Dinomischus

{{Automatic taxobox

| image = USNM PAL 198735 Dinomischus isolatus.jpg

| image_caption = The holotype of Dinomischus isolatus collected by Walcott

| fossil_range = {{fossil range|Chengjiang|Burgess Shale}}

| taxon = Dinomischus

| authority = Conway Morris, 1977

| type_species = {{extinct}}Dinomischus isolatus

| type_species_authority = Conway Morris, 1977

| subdivision_ranks = Other species

| subdivision = {{extinct}}D. venustus Peng et al., 2006

}}

Dinomischus is an extinct genus of stalked filter-feeding animals within the Cambrian period, with specimens known from the Burgess Shale and the Maotianshan Shales. While long of uncertain affinities, recent studies have suggested it to be a stem-group ctenophore.

History of study

In his pioneering excavations of the Burgess Shale, Charles Doolittle Walcott excavated the first, and at the time only, specimen. It had evidently caught his eye, for he had taken the trouble to carefully photograph it—but he never found the time to describe the organism, and it was not until 1977 that Simon Conway Morris described the animal. He tracked down two further specimens, collected by further expeditions by teams from Harvard and the Royal Ontario Museum, allowing him to produce a reconstruction.{{cite journal

| author = Conway Morris, S.

| year = 1977

| title = A new entoproct-like organism from the Burgess Shale of British Columbia

| url = http://cdn.palass.org/publications/palaeontology/volume_20/pdf/vol20_part4_pp833-845.pdf

| journal = Palaeontology

| volume = 20 |issue=4 | pages = 833–845

| author-link = Simon Conway Morris

}}

Description

File:Dinomischus environnement.jpg

Dinomischus isolatus reached 20 mm in height,

{{cite book

|author=Hou, X.-G.

|year=2004

|title=The Cambrian Fossils of Chengjiang, China : The Flowering of Early Animal Life

|publisher=Blackwell Publishing

|isbn=978-1-4051-0673-3

}} was attached to the sea floor by a stalk, and looked loosely like a flower. The cup-shaped body at the top of the stalk probably fed by filtering the surrounding seawater, and may have created a current to facilitate this.

{{cite web

|url=http://park.org/Canada/Museum/burgessshale/misc1-3.html

|title=Dinomischus isolatus

|publisher=Hooper Virtual Paleontological Museum

}} Its mouth and anus sat next to one another. Conway Morris was not able to say much about the organism. It consisted of a calyx (or body) on a long, thin stalk, surrounded by a whorl of 18 short "petals", which enclosed both openings of its U-shaped gut. The presence of this gut identified it as a metazoan, and the stem implied that it lived permanently attached to the sea floor by a small holdfast. The twenty or so "petals" borne by each organism were solid, plate-like structures, about two thirds the length of the calyx. It is speculated that they may have been covered with cilia—fine hairs—which would have wafted food down towards the organism's mouth.

Distribution

Further specimens have since been produced by similarly spectacular fossil sites in China. 13 have been found in the Chengjiang, then in 2006 one specimen was identified within the Kaili Formation.

{{cite journal

|author1=Peng, J. |author2=Zhao, Y. |author3=Lin, J.-P. | title = Dinomischus from the Middle Cambrian Kaili Biota, Guizhou, China

| url = http://www.cqvip.com/QK/86253X/2006004/22687085.html

| year = 2006

| journal = Acta Geologica Sinica

| volume = 80 | issue = 4 | pages = 498–501

}} These organisms merited the erection of a new species, D. venustus, as their corrugated "petals" possessed radial rays.

{{cite book

| author = Hagadorn, J.W.

| year = 2002

| chapter = Chengjiang: Early Record of the Cambrian Explosion

| chapter-url = https://books.google.com/books?id=pxlv0KbjfO4C&q=Dinomischus+venustus++Dinomischus+venustus+Chen,+Hou+%26+Lu,+1989

| publisher=Columbia University Press

| isbn =978-0-231-10255-1

}}

13 specimens of Dinomischus are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community.{{cite journal|last1=Caron |first1=Jean-Bernard|last2=Jackson |first2=Donald A.|title=Taphonomy of the Greater Phyllopod Bed community, Burgess Shale|journal=PALAIOS |volume=21 |issue=5 |pages=451–65|date=October 2006|doi=10.2110/palo.2003.P05-070R|jstor=20173022|bibcode=2006Palai..21..451C |s2cid=53646959 }}

Affinity

Dinomischus is not the only sessile, stalked organism from the Cambrian, but it has no obvious relatives in other genera. Siphusauctum gregarium (known as the "tulip animal") has been recovered from the Burgess Shale, but has a clearly different basic anatomy, with multiple openings at the base of the calyx, an anus at the top, and a large six-petaled internal organ interpreted as a filter-feeding device.{{Cite journal|last1=O'Brien|first1=Lorna J.|last2=Caron|first2=Jean-Bernard|date=2012-01-18|title=A New Stalked Filter-Feeder from the Middle Cambrian Burgess Shale, British Columbia, Canada|journal=PLOS ONE|language=en|volume=7|issue=1|pages=e29233|doi=10.1371/journal.pone.0029233|issn=1932-6203|pmc=3261148|pmid=22279532|bibcode=2012PLoSO...729233O |doi-access=free}} Dinomischus has also been likened to Eldonia and Velumbrella, although unlike Dinomischus these medusoid organisms have tentacles.{{Cite book |last=Dzik |first=Jerzy |title=The early evolution of Metazoa and the significance of problematic taxa |publisher=Clarendon Press |year=1991 |editor-last=Simonetta |editor-first=AM |location=Oxford |pages=47–56 |chapter=Is fossil evidence consistent with traditional views of the early metazoan phylogeny? |editor-last2=Conway Morris |editor-first2=S |chapter-url=https://www.paleo.pan.pl/people/Dzik/Publications/traditionalDzik.pdf}}

A number of affinities were considered, but on the basis of available evidence it didn't quite seem to fit into any extant phylum.

The most similar organisms were the much smaller entoprocts, but even these modern organisms are difficult to classify.

{{cite journal

| author = Lieberman, B.S.

| year = 2008

| title = The Cambrian radiation of bilaterians: Evolutionary origins and palaeontological emergence; earth history change and biotic factors

| journal = Palaeogeography, Palaeoclimatology, Palaeoecology

| volume = 258 | issue = 3 | pages = 180–188

| doi = 10.1016/j.palaeo.2007.05.021

| bibcode = 2008PPP...258..180L

}} The new data on D. venustus have added little to the debate; while a suggestion of echinoderm affinity has been floated,

{{cite journal

|author1=Chen, J.Y. |author2=Zhou, G.Q. | year = 1997

| title = Biology of the Chengjiang fauna

| journal = Bull. Natl. Mus. Nat. Sci.

| volume = 10 | pages = 11–105

}} no phyla are compellingly similar to the organism.

{{cite journal

| author = Conway Morris, S.

| year = 1987

| title = Cambrian enigmas

| journal = Geology Today

| volume = 3 | pages = 88–92

| doi = 10.1111/j.1365-2451.1987.tb00495.x

| issue = 3–4

| author-link = Simon Conway Morris

}} Other modern ideas, even if a little tenuous, include a suggestion that the organism may have been parasitic, dwelling on the carapaces of larger organisms.

{{cite journal

|author1=Bassett, M.G. |author2=Popov, L.E. |author3=Holmer, L.E. | year = 2004

| title = The Oldest-Known Metazoan Parasite?

| url = http://jpaleontol.geoscienceworld.org/cgi/reprint/78/6/1214.pdf

| journal = Journal of Paleontology

| volume = 78 | issue = 6 | pages = 1214–1216

| doi = 10.1666/0022-3360(2004)078<1214:TOMP>2.0.CO;2

|s2cid=86756106 | issn = 0022-3360

}}

In 2019, Dinomischus and other Cambrian forms were hypothesized to be stem-group ctenophores. This leads to the assertion that ctenophores evolved from immotile, suspensivorous forms, a lifestyle similar to that of polyps.{{Cite journal |last1=Zhao |first1=Yang |last2=Vinther |first2=Jakob |last3=Parry |first3=Luke A. |last4=Wei |first4=Fan |last5=Green |first5=Emily |last6=Pisani |first6=Davide |last7=Hou |first7=Xianguang |last8=Edgecombe |first8=Gregory D. |last9=Cong |first9=Peiyun |date=2019-04-01 |title=Cambrian Sessile, Suspension Feeding Stem-Group Ctenophores and Evolution of the Comb Jelly Body Plan |url=https://www.sciencedirect.com/science/article/pii/S0960982219302064 |journal=Current Biology |language=en |volume=29 |issue=7 |pages=1112–1125.e2 |doi=10.1016/j.cub.2019.02.036 |pmid=30905603 |s2cid=84844387 |issn=0960-9822|hdl=1983/40a6bcb8-a740-482c-a23c-7d563faea5c5 |hdl-access=free }} Cladogram after Zhao et al., 2019:

{{clade

|1={{clade sequential|Xianguangia|Daihua|Dinomischus|Siphusauctum|Galeactena|Crown Ctenophora}}

}}

A later study suggested that Dinomischus, Diahua and Xianguangia formed a clade, Dinomischidae, with Siphusauctum more closely related to modern ctenophores.{{Cite journal |last=Zhao |first=Yang |last2=Hou |first2=Xian-guang |last3=Cong |first3=Pei-yun |date=2023-01-01 |title=Tentacular nature of the ‘column’ of the Cambrian diploblastic Xianguangia sinica |url=https://www.zora.uzh.ch/id/eprint/234398/9/Tentacular_nature_of_the_column_of_the_Cambrian_diploblastic_Xianguangia_sinica.pdf |journal=Journal of Systematic Palaeontology |language=en |volume=21 |issue=1 |doi=10.1080/14772019.2023.2215787 |issn=1477-2019|doi-access=free }}

References

External links

{{Cite web|date=2011|title=Dinomischus isolatus|work=Burgess Shale Fossil Gallery|publisher=Virtual Museum of Canada|url=https://burgess-shale.rom.on.ca/fossils/dinomischus-isolatus/}}

Dinomischus

History of study

Description

Distribution

Affinity

See also

References

External links

Further reading