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Ediacaran Fossil Highlights Differences with Cambrian Animals

Tribrachidium (1).jpg

It looks like a three-armed spiral. What is it? It's one of those "enigmatic" organisms that lived before the Cambrian explosion. Named Tribrachidium (Latin for "three arms"), it's a member of the Ediacaran fauna. Not much is known about any of the Ediacarans, but since they lived some 10 million years before the Cambrian, evolutionists have been trying to link them up in some way with the complex animals that appeared later, as described in Stephen Meyer's book Darwin's Doubt.

A new theory about how Tribrachidium fed (yes, Ediacarans needed to eat) was published in the new open-access journal of the AAAS, Science Advances. The authors, Rahman et al., think it was a "suspension feeder," gathering nutrients passively from the water.

We show that the external morphology of Tribrachidium passively directs water flow toward the apex of the organism and generates low-velocity eddies above apical "pits." These patterns of fluid flow are inconsistent with osmotrophy and instead support the interpretation of Tribrachidium as a passive suspension feeder. This finding provides the oldest empirical evidence for suspension feeding at 555 to 550 Ma, ~10 million years before the Cambrian explosion, and demonstrates that Ediacaran organisms formed more complex ecosystems in the latest Precambrian, involving a larger number of ecological guilds, than currently appreciated. [Emphasis added.]

Live Science does a valiant job of trying to make this seem like a transitional form. Reporter Stephanie Pappas compares it to "modern suspension feeders" like "brittle stars, many crustaceans and bivalves," neglecting to mention the complex digestive systems, tissues, and organs of those Cambrian animals. Tribrachidium had "tentacle-like arms" and even had a purpose in life, she suggests:

Tribrachidium lived about 40 million years before the Cambrian explosion, when life on Earth expanded and diversified relatively rapidly. Scientists once thought Ediacaran organisms were very simple, Rahman told Live Science, but the new findings paint a more complex picture of this time period. It's possible that Tribrachidium even altered its environment.

But facts are stubborn things. "There's no evidence that Tribrachidium could move around," she admits. There's also no indication of specialized cells, tissues, and organs seen in real animal phyla, nor a body cavity. Neither is there evidence that this creature evolved into something else. As for symmetry, "humans have two-fold, or bilateral, symmetry, and starfish have five-fold symmetry," Pappas notes. "Nothing alive today has three-fold symmetry."

How complex is suspension feeding? In a section devoted to that question, "Complexity of Ediacaran shallow-marine ecosystems," Rahman and team try to turn these simple pillow-like hemispherical animals into engineers:

Ediacaran ecosystems are thought to have been relatively simple, comprising few unique modes of nutrient acquisition and characterized by limited biotic interactions between organisms [the "Garden of Ediacara"]. The "Cambrian explosion" is thus inferred to have been as much a behavioral and ecological revolution, including the appearance of predation, infaunal deposit feeding, and active filtering, as a rise in metazoan diversity and morphological disparity. Recent compilations restrict Ediacaran organisms' strategies for obtaining nutrients to osmotrophy, saprophagy, and surficial grazing, suggesting that these organisms constructed communities with limited trophic complexity and performed only restricted roles as "ecosystem engineers". Here, we provide quantitative and qualitative evidence to increase the number of known Ediacaran feeding modes to include suspension feeding, which performs a number of vital ecological roles in modern benthic marine ecosystems. This in turn suggests that Ediacaran ecosystems may have been more complex than previously appreciated and that Ediacaran organisms may have performed a role in engineering their environment by removing suspended organic matter from the water column in shallow-marine settings.

Through the use of models and simulations, they figured that the arms "altered ambient water flow to produce low-velocity circulation above extremely localized areas around the organism." It's a passive process. Tribrachidium didn't have to reach out and do anything. It just let slow-flowing water bring in tiny particles of food.

What's more instructive is the silence on key questions. There is no mention of evolution, transitional form, or phylogeny -- except in the need by evolutionists to find evidence for it:

However, ecological understanding of the complexity of Ediacaran ecosystems is likely constrained by limited paleobiological knowledge; the manner in which Ediacaran organisms reproduced, dispersed, or fed is [with rare exceptions] poorly understood. Inferring the feeding strategies of these enigmatic organisms has been particularly problematic because many Ediacaran organisms are characterized by body plans that are radically different from those of extant groups and hence lack any clear modern analogs. Nevertheless, establishing the feeding modes of Ediacaran organisms is critical to determining their phylogenetic affinities, the complexity of Ediacaran ecosystems, and the nature of bioavailable carbon in the water column. All of these topics are still debated and represent fundamental questions in Precambrian geobiology.

In short, Tribrachidium was a relatively simple organism -- possibly a colony of one-celled organisms -- sitting like a pillow on the ocean floor, passively collecting particles of organic material without benefit of a gut, articulated limbs, sense organs, or any of the other complex body parts of the Cambrian animals. Like the other Ediacarans, it appeared without ancestors, and died without descendants. RIP.

Image credit: Aleksey Nagovitsyn (Arkhangelsk Regional Museum) [GFDL or CC BY-SA 3.0], via Wikimedia Commons.