Wednesday 12 October 2016

Antennipatus montceauensis: A Velvet Worm from the Late Carboniferous of France.

Velvet Worms, Onychophora, are curious caterpillar-like organisms found in the tropics and temperate regions of the Southern Hemisphere. They show external segmentation, but are not internally segmented, have a soft cuticle rather that an exoskeleton, have non-segmented paired appendages, and thick, non-segmented paired antennae. Velvet Worms hunt Invertebrate prey, which they immobilize with a sticky slime fired from special organs behind the antennae, the slime papillae. There are two living families of Onychophora, the Peripatopsidae, found in Australia, New Zealand, South Africa and Chile, and the Peripatidae, found in West Africa, Southeast Asia, and the American Tropics. All known extant species are terrestrial, the only known Animal Phylum for which this is true, with their closest relatives being the Arthropods and Tardigrades. Phylogenetic analyses have shown the living Velvet Worms to be descended from the Lobopodians, a curious group of entirely marine soft-bodied animals known from a number of Cambrian locations, however how the Cambrian marine Lobopodians gave rise to the Modern terrestrial Velvet Worms is somewhat of a mystery, as there are almost no fossil specimens known for the intervening period; Cretoperipatus burmiticus, from Late Cretaceous Burmese Amber is a terrestrial form hard to distinguish from Modern Velvet Worms, Helenodora inopinata, from the Carboniferous Francis Creek Shale of Illinois is apparently an Onychophoran and a descendent of the Cambrian Lobophorians, but is not thought to be ancestral to, or closely related to, the living Velvet Worms, while all other putative post-Silurian  Onychophoran fossils have now been excluded from the group.

In a paper published in the journal Invertebrate Biology on 2 August 2016, Russell Garwood of the School of Earth, Atmospheric and Environmental Sciences at The University of Manchester and the Department of EarthSciences at The Natural History Museum, Gregory Edgecombe, also of the Department of Earth Sciences at The Natural History Museum, Sylvain Charbonnier of the Département Histoire de la Terre at the Muséum national d’Histoire naturelle, Dominique Chabard and Daniel Sotty of the Muséum d’Histoire naturelle d’Autun, and Gonzalo Giribet of the Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology at Harvard University and the Department of Life Sciences at The Natural History Museum. Describe a new species of Onychophoran from the Late Carboniferous Montceau-les-Mines Lagerstätte of France. 

Putative Onychophorans from these deposits have been recorded for over thirty years, however poor preservation of the material has prevented formal description of the material until now. Garwood et al. were able to supplement the light microscopy usually used to examine fossils of this type, with more modern methods, such as computerized tomography and digitally enhanced visualization.

The new species is named Antennipatus montceauensis, where 'Antennipatus' refers to the Antennae of the specimens, which is very similar to that of modern Velvet Worms, suggesting a close relationship (the suffix -patus is commonly used to describe modern genera within the group), and 'montceauensis' means 'coming from Montceau'. The specimens are essentially similar to modern Velvet Worms, including having what appear to be slime papillae. However it was not possible to place these Carboniferous Worms in either of the modern families, as none of the features which can be used to separate these group were (or were likely to be) preserved. This means it is impossible to say whether they belong to one of the two living families (which molecular clock data suggests separated in the Devonian), an unknown group sharing a common ancestor or a group which branched off before the divergence of the modern Onychophoran families.

The Carboniferous Onychophoran Antennipatus montceauensis from the Stephanian Montceau-les-Mines Lagerstätte, France. (A–C). First specimen, showing the head, including an antenna and five anterior segments of the trunk. Shown in light photograph (A), as rendered image from CT data employing low-angle lighting (B), and as a rendered image using a multicolored lighting rig (C). (D–E). Second specimen, showing the same region of the organism, but with one set of lobopods as protrusions rather than depressions. Shown as light photograph (D), lowangle lighting render (E), and multicolored lighting render (F). (G). An enlargement of (D), showing the antenna, a possible mouth, and slime papilla. (H). An SEM image of the trunk showing large primary papillae and ridges demarking plicae. (I.) A photomicrograph of the anterior of the fossil showing the left slime papilla, possible mouth, and antenna. (J). A photomicrograph of the trunk, showing the plicae and several well preserved lobopods. a, antenna; lb1–lb5, lobopods 1–5; m?, putative mouth; sp, slime papilla. Scales: A–G, 10 mm; H, 1 mm; I–J, 2 mm. Garwood et al. (2016).
The Montceau-les-Mines Lagerstätte is believed to have formed in and around a river delta flowing into a freshwater lake. The site produces in situ woody fossils (i.e. the trunks and roots of trees preserved in the position where they grew, interspersed with fluvial (river) and lucastrine (lake) sedments. There is no influence for any marine influence on the site. Therefore Antennipatus montceauensis could potentially have inhabbited a terrestrial environment similar to that favoured by modern Velvet Worms, or coud possibly have inhabited fresh water, a habitat no other Onychophoran, living or fossil, is known to have inhabited, but which is a plausible step between the fully marine habbit of ancient members of the group and the entirely terrestrial habitat favoured by moden Velvet Worms.

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