| Omilteme cottontail | |
|---|---|
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Lagomorpha |
| Family: | Leporidae |
| Genus: | Sylvilagus |
| Species: | S. insonus |
| Binomial name | |
| Sylvilagus insonus (E.W. Nelson, 1904) | |
 | |
| Omilteme cottontail range | |
| Synonyms | |
Lepus insonusE.W. Nelson, 1904 | |
TheOmilteme cottontail (Sylvilagus insonus), orOmiltemi cottontail (Spanish:conejo de Omiltemi), is aspecies ofcottontail rabbit in thefamilyLeporidae found only in the Mexican state ofGuerrero in theSierra Madre del Sur mountain range. It is anocturnal, largerabbit,rufous to black in fur color, with long ears and a short tail. This cottontail is restricted tocloud forests at elevations of up to 11,499 feet (3,505 meters).
First identified in 1904 byEdward William Nelson inOmilteme, Guerrero, Mexico under thescientific nameLepus insonus, the Omilteme cottontail was soon after reclassified as a member of the genusSylvilagus, the cottontail rabbits. It is closely related to theMexican cottontail (S. cunicularius) and thedesert cottontail (S. audubonii); the former species overlaps indistribution with the Omilteme cottontail.
The Omilteme cottontail is considered one of the most endangered mammal species in the world, and is only known from a few specimens. Once listed by theInternational Union for Conservation of Nature and Mexican authorities ascritically endangered, it is now considered adata deficient species. From the early 1900s up until the 1990s, no confirmed sightings of the cottontail were recorded, but two individuals were discovered in 1998, and more were found through the 2020s usingcamera traps. It is threatened bypoaching andhabitat destruction, and much about itsnatural history is unknown.
The Omilteme cottontail was first described byEdward William Nelson in 1904 as a new species ofLepus, "Lepus insonus". The description was made based on two specimens, which were collected with the assistance ofEdward Alphonso Goldman. Thetype of this species was a female specimen collected fromOmilteme,Guerrero, Mexico, stored at theNational Museum of Natural History. It was described as "[a] dark, coarse-haired species with small short tail" and noted as "obviously belonging in the same group as [Lepus]gabbi andL. truei", though it had ears that were twice as large as either species.[2] BothL. gabbi andL. truei are now known assubspecies of theCentral American tapeti (Sylvilagus gabbi), acottontail rabbit of widedistribution and unstabletaxonomy.[3] In June 1904, the month after Nelson published his description ofLepus insonus,Marcus Ward Lyon Jr. published his workClassification of the Hares and their Allies that clarified the genera of hares and rabbits. Nelson referred to this work in his 1909 publicationThe Rabbits of North America,[4] where he placed the Omilteme cottontail in the genusSylvilagus.[5]
There is no fossil evidence ofSylvilagus insonus, and it is only known from itstype locality in the province of Guerrero, Mexico.[6]Phylogenetic analysis of the relationships betweenS. insonus and other species in the genusSylvilagus yielded evidence that it is closely related to both theMexican cottontail (S. cunicularius) and thedesert cottontail (S. audubonii).[7] The former species issympatric withS. insonus.[8] Prior studies indicated a relationship with thecommon tapeti (S. brasiliensis), and it has been variously placed in thesubgeneraTapeti andSylvilagus,[9] butmorphological studies find that the common tapeti is more closely related toDice's cottontail (S. dicei) than it is toS. insonus.[7]
The Omilteme cottontail is a large rabbit (head and body length from 15.7 to 17.3 in (398 to 440 mm)) with long ears (2.4–3.0 in (60–76 mm)), hind feet of medium length (3.5–4.1 in (89–104 mm)) and a short tail (1.6–1.8 in (40–45 mm)).[7][10] Around the nose andorbital (eye) area, its fur coat is a dull gray. The external, convex surface of the ears is a dark brown-black color; the black is concentrated along the border and tips of the ears. The rabbit's back isrufous (a red-brown color) mixed with black, while the sides are gray-black in color. The medium-sized hind feet are white on thedorsal side and the soles are a dark brown.[6][8] The dorsal side of the tail is reddish-black while theventral side is darklybuff[7] or yellowish.[11]
The anatomy ofSylvilagus insonus has been described with particular focus on the skull. The skull is large, approximately 3.1 in (78 mm) in length and 1.3 in (32 mm) in depth, with a largepalate and a wide braincase (back and upper part of the skull;neurocranium). The supraorbital process (projecting bone structure above the eyes, orbrow ridge) is flat, attached to the braincase and has two extensions (anterior and posterior). The anterior extension of the supraorbital process is attached to the skull, while the posterior extension is slender and can be free of the brain case or attached with a slit in between the process and the braincase. The supraoccipital shield (bony structure above theocciput) is square shaped. Thetympanic bullae (bone structures that enclose the middle and inner ear, synonymous with but measured differently from the auditory bullae[12]) are small and less than 0.48 in (12.3 mm) in length. They have medium-sizedauditory bullae with a length of less than 0.38 in (9.6 mm). The width of thebasioccipital is narrow: less than 0.35 in (9 mm), but broad across thecarotid canals. The width of theinfraorbital canals is very narrow, being less than 0.72 in (18.3 mm). The width across the nasal structures is very narrow, and their length is less than 1.26 in (32.1 mm).[6][8]
The mouth consists of amandible whose height is less than 1.43 in (36.3 mm), with a mandibleramus depth of less than 0.44 in (11.3 mm). Theincisive foramen and thediastema are short. Thepremaxillaries have extensions on the dorsal side. Large maxillary and mandibular tooth rows are present. Like otherleporids, the Omilteme cottontail isheterodont with a total of 28 teeth; it hasincisors,premolars andmolars, lackscanines,[6] and itsdental formula is2.0.3.31.0.2.3.[13] The length of the first upper incisor is generally less than 0.30 in (7.5 mm).[6]
Sylvilagus insonus differs from other Central American species in its skeletal and external characteristics. Compared to thecommon tapeti (S. brasiliensis) andDice's cottontail (S. dicei), it has a larger skull, wider cheekbones, deeperrostrum, wide external openings for thecarotid arteries, and dorsal extensions of thepremaxillaries.S. insonus also has a narrower basioccipital and narrower post-dental process. The Omilteme cottontail has a longer bicolored tail (rufous and black) instead of a uni-colored tail (solely brown); hind feet with white and brown versus hind feet of only brown; and longer ears.[6][8] These characteristics are also useful in differentiating the species from theMexican cottontail (S. cunicularius), with which it shares its habitat.[11]S. insonus is smaller in the length of its upper incisors, its skull length, nasal length, width of the basioccipital, auditory bulla length, the depth of shield bullae, skull depth, width across infraorbital canals, mandible height and mandible ramus depth. The Omilteme cottontail is a rufous-black color dorsally, whereas the Mexican cottontail is only gray in the same areas.[8]
Sylvilagus insonus isendemic to Mexico[14] and is found only in the Sierra Madre del Sur in the state of Guerrero.[6][10][8] It is only known from its type locality,Omiltemi Ecological State Park, located in a wooded summit of a semi-isolated mountain range.[6] It occurs inhabitats ranging from 6,998 to 11,499 ft (2,133 to 3,505 m) in elevation.[7] Surrounding the wooded area is the village of Omiltemi at 7,651 ft (2,332 m) above sea level (in Municipio Chilpancingo).[10] The Omilteme cottontail is restricted to a region of less than 193 sq mi (500 km2).[10][14]
The Omilteme cottontail lives at the summit of a steep-sloped mountain range with manyravines covered with densecloud forests.[10] Common tree genera in the forests it inhabits arepine (Pinus),oak (Quercus), andalder (Alnus).[7]
Sylvilagus insonus shares its habitat with 37 other mammal species,[6] including one cottontail rabbit, the Mexican cottontail. In the dense cloud forests, the rabbit lives amongst theundergrowth where it makes runways andburrows under rocks and other objects. It is a mainlynocturnal mammal. The only known predator of the species ishumans through hunting,[7] though its habitat is frequented by predators such as thewolf,[15]jaguar, andcougar.[16] Very little is known regarding its ecology and reproductive habits.[7]
TheInternational Union for Conservation of Nature (IUCN), in itsRed List of Endangered Species, lists the Omilteme cottontail as "data deficient",[1] though it previously listed the species ascritically endangered in 1996 and 2004. A similar evaluation was given by the Mexican government around this time;[17] as of 2019, the same authority describes it as "endangered".[11] The major threats to the survival of this species arepoaching andhabitat destruction caused bydeforestation.[6][10] This rabbit went unreported in the wild from the early 1900s to the 1990s; however, two specimens were captured in 1998, confirming that the species was still extant.[6][10] A team of scientists began searching for evidence of the species in 2019, with several specimens received in 2020 from local hunters and additional rabbits discovered from 2020 to 2022 in theSierra Madre del Sur area within Guerrero, Mexico.[18] In ten regions surveyed bycamera traps, seven showed evidence of the species.[19] The expedition was part of a larger effort to rediscover species without documented observations in at least 10 years.[18] Prior to this expedition, the species was only known from five museum specimens[7] and less than 10 total records.[9]
Sylvilagus insonus is considered one of the most endangered mammals in the world, and though it is known to live within aprotected area, it is still at risk. Conservation actions have yet to be implemented by local authorities and theNational Commission of Natural Protected Areas, as additional studies are needed on the species'natural history to produce useful proposals.[7][19] Efforts to study the species further have been stymied by the rough terrain of the Sierra Madre del Sur and social issues in the inhabited areas.[11]
