Burgess shale type fauna
Encyclopedia
A number of assemblages bear fossil assemblages similar in character to that of the Burgess Shale
. While many are also preserved in a similar fashion to the Burgess Shale
, the term "Burgess Shale type fauna" covers assemblages based on taxonomic criteria only.
worms,
lobopods, arthropods and anomalocaridids. Assemblages are typically diverse, with the most famous localities each containing in the region of 150 described species.
The fauna of the Burgess Shale lived in the photic zone, as bottom-dwelling photosynthesisers are present in the assemblage.
Sirius Passet
is a lagerstätte
in Greenland
which was formed about 527 million years ago. Its most common fossils are arthropods, but there is only a handful of trilobite species. There are also very few species with hard (mineralized) parts: trilobites, hyoliths
, sponges, brachiopod
s, and no echinoderm
s or molluscs.
Halkieria
has features associated with more than one living phylum
, and is discussed below.
The strangest-looking animals from Sirius Passet are Pambdelurion
and Kerygmachela
. They are generally regarded as anomalocarids because they have long, soft, segmented bodies with a pair of broad fin-like flaps on most segments and a pair of segmented appendages at the rear
. The outer parts of the top surfaces of the flaps have grooved areas which are thought to have acted as gills. Under each flap there is a short, fleshy leg. This arrangement suggests the animals are related to biramous arthropods.
province. The most significant is the Maotianshan shale, a lagerstätte
which preserves soft tissues very well. The Chengjiang fauna date to between 525 million and 520 million years ago, about the middle of the early Cambrian epoch, a few million years after Sirius Passet and at least 10 million years earlier than the Burgess Shale
.
The Chengjiang sediments provide what are currently the oldest known chordates, the phylum to which all vertebrates belong. The 8 chordate species include Myllokunmingia
, possibly a very primitive agnathid (jawless fish) and Haikouichthys
, which may be related to lampreys. Yunnanozoon
may be the oldest known hemichordate (a phylum closely related to chordates).
Anomalocaris
was a mainly soft-bodied swimming predator which was gigantic for its time (up to 70 cm = 2¼ feet long; some later species were 3 times as long); the soft, segmented body had a pair of broad fin-like flaps along each side, except that the last 3 segments had a pair of “fans” arranged in a “V” shape. Unlike Kerygmachela and Pambdelurion (see above), Anomalocaris apparently had no legs, and the grooved patches which are thought to have acted as gills were at the bases of the flaps, or even overlapping on to its back. The two eyes were on relatively long horizontal stalks; the mouth lay under the head and was a round-cornered square of plates which could not close completely; and in front of the mouth were two jointed appendages which were shaped like a shrimp’s body, curved backwards and with short spines on the inside of the curve. Amplectobelua
, also found at Chengjiang, was similar, smaller than Anomalocaris but considerably larger than most other Chengjiang animals. Both are thought to have been powerful predators.
Hallucigenia
looks like a long-legged caterpillar with spines on its back, and almost certainly crawled on the seabed.
Nearly half of the Chengjiang fossil species are arthropods, few of which had the hard, mineral-reinforced exoskeletons found in most later marine arthropods; only about 3% of the organisms known from Chengjiang have hard shells, and most of those are trilobites (although Misszhouia
is a soft-bodied trilobite). Many other phyla
are found there: Porifera (sponges) and Priapulida
(burrowing “worms” which were ambush predator
s), Brachiopoda (these had bivalve-like shells, but fed by means of a lophophore
, a fan-like filter which occupied about of half of the internal space), Chaetognatha
(arrow worms), Cnidaria
(jellyfish, sea anemones), Ctenophora (comb jellies), Echinodermata (starfish, sea urchins, etc.), Hyolitha (enigmatic animals with small conical shells), Nematomorpha
(horse hair worms, parasites which are typically about 1 m long and 1 mm to 3 mm in diameter), Phoronida (horseshoe worms which live in chitinous tubes and feed by means of a lophophore), and Protista (single-celled animals).
The Burgess Shale
was the first of the Cambrian lagerstätte
n to be discovered (by Walcott
in 1909), and the re-analysis of the Burgess Shale by Whittington
and others in the 1970s was the basis of Gould
’s book Wonderful Life
, which was largely responsible for non-scientists' awareness of the Cambrian explosion. The fossils date from the mid Cambrian, about 515 million years ago and 10 million years later than the Chengjiang fauna.
The shelled fossils in the Burgess Shale are similar in proportions to other shelly fossil deposits; however, they are a minor component of the biota, accounding for only 14% of the Burgess Shale fossils. When organisms that were not preserved are entered into the equation, the shelly fossils probably represent about 2% of the animals that were alive at the time.
Arthropods are the most abundant and diverse group of organisms in the Burgess Shale, followed closely by sponges. Many Burgess Shale fossils are unusual and difficult to classify, for example:
Pikaia
resembled the modern lancelet
, and was the earliest known chordate until the discovery of the fish-like Myllokunmingia
and Haikouichthys
among the Chengjiang fauna.
But the “weird wonders”, creatures that resembled nothing known in the 1970s, attracted the most publicity, for example:
of Utah,
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
. While many are also preserved in a similar fashion to the Burgess Shale
Burgess shale type preservation
The Burgess Shale of British Columbia is famous for its exceptional preservation of mid-Cambrian organisms. Around 40 other sites have been discovered of a similar age, with soft tissues preserved in a similar, though not identical, fashion...
, the term "Burgess Shale type fauna" covers assemblages based on taxonomic criteria only.
Extent
The fauna of the middle Cambrian has a cosmopolitan range. All assemblages preserving soft-part anatomy have a very similar fauna, even though they span almost every continent. The wide distribution has been attributed to the advent of pelagic larvae.Composition
The fauna is composed of a range of soft bodied organisms; creatures with hard, mineralised skeletons are rare, although trilobites are quite commonly found. The major soft-bodied groups are sponges, palaeoscolecidPalaeoscolecid
The palaeoscolecids are a group of ecdysozoan worms resembling armoured priapulids. They are known from the Lower Cambrian to the late Silurian; they are mainly found as disarticulated sclerites, but are also preserved in many of the Cambrian lagerstatten...
worms,
lobopods, arthropods and anomalocaridids. Assemblages are typically diverse, with the most famous localities each containing in the region of 150 described species.
The fauna of the Burgess Shale lived in the photic zone, as bottom-dwelling photosynthesisers are present in the assemblage.
Sirius Passet fauna
Sirius Passet
Sirius Passet is a Cambrian Lagerstätte in Greenland. The Sirius Passet Lagerstätte was named after the Sirius sledge patrol that operates in North Greenland. It comprises six localities located on the eastern shore of J.P. Koch Fjord in the far north of Greenland. It was discovered in 1984 by A....
is a lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
in Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...
which was formed about 527 million years ago. Its most common fossils are arthropods, but there is only a handful of trilobite species. There are also very few species with hard (mineralized) parts: trilobites, hyoliths
Hyolitha
Hyolitha are enigmatic animals with small conical shells known from the Palaeozoic Era.-Shell morphology:The calcareous shells have a cover and two curved supports known as helens. Most are one to four centimeters in length and are triangular or elliptical in cross section...
, sponges, brachiopod
Brachiopod
Brachiopods are a phylum of marine animals that have hard "valves" on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the front can be opened for feeding or closed for protection...
s, and no echinoderm
Echinoderm
Echinoderms are a phylum of marine animals. Echinoderms are found at every ocean depth, from the intertidal zone to the abyssal zone....
s or molluscs.
Halkieria
Halkieria
Halkieria is a genus of fossil organisms from the Lower to Middle Cambrian. It has been found on almost every continent in Lower to Mid Cambrian deposits, forming a large component of the small shelly fossil assemblages...
has features associated with more than one living phylum
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
, and is discussed below.
The strangest-looking animals from Sirius Passet are Pambdelurion
Pambdelurion whittingtoni
Pambdelurion whittingtoni was a blind nektonic organism from the Sirius Passet Lagerstätte, from Cambrian Greenland. Its anatomy strongly suggests that it, along with its relative Kerygmachela kierkegaardi, was either an anomalocarid or a close relative thereof.P...
and Kerygmachela
Kerygmachela kierkegaardi
Kerygmachela kierkegaardi was a blind nektonic organism from the Sirius Passet Lagerstätte, from Cambrian Greenland. Its anatomy strongly suggests that it, along with its relative Pambdelurion whittingtoni, was either an anomalocarid or a close relative thereof...
. They are generally regarded as anomalocarids because they have long, soft, segmented bodies with a pair of broad fin-like flaps on most segments and a pair of segmented appendages at the rear
Cercus
Cerci are paired appendages on the rear-most segments of many arthropods, including insects and arachnids but not crustaceans. Cerci often serve as sensory organs, but they may also be used as weapons or copulation aids, or they may simply be vestigial structures.Typical cerci may appear to be...
. The outer parts of the top surfaces of the flaps have grooved areas which are thought to have acted as gills. Under each flap there is a short, fleshy leg. This arrangement suggests the animals are related to biramous arthropods.
Chengjiang fauna
There are several Cambrian fossil sites in the Chengjiang county of China’s YunnanYunnan
Yunnan is a province of the People's Republic of China, located in the far southwest of the country spanning approximately and with a population of 45.7 million . The capital of the province is Kunming. The province borders Burma, Laos, and Vietnam.Yunnan is situated in a mountainous area, with...
province. The most significant is the Maotianshan shale, a lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
which preserves soft tissues very well. The Chengjiang fauna date to between 525 million and 520 million years ago, about the middle of the early Cambrian epoch, a few million years after Sirius Passet and at least 10 million years earlier than the Burgess Shale
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
.
The Chengjiang sediments provide what are currently the oldest known chordates, the phylum to which all vertebrates belong. The 8 chordate species include Myllokunmingia
Myllokunmingia
Myllokunmingia is a chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high....
, possibly a very primitive agnathid (jawless fish) and Haikouichthys
Haikouichthys
Haikouichthys is an extinct genus of craniate believed to have lived c. 530 million years ago, during the Cambrian explosion of multicellular life...
, which may be related to lampreys. Yunnanozoon
Yunnanozoon
Yunnanozoon lividum is a suspected a hemichordate or chordate from the Lower Cambrian, Chengjiang biota of Yunnan province, China....
may be the oldest known hemichordate (a phylum closely related to chordates).
Anomalocaris
Anomalocaris is an extinct genus of anomalocaridid, which are, in turn, thought to be closely related to the arthropods. The first fossils of Anomalocaris were discovered in the Ogygopsis Shale by Joseph Frederick Whiteaves, with more examples found by Charles Doolittle Walcott in the famed...
was a mainly soft-bodied swimming predator which was gigantic for its time (up to 70 cm = 2¼ feet long; some later species were 3 times as long); the soft, segmented body had a pair of broad fin-like flaps along each side, except that the last 3 segments had a pair of “fans” arranged in a “V” shape. Unlike Kerygmachela and Pambdelurion (see above), Anomalocaris apparently had no legs, and the grooved patches which are thought to have acted as gills were at the bases of the flaps, or even overlapping on to its back. The two eyes were on relatively long horizontal stalks; the mouth lay under the head and was a round-cornered square of plates which could not close completely; and in front of the mouth were two jointed appendages which were shaped like a shrimp’s body, curved backwards and with short spines on the inside of the curve. Amplectobelua
Amplectobelua
Amplectobelua is an extinct genus of anomalocaridid, a group of very early marine animals. While completely different from any animal alive today, some scientists do believe that the very primitive anomalocarids were in fact somewhat related to arthropods...
, also found at Chengjiang, was similar, smaller than Anomalocaris but considerably larger than most other Chengjiang animals. Both are thought to have been powerful predators.
Hallucigenia
Hallucigenia
Hallucigenia is an extinct genus of animal found as fossils in the Middle Cambrian-aged Burgess Shale formation of British Columbia, Canada, represented by the species H. sparsa, and in the Lower Cambrian Maotianshan shale of China, represented by the species H. fortis...
looks like a long-legged caterpillar with spines on its back, and almost certainly crawled on the seabed.
Nearly half of the Chengjiang fossil species are arthropods, few of which had the hard, mineral-reinforced exoskeletons found in most later marine arthropods; only about 3% of the organisms known from Chengjiang have hard shells, and most of those are trilobites (although Misszhouia
Misszhouia
Misszhouia longicaudata is a species of blind, trilobite-like arthropod from the Cambrian period. In 1984 a well-preserved fossil of Misszhouia was discovered in the Maotianshan Shale; this discovery brought the shale to scientific attention.M...
is a soft-bodied trilobite). Many other phyla
Phylum
In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....
are found there: Porifera (sponges) and Priapulida
Priapulida
Priapulida is a phylum of marine worms. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis...
(burrowing “worms” which were ambush predator
Ambush predator
Ambush predators or sit-and-wait predators are carnivorous animals that capture prey by stealth or cunning, not by speed or necessarily by strength. These organisms usually hide motionless and wait for prey to come within striking distance. They are often camouflaged, and may be solitary...
s), Brachiopoda (these had bivalve-like shells, but fed by means of a lophophore
Lophophore
The lophophore is a characteristic feeding organ possessed by four major groups of animals: the Brachiopoda, Bryozoa, Entoprocta, and Phoronida. All lophophores are found in aquatic organisms.-Characteristics:...
, a fan-like filter which occupied about of half of the internal space), Chaetognatha
Chaetognatha
Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, that is belonging to the lowest zone of the ocean, or benthic zone, and can attach to algae and...
(arrow worms), Cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
(jellyfish, sea anemones), Ctenophora (comb jellies), Echinodermata (starfish, sea urchins, etc.), Hyolitha (enigmatic animals with small conical shells), Nematomorpha
Nematomorpha
Nematomorpha is a phylum of parasitic animals that are superficially morphologically similar to nematode worms, hence the name. They range in size in most species from long and can reach in extreme cases up to 2 metres, and in diameter...
(horse hair worms, parasites which are typically about 1 m long and 1 mm to 3 mm in diameter), Phoronida (horseshoe worms which live in chitinous tubes and feed by means of a lophophore), and Protista (single-celled animals).
Burgess Shale
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
was the first of the Cambrian lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
n to be discovered (by Walcott
Charles Doolittle Walcott
Charles Doolittle Walcott was an American invertebrate paleontologist. He became known for his discovery in 1909 of well-preserved fossils in the Burgess Shale of British Columbia, Canada.-Early life:...
in 1909), and the re-analysis of the Burgess Shale by Whittington
Harry B. Whittington
Harry Blackmore Whittington FRS was a British paleontologist based at the Department of Earth Sciences, Cambridge, and was affiliated to Sidney Sussex College. He attended Handsworth Grammar School in Birmingham, followed by a degree and Ph.D in geology from the University of Birmingham...
and others in the 1970s was the basis of Gould
Stephen Jay Gould
Stephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
’s book Wonderful Life
Wonderful Life (book)
Wonderful Life: The Burgess Shale and the Nature of History is a book on the evolution of Cambrian fauna by Harvard paleontologist Stephen Jay Gould...
, which was largely responsible for non-scientists' awareness of the Cambrian explosion. The fossils date from the mid Cambrian, about 515 million years ago and 10 million years later than the Chengjiang fauna.
The shelled fossils in the Burgess Shale are similar in proportions to other shelly fossil deposits; however, they are a minor component of the biota, accounding for only 14% of the Burgess Shale fossils. When organisms that were not preserved are entered into the equation, the shelly fossils probably represent about 2% of the animals that were alive at the time.
Arthropods are the most abundant and diverse group of organisms in the Burgess Shale, followed closely by sponges. Many Burgess Shale fossils are unusual and difficult to classify, for example:
- Marrella is the most common fossil, but Whittington’s re-analysis showed that it belonged to none of the known marine arthropod groups (trilobites, crustaceans, chelicerateChelicerataThe subphylum Chelicerata constitutes one of the major subdivisions of the phylum Arthropoda, and includes horseshoe crabs, scorpions, spiders and mites...
s; well-known modern chelicerates include spiders and scorpions). - YohoiaYohoiaYohoia is a tiny, extinct animal from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. It has been placed among the arachnomorphs, a group of arthropods that includes the chelicerates and trilobites. Their sizes range from 7 to 23 mm...
was a tiny animal (7 mm to 23 mm long) with: a head shield; a slim, segmented body covered on top by armor plates; a paddle-like tail; 3 pairs of legs under the head shield; a single flap-like appendage fringed with setae (bristles) under each body segment, probably used for swimming and/or respirationRespiration (physiology)'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
; a pair of relatively large appendages at the front of the head shield, each with a pronounced “elbow” and ending in four long spines which may have functioned as “fingers”. Yohoia is assumed to been a mainly benthic (bottom-dwelling) creature that swam just above the ocean floor and used its appendages to scavenge or capture prey. It may be a member of the arachnomorphs, a group of arthropods that includes the chelicerates and trilobites. - NaraoiaNaraoiaNaraoia is a genus of trilobites found in Cambrian strata of the Burgess Shale and the Maotianshan shales Lagerstätte. They were flattened, oval-shaped animals, with an uncalcified shield that was divided into two regions, a smaller region covering the head, and a larger section covering the...
was a soft-bodied animal (no mineralized parts) which is classified as a trilobite because its appendages (legs, mouth-parts) are very similar. - WaptiaWaptiaWaptia fieldensis was a small, shrimp-like stem group crustacean. Many Cambrian crustaceomorphs such as Waptia lack the mouthparts to be classified as crown group crustaceans that lived during the Middle Cambrian about 510 million years ago...
, CanadaspisCanadaspisCanadaspis was a Cambrian genus of crustacean or euarthropod, a benthic feeder that moved mainly by walking and possibly used its biramous appendages to stir mud in search of food...
and PlenocarisPlenocarisPlenocaris plena is a crustacean-like arthropod with a bivalved carapace, and is known from the Burgess shale and Chengjiang. It probably lacked pleopods, but had uropods.-External links:* of Plenocaris fossil-Further reading:...
had bivalve-like carapaces. It is uncertain whether these animals are related or acquired bivalve-like carapaces by convergent evolutionConvergent evolutionConvergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...
.
Pikaia
Pikaia
Pikaia gracilens is an extinct animal known from the Middle Cambrian Burgess Shale of British Columbia. -Discovery:It was discovered by Charles Walcott and was first described by him in 1911. It was named after Pika Peak, a mountain in Alberta, Canada. Based on the obvious and regular segmentation...
resembled the modern lancelet
Lancelet
The lancelets , also known as amphioxus, are the modern representatives of the subphylum Cephalochordata, formerly thought to be the sister group of the craniates. They are usually found buried in sand in shallow parts of temperate or tropical seas. In Asia, they are harvested commercially as food...
, and was the earliest known chordate until the discovery of the fish-like Myllokunmingia
Myllokunmingia
Myllokunmingia is a chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high....
and Haikouichthys
Haikouichthys
Haikouichthys is an extinct genus of craniate believed to have lived c. 530 million years ago, during the Cambrian explosion of multicellular life...
among the Chengjiang fauna.
- Whittington’s first presentation about OpabiniaOpabiniaOpabinia is an animal genus found in Cambrian fossil deposits. Its sole species, Opabinia regalis, is known from the Middle Cambrian Burgess Shale of British Columbia, Canada. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed,...
made the audience laugh. The reconstruction showed a soft-bodied animal with: a slim, segmented body; a pair of flap-like appendages on each segment with gills above the flaps, except that the last 3 segments had no gills and the flaps formed a tail; five stalked eyes; a backward-facing mouth under the head; a long, flexible, hose-like proboscisProboscisA proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
which extended from under the front of the head and ended in a “claw” fringed with spines. Subsequent research has concluded that Opabinia is a lobopodLobopodiaLobopodia is a group of poorly understood animals, which mostly fall as a stem group of arthropods. Their fossil range dates back to the Early Cambrian. Lobopods are segmented and typically bear legs with hooked claws on their ends....
, closely related to the arthropods and possibly even closer to ancestors of the arthropods. - AnomalocarisAnomalocarisAnomalocaris is an extinct genus of anomalocaridid, which are, in turn, thought to be closely related to the arthropods. The first fossils of Anomalocaris were discovered in the Ogygopsis Shale by Joseph Frederick Whiteaves, with more examples found by Charles Doolittle Walcott in the famed...
and HallucigeniaHallucigeniaHallucigenia is an extinct genus of animal found as fossils in the Middle Cambrian-aged Burgess Shale formation of British Columbia, Canada, represented by the species H. sparsa, and in the Lower Cambrian Maotianshan shale of China, represented by the species H. fortis...
were first found in the Burgess Shale, but older specimens have been found in the Chengjiang fauna. They are now regarded as lobopodsLobopodiaLobopodia is a group of poorly understood animals, which mostly fall as a stem group of arthropods. Their fossil range dates back to the Early Cambrian. Lobopods are segmented and typically bear legs with hooked claws on their ends....
, and Anomalocaris is very similar to Opabinia in most respects (except the eyes and feeding mechanisms) – see above. - OdontogriphusOdontogriphusOdontogriphus is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as in length, Odontogriphus is a flat, oval bilaterian which apparently had a single muscular foot, and a "shell" on its back that was moderately rigid but of a material unsuited to...
is currently regarded as either a mollusc or a lophotrochozoaLophotrochozoaThe Lophotrochozoa are a major grouping of protostome animals. The taxon was discovered based on molecular data. Molecular evidence such as a result of studies of the evolution of small-subunit ribosomal RNA supports the monophyly of the phyla listed in the infobox shown at right.-Terminology:The...
n, i.e. fairly closely related to the ancestors of molluscs (see above).
Other fauna
Other fauna include the Middle Cambrian Wheeler Shale FormationWheeler Shale
The Wheeler Shale is a Cambrian fossil locality world famousfor prolific agnostid and Elrathia kingii trilobite remains...
of Utah,