''Hurdia'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

hurdiid Hurdiidae (synonymous with the previously named Peytoiidae) is an extinct cosmopolitan distribution, cosmopolitan Family (biology), family of radiodonts, a group of Crown group#Stem groups, stem-group marine arthropods, which lived during the Pal ...

radiodont Radiodonta is an extinct order of stem-group arthropods that was successful worldwide during the Cambrian period. Radiodonts are distinguished by their distinctive frontal appendages, which are morphologically diverse and were used for a variety ...

that lived 505 million years ago during the

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

Period. Fossils have been found in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

, and the

Czech Republic The Czech Republic, also known as Czechia, and historically known as Bohemia, is a landlocked country in Central Europe. The country is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the south ...

Taxonomic history

''Hurdia'' was named in 1912 by Charles Walcott, with two species, the type species ''H. victoria'' and a referred species, ''H. triangulata''. The genus name refers to Mount Hurd. It is possible that Walcott had described a specimen the year prior as ''Amiella'', but the specimen is too fragmentary to identify with certainty, so ''Amiella'' is a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

''. Walcott's original specimens consisted only of H-elements of the frontal carapace, which he interpreted as being the carapace of an unidentified type of crustacean. P-elements of the carapace were described as a separate genus, ''Proboscicaris'', in 1962. In 1996, then-curator of the

Royal Ontario Museum The Royal Ontario Museum (ROM) is a museum of art, world culture and natural history in Toronto, Ontario, Canada. It is one of the largest museums in North America and the largest in Canada. It attracts more than one million visitors every year ...

Desmond H. Collins erected the taxon Radiodonta to encompass ''

Anomalocaris ''Anomalocaris'' (from Ancient Greek , meaning "unlike", and , meaning "shrimp", with the intended meaning "unlike other shrimp") is an extinct genus of radiodont, an order of early-diverging stem-group marine arthropods. It is best known fro ...

'' and its close relatives, and included both ''Hurdia'' and ''Proboscicaris'' in the group. He subsequently recognized that ''Proboscicaris'' and ''Hurdia'' were based on different parts of the same animal, and recognized that a specimen previously assigned to ''

Peytoia ''Peytoia'' is a genus of hurdiid radiodont, an early diverging order of stem-group arthropods, that lived in the Cambrian period, containing two species, ''Peytoia nathorsti'' from the Miaolingian of Canada and '' Peytoia infercambriensis'' fr ...

'' was also a specimen of the species. He presented his ideas in informal articles, and it was not until 2009, after three years of painstaking research, that the complete organism was reconstructed.Fossil fragments reveal 500-million-year-old monster predator
Sixty-nine specimens of ''Hurdia'' are known from the Greater

Phyllopod bed 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 later named Walcott Quarry), and was ...

, where they comprise 0.13% of the community.

Description

''Hurdia'' was one of the largest organisms in the Cambrian oceans, ''H. victoria'' reached between in length, while ''H. triangulata'' reached up to just long. Its head bore a pair of frontal appendages. These frontal appendages had 9 or more rarely 10 or 11 segments/podomeres, which were approximately rectangular and decreased in size towards the end of the appendage. The upper surface of the appendage was convexly curved. Podomeres 2 to 6 bore long downward pointing spines (ventral spines) with forward-curving tips. These ventral spines themselves bore up to 9 equally spaced forward-facing spines dubbed auxiliary spines, with podomeres 7 and 8 bearing shorter, smooth forward curving spines. The frontal appendages were used to bring food to its ring-shaped mouth (oral cone), in which four large plates are present, with inner rows of spines inside the main cone. Like other hurdiids, ''Hurdia'' bore a large frontal carapace protruding from its head composed of three

sclerite A sclerite (Greek language, Greek , ', meaning "hardness, hard") is a hardened body part. In various branches of biology the term is applied to various structures, but not as a rule to vertebrate anatomical features such as bones and teeth. Instea ...

s: a central component known as the H-element and two lateral components known as P-elements. Originally, it is estimated that body flaps ran along the sides of the organisms, from which large

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

were suspended. However, anatomy of ''

Aegirocassis ''Aegirocassis'' is an extinct genus of giant radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician in the Fezouata Formation of Morocco. It is known by a single species, ''Aegirocassis ...

'' clarified that ''Hurdia'' had both ventral and dorsal flaps, and gills were on trunk segments.

Distribution

''Hurdia'' had cosmopolitan distribution; two described species has been recovered from the

Burgess Shale The Burgess Shale is a fossil-bearing deposit exposed in the Canadian Rockies of British Columbia, Canada. It is famous for the exceptional preservation of the soft parts of its fossils. At old (middle Cambrian), it is one of the earliest fos ...

in British Columbia, Canada. In addition, ''H. victoria'' is also known from the

Spence Shale The Spence Shale is the middle member of the Langston Formation in southeastern Idaho and northeastern Utah. It is exposed in the Bear River Range, the Wasatch Range and the Wellsville Mountains. It is known for its abundant Cambrian trilobite ...

in Utah, USA. Unnamed species are known from

Qingjiang biota The Qingjiang biota are a major discovery of fossilized remains dating from the early Cambrian period approximately 518 million years ago. The remains consist at least 20,000 individual specimens, and were discovered near the Danshui River in the ...

Hubei Hubei is a province of China, province in Central China. It has the List of Chinese provincial-level divisions by GDP, seventh-largest economy among Chinese provinces, the second-largest within Central China, and the third-largest among inland ...

, China,

Pioche Shale The Pioche Shale is an Early to Middle Cambrian Burgess shale-type Lagerstätte in Nevada. It spans the Early–Middle Cambrian boundary; fossils from the Early Cambrian are preserved in botryoidal hematite, whereas those from the Middle Cambrian ...

in Nevada, USA, and

Wheeler Shale The Wheeler Shale (named by Charles Walcott) is a Cambrian ( 507 Ma) fossil locality world-famous for prolific agnostid and ''Elrathia kingii'' trilobite remains (even though many areas are barren of fossils) and represents a Konzent ...

in Utah, USA. ''Huangshandongia yichangensis'' and ''Liantuoia inflata'' from the Shuijingtuo Formation in Hubei, China, and ''Proboscicaris hospes'' from the Jince Formation near the town of

Jince Jince is a market town in Příbram District in the Central Bohemian Region of the Czech Republic. It has about 2,500 inhabitants. Administrative division Jince consists of four municipal parts (in brackets population according to the 2021 census) ...

, Czech Republic (which is identified as ''Hurdia hospes'' in some papers), and unnamed fossil from

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

Fezouata Formation The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Ordovician, Early Ordovician.

could represent species of ''Hurdia'' as well.

Ecology

''Hurdia'' is either suggested to have used its frontal appendages to sift small benthic prey (seafloor dwelling) from

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

, or to have used them as a trap to capture larger

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 the Ancient Greek word (), meaning "the depths". ...

prey.

References

External links