Possible Cryptic Species on the Roof of Africa? A New Morphotype of Trioceros on Mount Kilimanjaro

Mount Kilimanjaro is a legendary peak steeped in natural wonder and historical renown. First summited in 1889 by Hans Meyer and Ludwig Purtscheller, the mountain's etymology remains a subject of fascinating debate: widely interpreted through Swahili and Chagga roots as Kilima-Njaro—variously translated as the "Mountain of Greatness," "Mountain of Light," or "Mountain of Caravans."

Rising to 5,895 meters above the East African plains, it stands as the highest point on the African continent, a snow-crowned volcanic landmark visible across vast distances, an enduring national symbol of Tanzania, and an irresistible magnet for thousands of mountaineers, scientists, and naturalists each year.

The history of biological exploration on Kilimanjaro is rich and extensive. Early scientific surveying began with naturalists accompanying expeditions in the late 19th century—including Count Sámuel Teleki and Ludwig von Höhnel during their pioneering East African travels in 1887. They were followed by landmark biological work:

• Ferdinand Volkens (1893–1894): Conducted seminal botanical and altitudinal zonation studies along the slopes.
  
• Yngve Sjöstedt (1905–1906): Headed the Swedish Zoological Expedition to Kilimanjaro and Meru,establishing an extensive baseline for the invertebrate and vertebrate fauna.
  
• Subsequent 20th-century field herpetologists (including Arthur Loveridge and Hugh Cott): Further refined the herpetological catalog of the Northern Circuit massifs.
  

The Known Chameleon Fauna of Kilimanjaro

Despite the colossal footprint of the massif, the known chameleon fauna comprises a well-defined assemblage partitioned strictly by altitude and habitat:

1. Chamaeleo dilepis Leach, 1819: Confined to the lower, arid acacia-savannah foothills, represented by the typical savannah form.
   
2. Chamaeleo incognitus Gimenez, 2014: A mysterious, poorly resolved taxon; populations potentially referable to this species inhabit the transitional ecotones around the foothills and surrounding Arusha.
   
3. Chamaeleo gracilis Hallowell, 1844: An inhabitant of the mesic savanna and lower scrub woodland ringing the mountain's base.
   
4. Kinyongia tavetana (Steindachner, 1891): The two-horned montane specialist found extensively through the lush, mid-elevation submontane and montane evergreen forest belt.
   
5. Trioceros sternfeldi (Rand, 1963): The dominant highland dwarf chameleon inhabiting upper montane forest borders, scrub, and open heath-moorland zones up to substantial elevations. Trioceros sternfeldi is part of a complex radiation within the Trioceros bitaeniatus group. This radiation spans a series of isolated volcanic and highland massifs: Trioceros hanangensis on Mount Hanang, distinct populations across Mount Meru, Kilimanjaro, the Ngorongoro Conservation Area, and Mount Gelai in Tanzania, extending northward across the Kenyan border into the Loita Hills and reaching Mount Poror in the Samburu Hills.

Notable Biogeographical Absences

Two major phylogenetic elements could logically be expected in the high-elevation zones of Kilimanjaro, yet are conspicuously absent from its fauna:

• Trioceros jacksonii merumontanus (Rand, 1958):Confined strictly to neighboring Mount Meru, barely 70 km away, but absent on Kilimanjaro.
  
• High-altitude dwarf specialists of the Trioceros rudis subgroup: The classic "alpine" bitaeniate dwarf forms that occupy the cold afro-alpine and moorland summits elsewhere in East and Central Africa:
  
• Albertine Rift: Trioceros rudis (Boulenger, 1906) and Trioceros schoutedeni (Laurent, 1952).
  
• Kenyan Massifs: Trioceros schubotzi (Sternfeld, 1912) on Mount Kenya, Trioceros kinangopensis Stipala et al., 2012 on the Aberdare Range, and Trioceros ntunte (Nečas, Modrý & Šlapeta, 2005) on Mount Nyiro.
  

A New Discovery in the Moorland: Two Sympatric Morphotypes?

A recent field observation by J. Mboya in the Kilimanjaro moorland at elevations above 3,100 m—substantiated by photographic records on iNaturalist—has introduced an unexpected twist to this picture.

At high elevations, two distinct morphotypes appear to occur. Both unequivocally share affinities with the Trioceros bitaeniatus group, but their diagnostic morphological characters differ sharply:

Systematic Evaluation: Cryptic Taxon or Altitudinal Plasticity?

It is tempting to declare this small, rugose chameleon a cryptic, long-overlooked candidate species. In the past, several valid taxa have been described on far less substantial morphological divergence.

The differential diagnosis demonstrates character divergence that could function as character displacement between two syntopic, closely related forms sharing microhabitats at their upper elevational limits.

However, scientific prudence is required:

1. Altitudinal Phenotypic Plasticity: Dwarfism is a well-known physiological response to harsh alpine regimes (hypoxia, brief daily thermal windows, extreme cold).
   
2. Inconsistent Scalation Trends Across Cold Specialists:While a rugose body texture parallels T. rudis, it is not a universal high-altitude rule—Trioceros ntunte on Mount Nyiro thrives at high elevations without exhibiting rugose scalation.
   
3. The Limits of Classical Morphology: East African chameleons repeatedly demonstrate that striking morphological divergence and local convergence can deliver misleading conclusions when unverified by molecular genetics.
   

Detailed morphometrics across a wider specimen series and targeted molecular sequencing will be essential to establish whether Kilimanjaro's moorland harbors a genuine cryptic relict, or simply an extreme alpine ecomorph of Trioceros sternfeldi.