The petalonamids (Petalonamae) are an extinct group of archaic

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s typical of the

Ediacaran biota The Ediacaran (; formerly Vendian) biota is a Taxonomy (biology), taxonomic period classification that consists of all life forms that were present on Earth during the Ediacaran Period (). These were composed of enigmatic tubular and frond-sh ...

, also called frondomorphs, dating from approximately 635 million years ago to 516 million years ago. They are

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

and motionless animals, that have the shape of leaves,

frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...

s (frondomorphic), feathers or spindles and were initially considered

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

octocorals Octocorallia (also known as Alcyonaria) is a class of Anthozoa comprising around 3,000 species of water-based organisms formed of colonial polyps with 8-fold symmetry. It includes the blue coral, soft corals, sea pens, and gorgonians (sea fan ...

sea pens Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; 35 extant genera, and it is estimated that of 450 described species, around 200 are valid. Sea pens have a cosm ...

. It is now believed that there are no living descendants of the group, which shares a probable relation to the

Ediacaran The Ediacaran Period ( ) is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and th ...

animals known as Vendozoans. It is considered that the organisms were fluffy at least in appearance, as if "inflatable." They are particularly difficult to classify phylogenetically. Lacking mouths, intestines, reproductive organs, and with no preserved evidence of internal structures, these organisms' existence is very strange by current standards. The most widely accepted hypothesis is that they could suck nutrients from the water around them by

osmosis Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region of ...

. The fronds were composed of branched, tubular structures, and the organism was anchored to the ground by a bulbous structure. The symmetry is generally

bilateral Bilateral may refer to any concept including two sides, in particular: * Bilateria, bilateral animals *Bilateralism, the political and cultural relations between two states *Bilateral, occurring on both sides of an organism ( Anatomical terms of ...

, like a feather with one axis and two sides. It can also be trilateral, with one axis and three sides, as seen in the most basal ones, the

erniettomorph The Erniettomorphs are a form of Ediacaran fossil consisting of rows of airbed-like tubes arranged along a midline with a glide symmetry. Representative genera include '' Ernietta'', '' Phyllozoon'', ''Pteridinium'', ''Swartpuntia''. Undisputed ...

Distribution

Ediacaran of

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

and

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

Phylogeny

References

Notes

Hoyal Cuthill, Jennifer F.; Han, Jian; Álvaro, Javier. Cambrian petalonamid Stromatoveris phylogenetically links Ediacaran biota to later animals. Palaeontology 2018 11.MARTINSSON, ANDERS. Keys to German palaeontological and stratigraphical terminology. Lethaia October 1978.BOOK REVIEW. Integrative Zoology 2008 12.Glaessner, M.F.; Walter, M.R.. New Precambrian fossils from the Arumbera Sandstone, Northern Territory, Australia. Alcheringa: An Australasian Journal of Palaeontology 1975 01.Grazhdankin, Dmitriy. Patterns of Evolution of the Ediacaran Soft-Bodied Biota. Journal of Paleontology 2014 03.
Animal taxa Ediacaran life Petalonamae {{Ediacaran-stub

Distribution

Phylogeny

See also

References

Notes