Antennipatus is an extinct genus of Frenchonychophoran, a group colloquially known as velvet worms. The genus is notable for being the oldest confirmed onychophoran fossil, dating to the Stephanian stage of the Late Carboniferous. Antennipatus highly resembles modern velvet worms, having a pair of slime papillae, stubby legs, a pair of long antennae, a putative ventralmouth, and rings of dermal papillae along most its body. Based on having slime papillae and where it was found, Antennipatus was likely terrestrial. However, due to the way it was preserved, it is difficult to place the animal phylogenetically.
Antennipatus was known from the Montceau-les-Mineslagerstätte as far back as 1981.[1] A 1982 paper mentioned the animal, describing it as a definite onychophoran due to its well-preserved antennae and virtually identical to a fossil from Mazon Creek (Helenodora).[2] Later papers displayed some of the undescribed fossils and showed how the number of specimens rose from two to several.[3][4]
Antennipatus had onychophoran-like antennae with more than 40 annuli (rows of dermal papillae) present in the holotype. These antennae preserved alternating wide and narrow bands called plicae, a pattern seen in living velvet worms.[1] Behind the antennae were a pair of slime papillae, being most noticeable on MNHN SOT003121b. These structures were interpreted as such based on their location, lack of annulation compared to other limbs, and due to being noticeably shorter than the proceeding legs.[1] Two fossils of Antennipatus preserved what is likely a ventral (bottom-facing) mouth. In the holotype, this is preserved as hole that is longer vertically than horizontally and surrounded by a circular protrusion, probably the animal's lip papillae. Since the holotype lacks any jaws, its mouth was either closed or filled with sediment when being fossilized.[1] No specimen of Antennipatus preserves any eyes, though this could be due to poor preservation. Alternatively, the animal could have lacked eyes all together.[1]
Trunk and lobopods
No fossil of Antennipatus preserves the hind part of its anatomy, meaning how many legs it had, the position of its anus, and the position of its genital pad are unknown. Luckily, a few trunk segments managed to be preserved, giving some insight on its anatomy.[1]Antennipatus’s trunk had a minimum of 5 segments, with 8 plicae per segment. Similar to the annulated antennae, the plicae on the trunk are preserved as lines of dermal papillae and horizontal ridges.[1] Like in modern onychophorans, each segment of the trunk had a pair of legs known as lobopods. These also preserved annulations, with eight to ten per leg. However, the they didn’t preserve any claws or spinous pads.[1]Tracheal openings were also absent, though this is probably due to being really small and a feature unlikely to preserve outside of amber.[1]
Classification
MNHN SOT003122a & b. Notice the preservation of plicae by visible ridges and dermal papillae.
Before it's description, Antennipatus was considered virtually identical to Helenodora and possibly a member of the genus.[2][4] However, these animals differ in a few key ways. On its trunk, Helenodora has nine plicae per segment while Antennipatus has eight. Antennipatus was also significantly larger, though this may be caused by age.[1]
Antennipatus is difficult to place on the onychophoranfamily tree due to lacking several informative traits. The jaw blade and genital opening are either hidden or completely absent, preventing even a family-level assignment (Peripatidae or Peripatopsidae).[1] Based on a time-calibrated phylogeny, Antennipatus predates the diversification of Peripatopsidae by around 100 million years and is within the error bar of early Peripatidae diversification.[1][6]
Since it lived in the Northern Hemisphere and had a large body size, Antennipatus could have affinities with peripatids (either part of the crown or stem-group). Yet, as mentioned before, this can not be clearly demonstrated. The animal differs from living Peripatidae in the number of plicae on its trunk. Compared to Antennipatus’s 8, most peripatids have 12 but up to 24 plicae per segment.[1]Velvet worms are estimated to have first appeared in the Late Devonian.[1][6] Combined with the animal's terrestrial lifestyle and placement in time, Antennipatus could easily be a crown-group onychophoran.[1] However, later studies treat it a true onychophoran of uncertain position or conservatively as a stem-group representative.[5][7]
Paleobiology
Terrestriality
MNHN SOT003121a & b. This fossil has well preserved antenna, slime papillae, and a putative mouth with obscured jaws. Slime papillae are noticeably shorter than the other limbs.
Based on a variety of evidence, Antennipatus was a terrestrial or at least somewhat terrestrial animal. Two of the three fossils preserve slime papillae, with them best preserved in MNHN SOT003121a & b. Since these appendages can be drawn into the body, their absence does not indicate the animal lacked them.[1] For instance, in Cretoperipatus (a velvet worm preserved in amber), the slime papillae were barely distinguishable from the surrounding body, even in one of its best-preserved fossils.[8] These appendages imply terrestriality due to the way they oscillate to shoot slime, something that would not work in an aquatic environment. Other terrestrial features (such as spiracles) are absent due to being incredibly small.[1]
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