Amplectobelua Temporal range: Cambrian Stage 3, | |
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Reconstruction of Amplectobelua symbrachiata | |
Fossil specimen, showing frontal appendages, head carapace, gnathobase-like structures and body flaps | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Arthropoda |
Class: | † Dinocaridida |
Order: | † Radiodonta |
Clade: | † Amplectobeluidae |
Genus: | † Amplectobelua Hou, Bergström & Ahlberg, 1995 |
Type species | |
†Amplectobelua symbrachiata Hou, Bergström & Ahlberg, 1995 | |
Other species | |
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Amplectobelua (meaning "embracing beast") is an extinct genus of late Early Cambrian amplectobeluid radiodont, a group of stem arthropods that mostly lived as free-swimming predators during the first half of the Paleozoic Era.
Amplectobelua was a giant radiodont, with the largest specimen of A. symbrachiata reaching up to 90 cm (3.0 ft) in body length excluding the frontal appendages and tail. [2] A. stephenensis is much smaller, estimated up to 25 cm (9.8 in) long. [3] The body structures other than frontal appendages are only known from the type species Amplectobelua symbrachiata. Like other radiodonts, Amplectobelua had a pair of jointed frontal appendages, a head covered by dorsal and lateral sclerites (the latter had been misinterpreted as huge eyes [4] ), a limbless body with dorsal gills (setal blades), and a series of flaps on both sides that extended along the length of its body.
Amplectobelua had a specialized frontal appendage, in which it has a distinct 3-segmented shaft region and 12-segmented distal articulated region, and the spine on the fourth segment (first segment of distal articulated region) hooked forward to oppose the tip of the appendage, allowing it to grasp prey like a pincer. Amplectobelua had 11 pairs of body flaps in total, they are relatively elongated and straight in outline. The size of the flaps decrease posteriory, and each of their frontal margin have rows of vein-like structures (strengthening rays). The neck region have at least 3 pairs of slender, reduced anterior flaps. [4] The trunk terminated with a pair of long furcae (streamers).
Amplectobelua shares a unique feature among radiodonts with Ramskoeldia , in having gnathobase-like structures (GLSs) underneath its neck region, at least 6, up to eight. They functioned like the gnathobases of arthropods, being able to rotate and move to shred prey. They were connected to reduced anterior flaps. Additionally, the mouth (oral cone) of Amplectobelua were interpreted as different from typical radiodont, lacking the typical Peytoia -style oral cone and possessing numerous flat tooth-plates with unclear, but possibly non-radial arrangement. [4]
Two species are known, Amplectobelua symbrachiata from the Chengjiang biota and Amplectobelua stephenensis from the later Burgess Shale. [5] A. symbrachiata is known from complete specimens, while A. stephenensis is known only from isolated frontal appendages. A. stephenensis is more advanced, with the frontal appendages being more specialized for grasping: the fourth spine is larger and the spines on outer segments are reduced. A. symbrachiata is previously named as a species of Anomalocaris , Anomalocaris trispinata in 1992, before description of A. symbrachiata. [2] Some studies considered that name Amplectobelua trispinata should be used instead of A. symbrachiata. [6] [7]
Amplectobelua was likely nektonic predator. [3] Its frontal appendages were worked like pincers to pinch prey. Its structure was suitable to firmly grasp and manipulate prey to the mouth or tearing off pieces from larges carcasses. [8] Gnathobase-like structures were probably used to chew preys. [4] Research of 432 specimens resulted that it would be an extremely fast-growing animal for an arthropod. [2]
Sidneyia is an extinct arthropod known from fossils found from the Early to the Mid Cambrian of China and the Mid Cambrian Burgess Shale of British Columbia, Canada.
Dinocaridida is a proposed fossil taxon of basal arthropods, which flourished during the Cambrian period and survived up to the Early to Middle Ordovician. The putative Early Devonian member Schinderhannes bartelsi has been considered questionable by some researchers.
Anomalocaris is an extinct genus of radiodont, an order of early-diverging stem-group 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.
Parapeytoia is a genus of Cambrian arthropod. The type and only described species is Parapeytoia yunnanensis, lived over 518 million years ago in the Maotianshan shales of Yunnan, China. Unidentified fossils from the same genus also had been discovered from the nearby Wulongqing Formation.
Peytoia infercambriensis is a species of hurdiid radiodont in the genus Peytoia.
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.
Isoxys is a genus of extinct bivalved Cambrian arthropod; the various species of which are thought to have been freely swimming predators. It had a pair of large spherical eyes, and two large frontal appendages used to grasp prey.
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 latest surviving members include the Aegirocassisinae from the Early Ordovician of Morocco. The putative Early Devonian member Schinderhannes bartelsi from Germany has been considered questionable by some researchers.
Hurdia is an extinct genus of hurdiid radiodont that lived 505 million years ago during the Cambrian Period. Fossils have been found in North America, China and the Czech Republic.
Cucumericrus ("cucumber-leg") is an extinct genus of stem-arthropod. The type and only species is Cucumericrus decoratus, with fossils discovered from the Maotianshan Shales of Yunnan, China.
Kiisortoqia soperi is an extinct species of arthropod from the Early Cambrian Sirius Passet Lagerstätte in Greenland. While it had a superficially trilobite-like bodyform, it also possessed large frontal appendages similar to those of radiodonts.
Tamisiocarididae is a family of radiodonts, extinct marine animals related to arthropods, that bore finely-spined appendages that were presumably used in filter-feeding. When first discovered, the clade was named Cetiocaridae after a speculative evolution artwork, Bearded Ceticaris by John Meszaros, that depicted a hypothetical filter-feeding radiodont at a time before any were known to exist. However, the family name was not valid according to the International Code of Zoological Nomenclature, as no real genus named "Cetiocaris" exists, and in 2019 it was formally replaced by the name Tamisiocarididae, after the only valid genus of the clade at the time. The family is only known from Series 2 of the Cambrian, unlike other radiodont families, which persisted longer into the Cambrian. All known species would have lived in tropical or subtropical waters, suggesting a preference for warmer waters.
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.
Ramskoeldia is a genus of amplectobeluid radiodont described in 2018. It was the second genus of radiodont found to possess gnathobase-like structures and an atypical oral cone after Amplectobelua. The type species, Ramskoeldia platyacantha, was discovered in the Chengjiang biota of China, the home of numerous radiodontids such as Amplectobelua and Lyrarapax.
Kylinxia is a genus of extinct arthropod described in 2020. It was described from six specimens discovered in Yu'anshan Formation in southern China. The specimens are assigned to one species Kylinxia zhangi. Dated to 518 million years, the fossils falls under the Cambrian period. Announcing the discovery on 4 November 2020 at a press conference, Zeng Han of the Nanjing Institute of Geology and Paleontology, said that the animal "bridges the evolutionary gap from Anomalocaris to true arthropods and forms a key ‘missing link’ in the origin of arthropods," which was "predicted by Darwin’s evolutionary theory." The same day the formal description was published in Nature.
Titanokorys is a genus of extinct hurdiid (peytoiid) radiodont that existed during the mid Cambrian. It is the largest member of its family from the Cambrian, with a body length of 50 cm (20 in) long, making it one of the largest animals of the time. It bears a resemblance to the related genus Cambroraster. Fossils of T. gainesi were first found within Marble Canyon in 2018. The fossils were not named until 2021 because they were assumed to be giant specimens of Cambroraster.
Erratus is an extinct genus of marine arthropod from the Cambrian of China. Its type and only species is Erratus sperare. Erratus is likely one of the most basal known arthropods, and its discovery has helped scientists understand the early evolution of arthropod trunk appendages. Some of the stem-arthropods like radiodonts did not have legs, instead they had flap like appendages that helped them swim. Erratus on the other hand had not only flaps but also a set of primitive legs. It also supported the theory that the gills of aquatic arthropods probably evolved into the wings and lungs of terrestrial arthropods later in the Paleozoic.
Isoxyids are members of the order Isoxyida and the family Isoxyidae, a group of basal arthropods that existed during the Cambrian period. It contains two genera, Isoxys, with 20 species found worldwide, and Surusicaris known from a single species found in the Burgess Shale of Canada. They are distinguished by their bivalved carapaces and pair of upward curving grasping frontal appendages.