BEIJING, Oct. 30 (Xinhua) -- A group of fossilized tunnels dug by animals about 550 million years ago, discovered in the upper reaches of the Yangtze River in China, have offered new insights into how the earliest animal activities began to shape the seafloor environment.This undated photo provided by the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences shows a trace fossil discovered in central China's Hubei Province. (Xinhua)BEIJING, Oct. 30 (Xinhua) -- A group of fossilized tunnels dug by animals about 550 million years ago, discovered in the upper reaches of the Yangtze River in China, have offered new insights into how the earliest animal activities began to shape the seafloor environment.Previous research has shown that during a pivotal evolutionary period around 539 million years ago, known as the Ediacaran-Cambrian transition, animals began to shift from simply moving across the seabed to actively exploring deeper layers of sediment. The transition from 2D movement to 3D burrowing turned the ocean bottom from a single, uniform environment into a complex, animal-engineered habitat, fundamentally changing marine ecosystems.Now, a discovery from central China's Hubei Province indicates that this revolutionary change had started much earlier.Researchers from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences conducted a study on the Shibantan Biota, a treasure trove of ancient fossils in Hubei. This fossil biota dates back approximately 550 to 543 million years. They identified several types of burrows made by worm-like animals, indicating that complex animal behaviors were already shaping the seafloor environment nearly 10 million years earlier than previously thought.These findings were on Thursday published in the journal Science Advances. Researchers involved in the study noted their discovery of Treptichnus streptosus, a new type of fossilized, zig-zag burrow made by an ancient worm."Its structure suggests that trace-making creatures were capable of rhythmic and repeatable movement and exploring, which reflects a well-developed nervous system and muscular control," lead researcher Chen Zhe told Xinhua.Chen also mentioned other known traces found at the site, such as tadpole-shaped burrows and complex, compound tunnels created by ancient animals as they walked, searched for food and temporarily dwelled.These adaptations indicate that animal behaviors were already diverse and complex at that time -- earlier than the rapid burst of life known as the Cambrian explosion, Chen explained, while adding that the new study extends the timeline of animal evolutionary sophistication further back than before.This image provided by the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences shows a restoration picture of trace fossils discovered in central China's Hubei Province.(Xinhua)Complex digging behaviors inferred from trace fossils, notably, also caused a lot of disturbance in the sediment.They not only broke up the microbial mats covering the seafloor but also damaged the habitat of Ediacara organisms that lived there, which may have led to their decline, said co-author Liu Yarong, a PhD student at the institute.This means that early animal burrowing may have contributed to the first known mass extinction event -- the decline of the Ediacara biota around 550 million years ago.However, this disturbance also created new opportunities for other types of animals to evolve and diversify. Along with additional biological and environmental factors, early animal burrowing helped drive the major ecosystem transformation that took place at the dawn of the Cambrian period, according to the researchers.In 2018, paleontologists from China and the United States reported the discovery of trace fossils that represented some of the earliest known evidence for animal appendages or legs in the Shibantan Biota in the Yangtze Gorges area.The new study confirms that this biota, with its rich variety of trace and body fossils -- offers a unique window into one of the most important turning points in the history of life, namely the transition from simple life forms to complex ecosystems."Animals are not only shaped by their environment, but they also play a vital role in shaping it," Liu said. Enditem
A research team from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) has made progress in studying the Shibantan Biota in Yichang, Hubei Province, uncovering the oldest known complex three-dimensional burrow systems to date. Preserved in approximately 550-million-year-old strata, these trace fossils show that complex animal behaviors were modifying the seafloor environment nearly 10 million years earlier than previously thought.Schematic illustration of trace fossils in the Shibantan assemblage. (Image by NIGPAS)A research team from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) has made progress in studying the Shibantan Biota in Yichang, Hubei Province, uncovering the oldest known complex three-dimensional burrow systems to date. Preserved in approximately 550-million-year-old strata, these trace fossils show that complex animal behaviors were modifying the seafloor environment nearly 10 million years earlier than previously thought.The Ediacaran–Cambrian transition, around 539 million years ago, marks one of the most significant ecosystem revolutions in Earth's history. A key driver of this ecological shift was the transition of metazoan behavior from simple two-dimensional surface activities to three-dimensional exploration deep into sediments. This "substrate revolution" transformed the seafloor from a uniform, matground-dominated system into a heterogeneously, bioturbated modern-style seabed, permanently altering the trajectory of Earth's environmental and biological evolution.The researchers conducted a systematic study of trace fossils from the Shibantan Biota (approximately 550–543 million years old). They identified multiple ichnospecies within the genus Treptichnus and established a new ichnospecies, Treptichnus streptosus. By combining these findings with previously discovered three-dimensional trace fossils such as Lamonte and tadpole-shaped traces from the same biota, the study offers an in-depth analysis of the evolutionary and ecological significance of the emergence of animals' vertical exploration behavior.The findings, published in Science Advances on Oct. 29, reveal that complex animal behaviors emerged on the eve of the Cambrian explosion.Treptichnus is a landmark trace fossil, representing the first "3D exploration" of sediments by animals, and holds importance in evolutionary biology, animal behavior, and ecology. The first appearance of T. pedum, a member of this genus, formally defines the Ediacaran–Cambrian boundary. The new discovery from the Shibantan Biota predates this revolutionary behavior. In addition to reporting the new species T. streptosus, the study identifies other ichnospecies including T. cf. bifurcus, T. rectangularis, and T. pollardi, demonstrating that animal burrowing behaviors had already achieved considerable diversity by this period.Furthermore, the Shibantan Biota preserves other three-dimensional burrows, such as Lamonte and tadpole-shaped traces. The concentrated occurrence of these vertical exploration behaviors reflects early sedimentary ecological stratification and complex foraging strategies, indicating a gradually enhanced ability of trace-making organisms to engineer substrates.The study found that Lamonte caused intensive bioturbation within the Shibantan Biota. This not only disrupted microbial mats on the sediment surface but also dismantled the ecological environment of Ediacara-type organisms that depended on these mats. This suggests bioturbation may have been a contributing factor to the first extinction event of the Ediacara biota around 550 million years ago.The emergence of these complex behaviors and their cumulative ecological effects intensified toward the end of the Ediacaran Period. This led to the gradual decline of microbial mats, continuously eroding the ecological foundation of Ediacara-type organisms while creating new ecological opportunities for the diversification of other metazoans. Driven by the synergy of various biological and non-biological factors, this process ultimately contributed to the profound ecosystem transformation during the Ediacaran–Cambrian transition.This research further confirms that the rich and diverse assemblage of trace fossils and body fossils preserved in the Shibantan Biota provides a window for studying major ecosystem changes at the transition between the Precambrian and Phanerozoic Eons.This work was supported by the National Natural Science Foundation of China.
Chinese scientists' latest findings in ancient seabed community illustrate a biological mechanism capable of shaping community structure, operating beyond passive environmental constraints or initial larval settlement preferences, and highlight the potential for subtle anatomical features to exert significant ecological influence in deep time, according to a research article published on Monday by the Proceedings of the National Academy of Sciences of the United States of America (PNAS), a leading scientific journal in the world.Nucleospira calypta Photos: CCTV NewsChinese scientists' latest findings in ancient seabed community illustrate a biological mechanism capable of shaping community structure, operating beyond passive environmental constraints or initial larval settlement preferences, and highlight the potential for subtle anatomical features to exert significant ecological influence in deep time, according to a research article published on Monday by the Proceedings of the National Academy of Sciences of the United States of America (PNAS), a leading scientific journal in the world.Huang Bing and Rong Jiayu, research fellows from the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, cracked the mystery of social distancing by reporting exceptionally preserved soft, bristle-like structures ("setae") on 436-million-year-old brachiopods, enabling the analysis of ancient behavior.The research team worked on the 436-million-year-old early Silurian brachiopod fossil community discovered in Tongzi and Renhuai, Southwest China's Guizhou Province. For the first time, Huang and Rong identified a regular, checkerboard-like spacing pattern among these organisms, closely corresponding to their setae length. This demonstrates that these delicate structures played an important role in maintaining spacing between individuals, thereby influencing community organization on the ancient seabed.Their findings point to a previously unrecognized mechanism shaping ecosystem structure in deep time, demonstrating how subtle anatomical features could have exerted notable ecological impacts in their ancient environments.Nucleospira calyptaThe study focused on Nucleospira calypta. The fossil specimens buried in situ in this study completely preserved their true state at the last moment of their lives, opening a precious window for scientists to observe ancient biological communities.Setae are slender, flexible, hair-like structures growing on the edge of their mantles. They are extremely difficult to preserve in fossils, especially in the long geological history after the Cambrian period, approximately 541 million years ago. The specimens studied this time also rarely preserve the setae structure on the edge of the mantle of brachiopods.Through a variety of modern analytical techniques, the researchers not only clearly reconstructed the fine morphology of these setae with a diameter of about 20 microns but also confirmed one of the unique preservation mechanisms: the setae first rapidly pyritized in an oxygen-deficient environment and then were coated with a calcium shell in weakly acidic conditions to prevent compaction and oxidation. Therefore, even if the pyrite later converted into iron oxide, its microscopic morphology was still preserved perfectly.After the confirmation of the fine structures, the researchers focused on the layout of the entire community. Through analysis, they found that the distribution of these brachiopods was not random and chaotic, but presented a statistically significant, non-random, uniform distribution pattern that looks like a chessboard. This "chessboard-like" layout indicates that there is a mechanism between individuals.How was this precise spacing adjustment achieved?Through analysis, the researchers found that there is a clear quantitative relationship between the average distance between individuals in the fossil community and the length of their well-preserved setae. This kind of fine-tuning of position in seemingly immobile organisms is not without precedent. For example, modern Cirripedia can still migrate extremely slowly after being fixed to optimize their living space.When individuals are too close to each other, their extended setae will reach their neighbors. This continuous physical contact, after a long period of accumulation, eventually leads the entire population to a stable configuration where no interference is caused and space utilization is optimized. "This is crucial for filter-feeding organisms to minimize interference with each other's feeding water flow," said Huang in an interview with the Nanjing Daily.For the first time, the study directly links a subtle anatomical structure (setae) with a statistically significant spatial pattern of community, providing direct fossil evidence for the core question of paleoecology: "How do interactions between organisms shape distribution structure?" This shows that the formation of ancient communities was not only subject to passive environmental factors or the random fixation of larvae, but also that interactions between individual organisms caused by their morphological structures played a crucial role. This discovery not only deepens the understanding of the complexity of Paleozoic marine ecosystems, but also highlights the important ecological impacts that seemingly insignificant features may have in the process of evolution.
BEIJING, Jan. 25 (Xinhua) -- Chinese archaeologists have discovered a batch of fossils of multicellular eukaryotes that date back to 1.63 billion years ago, setting the world's oldest record of such fossils. BEIJING, Jan. 25 (Xinhua) -- Chinese archaeologists have discovered a batch of fossils of multicellular eukaryotes that date back to 1.63 billion years ago, setting the world's oldest record of such fossils. These well-preserved microfossils, Qingshania magnifica, were found in the Yanshan Mountains of north China, according to the findings published in the journal Science Advances this week. The discovery was made by researchers from the Nanjing Institute of Geology and Palaeontology under the Chinese Academy of Sciences. It marks another advancement after they found decimeter-sized fossils of multicellular eukaryotes in this region in 2016, and pushes back the emergence of such organisms by about 70 million years. The newly found fossils consist of large uniseriate and unbranched filaments with cell diameters up to 190 micrometers. A particular feature, the round intracellular structure in some cells, indicates that they might reproduce by spores, like many eukaryotic algae. Researchers further inferred that the fossils were most likely photosynthetic algae. The earliest eukaryotic fossils so far are unicellular forms dating back to 1.65 billion years ago found in north China and north Australia. Qingshania magnifica appeared slightly later, indicating that eukaryotes evolved to multicellularity very early in their history, said the paper. This undated photo provided by the Nanjing Institute of Geology and Palaeontology under the Chinese Academy of Sciences shows microfossils of Qingshania magnifica found in the Yanshan Mountains of north China. Chinese archaeologists have discovered a batch of fossils of multicellular eukaryotes that date back to 1.63 billion years ago, setting the world's oldest record of such fossils. (Xinhua)
In a study published in Science Advances on Jan. 24, researchers led by Prof. ZHU Maoyan from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences reported their recent discovery of 1.63-billion-year-old multicellular fossils from North China. In a study published in Science Advances on Jan. 24, researchers led by Prof. ZHU Maoyan from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences reported their recent discovery of 1.63-billion-year-old multicellular fossils from North China. These exquisitely preserved microfossils are currently considered the oldest record of multicellular eukaryotes. This study is another breakthrough after the researchers’ earlier discovery of decimeter-sized eukaryotic fossils in the Yanshan area of North China, and pushes back the emergence of multicellularity in eukaryotes by about 70 million years. All complex life on Earth, including diverse animals, land plants, macroscopic fungi, and seaweeds, are multicellular eukaryotes. Multicellularity is key to eukaryotes acquiring organismal complexity and large size, and is often regarded as a major transition in the history of life on Earth. However, scientists have been unsure when eukaryotes evolved this innovation. Fossil records offering convincing evidence show that eukaryotes with simple multicellularity, such as red and green algae, and putative fungi, appeared as early as 1.05 billion years ago. Older records have claimed to be multicellular eukaryotes, but most of them are controversial because of their simple morphology and lack of cellular structure. "The newly discovered multicellular fossils come from the late Paleoproterozoic Chuanlinggou Formation that is about 1,635 million years old. They are unbranched, uniseriate filaments composed of two to more than 20 large cylindrical or barrel-shaped cells with diameters of 20–194 μm and incomplete lengths up to 860 μm. These filaments show a certain degree of complexity based on their morphological variation," said MIAO Lanyun, one of the researchers. The filaments are constant, or tapered throughout their length, or tapered only at one end. Morphometric analyses demonstrate their morphological continuity, suggesting they represent a single biological species rather than discrete species. The fossils have been named Qingshania magnifica, 1989, a form taxon with similar morphology and size, and are described as being from the Chuanlinggou Formation. A particularly important feature of Qingshania is the round intracellular structure (diameter 15–20 μm) in some cells. These structures are comparable to the asexual spores known in many eukaryotic algae, indicating that Qingshania probably reproduced by spores. In modern life, uniseriate filaments are common in both prokaryotes (bacteria and archaea) and eukaryotes. The combination of large cell size, wide range of filament diameter, morphological variation, and intracellular spores demonstrate the eukaryotic affinity of Qingshania, as no known prokaryotes are so complex. Filamentous prokaryotes are generally very small, about 1–3 μm in diameter, and are distributed across more than 147 genera of 12 phyla. Some cyanobacteria and sulfur bacteria can reach large sizes, up to 200 μm thick, but these large prokaryotes are very simple in morphology, with disc-shaped cells, and are not reproduced by spores. The best modern analogues are some green algae, although filaments also occur in other groups of eukaryotic algae (e.g., red algae, brown algae, yellow algae, charophytes, etc.), as well as in fungi and oomycetes. "This indicates that Qingshania was most likely photosynthetic algae, probably belonging to the extinct stem group of Archaeplastids (a major group consisting of red algae, green algae and land plants, as well as glaucophytes), although its exact affinity is still unclear," said MIAO. In addition, the researchers conducted Raman spectroscopic investigation to test the eukaryotic affinity of Qingshania from the perspective of chemical composition, using three cyanobacterial taxa for comparison. Raman spectra revealed two broad peaks characteristic of disordered carbonaceous matter. Furthermore, the estimated burial temperatures using Raman parameters ranged from 205–250 °C, indicating a low degree of metamorphism. Principal component analysis of the Raman spectra sorted Qingshania and the cyanobacterial taxa into two distinct clusters, indicating that carbonaceous matter of Qingshania is different from that of cyanobacterial fossils, further supporting the eukaryotic affinity of Qingshania. Currently, the oldest unambiguous eukaryotic fossils are unicellular forms from late Paleoproterozoic sediments (~1.65 billion years ago) in Northern China and Northern Australia. Qingshania appeared only slightly later than these unicellular forms, indicating that eukaryotes acquired simple multicellularity very early in their evolutionary history. Since eukaryotic algae (Archaeplastids) arose after the last eukaryotic common ancestor (LECA), the discovery of Qingshania, if truly algal in nature, further supports the early appearance of LECA in the late Paleoproterozoic—which is consistent with many molecular clock studies—rather than in the late Mesoproterozoic of about 1 billion years ago. This study was funded by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Innovation Cross-Team of CAS. Multicellular fossils come from the late Paleoproterozoic Chuanlinggou Formation
A new study has shown that cicadas about 100 million years ago had yet to learn to produce the iconic buzzing sound that now characterizes summer days. A new study has shown that cicadas about 100 million years ago had yet to learn to produce the iconic buzzing sound that now characterizes summer days. Cicada, referring to the superfamily Cicadoidea, includes the globally widespread Cicadidae, commonly known as singing cicadas, and Australia-only Tettigarctidae. The former can produce the loudest sounds among insects, reaching nearly 120 decibels via tymbal mechanisms. In the study published in Nature Communications, a team of international scientists looked at 11 pieces of Cicadoidea fossils from Myanmar with a 100-million-year history and compared them with other fossils and extant cicadas. Although tymbal was identified in these fossils, the majority lacked intricate sound production and auditory systems, said Jiang Hui, lead author of the paper and a researcher with the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. "This suggests that most cicadas from 100 million years ago might have relied on more primitive means of communication -- to transmit body vibrations through substrates like tree trunks -- rather than amplifying sounds through abdominal vibrations and transmitting them through the air," said Jiang. "In other words, they might not have sung like today's cicadas," Jiang said. This study also reports powerful fossorial forelegs from nymphal fossils, akin to modern cicadas, suggesting similar robust capabilities for digging, subterranean long-term living, and root-feeding. (Xinhua)
An international team of scientists said a fossil dating back to about 130 million years ago suggests male mosquitoes likely sucked blood in ancient times. An international team of scientists said a fossil dating back to about 130 million years ago suggests male mosquitoes likely sucked blood in ancient times. Among modern-day mosquitoes, only females are hematophagous, meaning that they use piercing mouth parts to feed on the blood of humans and other animals. Scientists believe that insect hematophagy evolved from piercing-sucking mouthparts used to extract plant fluids but have difficulty studying this evolution due to the lack of insect fossil records. The scientists from China, Lebanon, France and the United States found in a Lower Cretaceous amber from Lebanon that the piercing mouthparts of two well-preserved male mosquitoes included an exceptionally sharp, triangular mandible and elongated structure with small, toothlike denticles, which suggested that they were then fed on blood. The new findings, published online in the journal Current Biology, may provide new evidence for the study of the evolution of mosquitoes, according to the scientists. "Lebanese amber is to date the oldest amber with intensive biological inclusions, and it is a very important material as its formation is contemporaneous with the appearance and beginning of radiation of flowering plants, with all that follows of co-evolution between pollinators and flowering plants," said Dany Azar, from Nanjing Institute of Geology and Paleontology under the Chinese Academy of Sciences, and the Lebanese University, who led the research. The new findings extended the definitive occurrence of the mosquito family of insects into the early Cretaceous, and with blood-sucking male mosquitoes, suggested that the evolution of hematophagy was more complicated than suspected. According to André Nel of the National Museum of Natural History of Paris, the scientists are going to study the "utility" of having hematophagy in ancient male mosquitoes and why they later stopped sucking blood. (Xinhua)
Researchers found these ancient bloodsuckers entombed in amber, which had been collected 15 years ago in central Lebanon. They represent the oldest known mosquito fossils yet found. If you smack at a mosquito on your arm or neck, chances are it’s a female. Only female mosquitoes suck blood, which they need for protein to produce their eggs. Males, which lack females’ skin-piercing mouthparts, feed on nectar and plant juices. But that might not have always been the case: Researchers reported Monday in Current Biology that some 125 million years ago, during the early Cretaceous, at least some male mosquitoes sported sharp mandibles and a long appendage with toothlike bristles, similar to modern females’ piercing parts. Researchers found these ancient bloodsuckers entombed in amber, which had been collected 15 years ago in central Lebanon. They represent the oldest known mosquito fossils yet found. The findings offer good evidence that the earliest known mosquitoes—male and female alike—supped blood from hosts, The New York Times reported on Monday. Rather than evolving to suck blood later in evolution, the researchers say, mosquitoes may have started off as bloodsuckers. If so, males may have only lost the ability as flowering plants proliferated during the Cretaceous period, offering them a food source without the risk of getting swatted. https://www.science.org/content/article/oldest-known-mosquito-fossils-show-males-too-once-sucked-blood
An international research team led by Prof. ZHANG Huaqiao from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) has reported the discovery of extraordinary early Cambrian (ca. 535 million years ago, or Ma) microfossils preserving the introvert musculature of cycloneuralians, a group of animals that include roundworms, horsehair worms, mud dragons, and many other creatures. An international research team led by Prof. ZHANG Huaqiao from the Nanjing Institute of Geology and Palaeontology of the Chinese Academy of Sciences (NIGPAS) has reported the discovery of extraordinary early Cambrian (ca. 535 million years ago, or Ma) microfossils preserving the introvert musculature of cycloneuralians, a group of animals that include roundworms, horsehair worms, mud dragons, and many other creatures. The discovery added fleshy insights into early Cambrian cycloneuralians, which are closely related to arthropods, the most successful animals on Earth. The study was published in Proceedings of the Royal Society B: Biological Sciences on Oct. 11. The Ecdysozoa superphylum represents the most diverse bilaterally symmetric animals. It contains Scalidophora (Kinorhyncha, Loricifera, Priapulida), Nematoida (Nematoda, Nematomorpha), and Panarthropoda (Tardigrada, Onychophora, Arthropoda). Scalidophora and Nematoida constitute the Cycloneuralia, whose monophyly is debated. Unambiguous ecdysozoan body fossils first appeared in the early Fortunian Age (ca. 535 Ma) and are represented by the total-group ecdysozoan taxon Saccorhytus and several crown-group cycloneuralian species. However, the preservation of Fortunian ecdysozoans is limited to cuticular integuments, with no labile internal tissues (e.g., muscles or nerve tissues) preserved, hampering further understanding of their functional morphology and evolutionary significance. In this study, the researchers described three phosphatized and millimeter-sized specimens from the early Fortunian Kuanchuanpu Formation (ca. 535 Ma) of China. Among them, one specimen (NIGP179459) is better preserved and consists of five successively larger rings that are interconnected with 19 radial and 36 longitudinal structures. The rings were compressed to certain degrees, implying that they were pliable when alive. The first ring is separated from the remaining four larger rings by a gap and is located almost co-planarly at the center of, or slightly apical to, the second ring. The radial structures connect the first ring with the third ring, whereas the longitudinal structures extend from the third ring to beyond the fifth ring. Some longitudinal structures become more fibrous in textural appearance toward the abapical end. In the reconstruction, the second to fifth rings are coaxially stacked and constitute an apically truncated cone, with hexaradially arranged internal longitudinal structures. Based on their patterns of arrangement, the fibrous texture, and the inferred pliability, the rings as well as the radial and longitudinal structures were interpreted as fossilized muscles. The preserved musculature consists of four groups of muscles, i.e., an inner circular, four outer circular, 19 radial, and 36 longitudinal muscles. This complex topology differs from that of the body-wall musculatures of basal animals such as cnidarians or ctenophores, and instead it likely represents musculature of bilaterian animals. The hexaradial symmetry imparted by the arrangement of the longitudinal muscles invites a comparison with scalidophorans, whose introvert exhibits radial symmetry both externally (i.e., longitudinal rows of scalids are radially disposed) and internally (i.e., longitudinal muscles are radially arranged). With a scalidophoran affinity, the researchers interpreted specimen NIGP179459 as the anterior introvert musculature. The authors interpreted the second to fifth rings as body-wall circular muscles, and the 36 longitudinal structures as body-wall longitudinal muscles. The body-wall circular and longitudinal muscles constitute a muscular grid. Since a similar body-wall muscular grid is present in priapulans but absent in loriciferans and kinorhynchs, specimen NIGP179459 was proposed to belong to the priapulans. Considering that the priapulan-like introvert may have characterized the last common ancestor of the Scalidophora, it is also possible that specimen NIGP179459 belongs to total-group Scalidophora. The total-group scalidophoran affinity of NIGP179459 is further supported by the first ring and radial structures. The researchers interpreted the first ring as an introvert circular muscle and the 19 radial structures as introvert circular muscle retractors. An introvert circular muscle is present in loriciferans, kinorhynchs, and the hatching larvae of priapulans, whereas introvert circular muscle retractors are present in kinorhynchs and the hatching larvae of priapulans. Furthermore, specimen NIGP179459 lacks a mouth cone and scalid-associated muscles, but these muscles are common in loriciferans and kinorhynchs. Thus, the total evidence supports a total-group scalidophoran affinity, possibly related to the priapulans. Scalidophorans as represented by specimen NIGP179459 were millimeter-sized and had an introvert with hexaradially arranged scalids, which correspond to the hexaradially arranged body-wall longitudinal muscle bundles inside. This musculature may have controlled the inversion of the introvert and thus facilitated locomotion and feeding. The absence of long introvert retractors indicates that the animals may have had very limited ability to retract their introvert, differing from modern scalidophorans that have long introvert retractors and thus can completely retract their introvert. Fig. 1 SEM images of NIGP179459 (Image by ZHANG Huaqiao) Fig. 2 Reconstructions of NIGP179459 (Image by ZHANG Huaqiao) Fig. 3 Schematic representation of scalidophoran musculatures (Image by ZHANG Huaqiao) Fig. 4 Phylogenetic position of scalidophorans represented by NIGP179459 (Image by ZHANG Huaqiao)
