Journal Article
Skeletal and muscular pelvic morphology of hillstream loaches (Cypriniformes: Balitoridae)
Crawford, C.H., Randall, Z.S., Hart, P.B., Page, L.M., Chakrabarty, P., Suvarnaraksha, A. and Flammang, B.E.
Record Number:
5093
Year:
2020
Journal:
Journal of Morphology
Pages:
1280-1295
Volume:
281
Abstract:
The rheophilic hillstream loaches (Balitoridae) of South and Southeast Asia possess a
range of pelvic girdle morphologies, which may be attributed to adaptations for locomotion
against rapidly flowing water. Specifically, the connectivity of the pelvic plate
(basipterygium) to the vertebral column via a sacral rib, and the relative size and
shape of the sacral rib, fall within a spectrum of three discrete morphotypes: long,
narrow rib that meets the basipterygium; thicker, slightly curved rib meeting the
basipterygium; and robust crested rib interlocking with the basipterygium. Species in
this third category with more robust sacral rib connections between the
basipterygium and vertebral column are capable of walking out of water with a
tetrapod-like lateral-sequence, diagonal-couplet gait. This behavior has not been
observed in species lacking direct skeletal connection between the vertebrae and the
pelvis. The phylogenetic positions of the morphotypes were visualized by matching
the morphological features onto a novel hypothesis of relationships for the family
Balitoridae. The morphotypes determined through skeletal morphology were correlated
with patterns observed in the pelvic muscle morphology of these fishes. Transitions
towards increasingly robust pelvic girdle attachment were coincident with a
more anterior origin on the basipterygium and more lateral insertion of the muscles
on the fin rays, along with a reduction of the superficial abductors and adductors
with more posterior insertions. These modifications are expected to provide a
mechanical advantage for generating force against the ground. Inclusion of the enigmatic
cave-adapted balitorid Cryptotora thamicola into the most data-rich balitorid
phylogeny reveals its closest relatives, providing insight into the origin of the skeletal
connection between the axial skeleton and basipterygium.
KEYWORDS
computed tomography, fish, musculature, pelvic morphology, phylogeny, walking
Times Cited:
3