Extinct genus of tetrapods
Antlerpeton is an extinct
stem tetrapod
that has affinities with later, more advanced forms. Its robust pelvis and hind limbs allowed for effective locomotion on land, but the animal was likely still tied to a semiaquatic lifestyle near the coast.
Description and history
The
Late Devonian and Early Carboniferous. The
type species A. clarkii was named for Charles W. Clark, a geologist of the Western Mining Corporation (an Australian mining company with an exploration office in Reno, Nevada) who discovered the holotype in 1990.
[1]The holotype of Antlerpeton consists of vertebrae, ribs, a
centrum and a pair of two small bones that fit in front of it. The spinal cord passes through the larger bones, while the smaller bones are positioned to either side of the midline. Pubo-ischiadic plates, primitive forms of the
pubis and
ischium of later tetrapods, are present, but it is unclear whether they were fused into a strong pelvic girdle. A small projection of bone is present on the
acetabulum, a depression in the pelvis that attaches with the end of the femur. This projection is also seen in the Late Devonian tetrapod
Ichthyostega. The femur of
Antlerpeton is much more robust than that of
Ichthyostega, and has prominent ridges like the
fourth trochanter that are attachment points for well-developed leg muscles.
Antlerpeton also has small scales covering its underside.
[1]Classification
Because the only specimen of Antlerpeton is incomplete and lacks a skull, its relationships with other early tetrapods are poorly understood. The compound vertebrae of Antlerpeton distinguish it from
lepospondyls and ally it with more primitive stem tetrapods.
Antlerpeton shows characteristics of both early rhachitomous tetrapods and later schizomerous tetrapods. Rhachitomous tetrapods have two types of bones in each vertebral segment: the
pleurocentrum and the
intercentrum. The intercentrum is the larger of the two bones in rhachitomes, while the pleurocentra are present as two smaller bones in a dorsal position between the intercentra.
Schizomerous tetrapods differ from rhachitomes in that their pleurocentra have descended to a more ventral position in the vertebral column. The pleurocentra enlarged in
lobe-finned fish like
Lohsania, suggesting that the feature is not unique to derived early tetrapods.
[1]Paleobiology
Antlerpeton had several adaptations for a terrestrial lifestyle. While early tetrapods like Ichthyostega and Acanthostega were mostly aquatic, Antlerpeton could probably move effectively on land with its robust legs and pelvic girdle. The femur is large, and many bony ridges provide anchorage for muscles that would have been useful for both swimming and moving on land. The thickened pubis and acetabulum of the pelvic girdle and the large sacral vertebrae that connect it with the vertebral column allowed Antlerpeton to withstand the stresses of terrestrial locomotion. The holotype specimen of Antlerpeton was found in rocks that were deposited in coastal and marine settings. Therefore, it is likely that Antlerpeton inhabited rivers or marshes near the coast and had some tolerance of salt water.[1]
References
