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''Antennacanthopodia'' is a small
lobopodia 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 ...
n from the
Chengjiang biota The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...
that dates to about 520 million years ago (
Cambrian Stage 3 Cambrian Stage 3 is the still unnamed third stage of the Cambrian. It succeeds Cambrian Stage 2 and precedes Cambrian Stage 4, although neither its base nor top have been formally defined. The plan is for its lower boundary to correspond approxima ...
). It is similar to the extant
Onychophora Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...
(velvet worm) and is the only widely accepted
stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...
-onychophoran
lobopodia 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 ...
n from the
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
period. ''Antennacanthopodia'' had nine pairs of stubby
leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...
s, a pair of potential
ocelli A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...
, and two pairs of antennae. The first pair of antennae were much longer than the second and are still present in modern onychophorans. The identity of the smaller antennae are less clear, but they might be homologous with either the
slime papillae Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...
or onychophoran jaw. The animal also had diminutive spines on its legs and trunk, highly
sclerotized Sclerosis (also sclerosus in the Latin names of a few disorders) is a hardening of tissue and other anatomical features. It may refer to: * Sclerosis (medicine), a hardening of tissue * in zoology, a process which forms sclerites, a hardened exo ...
foot pads, and possible pair of tendril-like
appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
s at the end of its body.


Discovery and naming

Both fossils of ''Antennacanthopodia'' were excavated from the upper Yu'anshan Member of the
Lower Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...
Heilinpu Formation. This is close to the famous
Maotianshan Shales The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...
of
China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...
's
Yunnan Province Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...
and probably makes them a part of the
Chengjiang Biota The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...
. The
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
(ELEL-EJ081876) was collected from the Erjie section of the Yu'anshan Member's Eoredlichia-Wutingaspis Biozone while the
paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...
(ELI-JS022643) was found in the Jianshan section. Both specimens date to around 520 million years old, placing them in the
Cambrian Series 2 Cambrian Series 2 is the unnamed 2nd series of the Cambrian. It lies above the Terreneuvian series and below the Miaolingian. Series 2 has not been formally defined by the International Commission on Stratigraphy, lacking a precise lower boundary ...
Stage 3 Stage, stages, or staging may refer to: Arts and media Acting * Stage (theatre), a space for the performance of theatrical productions * Theatre, a branch of the performing arts, often referred to as "the stage" * ''The Stage'', a weekly Brit ...
. Currently, the holotype is located at the Early Life Evolution Laboratory (ELEL) at the China University of Geosciences in
Beijing Beijing, Chinese postal romanization, previously romanized as Peking, is the capital city of China. With more than 22 million residents, it is the world's List of national capitals by population, most populous national capital city as well as ...
, China. The paratype can be found at the Early Life Institute (ELI) at
Northwest University Northwest University may refer to: *Northwest University (China) in Xi'an, Shaanxi, China *Northwest University (United States) in Kirkland, Washington, US *North-West University in Potchefstroom and Mahikeng, North West Province, South Africa *Nor ...
in
Xi'an Xi'an is the list of capitals in China, capital of the Chinese province of Shaanxi. A sub-provincial city on the Guanzhong plain, the city is the third-most populous city in Western China after Chongqing and Chengdu, as well as the most populou ...
, China. The genus gets its name from the
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
words "antennatus" and "acanthopodus", referring to the fossil's multiple antennae and spiny lobopods. The species name is from the
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
"gracilis" meaning "slender" or graceful".


Description

Both fossils of ''Antennacanthopodia'' were dorsoventrally compacted in
mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...
, with the
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
being far better preserved than the
paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...
. Excluding any appendages, the holotype specimen is tiny, only 1.4 cm long. The
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
s preserve soft tissues as a purplish black film and details of the
sclerotized Sclerosis (also sclerosus in the Latin names of a few disorders) is a hardening of tissue and other anatomical features. It may refer to: * Sclerosis (medicine), a hardening of tissue * in zoology, a process which forms sclerites, a hardened exo ...
cuticle as a reddish-brown.


Head

''Antennacanthopodia'' had two pairs of antennae. The first pair were double the length of the
head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...
and 1/4th of the length of the body. They also preserved faint ridges at their base. The second pair was shorter than the first and is likely a modified
appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
. However, which segment they correspond to is unclear, as apparently, the animal lacked jaws. In the animal's original description, the second antennae were hypothesized to be homologous with the
slime papillae Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...
. Thus, they would be part of the third head segment. Accounting for the lack of jaws, later studies disagreed. Instead, they considered the antennae to originate from the second head segment. At the base of the first antennae were a pair of rounded black specks. It can be reasonably assumed that these are
ocelli A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...
, a type of simple
eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...
found in modern velvet worms. When compared, these eyes have similar proportions relative to the body, have the same overall placement, and originate from the same segment of the
head A head is the part of an organism which usually includes the ears, brain, forehead, cheeks, chin, eyes, nose, and mouth, each of which aid in various sensory functions such as sight, hearing, smell, and taste. Some very simple ani ...
. The position of ''Antennacanthopodia''s
mouth A mouth also referred to as the oral is the body orifice through which many animals ingest food and animal communication#Auditory, vocalize. The body cavity immediately behind the mouth opening, known as the oral cavity (or in Latin), is also t ...
is unclear. A study on the
panarthropod Panarthropoda is a clade comprising the greatest diversity of animal groups. It contains the extant phyla Arthropoda (Euarthropoda), Tardigrada (water bears) and Onychophora (velvet worms), although the precise relationships among these remained ...
heads considered it to have a ventral-facing mouth based on ancestral character reconstruction. Still, due not being preserved in either
fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
, this is only a hypothesis.


Trunk

Like with the rest of the body, the outline of the
trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure, and the stem of woody plants * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Comput ...
is preserved by a reddish outer cuticle. The trunk is long and comprises nine segments, each bearing a pair of legs. After the legs, the trunk tapers off to an endmost projection with two tendrils known as "cirriform structures". The body's surface had rows of tiny spines, with four per segment. Spine rows were found on the dorsal and lateral sides from the second to fourth trunk segments. Because of this, the pattern of rows likely applied to the entire trunk. Unlike many other
lobopodia 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 ...
ns, ''Antennacanthopodia'' lacked
sclerotized Sclerosis (also sclerosus in the Latin names of a few disorders) is a hardening of tissue and other anatomical features. It may refer to: * Sclerosis (medicine), a hardening of tissue * in zoology, a process which forms sclerites, a hardened exo ...
plates or tube-like attachments on its back. Inside the outer cuticle is a purplish black film separated by a
sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
-filled void. The outer film is lighter, running along the cuticle and into the
leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...
s. Inside this is a straight black band that runs through the center of the body and takes up 50% of the trunk's width. The 2011 description interpreted the void as the animal's original
body cavity A body cavity is any space or compartment, or potential space, in an animal body. Cavities accommodate organs and other structures; cavities as potential spaces contain fluid. The two largest human body cavities are the ventral body cavity, a ...
, the lighter film as
musculature Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...
, and the darker film as a simple
midgut The midgut is the portion of the human embryo from which almost all of the small intestine and approximately half of the large intestine develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises ...
. However, later studies reject this. When looking at how modern velvet worms decay, the "body cavity" mentioned in the original description was likely a misinterpretation. Rather, it was a product of the
procuticle Arthropods are covered with a tough, resilient integument, cuticle or exoskeleton of chitin. Generally the exoskeleton will have thickened areas in which the chitin is reinforced or stiffened by materials such as minerals or hardened proteins. T ...
breaking down "Breaking Down" is a song by American rock band I Prevail, released as the second single from their second studio album ''Trauma''. In July 2019, it peaked at number three on the ''Billboard'' Mainstream Rock Songs chart. Background The song was ...
early on and then separating from the outer cuticle. A similar thing applies to the musculature and midgut. The musculature is likely a shrunken
epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...
, and the midgut was probably undifferentiated contents of the actual body cavity.


Legs

Both the
holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
and
paratype In zoology and botany, a paratype is a specimen of an organism that helps define what the scientific name of a species and other taxon actually represents, but it is not the holotype (and in botany is also neither an isotype (biology), isotype ...
preserve nine pairs of stubby, unjointed
leg A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element cap ...
s. These are splayed to the sides and slant slightly downward in the holotype. The original describers were unable to find any claws, but found that each leg had a highly
sclerotized Sclerosis (also sclerosus in the Latin names of a few disorders) is a hardening of tissue and other anatomical features. It may refer to: * Sclerosis (medicine), a hardening of tissue * in zoology, a process which forms sclerites, a hardened exo ...
, disc-shaped foot pad. This pad might have helped the animal with
walking Walking (also known as ambulation) is one of the main gaits of terrestrial locomotion among legged animals. Walking is typically slower than running and other gaits. Walking is defined as an " inverted pendulum" gait in which the body vaults o ...
and is likely homologous to those of velvet worms. The legs were circular and had small, conical spines arranged in at least 7 circlets per leg. Each circlet had around 10 spines that were distributed at equal distances. As you go from the base of the leg to where it meets with the body, the spines appear to get bigger. In its original description, the purplish-black lobes inside the leg's outer cuticle were interpreted as
musculature Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the others being cardiac muscle and smooth muscle. They are part of the somatic nervous system, voluntary muscular system and typically are a ...
. Similar to the trunk, this interpretation is likely wrong. Rather than leg musculature, these lobes are probably shrunken soft tissue of the original legs.


Cirriform Structures

''Antennacanthopodia'' might have had a pair of tendril-like
appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
s at the end of the body. These are known as "cirriform structures", measure around 60% of the body's length, and appear highly flexible. Nevertheless, they may instead be ruptured body contents from later stages of
decay Decay may refer to: Science and technology * Bit decay, in computing * Decay time (fall time), in electronics * Distance decay, in geography * Software decay, in computing Biology * Decomposition of organic matter * Mitochondrial decay, in g ...
.


Classification

So far'', Antennacanthopodia'' is the only widely accepted
stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...
-
onychophora Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...
n
lobopodia 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 ...
n from the
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
period. The affinity of other Cambrian lobopodians, especially outside those outside of the arthropod total-group, is heavily contested and varies from study to study. As such, ''Antennacanthopodia'' is critical in elucidating the origins of what is now a purely
terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...
phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...
. It shows that many onychophoran traits ( antenna with
ocelli A simple eye or ocellus (sometimes called a pigment pit) is a form of eye or an optical arrangement which has a single lens without the sort of elaborate retina that occurs in most vertebrates. These eyes are called "simple" to distinguish the ...
at their base, stubby legs with foot pads, modified second or third
appendage An appendage (or outgrowth) is an external body part or natural prolongation that protrudes from an organism's body such as an arm or a leg. Protrusions from single-celled bacteria and archaea are known as cell-surface appendages or surface app ...
s) had already evolved in the
Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
. However, as seen with ''
Antennipatus ''Antennipatus montceauensis'' is an extinct species of onychophoran, a group colloquially known as velvet worms, from the Montceau-les-Mines lagerstätte of what is now France. The animal is the sole member of its genus and notably the oldest c ...
'', characteristics such as
slime papillae Onychophora (from , , "claws"; and , , "to carry"), commonly known as velvet worms (for their velvety texture and somewhat wormlike appearance) or more ambiguously as peripatus (after the first described genus, ''Peripatus''), is a phylum of el ...
did not evolve until later, likely after colonizing the land. The cladogram below is simplified from Jean-Bernard Caron and Cédric Aria's paper describing the lobopodian ''
Ovatiovermis ''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. M ...
''.


References


External links

* {{Taxonbar, from=Q16828850 Lobopodia Maotianshan shales fossils Cambrian invertebrates Fossil taxa described in 2011 Monotypic prehistoric protostome genera Fossils of China Transitional fossils