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.
Dinocaridida is a proposed fossil taxon of basal arthropods, which flourished during the Cambrian period and survived up to Early Devonian. 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.
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 from Poland, dating to Cambrian Stage 3. Its two frontal appendages had long bristle-like spines, it had no fan tail, and its short stalked eyes were behind its large head.
Anomalocarididae is an extinct family of Cambrian radiodonts, a group of stem-group arthropods.
Kerygmachela kierkegaardi is a kerygmachelid gilled lobopodian from the Cambrian Stage 3 aged Sirius Passet Lagerstätte in northern Greenland. Its anatomy strongly suggests that it, along with its relative Pambdelurion whittingtoni, was a close relative of radiodont and euarthropods. The generic name "Kerygmachela" derives from the Greek words Kerygma (proclamation) and Chela (claw), in reference to the flamboyant frontal appendages. The specific name, "kierkegaardi" honors Danish philosopher Søren Kierkegaard.
Urokodia aequalis is an extinct genus of arthropod from the early Cambrian. The taxon is only known from the Maotianshan Shales of China based on some 15 specimens.Its segmentation resembles that of a millipede and it possessed head and tail shields with thorny spikes. It has some similarities to the arthropod Mollisonia that is known from both the Burgess Shale of Canada and the Kaili biota of China. Recently, the taxon has been considered a member of the order Mollisoniida, alongside Mollisonia, Thelxiope, and Corcorania, the group are suggested to be stem-chelicerates. However, a paper published in July 2024 found Urokodia to be the most basal artiopod instead.
The Wheeler Shale is a Cambrian (c. 507 Ma) fossil locality world-famous for prolific agnostid and Elrathia kingii trilobite remains and represents a Konzentrat-Lagerstätte. Varied soft bodied organisms are locally preserved, a fauna and preservation style normally associated with the more famous Burgess Shale. As such, the Wheeler Shale also represents a Konservat-Lagerstätten.
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 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 gainesi, Cambroraster falcatus and Amplectobelua symbrachiata. The later surviving members include the subfamily Aegirocassisinae from the Early Ordovician of Morocco and the Early Devonian member Schinderhannes bartelsi from Germany.
Emeraldella is a genus of arthropod known from the Middle Cambrian of North America. The type species E. brocki was described in 1912 from the Burgess Shale. 21 specimens of Emeraldella are known from the Greater Phyllopod bed, where they comprise < 0.1% of the community. A re-study on the species was done in 2012. A second species E. brutoni is known from the Wheeler Shale, which was described in 2011. An additional specimen of E. brutoni was described in 2019, which revealed more of the anatomy. It has been placed as a basal member of the clade Vicissicaudata within Artiopoda, a group of arthropods containing trilobites and their relatives.
Trilobites are used as index fossils to subdivide the Cambrian period. Assemblages of trilobites define trilobite zones. The Olenellus-zone has traditionally marked the top of the Lower Cambrian, and is followed by the Eokochaspis zone.
The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Early Ordovician. It was deposited in a marine environment, and is known for its exceptionally preserved fossils, filling an important preservational window beyond the earlier and more common Cambrian Burgess shale-type deposits. The fauna of this geological unit is often described as the Fezouata biota, and the particular strata within the formation which exhibit exceptional preservation are generally termed the Fezouata Lagerstätte.
Caryosyntrips ("nutcracker") is an extinct genus of stem-arthropod which known from Canada, United States and Spain during the middle Cambrian. It was first named by Allison C. Daley and Graham E. Budd in 2010, being the type species Caryosyntrips serratus.
Thelxiope is a genus of Cambrian and Ordovician arthropod. Four named species are known, the type species T. palaeothalassia is known from the Burgess Shale, Canada T. holmani is from the Wheeler Shale of Utah, Thelxiope tangi from the Linyi Lagerstätte of Shandong, China, and T. spinosa, which is known from both the Linyi Lagerstätte and the Wheeler Shale. An indeterminate species is also known from the Ordovician (Floian) Fezouata Formation in Morocco. It is a member of Mollisoniida, alongside close relatives Mollisonia, Corcorania and Urokodia. They are suggested to be stem-chelicerates.
The Drumian is a stage of the Miaolingian Series of the Cambrian. It succeeds the Wuliuan and precedes the Guzhangian. The base is defined as the first appearance of the trilobite Ptychagnostus atavus around 504.5 million years ago. The top is defined as the first appearance of another trilobite Lejopyge laevigata around 500.5 million years ago.
Amplectobeluidae is a clade of Cambrian radiodonts. It currently includes five definitive genera, Amplectobelua, Lyrarapax, Ramskoeldia, Guanshancaris and a currently unnamed genus from the lower Cambrian aged Sirius Passet site in Greenland. There is also a potential fifth genus, Houcaris, but that genus has become problematic in terms of its taxonomic placement.
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.
Pahvantia is an extinct genus of hurdiid radiodont from the Cambrian. It is known by a single species, Pahvantia hastata, described from Wheeler Shale and Marjum Formation in Utah. Although it was once considered as filter feeder using large number of putative setae, this structures are later considered as misidentification of trunk materials.
Zhenghecaris shankouensis is an enigmatic arthropod from the Lower Cambrian Maotianshan Shales, tentatively classified as a hurdiid (peytoiid) radiodont, and originally as a thylacocephalan. It is known from several specimens mostly preserving the carapace and eyes measuring roughly 15 cm (5.9 in) in width, which would have marked it as one of the largest thylacocephalans, behind Ostenocaris, Dollocaris and Ainiktozoon, as well as the earliest since all other thylacocephalans are Ordovician or younger. Better preserved fossils show that it was more similar to the domed sclerites of radiodonts such as Cambroraster, with two lateral spine processes on either side of the carapace, the eyes apparently fitting into the posterior notches. Additional isolated sclerites from the Chengjiang have been described as the lateral sclerites of Zhenghecaris due to their broad similarity to the P-elements of hurdiids (peytoiids), and because of their similar construction, ornamentation, and possession of two-pronged lateral spine processes. It has also been classified conservatively as Arthropoda incertae sedis, as the fragmentary remains cannot confidently be classified further due to the lack of associated appendages of trunk elements.
Nuucichthys is an extinct genus of stem-group vertebrates known from the Cambrian Marjum Formation of Utah, United States. The genus contains a single species, N. rhynchocephalus, known from a single individual, representing the first Cambrian vertebrate from the Great Basin region of North America. Nuucichthys provides insights into the diversity of Cambrian vertebrates, which are more rare in Laurentian deposits. Taxonomic studies recover this genus as closely related to other Laurentian stem-vertebrates such as Metaspriggina and Emmonaspis.
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