Trioceros Swainson 1839

Tilbury, Colin R. & Tolley, Krystal A., 2009, A re-appraisal of the systematics of the African genus Chamaeleo (Reptilia: Chamaeleonidae), Zootaxa 2079, pp. 57-68 : 65-67

Genus Trioceros Swainson 1839

Type species: Trioceros oweni Gray 1831

Generic synonyms:

Triceras Fitzinger 1843 . Type species Chameleon oweni Gray 1831 .

Pterosaurus Gray 1864 . Type species Chameleo cristatus Stutchbury 1837 . Ensirostris Gray 1864 . Type species Ensirostris melleri Gray 1865 .

Content: affinis , balebicornutus , bitaeniatus , camerunensis , chapini , conirostratus , cristatus , deremensis , eisentrauti , ellioti , feae , fuelleborni , goetzei , harennae , hoehnelii , incornutus , ituriensis , jacksonii , johnstoni , kinetensis , laterispinis , marsabitensis , melleri , montium , narraioca , ntunte , oweni , pfefferi , quadricornis , rudis , schoutedeni , schubotzi , sternfeldi , tempeli , werneri , wiedersheimi .

The genus has a tropical pan-African distribution extending from east to west, with the most southerly species occurring in Mozambique and Malawi ( T. melleri ) and the most northerly in Ethiopia ( T. affinis ). ( Fig. 3 ). Most of the species within Trioceros are confined to wet evergreen forest biotopes or their peripheries with only a few species found out of evergreen forest proper ( T. melleri , T. bitaeniatus , T. goetzei , T. schubotzi , T. rudis ).

This is the only genus where the development of cylindrical annulated bony horns is seen. This character does not occur in all species of this genus but is found in representatives across the various sub-groups within the genus. These structures may be considered to be a synapomorphy for the genus Trioceros ( Klaver & Böhme 1986) . Other head ornamentation may include such features as occipital lobes and dual gular crests although these are not only found within this genus. The scalation is variable from sub-homogeneous and granular to markedly heterogeneous. The plantar surfaces are smooth and the claws simple.

The lungs of this genus are characterized by having between one to three large septae that are attached to and possibly arise from the ventral, medial and lateral walls of the lung Klaver 1973, 1977, 1981). The origin and the nature of these septae is regarded as a synapomorph character for the genus ( Klaver & Böhme 1986). The septae sub-divide the lung into two to four chambers. The chambers are arranged from anterior to posterior. The septae do not reach the dorsal wall allowing all chambers to communicate with each other via a common space in the dorsal zone. A membrano-fibrous diaphragm partially delimits a small dorso-cranial compartment at the anterior end of the lung. Varying numbers of small partial septae arise from the anterodorsal and antero-ventral walls of the lung. In all species examined so far, the inferior and posterior surfaces of the lungs are festooned with diverticulae of varying length, structure and numbers.

The hemipenes are calyculate with a plesiomorphic four rotulae apical ornamentation ( Klaver & Böhme 1986). Several subsequent species descriptions in the genus validate this as a general statement ( Tilbury 1998, Necas et al 2003, 2005). The species differ in the finer detail of calyceal structure, rotulae size, orientation and number and site of apical papillae.

The karyotype of representative species of two of the groups differs from 2n=36=12M+ 24m in the cristatus group ( Matthey 1957) to 2n=24=20M+ 4m in the bitaeniatus group (Matthey & van Brink 1956, Klaver & Böhme 1986).

This African genus comprises a somewhat heterogeneous collection of chameleons which encompasses at least four species complexes ( affinis cristatus , bitaeniatus , werneri – Hillenius 1959, Klaver 1981, Koreny 2006) which are currently loosely named “groups” as well as a single species that does not fit into any of the other groups viz: T. melleri . Three of the five sub-groups within this genus have probably independently developed a viviparous reproductive strategy ( affinis , bitaeniatus and werneri groups), whilst the fourth group ( cristatus ) and T. melleri have retained oviparous modes of reproduction. The viviparous groups have a dense melanotic infiltration of the parietal pigmentation – a condition usually associated with viviparity in the Chamaeleonidae .

Figures

FIGURE 3. Map showing the recorded distributions of the combined species within the genus Trioceros demonstrating its tropical African spread.