PZ Myers. 2004 Aug 27. Ediacaran fossils from Newfoundland. <http://pharyngula.org/index/weblog/ediacaran_fossils_from_newfoundland/>. Accessed 2008 Dec 01.

Posted on M00o93H7pQ09L8X1t49cHY01Z5j4TT91fGfr on Friday, August 27, 2004

Ediacaran fossils from Newfoundland

I told you I liked fossils, and here are some more that put yesterday's Junggarsuchus to shame in both age and weirdness. Everyone has heard of the Cambrian 'explosion', but there are also collections of pre-Cambrian fossil animals that have always been rather enigmatic—they just don't seem to correspond well to the morphology of Cambrian, or modern, forms.

Some new specimens from the pre-Cambrian have been described in a paper titled, "Modular construction of early Ediacaran complex life forms." They have been collected from 560 million year old rocks in Newfoundland, Canada. The focus of the paper is on patterns of organization: as the title says, these organisms appear to be modular in form, but it isn't the segmental modularity we see today. Instead, these pre-Cambrian animals were built on a fractal branching plan, repeated iterations of a structure called the "rangeomorph frondlet". The result was a creature that looked feathery or fern-like, and when described, it's hard to avoid using terms we usually associate with plants, like "stalk" and "leaf-like". But don't be confused, these are not plants, nor are they anything like modern animals, such as sea-pens, which have also adopted this kind of morphology.

All taxa at the new Spaniard's Bay locality, and most of the 20 to 30 other taxa of the Mistaken Point assemblage elsewhere, are composed of varying constructions of the same architectural building block—a centimeter-scale module herein termed a "rangeomorph frondlet". Each frondlet consists of inflated, self-similar branches that are indistinguishable from the "fractal pneus" defined by Seilacher. Pneus pass from the midline at an acute angle in an alternate pattern, but variable orientations of rangeomorph frondlets can give the appearance of asymmetric branch lengths or even branching on only one side of the frondlet. The pattern of branching is remarkably self-similar over three orders of fracticality: Major branches with diameters ranging from 1 to 5 mm are composed of minor branches 0.3 to 0.6 mm in diameter, which, in the best preserved specimens, appear to be composed of tertiary branches <150 µm in diameter.

Here's what a rangeomorph frondlet looks like:

Rangeomorph architecture from the Trepassey Formation at Spaniard's Bay. (A) Isolated rangeomorph frondlet. Specimen whitened with ammonium chloride. (B) Enlarged view of the area indicated in (A), showing details of the fractal-like branching pattern. The smallest branches are indicated by the arrow. (C) Plumose rangeomorph. Latex mold whitened with ammonium chloride. (D) Enlarged view of the area indicated in (C), showing details of the fractal-like branching pattern and the cylindrical cross section of the branches in the ripped and partially overturned frondlet in the upper left. Scale bars, 0.25 cm [(A) and (B)], 0.5 cm [(C) and (D)].

And here are some examples of the kinds of creatures made up of these frondlets:

Rangeomorph constructions from the Trepassey Formation at Spaniard's Bay (upper panels) and from the Mistaken Point Formation at Mistaken Point (lower panels). All specimens are latex molds whitened with ammonium chloride. (A) Long-stemmed rangeomorph frond with leaf composed of overlapping rangeomorph frondlets attached at their bases to the central stalk. Elements are partially deflated. (B) Short-stemmed rangeomorph frond with leaf composed of pendant rangeomorph frondlets hanging from a thin central stalk with side struts. (C) Enlarged view of the area indicated in (B). (D) Charnia-like frond with quilted array of major and minor branches overlying an internal organic skeleton. (E) Bush-shaped rangeomorph construction. (F) Spindle-shaped rangeomorph construction. Scale bars, 1 cm.

An accompanying review by Brasier and Antcliffe tries to give a bit more perspective on the Ediacaran fauna as a whole. As you can see from this diagram, the animals of the Ediacara had an almost 40 million year reign, during which they were the biggest, most complex forms on the planet.

Distribution of Ediacaran fossil forms in the prelude to the Cambrian explosion of animal life. New discoveries from the Trepassey Formation in southeastern Newfoundland (3) are shown alongside taxa that share the unique features of rangeomorph frondlets (3) and a Dickinsonia-like quilted pneu structure (10#12). The frondose Charnia may be an archetype from which other forms emerged through heterochronic evolution (4-6). (Bottom) A wide spectrum of Ediacaran fossil forms can be found clustered in the same geological bedding plane. Depicted are four such forms from the new fossil finds in Newfoundland, as well as fossil forms found in England,Russia,and Australia.Their intergrading morphologies may be related in one of three ways:through growth stages within the whole life cycle (ontogeny),ecologically controlled phenotypes, or sister taxa that have evolved by suppressing or expanding different parts of the life cycle (heterochrony).The basal segments of Charnia grandisare reconstructed to show up to four levels of inferred "fractal" quilting.The fossils are shown at a comparable scale except the rangeomorph frondlet [Inset (E), 4 cm long].

The review makes another interesting point: that we may be able to better understand the evolution of the Ediacaran fauna, given enough samples, by taking a developmental approach and analyzing life cycles. The bottom part of the diagram illustrates that point. Some of the different forms may represent different stages in the life history of the organisms. At the same time, evolution often works by shifting the timing of development, a process called heterochrony, so as you look at different fossils over long periods of geological time, you may also be seeing shifts in form that are consequences of shifts in development. The authors presented no data on this idea (which is unfortunate, and a little odd), but I agree that the evo-devo approach is a promising one.

The Narbonne paper summarizes what we do know right now about the pre-Cambrian biota.

The morphologic features described above provide strong support for the view that rangeomorphs represent a single clade, a high-level taxon that went extinct in the terminal Proterozoic. It is probable that the Ediacara biota included stem groups for the Cambrian explosion of animals, but there are no obvious analogs for rangeomorph architecture and construction among modern taxa. Recent comparison of rangeomorph structure with the radial canals of fossil and recent ctenophores seems remote from a morphological standpoint and is also inconsistent with the internal organic skeletons documented above. It would be tempting to regard the two-dimensional view of a rangeomorph frondlet as representing the bases of an array of open tubes that housed polyps or other filter-feeding organisms, but this is not consistent with partially overturned specimens that show that both sides are identical; the very small diameter of the secondary (300 to 600 µm) and tertiary (<150 µm) pneus would also specifically rule out cnidarian polyps as the originators of the tubes.
These modular constructions effectively partitioned food resources: Spindle-shaped rangeomorph recliners lay on the sea floor, whereas bush-, plume-, comb-, and frond-shaped rangeomorphs were elevated above the sea floor and fed from different levels within the water column. Rangeomorphs dominated the earliest Ediacaran ecosystems, with no evidence for burrowing, mobile, or metameric megascopic organisms among the taxa of the Mistaken Point assemblage. Rangeomorphs occur only sporadically in younger Ediacaran assemblages, perhaps as a result of competition with early animals, and have not been reported from any Phanerozoic assemblage including fossil Lagerstätten such as the Burgess Shale. It is difficult to relate rangeomorphs to any modern group of macroscopic organisms, and they appear to represent a "forgotten" architecture and construction that characterized early stages in the terminal Neoproterozoic evolution of complex multicellular life.

Brasier M, Antcliffe J (2004) Decoding the Ediacaran enigma. Science 305:1115-1117.

Narbonne, GM (2004) Modular construction of early Ediacaran complex life forms. Science 305:1141-1144.

1. Fascinating. Aliens and artificial life with fractal anatomies seem be popular in science fiction these days (e.g. the multipliers in Ken Macleod's Engine City, and the inhibitors in Alastair Reynold's Redemption Ark. It's great to see real organisms with similar architecture.
   #: Posted by  on  08/27  at  07:09 AM
2. Yeah but they're still only rangomorphs. It's not like you have fossils of rangomorphs turning into whales which is what the failed religion of Darwinism would have it's cult members believe. So God wins again!
   
   Speaking of rangomorphs, did anyone ever answer Grllvng4god's formal challenge "So, how does evolution expalin the Carribean Explosion?"
   
   No I think not! Hmmmm...could it be because you hell bound practictioners of a false atheist faith have no answer? Furthermore if the universe all came from a spinning dot hen there's no way planets like triton could orbit the sun backwards, it's a simple law spinning...things.
   #: Posted by  on  08/27  at  07:45 AM
3. How breathtakingly beautiful. There just is nothing more to say although I'm glad that others do have much to tell us about them but for sheer looking and appreciating these are glorious to behold. And what a great new term "rangeomorph frondlet." Thanks for the comments about the research and findings as well as the photographs and diagram. Darwin had it right as usual: there is grandeur in this view of life.
   #: Posted by  on  08/27  at  12:13 PM