Comparative anatomy of the forearms of different chameleons

Comparative anatomy of the forearms of different chameleons

by Alex Laube Tiermedizin Science

The anatomy of chameleons seems to be strongly adapted to their way of life. Tree-dwellers differ in many aspects from ground-dwellers. Several studies at the University of South Dakota this year have already looked at various anatomical aspects of chameleons. A new study is dedicated to the hands and arms.

For the investigation, the arms and hands of a total of 12 chameleons were isolated from existing microcomputer tomography scans and displayed in 3D. These were measured to about 30 different lengths and widths using software. Scans of the species Bradypodion damaranum, Bradypodion occidentale, Calumma hilleniusi, Calumma crypticum, Chamaeleo namaquensis, Chamaeleo zeylanicus, Furcifer balteatus, Furcifer campani, Rhampholeon spinosus, Rhampholeon temporalis, Trioceros goetzei goetzei and Trioceros werneri were evaluated. When selecting the species, care was taken to select one strictly tree-inhabiting chameleon and one more ground-inhabiting chameleon per genus.

The evaluation revealed that tree-dwelling chameleons show few differences in forelimb anatomy compared to ground-dwelling chameleons. Tree-dwelling species showed a majority of separated metacarpal bones 1-3, while ground-dwelling species showed fused metacarpal bones. Interestingly, this study differs from earlier studies by other authors, which yielded different results. The relatively small number of animals studied may be related to this. Larger studies could be helpful here.

Ecological and evolutionary drivers of chameleon forelimb variation
Ellie M. Schley
Honors Thesis 302 der Universität von South Dakota, 2023
DOI: gibt es nicht

Comparison of pelvic girdles in chameleons

Comparison of pelvic girdles in chameleons

by Alex Laube Science

The anatomy of chameleons is strongly adapted to their way of life. Tree-dwellers differ in many aspects from ground-dwellers. The pelvic girdle has been little studied anatomically in chameleons so far – a publication from the USA now deals with it in more detail.

For the study, the pelvic girdles of 22 chameleons were isolated from existing microcomputer tomography scans and displayed in 3D. These were measured to 16 different lengths and angles using software. Archaius tigris, Bradypodion damaranum, Calumma gallus, Calumma parsonii parsonii, Chamaeleo zeylanicus, Furcifer balteatus, Kinyongia matschiei, Kinyongia tavetana, Nadzikambia mlanjense and Trioceros quadricornis gracilior were assigned to tree dwellers. Brookesia brygooi, Chamaeleo namaquensis, Palleon nasus nasus, Rhampholeon temporalis and Rieppeleon brachyurus were attributed to ground-dwelling species. The species Bradypodion occidentale, Brookesia ebenaui, Chamaeleo anchietae, Furcifer campani, Rhampholeon spinosus, Rieppeleon kerstenii kerstenii and Trioceros goetzei goetzei were classified as semiarboreal. Mainly males were examined.

As expected, the evaluation showed that tree-dwelling chameleons had narrower, shorter girdles than ground-dwelling ones. The narrower pelvic girdle makes it easier to hide behind branches and flatten the body to the maximum. It also ensures that the body’s centre of gravity is closer to the branch and thus increases stability when climbing. Ground-dwelling chameleons, on the other hand, had larger and wider pelvic girdles. These allow them to step more quickly and provide greater stability when walking on ground surfaces.

How phylogeny and arboreality affect pelvic girdle anatomy of chameleons
Dakota J. John
Honors Thesis 299, University of South Dakota, 2023
DOI: none

 

Spines of tree- and ground-dwelling chameleons

Spines of tree- and ground-dwelling chameleons

by Alex Laube Tiermedizin Science

Various anatomical adaptations of the spine between ground and tree dwellers are known from mammals, especially primates. In some cases, the different vertebrae are even associated with certain movement patterns and bodily functions. In a comparative study, two scientists from New York (USA) have now investigated how the spine of ground- and tree-dwelling chameleons differs.

They measured the already existing CT scans on Morphosource.org of a total of 28 chameleons of different species. Brookesia perarmata, Brookesia superciliaris, Brookesia thieli, Palleon nasus, Rhampholeon platyceps, Rhampholeon spectrum, Rieppeleon brevicaudatus and Rieppeleon kerstenii were classified as ground dwellers. Archaius tigris, Bradypodion melanocephalum, Bradypodion pumilum, Bradypodion thamnobates, Calumma amber, Calumma brevicorne, Calumma parsonii, Chamaeleo calyptratus, Chamaeleo gracilis, hamaeleo zeylanicus, Furcifer lateralis, Furcifer pardalis, Furcifer verrucosus, Kinyongia carpenteri, Kinyongia tavetana, Kinyongia xenorhina, Nadzikambia mlanjensis, Trioceros feae, Trioceros jacksonii and Trioceros quadricornis were considered arboreal. The vertebrae were counted and the width of the lamina, length, width, height of the vertebral body, and the height of the spinous process and transverse processes on each vertebra were measured. In addition, the so-called prezygapophysial angle was determined. This is the angle of the intervertebral joint, i.e. the contact surfaces between the individual vertebrae. The measurements of ground and tree dwellers were compared and statistically evaluated. Only the vertebral column of the trunk was considered, the caudal vertebral column was left out.

First of all, the results showed that ground-dwelling chameleons generally have fewer trunk vertebrae (15 to 19) than tree-dwelling chameleons (18 to 23). The trunk spine of almost all species could be divided into the already known three areas: Cervical spine and anterior and posterior dorsal spine. A thoracic and lumbar spine as in mammals is generally not distinguished in chameleons because of the continuous ribs. Five chameleon species had four regions instead of three: they had an anterior and a posterior cervical spine, the anterior one consisting of only two vertebrae with rib processes. Six chameleon species had two additional lumbar vertebrae and one species had three transitional vertebrae in the region between the cervical and dorsal spine. In Kinyongia carpenteri, a total of five regions could be distinguished in the trunk spine: The chameleon had anterior and posterior cervical vertebrae as well as anterior and posterior dorsal vertebrae and two additional lumbar vertebrae. Brookesia perarmata was also a special case: the trunk spine of this chameleon consisted of only two regions and at the same time the smallest number of vertebrae of all species studied.

The greatest differences between ground and tree-dwelling chameleons were found in the prezygapophyseal angle (PZA) and the height of the spinous process. The intervertebral joint surfaces in the anterior dorsal vertebrae of tree-dwelling chameleons were clearly more dorsoventrally oriented and smaller than in ground-dwelling species. Several tree-dwellers showed a PZA of less than 90°. In tree-dwelling chameleons, the largest spinous processes were located at the transition from the cervical to the dorsal spine. Among the ground-dwelling species, the spinous processes were similar only in Palleon nasus. In ground-dwelling chameleons, the appearance of the spinous process varied greatly. Rieppeleon, for example, showed narrow, backward-sloping spinous processes, while the spinous processes in Brookesia were more like a kind of bone bridge than a process. Archaius tigris was an exception: The spinous processes in this chameleon hardly differed along the entire spine.

The authors conclude from the results that the anatomy of the different vertebrae is strongly related to the chameleons’ way of life and different locomotion. The intervertebral joint surfaces in tree-dwelling chameleons are probably important for climbing by supporting the function of the shoulder girdle. Reduced mobility in the mediolateral plane provides greater trunk stiffness, which facilitates climbing in arboreal dwellers. Stiffening of the axial skeleton (skull, trunk spine and thorax) is also known from tree-dwelling mammals. The larger spinous processes in larger chameleons could facilitate shoulder girdle rotation and muscle movement, resulting in increased stride length, better head support, and thus possibly easier feeding.

Morphological and functional regionalization of trunk vertebrae as an adaption for arboreal locomotion in chameleons
Julia Molnar, Akinobu Watanabe
Royal Society Open Science 10, 2023: 221509
DOI: 10.1098/rsos.221509

Illustration: Spines of different chameleon species

Comparisons on limbs of Hadramaut agama and Veiled Chameleon

Comparisons on limbs of Hadramaut agama and Veiled Chameleon

by Alex Laube Science

A Yemeni biologist at Al Saeed University recently took measurements on two different reptile species to compare their forelimbs and hindlimbs structurally and functionally. Both the Hadramaut Agama (Acantocercus adramitanus) and the Veiled Chameleon (Chamaeleo calyptratus) occur in the same habitats in Yemen, but they inhabit different microhabitats and move differently. While the agama lives mainly on the ground and in low bushes, the Veiled Chameleon is a pure tree dweller.

For the study, 10 specimens of each species were taken from the wild in Taiz. The head-torso length of the agamas ranged from 52 to 125 mm, and that of the chameleons from 90 to 200 mm. The animals were killed and the limbs were removed, stained, and then measured.

The structure of the limbs was basically the same in both species, but the hands and feet were clearly different. The Hadramaut Agama has five carpal bones, whereas, in the Veiled Chameleon, the distal carpal bones 2,3, and 4 are fused. Both species lack distal tarsal bones 2 and 5. The Veiled Chameleon lacks the sesamoid ossicles, which are variable in the agama. As expected, the long bones of the Veiled Chameleons were almost equally long on the forelimbs and hindlimbs, while in the agamas the forelimbs were significantly shorter than the hindlimbs. Overall, all long tubular bones were longer in the chameleon than in the Hadramaut Agama.

The skeletal characteristics of limb of two endemic lizard species (Acantocercus adramitanus and Chamaeleo calyptratus) in Yemen
Yaser H.A. Obady
Al-Saeed University Journal of Humanities and Applied Sciences 06 (1) 2023: pp. 188-210
DOI: 10.17161/randa.v30i1.18614