Xenusion
Encyclopedia
Xenusion is a possible very primitive arthropod/onychophore
known from two specimens found in glacial debris in Germany. They probably originated in the Kalmarsund Sandstone of Southern Sweden
(Jaeger and Martinsson 1966) and are probably late Neoproterozoic
. The specimens are not especially well preserved. The older specimen is 10 cm or so in length with a narrow, weakly segmented body. A depression runs up the bottom on all but the rearmost segments. There is a slightly bulbous tail, and each segment beyond that seems to have a single pair of tapering annulated legs similar to the modern onychophore
, but without claws. Nine segments are present. There is a spine on each body bump and faint transverse parallel striations on the annulations on the legs. The legs of what is possibly the foremost segments are either missing or not preserved. The head is believed to be missing or is poorly preserved. If Xenusion is an arthropod/onychophore
, it is one of the oldest currently known fossils of a mobile, modern animal.
Xenusion has been reinterpreted as an Ediacaran frond animal by Tarlo, and a convincing drawing of that interpretation has been presented by McMenamin. If the creature is actually an onychophore
, the original specimen would appear to be part of an onychophore
about 20 cm in length, which is much larger than most extant species.
In a photograph presented in The Treatise on Invertebrate Paleontology
Volume O, the organism's appearance seems to support the original interpretation more. The presence of 'worm tubes' (Skolithes) in the Kalmarsund Sandstone would seem to make Xenusion somewhat younger than most Vendian fossils. Another likely onychophore
, Aysheaia
, is known from the slightly younger Burgess Shale
of British Columbia.
There is one known species of Xenusion, known as Xenusion auerswaldae.
A picture of Xenusion can be found here.
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
known from two specimens found in glacial debris in Germany. They probably originated in the Kalmarsund Sandstone of Southern Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
(Jaeger and Martinsson 1966) and are probably late Neoproterozoic
Neoproterozoic
The Neoproterozoic Era is the unit of geologic time from 1,000 to 542.0 ± 1.0 million years ago. The terminal Era of the formal Proterozoic Eon , it is further subdivided into the Tonian, Cryogenian, and Ediacaran Periods...
. The specimens are not especially well preserved. The older specimen is 10 cm or so in length with a narrow, weakly segmented body. A depression runs up the bottom on all but the rearmost segments. There is a slightly bulbous tail, and each segment beyond that seems to have a single pair of tapering annulated legs similar to the modern onychophore
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
, but without claws. Nine segments are present. There is a spine on each body bump and faint transverse parallel striations on the annulations on the legs. The legs of what is possibly the foremost segments are either missing or not preserved. The head is believed to be missing or is poorly preserved. If Xenusion is an arthropod/onychophore
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
, it is one of the oldest currently known fossils of a mobile, modern animal.
Xenusion has been reinterpreted as an Ediacaran frond animal by Tarlo, and a convincing drawing of that interpretation has been presented by McMenamin. If the creature is actually an onychophore
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
, the original specimen would appear to be part of an onychophore
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
about 20 cm in length, which is much larger than most extant species.
In a photograph presented in The Treatise on Invertebrate Paleontology
Treatise on Invertebrate Paleontology
The Treatise on Invertebrate Paleontology published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and covering every phylum, class, order, family, and genus of fossil and...
Volume O, the organism's appearance seems to support the original interpretation more. The presence of 'worm tubes' (Skolithes) in the Kalmarsund Sandstone would seem to make Xenusion somewhat younger than most Vendian fossils. Another likely onychophore
Velvet worm
The velvet worms are a minor ecdysozoan phylum. These obscurely segmented organisms have tiny eyes, antennae, multiple pairs of legs and slime glands. They have variously been compared to worms with legs, caterpillars and slugs...
, Aysheaia
Aysheaia
Aysheaia was a genus of soft-bodied, caterpillar-shaped organisms average body length of 1–6 cm. The genus name commemorates a mountain peak named "Ayesha" due north of the Wapta Glacier. This peak was originally named Aysha in the 1904 maps of the region, and was re-named Ayesha after the heroine...
, is known from the slightly younger Burgess Shale
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
of British Columbia.
There is one known species of Xenusion, known as Xenusion auerswaldae.
A picture of Xenusion can be found here.