Kylinxia

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Kylinxia
Temporal range: Cambrian Stage 3 518  Ma
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20210310 Kylinxia zhangi.png
Artist's restoration, following three eye interpretation
Scientific classification
Kingdom:
Phylum:
Genus:
Kylinxia
Species:
K. zhangi
Binomial name
Kylinxia zhangi
Zeng et al., 2020

Kylinxia is a genus of extinct arthropod described in 2020. It was described from six specimens discovered in Yu'anshan Formation (Maotianshan Shales) in southern China. The specimens are assigned to one species Kylinxia zhangi. [1] Dated to 518 million years, the fossils falls under the Cambrian period. [2] 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," [3] which was "predicted by Darwin’s evolutionary theory." [4] The same day the formal description was published in Nature . [1]

Contents

Discovery

Kylinxia zhangi was discovered among the Maotianshan Shales from Yu'anshan Formation at Yunnan in southern China in 2019. Zeng Han, Zhao Fangchen, and Huang Diying of the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, made the formal description and taxonomy in Nature in 2020. They found six specimens which are well preserved and complete. The original specimens (holotype) is kept at the Nanjing Institute of Geology and Palaeontology, while the additional specimens (paratypes) are maintained at the Yingliang Stone Natural History Museum. [1]

Etymology

The genus name Kylinxia refers to a mixture of arthropod characters; kylin ( qilin ) is derived from the chimeric creature in Chinese mythology, while xia (蝦) is a Chinese word for shrimp-like arthropod. The species name zhang is after Yehui Zhang who contributed the additional specimens (paratypes). [1] [2]

Description

Size chart 20210320 Kylinxia size.png
Size chart
Frontalmost appendage of Kylinxia zhangi 20210313 Kylinxia zhangi Frontalmost appendage.png
Frontalmost appendage of Kylinxia zhangi
Various interpretations of eye placement of Kylinxia.
A: 1 pair of large lateral eyes, 3 small median eyes after Zeng et al. (2020)
B: 2 pairs of small lateral eyes, single large median eye after Moysiuk and Caron (2022)
C: 1 pair of small lateral eyes, single large median eye, anterior sclerite present, after O'Flynn et al. (2023) 20220718 Kylinxia eye interpretations.png
Various interpretations of eye placement of Kylinxia.
A: 1 pair of large lateral eyes, 3 small median eyes after Zeng et al. (2020)
B: 2 pairs of small lateral eyes, single large median eye after Moysiuk and Caron (2022)
C: 1 pair of small lateral eyes, single large median eye, anterior sclerite present, after O’Flynn et al. (2023)

Kylinxia is a tiny shrimp-like arthropod, measuring about 5 centimetres (2.0 in) long and about 1.2 cm (0.47 in) broad at the widest part of the body. [1] Its body is segmented and divisible into three regions, namely head, trunk and the pygidium. [1] [7] Kylinxia possesses a mixture of characters resembling various Cambrian arthropod taxa, notably Opabinia (eyes), radiodonts (frontalmost appendages) and megacheirans (trunk). [1]

The head of Kylinxia covered by a fused carapace with rounded genal corner comparable to those of the megacheiran Haikoucaris . [8] [1] Similar to the purported basal arthropod Opabinia, [9] [10] the head was initially suggested to have borne five eyes that were attached through eye stalks, [1] however a later 2023 study suggested that there were only three eyes, one central medial eye and two lateral eyes. [6] In contrast to the fused proboscis of Opabinia [11] and the hand-like great appendages of megacheirans, the head region of Kylinxia has a pair of unfused, 16-jointed frontalmost appendages each of which has terminal and paired, serrated inner spines (endites), similar to those seen in the radiodont [2] genera Anomalocaris (overall proportion) and Ramskoeldia (endites). [12] [1] Unlike radiodonts, the frontalmost appendages face upward and lack outer spines, which is a feature shared by the great appendages of megacheirans. [8] [1]

Similar to the multisegmented megacheirans, the trunk of Kylinxia covers most of the body length and is composed of up to 26 [6] metameric segments (tergites) each corresponded to a pair of appendages. [1] Within the post-oral appendages, the anteriormost 4 pairs are considered as reduced flap-like structures which arose from the head and two anterior trunk segments, [1] later 2023 study considered these are two-branched (biramous) and all from head. [6] The remaining appendages are all biramous, with the leg-like inner branches (endopod) each composed of at least seven segments and the suboval outer branches (exopods) each possess marginal lamellae. [1] The triangular pygidium covers at least 5 pairs of appendages, terminated with a three-lobed tail fan consisting of a middle and a pair of lateral lobes as seen in several Cambrian arthropods such as hymenocarine and fuxianhuiids. [13]

Taxonomy

Kylinxia has generally been placed as one of the most basal members of Deuteropoda. A close relationship with the genus Fengzhengia has been proposed. [6]

See also

Related Research Articles

<i>Opabinia</i> Extinct stem-arthropod species found in Cambrian fossil deposits

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.

<span class="mw-page-title-main">Dinocaridida</span> Extinct class of basal arthropods

Dinocaridida is a proposed fossil taxon of basal arthropods that flourished in the Cambrian period with occasional Ordovician and Devonian records. 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.

<i>Anomalocaris</i> Extinct genus of cambrian radiodont

Anomalocaris is an extinct genus of radiodont, an order of early-diverging stem-group arthropods.

<i>Peytoia</i> Extinct genus of radiodont

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.

<i>Jianfengia</i> Extinct genus of arthropods

Jianfengia is an extinct genus of Middle Cambrian (Atdabanian) megacheiran arthropod found in the Maotianshan Shale Lagerstätte of China. It contains the single species Jianfengia multisegmentalis. The body is extremely elongated, though the animal itself was relatively small at less than 4 centimetres (1.6 in) in length. The head has a pair of stalked eyes, a hypostome/labrum complex, a pair of great appendages with five podomeres, and four pairs of biramous limbs. The maximum known number of trunk segments is 27, though most known specimens have 20, which are associated with pairs of biramous appendages, and the body ends with a telson spine. It has been placed as a member of the family Jiangfengiidae, alongside Fortiforceps and Sklerolibyon as well as possibly Parapeytoia.

<i>Parapeytoia</i> Extinct genus of 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.

<i>Peytoia infercambriensis</i> Extinct species of arthropod

Peytoia infercambriensis is a species of hurdiid radiodont in the genus Peytoia.

<span class="mw-page-title-main">Megacheira</span> Extinct class of arthropods

Megacheira is an extinct class of predatory arthropods defined by their possession of spined "great appendages". Their taxonomic position is controversial, with studies either considering them stem-group euarthropods, or stem-group chelicerates. The homology of the great appendages to the cephalic appendages of other arthropods is also controversial. Uncontested members of the group were present in marine environments worldwide from the lower to middle Cambrian.

<i>Schinderhannes bartelsi</i> Extinct species of radiodont

Schinderhannes bartelsi is a species of hurdiid radiodont (anomalocaridid) known from one specimen from the lower Devonian Hunsrück Slates. Its discovery was astonishing because previously, radiodonts were known only from exceptionally well-preserved fossil beds (Lagerstätten) from the Cambrian, 100 million years earlier.

<i>Haikoucaris</i> Extinct genus of arthropods

Haikoucaris is a genus of megacheiran arthropod that contains the single species Haikoucaris ercaiensis. It was discovered in the Cambrian Chengjiang biota of China.

<i>Occacaris</i> Extinct genus of arthropods

Occacaris oviformis is an extinct nektonic predatory arthropod from the Lower Cambrian Maotianshan shale Lagerstätte. It bears a superficial resemblance to the Cambrian arthropod, Canadaspis, though, was much smaller, and had a pair of "great appendages", with which it may have grasped prey. It was originally considered to belong to Megacheira, however it is questioned in later study.

<span class="mw-page-title-main">Pectocaris</span> Extinct genus of crustaceans

Pectocaris is an extinct genus of bivalved arthropods from the Cambrian Maotianshan Shales, Yunnan Province of China. There are currently three known species within the genus.

<span class="mw-page-title-main">Radiodonta</span> Extinct order of basal arthropods

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 Ordovician Aegirocassis benmoulai and the Devonian Schinderhannes bartelsi.

<i>Cucumericrus</i> Extinct genus of arthropod

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.

<i>Houcaris</i> Genus of radiodonts

Houcaris is a possibly paraphyletic radiodont genus, tentatively assigned to either Amplectobeluidae, Anomalocarididae or Tamisiocarididae, known from Cambrian Series 2 of China and the United States. It contains two species, Houcaris saron and Houcaris magnabasis, both of which were originally named as species of the related genus Anomalocaris. The genus Houcaris was established for the two species in 2021 and honors Hou Xianguang, who had discovered and named the type species Anomalocaris saron in 1995 along with his colleagues Jan Bergström and Per E. Ahlberg.

<i>Erratus</i> Extinct genus of Cambrian arthropod

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.

<i>Laminacaris</i> Genus of extinct arthropods

Laminacaris is a genus of extinct stem-group arthropods (Radiodonta) that lived during the Cambrian period. It is monotypic with a single species Laminacaris chimera, the fossil of which was described from the Chengjiang biota of China in 2018. Around the same time, two specimens that were similar or of the same species were discovered at the Kinzers Formation in Pennsylvania, USA. The first specimens from China were three frontal appendages, without the other body parts.

Innovatiocaris is a genus of radiodont of uncertain family from the early Cambrian Chengjiang Lagerstätte of Yunnan Province, China. The genus contains two named species, I. maotianshanensis, known from a nearly complete individual measuring over 14.6 cm (5.7 in) and isolated frontal appendages, and I.? multispiniformis, known from a complete frontal appendage.

<i>Sklerolibyon</i> Extinct genus of megacheiran

Sklerolibyon is an extinct genus of megacheiran arthropod, known from the Cambrian aged Chengjiang biota of Yunnan, China. It is a member of the family Jianfengiidae, alongside Jianfengia and Fortiforceps, and possibly also Parapeytoia. Specimens are around 2.5 centimetres (0.98 in) in length. The body is greatly elongated, and head shield is heavily sclerotised, with a pair of spines radiating outward from the sides. Alongside the pair of great appendages, there are a pair of stalked eyes and at least two other pairs of limbs on the cephalon. The trunk has 34 segments with corresponding biramous appendages, with typically megacheiran paddle-shaped exopods. The tail is unknown but like Jianfengia probably ended in a telson spine.

<i>Fortiforceps</i> Extinct genus of arthropods

Fortiforceps is an extinct genus of Cambrian megacheiran arthropod known from the Chengjiang biota of Yunnan, China. It was originally described by Hou and Bergström in 1997, and redescribed in 2020. It was relatively small, at 4 centimetres (1.6 in) or less in length. The head had a large pair of stalked eyes, a pair of frontal projections, as well as a pair of great appendages, like other megacheirans, along with two other cephalic appendages. The trunk had either 20 or 22 segments, depending on the specimen. These segments had pronounced blade-like spines on their upper-outer edge. Each of the trunk segments were associated with pairs of biramous limbs, which probably have seven podomeres and like other megacheirans, have paddle-shaped exopods. The trunk terminated with a forked tailpiece, which on their outer edges had rod-like structures. The two lobes were separated by a rectangular central piece. It has been placed as a member of the family Jiangfengiidae, alongside Jianfengia, Sklerolibyon and possibly Parapeytoia.

References

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