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What do we know about Intrites punctatus?


SpringGroveUK

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I acquired my first Ediacaran fossil recently, a little slab of Intrites punctatus from the Burway Formation in Shropshire, England. I've found scant information about these organisms, though. From what little I've seen, these appear to be impressions in the rock with such impressions being all that have ever been found from the species. What is the latest knowledge on them? Definite taxonomy? Has anything other than discoid impressions been found? The Ediacaran can be so murky.

indrites.jpg

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Here are the competing theories.  The most recent paper claims they are microbially-induced sedimentary structures.

 

 

Simple discoidal impressions are the only evidence of complex life in some Ediacaran and older rocks, but their interpretation is notoriously difficult. We reassessed a puzzling discoidal form from the c. 560 Ma upper Burway Formation of the Ediacaran Longmyndian Supergroup, Shropshire, UK. The structures, previously described as Intrites punctatus Fedonkin, are found on both the bed tops and soles. They vary in morphology from mounds with central depressions to incomplete rings and pairs of short ridges. Examination of the purported Intrites documented from the Longmyndian in cross-section revealed a torus-shaped structure bounded by microbial mat layers and commonly containing white laminae. We interpret the ‘Longmyndian Intrites’ as a product of microbial trapping, sediment binding and authigenic clay mineral and carbonate precipitation on the flanks of small sediment volcanoes. Subsidence of the ring-like structure into muddy sediments resulted in a torus-shaped microstromatolite. Preferential stromatolitic growth parallel to the prevailing current produced the observed partial rings or parallel ridges and explains their preferential orientation as current alignment. This interpretation of ‘Longmyndian Intrites’ expands the known variety of microbially-induced sedimentary structures (MISS) and emphasizes the importance of considering microbially-induced structures and abiological processes when interpreting discoidal impressions in ancient rocks.

 

Menon, L.R., McIlroy, D., & Brasier, M.D. (2016)

Intrites’ from the Ediacaran Longmyndian Supergroup, UK: a new form of microbially-induced sedimentary structure (MISS).

Geological Society, London, Special Publications, 448, (ahead-of-print publication)

 

 

Intrites, a subcircular blob, has been reinterpreted as a body fossil of uncertain affinities (Gehling et al. 2000). Intrites is now considered to be a body fossil (Gehling et al. 2000 ) and almost all Ediacaran occurrences of Bergaueria have been called into question as dubiofossils or body fossils (Seilacher et al. 2005 ; Jensen et al. 2006 ; see Chap. 2 ). A few additional ichnogenera have been listed for these units but further work is necessary to document the ichnotaxonomic composition of these assemblages.

 

Mángano, M.G., & Buatois, L.A., eds. (2016)
The Trace-Fossil Record of Major Evolutionary Events: Precambrian and Paleozoic
Springer Scientific Publishing, Topics in Geobiology, 39:1-358 

 

 

The biological affinities of Palaeopascichnus, Intrites and Yelovichnus are likely to be with body fossils of organisms that grew on the substrate. It is unclear whether they are bacterial colonies, algae, egg masses (Text-fig. 9A) or even serially arranged budding specimens of Aspidella. The coincidence in style of preservation and co-occurrence on the same bedding planes of these characteristic Ediacaran taxa with large numbers of Aspidella requires that the latter cannot be inorganic in the presence of the former.

 

Gehling J.G., Narbonne G.M., & Anderson, M. (2000) 
The first named Ediacaran body fossil, Aspidella terranovica
Palaeontology, 43:427-456

 

 

image.png.a84de26dad44fb03836a743755df237c.png

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let me provide some food for thought here:

2011 No_16 031-043 Liu - Ediacaran.pdf

 

Fedonkin_reviewmetazoa,2003.pdf

https://digital.library.adelaide.edu.au/dspace/bitstream/2440/21668/2/02whole.pdf

The problem with most of the macroscopic Neoproterozoic biota is the absence of modern analogs,hence actualistic models fail. 

The problems are confounded by uncertain stratigraphy,and uncertain sedimentological insights.

Like Scott already said ,even telling apart body fossils,ichnofossils and simple sedimentary structures is very,very hard.

One only has to look at the very disparate views on the affinities e.g. Spriggina or Dickinsonia to to get an inkling of the interpretational problems.

 

 

 

 

 

 

 

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piranha wrote:

 

"Menon, L.R., McIlroy, D., & Brasier, M.D. (2016)

‘Intrites’ from the Ediacaran Longmyndian Supergroup, UK: a new

form of microbially-induced sedimentary structure (MISS).

Geological Society, London, Special Publications, 448, (ahead-of-

print publication)"

 

The PDF file of this paper is available at:

https://www.researchgate.net/publication/307907308_Intrites_from_the_Ediacaran_Longmyndian_Supergroup_UK_a_new_form_of_MISS

 

Yours,

 

Paul H.

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Nice specimen, where did you get that one? I have a smaller piece of the same taxon (supposedly, but the 'bumps' don't look quite the same as yours) from the same location. They're rather expensive on 'The Auction Site'.

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45 minutes ago, Wrangellian said:

Nice specimen, where did you get that one? I have a smaller piece of the same taxon (supposedly, but the 'bumps' don't look quite the same as yours) from the same location. They're rather expensive on 'The Auction Site'.

 

Thanks, Wrangellian. I got mine from Indiana9. They've got different sized pieces for different prices.

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17 hours ago, Wrangellian said:

Ah.. I haven't noticed them on ebay, but I found their website.

Yes, that's where I got it. I don't know if they're on the auction sites.

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I thought they were at one time (I don't recall getting my piece thru their website)

You got a good one, even compared to those ones they have now.

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Genus: Intrites

Species: I. punctatus Fedonkin, 1980

Lower Neoproterozic, Upper Ediacaran, (566 ± 2.9 - 555.9 ± 3.5  Ma) (Compston et al., 2002)

Upper Burway Formation, Stretton Group, Longmyndian Supergroup, Ratlinghope, Nr. Church Stretton, Shropshire, England.

‘The Longmyndian Supergroup has been deformed into a tight NNE-SSW trending syncline. Fault patterns and strain markers within the Longmyndian indicate that it was deformed during sinistral transpression. The adjacent Pontesford-Linley and Church Stretton fault systems are considered to be major strike-slip fault systems which were initiated at about the same time as the deformation of the Longmyndian Supergroup. Strike-slip movements along these fault systems resulted in the juxtaposition of the Uriconian Volcanic Complex with the Longmyndian Supergroup’ (Pauley, 1990).

Liu (2011) states that ‘the Longmyndian Supergroup, outcropping on the eastern flanks of the Long Mynd, Shropshire, is dated at ~567–555 Ma.’

 

 ‘The base of the Burway Formation is taken at the base of the rhyolitic tuffs of the Buxton rock member. The Burway Formation shows a coarsening upward trend from thin to thick bedded turbidite lobe facies followed by shallow marine mudstones and deltaic sandstones.The Cardingmill grit at the top is interpreted as fluvial deposit’ (Mcilroy and Horak in Brenchley, 2006.)

 

‘The Longmyndian Supergroup of Shropshire, England, has been interpreted as an expanded Ediacaran siliciclastic succession, ranging from marine deltaic to alluvial plain or fluvial palaeoenvironments. No large Ediacaran frondose macrofossils are known, although an array of unusual bedding plane markings… have been described’ (Callow and Brasier, 2009).

 

‘The Iapetus Oceon (proto-Atlantic) was well-established and widening by late-Precambrian times, and Shropshire lay on its “south eastern” margin, perhaps a few hundred kms within the continental mass. The Uriconian volcanics represented continental “Andean type” vulcanicity on the continental side of a subduction zone established near Anglesey which caused late Precambian metamorphism in that area. The subduction zone was inclined south-east under Shropshire and vulcanicity initiated within the continental mass. The Pontesford-Linley Church Stretton fault system were initiated at this time parallel to the subduction zone, and subsidence between these two faults led to the formation of a shallow marine trough in which the Longmyndian was deposited. All the Longmyndian sediments suggest a shallow water environment, with dying bursts of Uriconian-type vulcanity in the east’ (Toghill and Chell, 1984).

 

Intrites punctatus was first described as a trace fossil by Fedonkin (1980) from the Valdai Series of Vendian age on the shores of the White Sea in northern Russia.

 

The Ediacaran bioto are often divided into three assembleges, the oldest being the Avalon assemblage (the original is in Newfoundland.) The Stretton Group contains Avalon-type fossils.

 

According to McIlroy, Crimes and Pauley (2005), the majority of fossils in the Longmyndian Supergroup are to be found in the transitional Burway, Synalds and Lightspout Formations. These three formations document a shift from very shallow nearshore, possibly deltaic, deposits through to alluvial and fluvial sedimentation.

 

They offer this description of I. punctatus: ‘Numerous specimens preserved mainly in positive hyporelief and negative epirelief, occasionally in positive epirelief and negative hyporelief. The fossil thus consists of a circular protrusion with a shallow, well-defined, circular central depression only 1–7 mm diameter and with height always less than diameter. The central depression is typically a fraction of a millimetre in diameter but may be up to 2 mm. In negative hyporelief the trace comprises a circular moatlike depression several millimetres in diameter with a central protuberance up to 1 mmin diameter. None of the fossils bear any ornament and they commonly occur in profusion.’

 

Intrites punctatus is shaped like a doughnut 10 to 15 mm in diameter having a raised central pyritized core less than 3 mm in diameter. In the words of Shen et al (2007) it ‘consists of serially arranged segments,… the segments are circular to subcircular rings. It is possible that the segments of Intrites punctatus were originally tablet-shaped. Their circular to subcircular shape may have resulted from oblique to flat compression of disarticulated and deflated segments. Thus, lntrites punctatus may also be related to Palaeopascichnus [delicatus]’.

 

Fedonkin, Gehling, Grey, Narbonne and Vickers-Rich (2007) note that I. punctatus consists of ‘individuals of circular shape, with a wavy surface with a depression in the middle, preserved on the sole of bed; represent forms that were cyndralical in shape and slightly titled in orientation; diameter ranges from 1 to 5mm with smaller forms predominating; height ranges from 1 to 2mm and diameter of central depression is 0.5[mm]’.

 

According to Menon, McIlroy and Brasier (2016), ‘Intrites punctatus Fedonkin, are found on both the bed tops and soles. They vary in morphology from mounds with central depressions to incomplete rings and pairs of short ridges. Examination of the purported Intrites documented from the Longmyndian in cross-section revealed a torus-shaped structure bounded by microbial mat layers and commonly containing white laminae. We interpret the ‘Longmyndian Intrites’ as a product of microbial trapping, sediment binding and authigenic clay mineral and carbonate precipitation on the flanks of small sediment volcanoes. Subsidence of the ring-like structure into muddy sediments resulted in a torus-shaped microstromatolite.  Preferential stromatolitic growth parallel to the prevailing current produced the observed partial rings or parallel ridges and explains their preferential orientation as current alignment. This interpretation of ‘Longmyndian Intrites’ expands the known variety of microbially-induced sedimentary structures (MISS) and emphasizes the importance of considering microbially-induced structures and abiological processes when interpreting discoidal impressions in ancient rocks.’

 

In 1856, the Geological Survey palaeontologist John William Salter suggested that the Longmyndian discoidal impressions may have been caused by raindrops. He also observed the presence of some presumed trace fossils, as well as ‘sun-cracks’ and surf-ripples’.

 

Kindle (1916) thought that they represented bubbles produced by the degassing of fresh sediment. Spricer (1904) noted that the bubbles (if that is what they were) may have resulted from the decay of organic matter. Gas generated by microbial activity was suggested as another possible abiogenetic cause.

 

However, ‘the absence of sedimentary deformation beneath these same discoidal impressions…, and substantial morphological disparity throughout the assemblage, would argue against a gas escape explanation’ (Liu. 2011).

Intrites may represent the earliest coelenterate (possibly cnidarian) resting place (Lipps and Signor, 1992,) a protistan organism (Schopf and Klein, 1992), or a small medsua (its lack of concentric 'growth rings' in the main body and its prominent median pore is characteristic of other Cyclomedusa species.)

Gehling, Nabonne and Anderson (2003) wrote that ‘the serial sets of curved sausage-shaped and bead-like elements in close contact, known variously as Palaeopascichnus, Intrites, Yelovichnus and Neonereites renarius are common on many of the beds where Aspidella is concentrated… The interpretation of these serial forms as trace fossils is not consistent with the branching arrangement observed in many examples, or the ring-like collapse of elements found in these taxa. The biological affnities of Palaeopascichnus, Intrites and Yelovichnus are likely to be with body fossils of organisms that grew on the substrate. It is unclear whether they are bacterial colonies, algae, egg masses or even serially arranged budding specimens of Aspidella.’

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