In all recently published
molecular phylogenies, the South American Xenodontinae form a clade that
comprises
several monophyletic units
(tribes), one of which consists of the three genera of the tribe Hydropsini (Helicops,
Hydrops and Pseudoeryx.
Complete information on the bony skull is available for nearly a third (29
genera) of the Dipsadidae genera, whereas fragmentary descriptions were
published for an additional 29 genera. Information on the bony skull of
Hydropsini is more complete, since descriptions are available for Helicops
carinicaudus, H. infrataeniatus, Hydrops marti, H.
triangularis, and Pseudoeryx plicatilis.
A comparison of the cranial
osteology among the three Hydropsini genera may prove useful characters to discuss
the systematic value of previously studied features and to identify new ones
that could unravel relationships among species within the tribe. Di Pietro and colleagues (2014) describe the
bony skull variation of Helicops
infrataeniatus, H.
leopardinus, Hydrops caesurus, and Pseudoeryx plicatilis and
compare it to that of Dipsadidae
species. This comprehensive
comparison includes terrestrial, semi-fossorial, fossorial, semi-aquatic,
fully-aquatic, and arboreal forms
of Dipsadidae.
The authors compare them with
several genera of Dipsadidae and found that the unpaired foramen on the
parabasisphenoid with anterior position is the only skull feature shared by all
Hydropsini genera. This feature also occurs in the semi-aquatic (Erythrolamphrus
semiaureus) and fully-aquatic (Farancia abacura) dipsadids. All
species of Hydrops with available skull descriptions and Pseudoeryx
plicatilis share four features: (1) The anterior border of the angular is
higher than the posterior border of the splenial, (2) the vomerine processes of
the premaxilla are long, (3) the ascending process of the premaxilla overlaps
the horizontal lamina of the nasals, and (4) an anterior projection of the
prefrontal is present.
All species of Helicops with
available skull descriptions and Pseudoeryx plicatilis share three
features: (1) A vertical
lamina of the nasal with a notch,
(2) a single foramen rotundum, and (3) the presence of a ventral projection of
the
transverse crista of the
basioccipital. Finally, they also found small, paired parietal foramina in most
of the dipsadids studied here, which are filled with a Sudan-Black-positive
tissue of possible nervous origin.
The species studied here and those
for which are available skull descriptions, Helicops and Hydrops share
no unique features. These authors found the two genera share a long and
triangular-shaped maxillary process of the palatine,
a character not found in the
species of Helicops and Hydrops reported on by previous authors.
Citation
Di
Pietro, D. O., Alcalde, L., & Williams, J. D. (2014). New cranial
characters in the tribe Hydropsini (Serpentes: Dipsadidae: Xenodontinae). Acta Herpetologica, 9(1), 1-14.
