Densignathus

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.

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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. 

References:

Daeschler, E. B., 2000, Early tetrapod jaws from the Late Devonian of Pennsylvania, USA: Journal of Paleontology, v. 74, n. 2: 301-308.