| Aysheaia Temporal range: | |
|---|---|
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| Aysheaia specimen number USNM 365608 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| (unranked): | Panarthropoda |
| Phylum: | † "Lobopodia" |
| Class: | † Xenusia |
| Order: | † Protonychophora |
| Family: | † Aysheaiidae Walcott, 1911 |
| Genus: | † Aysheaia Walcott, 1911 |
| Species: | †A. pedunculata |
| Binomial name | |
| †Aysheaia pedunculata Walcott, 1911 | |
Aysheaia is an extinct genus of soft-bodied lobopodian, known from the Middle Cambrian Burgess Shale of British Columbia, Canada
Aysheaia has ten body segments, each of which has a pair of spiked, annulate legs. The animal is segmented, and looks somewhat like a bloated caterpillar with a few spines added on — including six finger-like projections around the mouth and two grasping limbs on the "head". Each leg has a subterminal row of about six curved claws. [1] No jaw apparatus is evident. [2] A pair of legs marks the posterior end of the body, unlike in onychophorans where the anus projects posteriad; this may be an adaptation to the terrestrial habit. [2] [3]
Some specimens of Aysheaia have been found associated with sponges, though this does not provide direct evidence of diet. [4]
Aysheaia is a lobopodian, an extinct phylum of marine animals that are similar to modern terrestrial Onychophora (velvet worms). Notable differences are the lack of jaws and antennae, possible lack of visual organs, [5] and the terminal mouth. [2]
Aysheaia is known from fossils found in the middle Cambrian Burgess shale of British Columbia. [2] Similar taxa are known from the lower Cambrian Maotianshan shales of China. Other than the 20 specimens from the Greater Phyllopod bed, where they comprise 2% of the community, [6] only 19 specimens of A. pedunculata are known. A. prolata was described as a separate species from the similarly-aged Wheeler Shale Formation of Utah but in fact represents the frontal appendage of a Stanleycaris -like radiodont. [7]
Aysheaia was described by Walcott in his 1911 work on annelid worms; Walcott imagined that a head (not observed) was present to support a polychaete affinity. [1] His attention was soon drawn to the organism's resemblance to velvet worms, [1] which was supported by other early researchers (1920s-30s) who also recognized a similarity with the onychophora, [8] although because Aysheaia does not fall within the range of living onychophora, it has also been allocated to a phylum of its own. [9] Nevertheless, an Onychophoran affinity represented the common opinion until the fossil was redescribed in the late 1970s. [2]
In the 1970s, Whittington undertook a thorough redescription, [1] and associated Aysheaia with the tardigrade lineage concept promoted a couple of years earlier by Delle Cave and Simonetta, [10] [3] and first proposed in 1958. [11] Thus, his interpretation places Aysheaia in the stem group to Tardigrada + Onychophora, although the view at the time was that these two modern phyla represented a group within a polyphyletic Arthropoda. [1] A possible link to Xenusion was also brought up, although at this time the affinities of this group were unclear, and a link to the rangeomorphs had been proposed. [1]
The response to Whittington's redescription can be loosely classed into three camps: one school, predominantly Bergström, downplayed the similarities to the Onychophora and focussed on the Tardigrade interpretation; whereas others (after Simonetta and Delle Cave) recognized a group of lobopods containing Onychophora, Tardigrada, and Aysheaia (with features of both). [2] [3] Robison preferred to interpret Onychophora as the sister group to Arthropoda, and placed Aysheaia in the Onychophoran stem group in a taxon called Protonychophora (solely containing Aysheaia). These were differentiated from Euonychophora (the crown group) by the number of lobopod legs and claws, the unusual head appendages, the absence of eyes, jaws, antennae and slime glands, the morphology of the rear of the body, and the terminal mouth. [2]
Later work uncovered further material of Xenusion and relatives, particularly from the Chinese fossil deposits. In light of the cladistic revolution of the 1990s, Aysheaia and its relatives were recognized as early offshoots of the lineage leading to arthropods and onychophorans.
Looking from the opposite direction, Budd points out that there are no characters that exclude Aysheaia from the Arthropoda. [12] It may be premature to assign Aysheaia to the Onychophora over Arthropoda, as it lacks any distinctive features of the onychophoran crown group; rather, both Onychophora and Arthropoda may have arisen from animals resembling Aysheaia and its kin. [13] Budd sees Aysheaia-like organisms as representing a paraphyletic grade from which both modern onychophoran and arthropods evolved. [12] [14]
The genus name commemorates a mountain peak named "Ayesha" due north of the Wapta Glacier. This peak was originally named Aysha in the 1904 maps of the region, and was renamed Ayesha after the heroine of Rider Haggard's 1887 novel She . [15]
Lobopodians are members of the informal group Lobopodia, or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, marine worm-like fossil panarthropods such as Aysheaia and Hallucigenia.
Hallucigenia is a genus of lobopodian, known from Cambrian aged fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Lobopodians are a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose.
Opabinia regalis is an extinct, stem group arthropod found in the Middle Cambrian Burgess Shale Lagerstätte of British Columbia. Opabinia was a soft-bodied animal, measuring up to 7 cm in body length, and its segmented trunk had flaps along the sides and a fan-shaped tail. The head shows unusual features: five eyes, a mouth under the head and facing backwards, and a clawed proboscis that probably passed food to the mouth. Opabinia probably lived on the seafloor, using the proboscis to seek out small, soft food. Fewer than twenty good specimens have been described; 3 specimens of Opabinia are known from the Greater Phyllopod bed, where they constitute less than 0.1% of the community.
Marrella is an extinct genus of marrellomorph arthropod known from the Middle Cambrian of North America and Asia. It is the most common animal represented in the Burgess Shale of British Columbia, Canada, with tens of thousands of specimens collected. Much rarer remains are also known from deposits in China.
Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada and Onychophora. Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members (stem-group) of each extant panarthropod phylum are thought to have risen. However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well.
Dinocaridida is a proposed fossil taxon of basal arthropods that flourished in the Cambrian period with occasional Ordovician and Devonian records. Characterized by a pair of frontal appendages and series of body flaps, the name of Dinocaridids refers to the suggested role of some of these members as the largest marine predators of their time. Dinocaridids are occasionally referred to as the 'AOPK group' by some literatures, as the group compose of Radiodonta, Opabiniidae, and the "gilled lobopodians" Pambdelurion and Kerygmachelidae. It is most likely paraphyletic, with Kerygmachelidae and Pambdelurion more basal than the clade compose of Opabiniidae, Radiodonta and other arthropods.
Banffia is a genus of animals described from Middle Cambrian fossils. The genus commemorates Banff, Alberta, near where the first fossil specimens were discovered. Its placement in higher taxa is controversial. It is considered to be a member of the enigmatic phylum Vetulicolia.
Naraoia is a genus of small to average size marine arthropods within the family Naraoiidae, that lived from the early Cambrian to the late Silurian period. The species are characterized by a large alimentary system and sideways oriented antennas.
Pambdelurion is an extinct genus of panarthropod from the Cambrian aged Sirius Passet site in northern Greenland. Like the morphologically similar Kerygmachela from the same locality, Pambdelurion is thought to be closely related to arthropods, combining characteristics of "lobopodians" with those of primitive arthropods.
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.
Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. They may be referred to as radiodonts, radiodontans, radiodontids, anomalocarids, or anomalocaridids, although the last two originally refer to the family Anomalocarididae, which previously included all species of this order but is now restricted to only a few species. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and used for a variety of functions. Radiodonts included the earliest large predators known, but they also included sediment sifters and filter feeders. Some of the most famous species of radiodonts are the Cambrian taxa Anomalocaris canadensis, Hurdia victoria, Peytoia nathorsti, Titanokorys gainessii, Cambroraster falcatus and Amplectobelua symbrachiata, the Ordovician Aegirocassis benmoulai and the Devonian Schinderhannes bartelsi.
The fossils of the Burgess Shale, like the Burgess Shale itself, are fossils that formed around 505 million years ago in the mid-Cambrian period. They were discovered in Canada in 1886, and Charles Doolittle Walcott collected over 65,000 specimens in a series of field trips up to the alpine site from 1909 to 1924. After a period of neglect from the 1930s to the early 1960s, new excavations and re-examinations of Walcott's collection continue to reveal new species, and statistical analysis suggests that additional discoveries will continue for the foreseeable future. Stephen Jay Gould's 1989 book Wonderful Life describes the history of discovery up to the early 1980s, although his analysis of the implications for evolution has been contested.
The Phyllopod bed, designated by USNM locality number 35k, is the most famous fossil-bearing member of the Burgess Shale fossil Lagerstätte. It was quarried by Charles Walcott from 1911–1917, and was the source of 95% of the fossils he collected during this time; tens of thousands of soft-bodied fossils representing over 150 genera have been recovered from the Phyllopod bed alone.
Caryosyntrips ("nutcracker") is an extinct genus of stem-arthropod which known from Canada, United States and Spain during the middle Cambrian.
The Luolishaniidae or Luolishaniida are a group of Cambrian and Ordovician lobopodians with anterior 5 or 6 pairs of setiferous lobopods. Most luolishaniids also have posterior lobopods each with a hooked claws, and thorn-shaped sclerites arranged as three or more per trunk segment. The type genus is based on Luolishania longicruris Hou and Chen, 1989, from the Chengjiang Lagerstatte, South China. They are presumed to have been benthic suspension or filter feeders.
Tactopoda or Arthropodoidea is a proposed clade of protostome animals that includes the phyla Tardigrada and Euarthropoda, supported by various morphological observations. The cladogram below shows the relationships implied by this hypothesis.
Collinsovermis is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Burgess Shale in British Columbia, Canada. It is monotypic having only one species, Collinsovermis monstruosus. After its initial discovery in 1983, Desmond H. Collins popularised it as a unique animal and was subsequently dubbed "Collins' monster" for its unusual super armoured body. The formal scientific description and name were given in 2020.
Acinocricus is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Spence Shale of Utah, United States. As a monotypic genus, it has one species Acinocricus stichus. The only lobopodian discovered from the Spence Shale, it was described by Simon Conway Morris and Richard A. Robison in 1988. Owing to the original fragmentary fossils discovered since 1982, it was initially classified as an alga, but later realised to be an animal belonging to Cambrian fauna.
Hallucigeniidae is a family of extinct worms belonging to the group Lobopodia that originated during the Cambrian explosion. It is based on the species Hallucigenia sparsa, the fossil of which was discovered by Charles Doolittle Walcott in 1911 from the Burgess Shale of British Columbia. The name Hallucigenia was created by Simon Conway Morris in 1977, from which the family was erected after discoveries of other hallucigeniid worms from other parts of the world. Classification of these lobopods and their relatives are still controversial, and the family consists of at least four genera.
Carbotubulus is a genus of extinct worm belonging to the group Lobopodia and known from the Carboniferous Carbondale Formation of the Mazon Creek area in Illinois, US. A monotypic genus, it contains one species Carbotubulus waloszeki. It was discovered and described by Joachim T. Haug, Georg Mayer, Carolin Haug, and Derek E.G. Briggs in 2012. With an age of about 300 million years, it is the first long-legged lobopodian discovered after the period of Cambrian explosion.