''Hurdia'' is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

hurdiid Hurdiidae is an extinct cosmopolitan family of radiodonts, a group of stem-group arthropods, which lived during the Paleozoic Era. It is the most long-lived radiodont clade, lasting from the Cambrian period to the Devonian period. Description ...

radiodont Radiodonta is an extinct Order (biology), 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 ...

that lived 505 million years ago during the

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

Period. As a radiodont like ''

Peytoia ''Peytoia'' is a genus of hurdiid radiodont that lived in the Cambrian period, containing two species, ''Peytoia nathorsti'' from the Miaolingian of Canada and ''Peytoia infercambriensis'' from Poland, dating to Cambrian Stage 3. Its two frontal ...

'' and ''

Anomalocaris ''Anomalocaris'' ("unlike other shrimp", or "abnormal shrimp") is an extinct genus of Radiodonta, radiodont, an Order (biology), order of early-diverging stem-group arthropods. The first fossils of ''Anomalocaris'' were discovered in the ''Ogygop ...

'', it is part of the ancestral lineage that led to

euarthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chitin, oft ...

Description

20210812 Hurdia frontal appendage mobility

''Hurdia'' was one of the largest organisms in the Cambrian oceans, ''H. victoria'' reached approximately in length, while ''H. triangulata'' reached up to just . Its head bore a pair of rake-like frontal appendages which shovelled food into its pineapple-ring-like

mouth In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on ...

(oral cone). Like other hurdiids, ''Hurdia'' bore a large frontal carapace protruding from its head composed of three

sclerite A sclerite (Greek , ', meaning "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. Instead it refers most commonly ...

s: a central component known as the H-element and two lateral components known as P-elements. The function of this organ remains mysterious; it cannot have been protective as there was no underlying soft tissue. 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 radiodont arthropod belonging to the family Hurdiidae that lived 480 million years ago during the early Ordovician. It is known by a single species, ''Aegirocassis benmoulai''. Van Roy initiated scientific ...

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

Ecology

''Hurdia'' was a

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

, or possibly a

scavenger Scavengers are animals that consume dead organisms that have died from causes other than predation or have been killed by other predators. While scavenging generally refers to carnivores feeding on carrion, it is also a herbivorous feeding b ...

. Its frontal appendages are flimsier than those of ''Anomalocaris'', suggesting that it fed on less robust prey. It displayed a cosmopolitan distribution; it 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 foss ...

as well as sites in the US, China and Europe.

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 Mount Hurd is a mountain in the Ottertail Range of the Canadian Rockies in British Columbia, Canada. It was named after Major Marshall Farnam Hurd (1823-1903) a Canadian Pacific Railway engineer and explorer. It was featured on a 1928 Canada Post ...

. 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 s ...

''. 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 Desmond H. Collins is a Canadian paleontologist, associate professor of zoology at the University of Toronto and retired curator of invertebrate paleontology at the Royal Ontario Museum The Royal Ontario Museum (ROM) is a museum of art, world c ...

erected the taxon Radiodonta to encompass ''

'' 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'' 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

/ref> 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 t ...

, where they comprise 0.13% of the community.

References

External links

* Dinocarida Burgess Shale fossils Cambrian arthropods Anomalocaridids Cambrian genus extinctions {{paleo-arthropod-stub