Genus: Densignathus DAESCHLER, 2000
Etymology:Latin, densus, "thick”, and Greek, gnathos, "jaw”: Thick jaw.
Diagnosis:Densignathus is diagnosed by a unique combination
of characters. Primitive features include; the presence of
coronoid fangs, ossified Meckelian element, denticles on the
prearticular, and a partially closed mandibular canal. Derived
features of other stem tetrapods and Densignathus include; the
presence of a fang-bearing parasymphysial plate, mesial and lateral
parasymphysial foramina, chamfered (beveled) dentary
loosely attached to infradentaries, coronoid fangs within the
marginal tooth row, and contact between the anterior coronoid
and the parasymphysial plate. Unique features of Densignathus
are; a lower jaw that is very robust anterior to adductor fossa
(the width of the ramus at the middle coronoid is equal to height
of the ramus at the same location), parasymphysial plate with a
single large fang and an isolated small denticle, shagreen texture
on the dorsal lip of the prearticular occurs in a distinct band
without denticles grading into it from the mesial surface of the
prearticular, and the absence of strong radiating ornament on the
lateral surface of the infradentaries.
Species: D. rowei DAESCHLER, 2000
Etymology: In honor of Norman Douglas Rowe in recognition of his discovery of the type material of Densignathus and his many important contributions to reseach at the Red Hill locality.
Holotype:ANSP 20637 - Breakdown as follows;
20637.1: Anterior portion of lower jaw.
20637.2: Posterior portion of left lower jaw.
20637.3: Posterior portion of right lower jaw.
Note: these 3 specimens are considered to be from a single individual because they were found in very close proximity to each other on the same bedding plaine and the 2 posterior segemints are mirror images of one another.
Locality:North side of Route 120, 2 km west of Hyner, 41°20.645’N, 77°40.800’W, Red Hill, Clinton County, Pennsylvania.
Horizon:Duncannon Member, Catskill Formation.
Age:Early late Famennian Stage, Upper Late Devonian.
Referred Material: none
Comments:Recent paleontological fieldwork in the Upper Devonian Catskill Formation at Red Hill in Clinton County, Pennsylvania,
USA, has produced a diverse assemblage of vertebrate fossils including early tetrapods. The tetrapod Hynerpeton bassetti was described
from the site in 1994 and a recently recognized partial lower jaw of that taxon is described here. Additionally, this paper describes a
new Late Devonian tetrapod, Densignathus rowei new genus and species, based on a well-preserved lower jaw. This new taxon is
characterized by dramatic widening of the jaw anterior of the adductor fossa, a pronounced twist in the orientation of ventral margin
of the jaw, an uninterrupted exposure of Meckelian bone on the mesial surface, and weakly-developed radiating ornament on the lateral
surface of the infradentaries. Although phylogenetic resolution within stem tetrapods is lacking, Densignathus rowei, n. gen. and sp.,
informs several topics including the sequence of character acquisition in the lower jaw, morphological diversity, and paleoecology of
the earliest tetrapods.
Fossil jaw of Densignathus.
Densignathus rowei, holotype, left lower jaw.
Daeschler, E. B., 2000, Early tetrapod jaws from the Late Devonian of Pennsylvania, USA: Journal of Paleontology, v. 74, n. 2: 301-308.