Many people associate early organisms with the Cambrian Explosion. This event 542 million years ago brought about a massive expansion of life in the ocean. Often forgotten is the Precambrian, where both single and multicellular life began. In the late Precambrian, early forms of multicellular algae spread across the ocean, as well as other small, soft-bodied forms of life. In a Mongolian excavation that took place in 2015, paleontologists uncovered two new species of this multicellular algae from the Ediacaran period. These fossils give new information to paleontologists about how early life forms lived, but still leave other mysteries in the dark.
The Ediacaran Period ends directly before the Cambrian Period 542 Ma. Because the Cambrian Explosion resulted in such a massive diversification of life, fossils predating this event (and possibly explaining it) are highly sought after. Fossils predating the Cambrian Period should be transition phases for the advanced animals and other life forms that are seen during the Cambrian, yet all the fossils found are simplistic life forms that only show evolutionary expansion on multicellularity. Multicellularity is the presence of an organism that is made up of more than one cell. Many bacteria are single-celled organisms, while advanced organisms such as plants and animals can be made up of billions of cells or more. Ediacaran fossils are not only simplistic in form, but fairly rare to find. Both the Ediacaran and Cambrian rock layers are made up of Burgess Shale, and preservation methods for both sections are very similar, so it remains puzzling that there are so few fossils found in Ediacaran rock layers.
Paleontologists working for the University of Wisconsin-Milwaukee recently excavated several specimens of Ediacaran multicellular algae, adding two new species to the list of Ediacaran biota. These fossils appear as whispy scratch marks on slates of shale to the untrained eye, but are in fact an early form of seaweed. The species, named Chinggiskhannia bifurcata and Zuunartsphyton delicatum, were identified as two new forms of benthic algae. This type of algae, as well as benthic organisms in general, inhabit the lowest level in a water ecosystem. Benthic organisms (who live in the benthic zone) are found in the bottom layer of silt and many, such as corals and some types of seaweed, are permanently attached to the bottom.
C. bifurcata and Z. delicatum were found in a Burgess Shale formation called the Zuun-Arts Formation, which is part of the Zavkhan Province of western Mongolia. Before this discovery, many of the oldest Ediacaran fossil specimens had only dated back to 555 Ma. These new fossils were found just below the oldest fossil layer, and predate (just barely) the age of 555 million years. That alone makes these fossils extremely valuable to science, being some of the oldest multicellular algae ever found.
C. bifurcata is known from several specimens that were excavated in the Mongolian location, while Z. delicatum is only known from 3 specimens. C. bifurcata appears to have grown similarly to many extant seaweeds, in long strands that do not often branch off. It was found not to grow densely together, and the most dense specimen found had only four strands. Z. delicatum is the opposite of the former species, growing in dense shrub-like clumps that have many curling and branching filaments. Paleontologists assume that these fossil specimens reflect their density at the time they were preserved, meaning that C. bifurcata was much more common than its Z. delicatum counterpart. Benthic algae and other benthic organisms often depict an accurate state of the water quality at the time, given that they live in the area with the least amount of sunlight but the most nutrients (as well as pollutants that may enter the water system).
One thing that paleontologists were seeking out but did not find was definitive evidence of animal life in the Ediacaran period. The Ediacaran period is most famous for its strange trace fossils of a mysterious form of life referred to as the “Ediacara Biota,” not to be confused with normal biota such as algae that occurred during this time. This group of fossils is not plant, animal, or really anything that palaeontologists and scientists alike can put a name to. Many of these life forms have strange geometric shapes unlike any living or extinct animal previously described. They have previously been considered protozoans, algae, lichens, early forms of worms or even a separate kingdom of life that no longer exists. Either way, they certainly aren’t definitive evidence of animal life previous to the Cambrian.
One hypothesis to the mysterious lack of fossils is that there simply were not enough life forms around to be preserved. It is possible that no organisms existed that contained easily preserved structures, such as the presence of a cuticle (hard shell-like material) or bones. No definitive animals have been identified before the Cambrian, although many paleontologists suspect that they did in fact exist, as the jump in evolution from the Ediacaran to the Cambrian is too vast. The recent discoveries of the multicellular algae show evidence that life did indeed flourish before the Cambrian Explosion, and that delicate organisms can be preserved. More excavation and exploration is needed to discover new species to help answer these questions, and hopefully the Zuun-Arts Formation has more species in store
Great article! There are many examples of definitive animals in the Precambrian such as the biomineralizers Cloudina and Namacalathus. These animals can be found in the latest Precambrian but go extinct near the Cambrian boundary.
I suspect that one of the preservational limits is a change in ocean chemistry between Ediacaran & Cambrian (the three main Cambrian lagerstatten, & striking that there are as many as that, are all equatorial deposits). The existence of apparent predation marks on Cloudina suggests an ecosystem of predator/prey is there, but “invisible” because no lagerstatten class preservation level for soft parts. Phosphatization (which has preserved precambrian embryos) also has limit (only half a millimeter) meaning more cell growth beyond that size can’t get preserved, so can’t resolve what it is that is being preserved.