| Diania Temporal range: | |
|---|---|
 | |
| Diania cactiformis fossil (ELEL-SJ102058) showing anterior trunk segments. [1] | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| (unranked): | Panarthropoda |
| Phylum: | † "Lobopodia" |
| Class: | † Xenusia |
| Genus: | † Diania |
| Species: | †D. cactiformis |
| Binomial name | |
| †Diania cactiformis Liu et al., 2011 | |
Diania is an extinct genus of lobopodian panarthropod found in the Lower Cambrian Maotianshan shale of China, represented by a single species - D. cactiformis. Known during its investigation by the nickname "walking cactus", this organism belongs to a group known as the armoured lobopodians, and has a simple worm-like body with robust, spiny legs. Initially, the legs were thought to have a jointed exoskeleton and Diania was suggested to be evolutionarily close to early arthropods, [2] but many later studies have rejected this interpretation. [3] [4] [5] [1]
Fossils of Diania were discovered independently by Jianni Liu from the Northwest University (China) in Xi’an, Qiang Ou from the China University of Geosciences in Beijing and Michael Steiner of the Free University Berlin. The fossils come from the famous Chengjiang deposit – or Maotianshan shale – of south-west China and are about 520 million years old. Specifically, they come from the Yu'anshan Formation, dated to the Cambrian Stage 3. [2]
The name Diania comes from "Dian" (Chinese: 滇), which is an abbreviation in the Chinese language for Yunnan; the province where the fossils were discovered. [2] The specific epithet cactiformis is based on its spiny, cactus-like appearance, [2] which led to it being informally called the "walking cactus" by the research team working on the fossils.
The largest complete fossils of Diania are about 6 centimetres (2.4 in) in full length. [2] Both the trunk and legs were covered by a soft cuticle with a series of annulations (ring-like grooves) and spines. [1] The appendages (lobopods) are arranged in a more much lateral position than those of other lobopodians, giving the animal a similar dorsoventral aspect. [5]
The worm-like body of Diania is composed of 10 trunk segments, each associated with a series of median circular structures and a pair of legs. [2] [5] Due to the subequal morphology between each trunk segment and the usually poor preservation of both trunk ends, it is difficult to define the anterior-posterior axis of the animal. [5] The only sign of a head is in specimen ELEL-SJ102058, which shows a helmet-like structure, with a pair of lateral spines and median protrusion that is presumed to be the location of mouth opening. [1] A pair of tiny, modified appendages are located immediately behind the head. [1]
The most recognisable feature of Diania is the robust, spiny legs (walking lobopods [1] ) which led to it being nicknamed "walking cactus". [2] [5] While the leg base is narrow and simple, the remaining sections are subequally robust to the trunk, [1] with 15 widely-spaced annulations [5] and 4 rows of well-developed spines. [2] Although the widen ring-like annulations superficially resembled the rigid, segmented exoskeleton of arthropod appendages (which had led to the previous misinterpretation as such [2] ), there are no signs of any hardened exoskeleton nor segmentation, with deformation from various fossil materials confirming their soft and unsegmented nature. [5] [1] Instead of terminal claws like most other lobopodians, the leg of Diania terminates with multiple (up to 3) spines similar to the preceding annulation. [5] [1]
Diania may had been a benthic scavenger, using its robust legs to walk on the sea floor. [5] The absence of sedimental gut content and terminal claws suggest Diania was unlikely to be a sediment feeder nor a good climber. [5] The modified appendages behind its head may had played a sensing and/or food-manipulating role, similar to the tentacle-like appendages of Hallucigenia . [1] Similar to the dorsal spines of other armoured lobopodians (e.g. Hallucigenia and Luolishania ), the spines of Diania may had provided protection against predators. [5]
Diania belongs to a group of extinct animals known as the lobopodians. These have long been assumed to be related in some way to Arthropoda and it seems likely that arthropods evolved from somewhere within this group. However, all previously discovered lobopodians showed soft, annulated (ring-like grooves), but not segmented appendages called lobopods. In the original description (Liu et al. 2011), Diania was thought to be a lobopodian which appears to have evolved the name-giving character of the arthropods: scleritzed (hardened exoskeleton) and segmented appendages, which led to the suggestion of Diania being close to the origins of arthropods. [2] Based on this interpretation, Liu et al. 2011 also suggests that Diania is an evidence showing arthropodization (i.e. the appearance of exoskeleton and segmentation around the appendages) evolved before arthrodization (i.e. exoskeleton and segmentation around the body). The phylogenetic analysis provided by Liu et al. 2011 resolved Diania as the sister group of Schinderhannes and the remaining arthropods, although the possibility of Diania emerging before the evolution of stem-arthropods like Gilled lobopodians and radiodonts also had been discussed. [2]
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| Phylogenetic position of Diania following Liu et al. 2011. [2] Lobopodian taxa indicaded by asterisk. |
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| Neutralized phylogenetic position of Diania following the restudies after Ma et al. 2013. [5] [6] [7] [8] [9] [10] Lobopodian taxa indicaded by asterisk. |
However, both the phylogenetic and morphological interpretations provided by Liu et al. 2011 were soon being questioned by multiple later studies. [3] [4] [5] The data provided by Liu et al. 2011 are inconsistent with the suspected phylogenic relationships, as the analysis run by Mounce & Wills 2011 and Legg et al. 2011 could only resolve Diania as a lobopodian indirectly related to arthropods, even using the same method by Liu et al. 2011 and coding Diania as the bearer of arthropod-like appendages. [3] [4] Furthermore, the re-examination of Ma et al. 2013 and Ou & Mayer 2018 even clarified that the ring-like structures of Diania's leg were soft annulation shared by the lobopods of other lobopodians, lacking any characters comparable to those of an arthropod appendage (e.g. exoskeleton, segmentation, pivot joint and arthrodial membrane). [5] [1] This conclusion eventually rejected the evidence of arthropodization on Diania, as well as the link between Diania and the origin of arthropod appendages. [5] [1]
After a series of restudies, Diania remain as a unique lobopodian with uncleared, non-arthropod related phylogenetic position. [5] Further phylogenetic analysis inconsistently placing Diania as a basal member of the onychophoran stem-group alongside Xenusion , [6] [7] [8] [9] or a basal lobopodian branched before the total-groups of each panarthropod phylum. [5] [10]
Other than the lacking of arthropodization, Restudy of Diania by Ma et al. 2013 also revealed the structure thought to be a stout head/proboscis by Liu et al. 2011 was in fact one of the animal's leg, the maximum number of leg annulations is 15 instead of 17, and the terminal leg structures are spines instead of claws. [5] A putative head was first revealed by Ou & Mayer 2018 from the specimen ELEL-SJ102058. [1]
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.
Xenusion auerswaldae is an early lobopodian known from two specimens found in glacial erratics on the Baltic coast of Germany. They probably originated in the Kalmarsund Sandstone of Southern Sweden, which was deposited in the Lower Cambrian. It is the oldest currently known lobopodian with soft body fossils.
Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada and Onychophora. Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members (stem-group) of each extant panarthropod phylum are thought to have risen. However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well.
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.
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.
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.
Jianshanopodia is a monotypic genus of Cambrian lobopodian, discovered from Maotianshan Shales of Yunnan, China.
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.
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.
Mureropodia is an animal that existed in what is now the Valdemiedes Formation of Spain during the early Cambrian period. It was described by José Antonio Gámez Vintaned, Eladio Liñán and Andrey Yu. Zhuravlev in 2011, and the type and only species is M. apae.
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.
Megadictyon is a genus of Cambrian lobopodian with similarities to Jianshanopodia and Siberion. Occasionally mis-spelt Magadictyon.
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.
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.
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.
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.
