor of all living groups), Cycloneuralians (the group that includes Kinorynches, Priapulids and Nematodes), Deuterostomes (the group that includes Vertebrates and Echinoderms), Lobopodians (the probable Cambrian ancestors of the Modern Velvet Worms), and a variety of Arthropods, including Trilobites, Carapace-bearing Arthropods (which may be related to the later Crustaceans), Megacheirans (an extinct group of probably predatory Arthropods), Xenopods (an extinct group of soft-bodied Arthropods) and enigmatic forms such as Meristosoma paradoxum and Utahcaris orion.

The new species is named  Siphusauctum lloydguntheri, in honour of palaeontologist and Trilobite-expert Lloyd Gunther. The species is described from a single specimen collected by Gunther in 1976 and donated to the Biodiversity Institute at the University of Kansas. The specimen is a stalked animal with an obovate (roughly oval, but wider at the top than at the base) upper part measuring 35.1 by 29.9 mm and a long stalk measuring 45.6 by 5.7 mm.

Holotype of Siphusauctum lloydguntheri from the Spence Shale, middle Cambrian, Antimony Canyon, Utah, in lateral view: (1) part; (2) counterpart. Scale bar represents 10 mm. Kimmig et al. (2017).

The stem of Siphusauctum lloydguntheri is double-layered, with an inner and outer part; the outer part does not reach all the way to the end of the stem, but this is thought to be a preservational artifact, suggesting that the inner part of the stem was more durable that the outer. At the tip of the stem is a holdfast 5.7 mm wide and 0.9 mm high, and apparently made of the same material as the inner stem.

Close-up of the stem of Siphusauctum lloydguntheri from the Spence Shale, middle Cambrian, Antimony Canyon, Utah: (1) part; (2) explanatory drawing of the part, dashed line indicates uncertain outline. Scale bar represents 5 mm. Abbreviations: H, Holdfast, IS, Inner Stem, OS, Outer Stem. Kimmig et al. (2017).

The upper part of the animal appears to have been covered by a thick upper sheaf. Half way up this sheaf are a series of small protrusions which may have been openings. Two dark carbonaceous structures are preserved inside this outer structure, which may have been part of the lower digestive tract. There are two grows close to the top of this structure which may represent the location of the location of the anus. A series of striations may have formerly been the attachment for a filter-feeding apparatus.

Close-up of the calyx of Siphusauctum lloydguntheri from the Spence Shale, middle Cambrian, Antimony Canyon, Utah: (1) part; (2) explanatory drawing of the part, dashed line indicates uncertain outline. Scale bar represents 5 mm. Abbreviations: A, Anus, ES, External Sheath, LDT, Lower digestive tract, G, Gut. Kimmig et al. (2017).

The taxonomic affinities of Siphusauctum gregarium have to date been impossible to decipher, however Siphusauctum lloydguntheri shows a number of similarities to Dinomischus isolatus, a Burgess Shale animal interpreted as an early Entoproct. Such an affinity had been ruled out for Siphusauctum gregarium, due to the presence of feeding structures unlike those of Entoprocts, but these are not present in the new species, which implies that either they were lost between he death and preservation of the specimen, or that these were novel structures which arose in Siphusauctum gregarium and were not present in even close relatives.In addition both Siphusauctum and Dinomischus appear to have had a six-fold radial symmetry, something also found in Entoprocts, but otherwise somewhat rare (it is also sometimes seen in Cnidarians and Echinoderms, but Siphusauctum seems unlikely to have been closely related to either of these groups.

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A possible Cnidarian from the Late Ediacaran of Newfoundland.

The fossils of the Ediacaran Period record the first widespread macrofossils in the rock-record. Many of these fossils do not appear to belong to any modern group, but instead are thought to belong to an extinct taxa (sometimes known as ‘Vendobionts’), which may-or-may-not be related to modern Animals, though some fossils have been linked to Sponges (a group which also has pre-Ediacaran potential members), Anthozoan, Hydrozoan and Scyphozoan Cnidarians, Ctenophores, Placozoans, early Molluscs and even Ascidian Chordates. Most of these potential members of modern groups are from the latest part of the period, between 555 and 541 million years ago, when these groups are predicted to have existed, but remain rather controversial.

In a paper published in the Proceedings of the Royal Society SeriesB; Biological Sciences on 27 August 2014, Alexander Liu of the Department of Earth Sciences at the University of Cambridge, Jack Matthews and Latha Menon of the Department of Earth Sciences at the University of Oxford, Duncan McIlroy of the Department of Earth Sciences at the Memorial University of Newfoundland and Martin Brasier of the Department of Earth Sciences at the University of Oxford and the Department of Earth Sciences at the Memorial University of Newfoundland, describe a new Ediacaran fossil from the 560 million year old Fermeuse Formation on the Bonavista Peninsula, Newfoundland, which they interpret as an impression of a fibrous, muscular, quadrilaterally symmetrical organism.

The new fossil is named Haootia quadriformis, where ‘Haootia’ means ‘Demon’ in the indigenous Beothuk language of Newfoundland, and ‘quadriformis’ means ‘fourfold-form’ in Latin. Haootia quadriformis has a 56 x 37 mm discoid structure interpreted as a basal disk, and a 49 x 72 mm roughly rectangular body, covered with linear ridges interpreted as muscle fibres. At each of the corners bundles of fibres bifurcate (split in two) several times.

Digitized images of Haootia quadriformis, emphasizing the convergence of fibrous linear features at the corners of the body, and the symmetry ofthe fossil. (a) Photograph of the specimen as it appears in situ. (b) Interpretive sketch of the non-retrodeformed specimen. Labels indicate: (a) muscle bundles, (b) expanded bundles, (c) ‘contracted’ bundles, (d) twisting fibres, (e) superimposed fibres and (f ) disc. Liu et al. (2014).

This is very different from the typical anatomy of a frondose Ediacaran, which usually have a circular basal disk with a single leaf-like frond, and which have never been found to have anything resembling muscle fibres. Quadrilateral symmetry is not found in other Ediacarans, but it is the most common body-plan within both modern and ancient Cnidarians, and thought to be the ancestral state within the group.

Artistic reconstruction of Haootia quadriformis. Liu et al. (2014).

Not only does Haootia quadriformis have a bodyplan that strongly suggests Cnidarian affinities, it actually resembles the structure of a group of modern Cnidarians, the Staurozoans, which have a cup-like body attached to a circular basal disk, with branching arms at each corner. While the specimen does not preserve enough features for Liu et al. to place it within this group, would be an exceptionally large member of the group, and has multiply branching limbs at each corner while modern members have limbs that branch only once, the presence of a member of this group within strata of this age (about 560 million years old) would not fall outside our understanding of the history of the group. Staurozoans are placed within the Medusozoa (the group of Cnidarians which includes Jellyfish), which are predicted by molecular data to have split from their closest relatives, the Octocorallia, about 571 million years ago. Within the Medusozoa, the Staurozoans are thought to be the group which split from all other (known) members the earliest, making the presence of such an organism in 560 million year old sediments quite possible.

The extant staurozoan Lucernaria quadricornis, exhibiting abody plan similar to that hypothesized for Haootia quadriformis. Liu et al. (2014).

See also…

The nature and development of the mysterious Cambrian fossil Olivooides.

In 1997 Stefan Bengtson of the Department of Palaeozoology at the Swedish Museum of Natural History and Yue Zhao of the  Institute of Geology of the Chinese Academy of Geological Sciences announced...

Punctatus emeiensis, not a Cnidarian after all?                                                         Punctatus emeiensis is an enigmatic fossil from the earliest Cambrian of northern China. Many thousands of specimens have been found from a number of...

The Ediacaran Fauna; not animals after all?   Most modern animal groups appear abruptly at, or very shortly after, the beginning of the Cambrian period...

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The nature and development of the mysterious Cambrian fossil Olivooides.

In 1997 Stefan Bengtson of the Department of Palaeozoology at the Swedish Museum of Natural History and Yue Zhao of the  Institute of Geology of the Chinese Academy of Geological Sciences announced the discovery of fossilized animal embryos from basal Cambrian rocks in China in a paper in the journal Science. Since this time these embryos have been studied extensively and a number of development stages leading to an apparent mature animal have been discovered, and a number of different theories as to the precise nature of these fossils, named Olivooides, have been put forward, without any general consensus being reached.

In a paper published in the Proceedings of the Royal Society Series B Biological Sciences on 27 February 2013, a team of scientists led by Xi-Ping Dong of the School of Earth and Space Science at Peking University and the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Science, describe a series of Olivooides fossils showing preserved internal anatomical features and providing a more complete set of developmental stages, from which they are able to discuss the nature of Olivooides and draw conclusions about its affinities. 

Embryos and polyps of Olivooides. (a) Cleavage-stage embryo. (b) Stellate embryo with raised apertural rays. (c) Stellate embryo with a raised apertural region. (d) Stellate embryo with an infolded apertural region. (e–f) Stellate embryo showing a characteristic pattern of bulges in (e) lateral, and (f) apertural aspect. (g) Embryo within fertilization envelope that preserves the characteristic pattern of bulges, but not the stellate tissue. (h–j) Early post-embryonic polyp stage exhibiting characteristic stellate integument of embryonic stage, but exhibiting the annulated striated adapertural tissue, and the pentamerally enfolded aperture, in (h) lateral, (i) apertural and (j) oblique aspects. (k) Later polyp-stage specimen in lateral aspect. Scale bars: (a) 69 mm, (b) 116 mm, (c) 139 mm, (d ) 125 mm, (e,f ) 132 mm, (g) 164 mm, (h) 275 mm, (i) 118 mm, ( j) 250 mm, (k) 262 mm. Dong et al. (2013).

Dong et al. considered three main theories on the affinities of Olivooides that have previously been proposed, namely that it is a Priapulid, an Echinoderm or a Cnidarian. 

Olivooides shows some resemblance to the larvae of a Priapulid in overall morphology, and shows pentaradial symmetry, which is rare outside of Echinoderms, but which is found in the mouthparts and pharynx of Priapulids. However Olivooides lacks a through gut, which is seen in both larval and adult Priapulids, and appears to develop directly (gradually) from the embryo stage to the adult, unlike Priapulids which undergo a distinct metamorphosis between their juvenile and adult stages. 

The pentaradial symmetry seen in Olivooides is most common in Echinoderms, and is often considered diagnostic of the group. However Olivooides lacks any of the other features diagnostic of this group, notably a multi-element calcite exoskeleton, a through gut and tube feet. 

Cnidarians lack a true gut, as is the case in Olivooides, and also typically show direct development. Olivooides also shows some affinities with the polyps of extant Coronate Scyphozoans (Jellyfish), as well as with contemporary Cambrian Conulariids. Cnidarians do not typically show pentaradial symmetry, however it is seen in some Cnidarians with fluctuating symmetry, so an exclusively penetaradial species among the earliest members of the group would not be that surprising. 

Finally some specimens of Olivooides show a strange stellate organ, which is hard to interpret as analogous with any organ seen in Priapulids or Echinoderms, but which Dong et al. interprest as budding medusa larvae on the Cnidarian polyp. Medusa larvae are a motile stage produced by many attached Cnidarians, a form of asexual reproduction in which a larvae buds of then swims freely in the water column as a miniature Jellyfish for some time before settling down to develop into a new attached polyp. Such species often alternate sexual reproduction, which produces embryos with two parents, with asexual reproduction, producing medusa larvae which are clones of their single parent, so a form that develops from an embryo to an adult with budding medusa larvae is entirely in keeping with a Cnidarian interpretation of Olivooides.

Two adpressed ephyra-stage Olivooides specimens. (a) SEM image showing the whole specimen in aboral view. (b) SEM image showing a detail of the aboral surface; note the alternately overlying and underlying arms. (c) SRXTM surface rendering showing a detail of the adoral surface including the presumed mouth. Scale bars: (a) 49 mm, (b) 27 mm, (c) 28 mm. Dong et al. (2013).

The life cycle of a modern Scyphozoan Jellyfish. Tree of Life.

See also…

 A new species of Jellyfish from the North Adriatic Sea.

While instantly familiar and biologically simple, Jellyfish (Scyphozoa) are still in many ways poorly understood, with frequently poorly understood life-cycles and population structures, leading to unexpected shifts in population and sudden blooms of...

 Jellyfish force closure of Swedish nuclear power plant.

The Oskarshamn Nuclear Power Plant in Kalmar County on...

 Punctatus emeiensis, not a Cnidarian after all?

Punctatus emeiensis is an enigmatic fossil from the earliest Cambrian...

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A Marrellomorph Arthropod from the Late Ordovician of the Czech Republic.

The enigmatic fossil Furca bohemica was first recorded from Late Ordovician deposits at Veselá Gorge, in what is now the Czech Republic, by the French Palaeontologist Joachim Barrande in 1846, though he never formally described the specimens. A formal description was provided by Antonin Fritsch in 1908, who interpreted it as a larval Echinoderm. Since 1919 it has generally been recognized as being an Arthropod, but palaeontologists have disagreed as to its affinities, with different scientists regarding it to be a Trilobite, a Chelloniellid and a Marrellomorph.

In a paper published in the August 2013 edition of the journal Acta Palaeontologica Polonica Štěpán Rak of the Institute of Geology and Palaeontology at Charles University, Javier Ortega−Hernández of the Department of Earth Sciences at the University of Cambridge and David Legg of the Department of Earth Sciences and Engineering at Imperial College London describe the discovery of a large number of new specimens of Furca bohemica a recently discovered section of the Letná Formation on the southern slope Ostrý Hill in Beroun and in a debris of the classical site Veselá Gorge. These new finds enable a better description of the species, and enable them to more confidently place it within the Marrellomorpha.

Specimen of Furca bohemica preserved in fine sandstone. Scale bar is 10 mm. Rak et al. (2013).

Furca bohemica has a six-spined shield shape, typical of Marrellomorph Arthropods, but is surrounded by secondary structures which are harder to explain, and which if legs or cilia would rule out placing the fossils in any known Arthropod Group. Rak et al. interpret these as a fringe of secondary spines surrounding the main shield, an interpretation which does not rule out Arthropod affinities, and which allows the placement of Furca bohemica confidently within the Marrellomorph Arthropods.

New morphological reconstruction of the Marrellomorph Arthropod Furca bohemica in dorsal view. Scale bar is 10 mm. Rak et al. (2013).

See also The first Arthropod? The enigmatic Carboniferous Arthropod Camptophyllia, Preserved Trilobite digestive tracts from the Middle Cambrian of Utah and A partial Marrellomorph Arthropod from Western Queensland.

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Punctatus emeiensis, not a Cnidarian after all?

Punctatus emeiensis is an enigmatic fossil from the earliest Cambrian of northern China. Many thousands of specimens have been found from a number of different sites, providing complete growth series for the animal, from single celled eggs to mature individuals a few millimeters in length. The adults have diploblastic (two layered) body, radial symmetry, a simple gut in which the mouth also serves as an anus and a segmented external body lacking limbs or tentacles. For many years scientists have either ignored their higher classification, of placed them within the Phylum Cnidaria (which includes modern Jellyfish, Corals and Sea Anemones), with possible affinities to the extinct Conularids.

In a paper published in the journal PLoS One on 20 June 2013, a team of scientists led by Kinya Yasui of the Department of Biological Sciences at the Graduate School of Science at Hiroshima University, discuss the results of a study in which they examined over 10 000 individual Punctatus with the aim of better understanding their development, biology and taxonomic affinities.

The development of Punctatus from an egg to a mature individual several millimeters long. Yasui et al. (2013).

Diploblastic animals develop from two layers of cells, one of which becomes the lining of the gut and tissues derived from it, the other the external skin and tissues derived from it. This method of development is found in two modern groups of animals, the Cnidarians (Jellyfish etc.) which have radial symmetry and a simple gut with a single opening that serves as both mouth and anus, and the Ctenaphores (Comb Jellies) which are bilaterally symmetrical and have a through gut. Apart from the Sponges (Porifera), which lack any true tissues or even much cell differentiation, every other modern animal, from Worms to Pandas via Starfish and Snails, has triploblastic development, with a third layer of tissue between the inner and outer layer, from which many of the internal organs develop. It should be noted that which layer an organ develops from does not entirely determine what sort of tissue it becomes; in humans the skull, pelvis and shoulder blades develop from the external layer and most other bones from the middle layer.

Development patterns seen in Poriferans, Ctenaphores, Cnidarians and Punctatus emeiensis. Yasui et al. (2013).

Beyond this, however, the similarities between Punctatus and the Cnidarians is less convincing. Yasui et al. note that Punctatus appears to lack any divisions within the gut, something seen in almost all Cnidarians, including species smaller than Punctatus. These divisions of the gut greatly increase the surface area over which Cnidarians digest food, so any animal lacking them would have a correspondingly lower food intake, and therefore its metabolism and biology are likely to be quite different to those of a Cnidarian. Secondly, Punctatus shows no signs of having had any tentacles, a trait seen in almost all Cnidarians. Yasui et al. note that in theory Punctatus could have had tentacles which have not survived the preservation process, but given the very large number of specimens, and the excellent preservation of soft tissues of the mouth-flaps seen in many of these specimens, this seems rather unlikely. Thirdly Punctatus has no trace of a sticky holdfast, something seen in almost all benthic Cnidarians. Fourthly Punctatus has pentameral (five-way) radial symmetry, unlike Cnidarians which have tetrameral (four-way) radial symmetry. Fifthly Punctatus seems to have reproduced exclusively sexuallym whereas almost all Cnidarians also reproduce by budding or dividing to form clones of the parent. Finally Punctatus grew throughout its life by the development of new segments around the oral area, so that the embryonic body is retained as the tip of the tail in adults, which the mouth is always the youngest part of the organism. This is quite unlike anything seen Cnidarians.

Postembryonic growth of Punctatus. (A) Hatchling  and (B) young with two annular fringes.  (C) Rendering from micro-CT data of a young with four annular fringes, (D) transverse CT-section at gut level, and (E) median section showing a completely empty body cavity (blastocoel) and small gut. (F) Apical portion of mature specimen and (G) a mature specimen with more than 12 annular fringes. (H) Clearly demarcated embryonic body at the tip of adult specimen. Abbreviations: bc, blastocoel (body cavity); eb, embryonic body; g, gut; mo; mouth; pb, postembryonic body. Scale bars are 0.5 mm. Yasui et al. (2013).

Based upon this data, Yasui et al. suggest that Punctatus cannot comfortably be placed within any the Cnidarians as we currently define the group, and suggest that either it should be regarded as the sister taxon to all other known Cnidarians, having split from the group before all other taxonomic diversification took place (not unreasonable in an earliest Cambrian animal) or that it be considered an entirely separate animal sharing only a common level of development with the Cnidarians. 

They were not able to make any firm predictions about how Punctatus fed, beyond that it could not have fed in the same way as familiar Cnidarians. They suggest that its simple, undivided stomach cavity may have contained symbiotic algae or bacteria.

Map showing the distribution of sites that have produced Punctatus fossils. Paleobiology Database.

See also The mysterious ebb and flow of Jellyfish populations, A new species of Hydrozoans from British Columbia, The oldest animals - Pre-Ediacaran Sponges from Namibia(?), Mysterious new animal from the Burgess Shale and The Ediacaran Fauna; not animals after all?

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The first Arthropod?

The Arthropods are one of the most abundant and diverse groups of animals alive today, and the fossil record suggests this has been the case for most of the last 500 million years. However the origin of the group remains obscure. There are a wide variety of Arthropods in early Cambrian faunas, though these are strange, unfamiliar forms, as well as members of groups thought to be related but outside the group, such as the Lobopodians and Anomalocarians, but the precise nature of the earliest Arthropods is still highly debatable.

In a paper published in the Proceedings of the Royal Society Series B: Biological Sciences on 10 October 2012, David Legg of the Department of Earth Sciences and Engineering at Imperial College London and the Department of Earth Sciences at the The Natural History Museum, Mark Sutton of the Department of Earth Sciences and Engineering at Imperial College London, Gregory Edgecombe of the Department of Earth Sciences at the The Natural History Museum and Jean-Bernard Caron of the Department of Natural History (Palaeobiology Section) at the Royal Ontario Museum and the Department of Ecology and Evolutionary Biology at the University of Toronto describe a new fossil from the Burgess Shale Lagerstätten (rich fossil find) in British Columbia which they believe may illustrate the form of the earliest Arthropods.

The new fossil is named Nereocaris exilis, where Nereocaris  means 'Nereo's crab' (Nereo was a Titan, form Greek mythology, often depicted with a fish's tail), and exilis means slender. It is a member of a group known as the 'Bivalved Arthropods', which have bilaterally flattened, elongate bodies with their limbs held within the valves. 

Nereocaris exilis is a 142 mm Bivalved Arthropod with stalked lateral eyes and a single rod-shaped median eye; a bivalved carapace with a postero-dorsal keel; the limbs are entirely encased within this carapace. Behind the carapace is an elongate, tail-like abdomen, composed of about 60 ring-like segments, terminated by a telsion (final group of segments, with small median and elongate lateral processes.

Reconstruction of Nereocaris exilis. Legg et al. (2012).

Based upon their interpretation of Nereocaris, Legg et al. have created a cladistic analysis (family tree, but with maths) of the earliest Arthropods, and the order in which they gained the features typical of the group. Working on the assumption that the Anomalocarians are outside the true Arthropods, this suggests that Nereocaris is the most primitive arthropod yet discovered.

Cladistic reconstruction of the origin of the Arthropods, based upon the accumulation of typical Arthropod features. (1) Development of compound eyes (some groups have subsequently lost, and even re-evolved these). (2) Appearance of Arthropod-like jointed limbs. (3) Appearance of such limbs on the trunk, Branched limbs appear on the trunk, segmented, mineralized exoskeleton. (4) Specialized cephalic (head) appendages. (5) Development of distinct dorsal and ventral sides to the body segments (as opposed to the simple ring-like segments that had occurred before). (6) Reduction in number and greater specialization of the limbs. (7) Modification of appendages into distinct antennae. (8) Appearance of mandibles capable of 'chewing' food. Legg et al. (2012).

See also Insect nymphs from the Carboniferous Montceau-les-Mines Lagerstätte of France, Are the Vetulicolians Deuterostomes? A fossil Insect from the Late Devonian of Belgium, The enigmatic Carboniferous Arthropod Camptophyllia and Preserved Trilobite digestive tracts from the Middle Cambrian of Utah.

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The enigmatic Carboniferous Arthropod Camptophyllia.

The Carboniferous Arthropod Camptophyllia is known from coal measure deposits in northern England. It is always preserved as a dorsal exoskeleton about 25 mm in length, made up of 10 segments, each segment being split into five plates; three apparently dorsal and two apparently lateral. Since its discovery in the 1920s it has been assigned to a number of different Arthropod groups, but none with any degree of confidence.

Line drawing of Camptophyllia. Gill (1924).

In a paper published in the journal Palaeontologica Electronica in April 2012, Russell Garwood of the Manchester X-ray Imaging Facility at the School of Materials at The University of Manchester and Mark Sutton of the Department of Earth Science and Engineering at Imperial College London present the results of a high-resolution X-ray micro-tomography study of Camptophyllia, which attempted to gain a better insight into the structure and affinities of the animal.

Examples of Camptophyllia from museum and private collections. (1) 44 mm specimen from the Tyne Coalfield, Natural History Museum, London. (2) 28 mm specimen from Crawcrook, near

Ryton-On-Tyne, Durham, Natural History Museum, London. (3) Counterpoint to (2), 30 mm. (4) 39 mm specimen from the Tyne Coalfield, Natural History Museum, London. (5) 42 mm specimen from Crock Hey, private collection of Stephen Livesley. (6) 35 mm Specimen from Crock Hey, private collection of Sean Sale. (7) 18 mm specimen from Coseley Colliery, Natural History Museum. (8) 13 mm specimen from Coseley Colliery, Natural History Museum, London. (9) 20 mm specimen from Coseley Colliery, Natural History Museum, London. (10) 20 mm specimen from Coseley Colliery, Natural History Museum, London. Garwood & Sutton (2012).

Garwood and Sutton carried out high-resolution X-ray micro-tomography studies of six specimens from the Natural History Museum in London and from the private collections of Stephen Livesley and Sean Sale. These were not, however able to resolve any features of the underside of Camptophyllia on any specimen. They concluded that this was unlikely to be a coincidence, and that therefore the undersides had not been preserved for a common reason. Arthropods shed their outer shells periodically as they grow, making it possible that the Camptophyllia specimens are in fact shed carapaces. However no known Arthropod sheds its dorsal carapace intact in this fashion without any other part of the exoskeleton, making this scenario unlikely. For this reason Garwood and Sutton favor the alternative possibility, that the dorsal shell of Camptophyllia was significantly mineralized, but that the underside was not; a pattern found in several Arthropod groups. Unfortunately this in no way helps to resolve the problem of Camptophyllia's taxonomic position.

Garwood and Sutton have placed two animations made from high-resolution X-ray micro-tomographs of specimens online. (Animation 1. Animation 2.).

Even thought they were unable to resolve the taxonomic position of Camptophyllia Garwood and Sutton were able to make some deductions from their study. A heavily mineralized dorsal skeleton, combined with soft underparts, is often associated with an ability to roll up into a ball for defensive reasons, something which would seem to be possible from Camptophyllia's bodyplan. None of the preserved specimens show any sign of eyes or similar structures, suggesting that Camptophyllia lived in an environment where vision was not a useful sense. The fossils have previously been identified as coming from shallow lacustrine (lake) environment, which could quite possibly have been murky or cloudy. In addition Camptophyllia has a 'snowshoe' shape, which is often associated with animals that live on soft sediments, and need to avoid sinking in such.

See also An Eocene False Scorpion from Baltic amber, Two new species of True Bug from the Mesozoic of China, An Assassin Bug from the Palaeocene of Spitsbergen Island, A fossil termite from the Late Oligocene of northern Ethiopia and Preserved Trilobite digestive tracts from the Middle Cambrian of Utah.

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