Entothyreos Temporal range: Middle Cambrian | |
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Life restoration | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
(unranked): | Panarthropoda |
Phylum: | † "Lobopodia" |
Family: | † Luolishaniidae |
Genus: | † Entothyreos Aria & Caron, 2024 |
Species: | †E. synnaustrus |
Binomial name | |
†Entothyreos synnaustrus Aria & Caron, 2024 | |
Entothyreos is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Burgess Shale in British Columbia, Canada. The genus contains a single species, Entothyreos synnaustrus (meaning "convergent inner shield"), described in 2024. [1] Entothyreos is significant for possessing a remarkable degree of sclerotization among lobopodians, comparable to that of arthropods.
Entothyreos is a stout collinsovermid lobopodian, capable of reaching roughly 5 cm in length. The dorsum was protected by numerous paired sclerite spines (2 pairs per trunk segment). The spines are longest at the middle of the body. These spines are associated (although still dissociable) with subrectangular sclerotic sheets which lie just below the cuticle surface. These sclerite sheets may have increased body rigidity, allowing easier erection of the body to allow for suspension feeding from the water column. They are comparable with the sclerotic rings found in other luolishaniids, which probably evolved at first to allow for the otherwise soft body to carry numerous large spines. Additionally, the head segment bears 2 pairs of small sclerite spines (with no apparent underlying sclerotic sheet), and a pair of soft antenniform sensory structures.
Entothyreos possessed 11 pairs of lobopodous limbs, divided into two sets. The anterior set of 6 limb pairs are elongate and lined with 2 rows of large, sclerotized setae, which allowed the animal to sieve food particles from the water. These limbs were also covered in numerous shorter, fine setae on their dorsal side, and tipped with a pair of sickle-shaped claws. The posterior 5 pairs are thick and conical, each tipped with a single, large, highly developed claw. The annuli of these posterior limbs are highly sclerotized, the margins of which are lined with short setae of alternating lengths. The posterior claws have an additional branch near their base opposing the tip like a claw, unique to Entothyreos, which aided in anchoring to substrate. The final, posterior-most pair of limbs have annuli differentiated into 7 sclerotized sheets, which covered at least the dorsal surface of the limb, probably for further protection. While not truly arthropodized (they are likely not articulated with an arthrodial membrane), the degree of sclerotization present does represent a remarkable convergence with arthropods.
Entothyreos is relatively common compared with other Burgess Shale lobopodians, being initially described from a suite of 51 fossil specimens. One slab, preserving a large amount of organisms including Anomalocaris , Peytoia , and some sponges, contains 9 different individual specimens of Entothyreos. All fossil specimens derive from the Tulip Beds locality of the Burgess Shale (found at the base of the Campsite Cliff Shale Member, making it one of the oldest Burgess Shale localities [2] ), which represents a more distal environment, further from the Cathedral Escarpment than the more famous Walcott Quarry. The Tulip Beds palaeoenvironment is dominated by sessile animals, particularly suspension feeders. Entothyreos likely used its posterior limb pairs to anchor itself to a raised substrate (e.g. sponges), and then used its frontal limb pairs to sieve food particles from the water column. The posterior portion of the body is often poorly preserved, which the authors speculate could be caused by kinetic force of burial (a mudflow) tearing apart the body, as the anchoring claws are still firmly embedded in substrate. Comparable signs of tearing are seen in other sessile Burgess Shale taxa. [3]
Lobopodians are members of the informal group Lobopodia, or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, marine worm-like fossil panarthropods such as Aysheaia and Hallucigenia.
Hallucigenia is a genus of lobopodian known from Cambrian aged fossils in Burgess Shale-type deposits in Canada and China, and from isolated spines around the world. The generic name reflects the type species' unusual appearance and eccentric history of study; when it was erected as a genus, H. sparsa was reconstructed as an enigmatic animal upside down and back to front. Lobopodians are a grade of Paleozoic panarthropods from which the velvet worms, water bears, and arthropods arose.
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.
Marrella is an extinct genus of marrellomorph arthropod known from the Middle Cambrian of North America and Asia. It is the most common animal represented in the Burgess Shale of British Columbia, Canada, with tens of thousands of specimens collected. Much rarer remains are also known from deposits in China.
Canadaspis is an extinct genus of bivalved Cambrian arthropod, known from North America and China. They are thought to have been benthic feeders that moved mainly by walking and possibly used its biramous appendages to stir mud in search of food. They have been placed within the Hymenocarina, which includes other bivalved Cambrian arthropods.
Habelia is a genus of extinct arthropod from the Middle Cambrian, thought to be one of the earliest known relatives of chelicerates. Its fossils have been found in the Burgess Shale in British Columbia, Canada. Fifty-four specimens of Habelia are known from the Greater Phyllopod bed, where they comprise 0.1% of the community.
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 later surviving members include the subfamily Aegirocassisinae from the Early Ordovician of Morocco and the Early Devonian member Schinderhannes bartelsi from Germany.
Stanleycaris is an extinct, monotypic genus of hurdiid radiodont from the middle Cambrian (Miaolingian). The type species is Stanleycaris hirpex. Stanleycaris was described from the Stephen Formation near the Stanley Glacier and Burgess Shale locality of Canada, as well as Wheeler Formation of United States. The genus was characterized by the rake-like frontal appendages with robust inner spines.
The Luolishaniidae or Luolishaniida are a group of Cambrian and Ordovician lobopodians with anterior 5 or 6 pairs of setiferous lobopods. Most luolishaniids also have posterior lobopods each with a hooked claws, and thorn-shaped sclerites arranged as three or more per trunk segment. The type genus is based on Luolishania longicruris Hou and Chen, 1989, from the Chengjiang Lagerstatte, South China. They are presumed to have been benthic suspension or filter feeders.
Ovatiovermis is a genus of filter-feeding lobopodian known from the Burgess Shale. Like many lobopodians, it had nine pairs of lobopods (legs). It was well adapted to filter-feeding and probably did so from the nearest high vantage point.
Onychodictyon is a genus of extinct lobopodian known from the Lower Cambrian Chengjiang Maotianshan Shales in the Yunnan Province in China. It was characterized by a stout body covered by fleshy papillae and pairs of sclerotized plates with spines, representing part of the diverse "armoured lobopodians" alongside similar forms such as Microdictyon and Hallucigenia.
Collinsovermis is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Burgess Shale in British Columbia, Canada. It is monotypic having only one species, Collinsovermis monstruosus. After its initial discovery in 1983, Desmond H. Collins popularised it as a unique animal and was subsequently dubbed "Collins' monster" for its unusual super armoured body. The formal scientific description and name were given in 2020.
Acinocricus is a genus of extinct panarthropod belonging to the group Lobopodia and known from the middle Cambrian Spence Shale of Utah, United States. As a monotypic genus, it has one species Acinocricus stichus. The only lobopodian discovered from the Spence Shale, it was described by Simon Conway Morris and Richard A. Robison in 1988. Owing to the original fragmentary fossils discovered since 1982, it was initially classified as an alga, but later realised to be an animal belonging to Cambrian fauna.
Luolishania is an extinct genus of lobopodian panarthropod and known from the Lower Cambrian Chiungchussu Formation of the Chengjiang County, Yunnan Province, China. A monotypic genus, it contains one species Luolishania longicruris. It was discovered and described by Hou Xian-Guang and Chen Jun-Yuan in 1989. It is one of the superarmoured Cambrian lobopodians suspected to be either an intermediate form in the origin of velvet worms (Onychophora) or basal to at least Tardigrada and Arthropoda. It is the basis of the family name Luolishaniidae, which also include other related lobopods such as Acinocricus, Collinsium, Facivermis, and Ovatiovermis. Along with Microdictyon, it is the first lobopodian fossil discovered from China.
Thanahita is a genus of extinct lobopodian and known from the middle Silurian Herefordshire Lagerstätte at the England–Wales border in UK. It is monotypic and contains one species, Thanahita distos. Discovered in 2018, it is estimated to have lived around 430 million years ago and is the only known extinct lobopodian in Europe, and the first Silurian lobopodian known worldwide.
Hallucigeniidae is a family of extinct worms belonging to the group Lobopodia that originated during the Cambrian explosion. It is based on the species Hallucigenia sparsa, the fossil of which was discovered by Charles Doolittle Walcott in 1911 from the Burgess Shale of British Columbia. The name Hallucigenia was created by Simon Conway Morris in 1977, from which the family was erected after discoveries of other hallucigeniid worms from other parts of the world. Classification of these lobopods and their relatives are still controversial, and the family consists of at least four genera.
Lenisambulatrix is a genus of extinct worm belonging to the group Lobopodia and known from the Lower Cambrian Maotianshan shale of China. It is represented by a single species L. humboldti. The incomplete fossil was discovered and described by Qiang Ou and Georg Mayer in 2018. Due to its missing parts, its relationship with other lobopodians is not clear. It shares many structural features with another Cambrian lobopodian Diania cactiformis, a fossil of which was found alongside it.
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.
Surusicaris is an extinct genus of bivalved arthropod, known from the Cambrian Burgess Shale of British Columbia, Canada. It is considered to be closely related to Isoxys, and like it has spined grasping frontal appendages.