Vilevolodon is an extinct, monotypic genus of volant, arboreal euharamiyids from the Oxfordian age of the Late Jurassic of China. The type species is Vilevolodon diplomylos. The genus name Vilevolodon references its gliding capabilities, Vilevol (Latin for "glider"), while don (Greek for "tooth") is a common suffix for mammalian taxon titles. The species name diplomylos refers to the dual mortar-and-pestle occlusion of upper and lower molars observed in the holotype; diplo (Greek for "double"), mylos (Greek for "grinding"). Vilevolodon is known from the Tiaojishan Formation in Qinglong County, China. Due to its unique combination of characters, Vilevolodon provides additional evidence to an increasingly complex scope of mammalian morphology and niche inhabitation. As the volant herbivorous lifestyle is previously only known from therian gliders, Vilevolodon stands as evidence of locomotor convergence, as well as mammaliaform evolutionary experimentation during the Jurassic. Along with Maiopatagium, Vilevolodon represents the most primitive known gliders in mammalian evolution, appearing approximately 100 million years before the earliest known therian gliders. Based on the melanosomes preserved in its fur, Vilevolodon likely had a uniformly dark-brown coloration, similar to that of other early mammaliaforms including Arboroharamiya and Megaconus.
History and Discovery Vilevolodon diplomylos was described by Luo et al in 2017 concurrently with another euharamiyid, Maiopatagium furculiferum. Descriptions were carried out based on a skull with preserved teeth in occlusion and a mandibular inner ear, and a fairly complete post-cranial skeleton with carbonized residue of a patagial skin membrane, which has been interpreted as a gliding mechanism. The holotype is represented by a slab and counter-slab with fossil elements preserved across both samples. The holotype was found at the Nanshimen site of the Tiaojishan Formation in Quinglong County, Hebei Province, China, and is currently housed at the Beijing Museum of Natural History.
Paleobiology
Feeding ecology Based on dental morphological characteristics, Vilevolodon is inferred have had an herbivorous diet, likely consisting largely of seeds and soft plant tissues. Cusp likeness to sciurid rodents, which have a diet of nuts, seeds and fruits, and supplemented by insects, suggests some potential for omnivory. Luo posits that Vilevolodon was not a folivore however, as the teeth lack strong crests which are characteristic of folivorous taxa, including modern marsupial gliders. All extant mammalian gliders are primarily herbivorous, thus an herbivorous dietary inference for Vilevolodon is consistent with modern, analogous gliders. Overall, the distinctive teeth of Vilevolodon expand the known dental morphology of mammaliaforms, especially when compared to Triassic haramiyids of the same clade, whose teeth are often much less transformed with reduced basins, and lie in straight, organized rows within the jaw.
Locomotion Vilevolodon is interpreted as volant and capable of gliding. Meng et al cited the relative proportions of limb bones, and the acromion-clavicle joint which allowed for significant shoulder mobility as supportive of a stance required for gliding locomotion. The acromion-clavicle joint structure is persistent throughout eleutherodonts and represents an adaptation for volant locomotion running convergent to the increased mobility of the sternum-clavicle joint observed across therian gliders. The shortened shape of the astragalus and calcaneus resemble those of a modern bat, and the proximal pedal phalanx has a pronounced groove used for tendon attachment which is observed in mammals with enhanced grasping capabilities. Elongated necessary for roosting and hanging behavior. When considered together, the gliding capabilities and modified feet with climbing and roosting specializations suggest an arboreal lifestyle for Vilevolodon. This is consistent with other members of the clade Eleutherodontia, of which the taxa, like Maiopatagium, were a majority arboreal.
Description
Patagium Preserved alongside skeletal elements is what Luo et al has interpreted as a patagium, or a membranous structure used in gliding or flight assistance. Propatagium, plagiopatagium and uropatagium sub-structures have been identified as well. Morphometric analyses carried out contiguously with another gliding Haramiyid, Maiopatagium furculiferum, from the same locality are consistent with the gliding adaptations of extant mammals and other fossil taxa. The pelage of Vilevolodon is preserved as a mat of carbonized fur and long guard hairs which was compressed upon patagial membranes. Among therian gliders, this patagium is most comparatively similar to the gliding sciurid rodents based upon similar proportions of propatagium, plagiopatagium, and uropatagium structures. This structure, and other gliding structures seen among eleutherodonts, differs from modern anomalurids in that the plagiopatagium extends to reach the ankle and wrist, and they also differ from modern rodent gliders and the marsupial glider, Petauroides volans, in that they lack a styliform structure from the wrist or ulnar olecranon. Vilevolodon also exhibits strongly developed uropatagia and propatagia, where these structures in marsupial gliders are much less prominent. Analysis on the fur impressions of Vilevolodon revealed high concentration of copper associated with eumelanin, indicative of uniformly dark-brown coloration with no evidence of color patterns, which was also the case in other early mammaliaforms from China: Arboroharamiya, Megaconus, indeterminate docodonts (SDUST-V0006 and SDUST-V0007) and indeterminate eutherian (SDUST-V0008).
… excerpt ends here. Continue reading the full article.
