It’s All About That Base

Meghan TrainorNo, not the bass that Meghan Trainor’s been singing about so infectiously all summer. It’s all about the base of the animal tree of life. This month’s science news is full of stories from the deep past, which means we know a bit more about the murky ancient world of jellies.

560 million year old fossil showing lines of muscle fibers
560 million year old fossil showing lines of muscle fibers

A group of researchers from the University of Cambridge discovered a 560 million year old fossil in a cave Newfoundland, Canada. Like the few known fossils from that time, it’s soft bodied. Unlike any other fossil of that age, parallel rows run through the stone like rake-lines in the sand. These are the oldest muscles we’ve ever found: they predate the previous record-holder by 100 million years. And we are pretty sure they belonged to a type of jellyfish.

Scientists named the brawny creature Haootia quadriformis. Haoot comes from the language of the indigenous people of Newfoundland meaning demon, “for the striking appearance” of the fossil. Quadriformis is for its four-part symmetry, a feature shared with today’s jellies and corals.

A living staurozoan looks a lot like the artist's reconstruction of Haootia. Scale bar, 10 mm.
A living staurozoan looks a lot like the artist’s reconstruction of Haootia. Scale bar, 10 mm.

The animal has other features that recommend it to the jelly family too. It has no pores or spicules like sponges. It has no comb rows like comb jellies. The shape of its muscles looks like a well-studied parasitic jellyfish. Its tentacles branch the way cube jelly tentacles do.

But mostly, its overall shape looks a lot like a poorly-studied group of jellies called staurozoa that live upside down— wine glass-like—and attached to a stalk. There are about 50 known species and for decades everyone thought they favored cold waters close to the coast. But in 1998, during deep-sea submersible dives to hydrothermal vents in the Pacific Ocean, scientists discovered entire ecosystems where fields of staurozoa flourish.

Screen Shot 2014-09-29 at 8.51.06 AM
Staurozoa wave in the currents deep below the surface. From Lutz et al. Deep-Sea Research II 45 (1998) 329—334









Serendipitously, staurozoa weren’t the only stalked jelly-like creature making headlines this month. Researchers from the Natural History Museum in Copenhagen published a paper describing fifteen “little, funny mushroom-shaped animals” that they scraped from the ocean floor about a kilometer below the Tasman Sea. What’s astonishing is that the creatures don’t fit into any known animal group.

All of the Dendrogramma collected. D. enigmatica and (with *) D. discoides. doi:10.1371/journal.pone.0102976.g001
Two species of Dendrogramma were collected. D. enigmatic have a notched top not seen in D. discoids (marked with a star). doi:10.1371/journal.pone.0102976.g001

The animals, which look like chanterelles, share a number of features with both jellyfish and comb jellies, except they don’t seem to be one or the other. Like jellies and comb jellies, they have a single mouth/anus that leads to a gut and they have a layer of gelatinous material between their inner and outer cell layers. But they don’t have any stinging cells like jellies or comb rows like comb jellies. And while they have muscles, they can’t swim. DNA analysis could help sort things out, but the way that the animals were preserved might have degraded the DNA too much to use.

Scientists not connected with the study suggested that the creatures may be an entirely new kind of prehistoric animal, deserving of their own phylum. The authors of the paper concur, but are hesitant to draw such a weighty conclusion.

The researchers have given the creatures the name Dendrogramma, because the branching pattern of the guts looks like a dendrogram, the trees used to show evolutionary relationships among animals. The name is apt. Their position on the tree of life is highly in question, and it could change the way we think about where animals came from.

The cool thing about the Dendrogramma discovery is that it’s all about that base. Recent genetic studies on comb jellies, also called Ctenophora, mean that their relationship to all other animals might be shifting. And that affects Dendrogramma too because Dendrogramma seems to be related to both jellies and comb jellies. Dendrogramma could be a recent offshoot of the jellies and the comb jellies. Or, tantalizingly, Dendrogramma could be related to all of us through the most ancient animal of all.

Dendrogramma could fit any number of places along the base of the animal tree of life. doi:10.1371/journal.pone.0102976.g008
Dendrogramma could fit any number of places along the base of the animal tree of life. doi:10.1371/journal.pone.0102976.g008

Leave a Comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.