Jason Philip Downs

Delaware Valley University · Biology

New material from the Upper Devonian (Frasnian) Fram Formation of Ellesmere Island, Nunavut, Canada, represents the second holoptychiid (Porolepiformes) species to be described from the formation. The quality of preservation and preparation of the material enables description of underrepresented anatomy for Holoptychius including the braincase (eth...

Recent work in the Late Devonian (Frasnian) Fram Formation of Ellesmere Island, Nunavut, Canada, has produced the first North American record of Laccognathus (Sarcopterygii, Porolepiformes), a taxon previously known only from Latvia and Russia. Represented by a large sample that includes cranial material from 22 individuals, Laccognathus embryi, sp...

We analyze a new sample of very small Bothriolepis from the Catskill Formation (Upper Devonian, Famennian Stage) in Tioga County, Pennsylvania, USA. The material was collected in a series of rock slabs, each of which carries as many as thirty-one individuals in densely-packed groups with little to no overlap and with a preferred orientation. Althou...

We used light microscopy and scanning electron microscopy to compile a complete histological description of the dermal skeleton of the antiarch placoderm, Bothriolepis canadensis. Placodermi is most often cited as the sister group of crown group Gnathostomata, but some recent authors propose that placoderms instead represent a paraphyly of forms le...

Among the morphological changes that occurred during the 'fish-to-tetrapod' transition was a marked reorganization of the cranial endoskeleton. Details of this transition, including the sequence of character acquisition, have not been evident from the fossil record. Here we describe the braincase, palatoquadrate and branchial skeleton of Tiktaalik...

A new species of Langlieria is described from the Upper Devonian (Frasnian) Irish Valley Member of the Catskill Formation. The type material was collected from a road cut exposure on the north side of the westbound lanes of Pennsylvania Route 322 west of Port Matilda, Centre County, Pennsylvania, U.S.A. The new species of Langlieria, the second fro...

A new species of Eusthenodon from the Upper Devonian (Famennian) Catskill Formation was collected from talus blocks at the base of a road cut along the Cogan House Exit Ramp on U.S. 15/Interstate 99 in Lycoming County, Pennsylvania, U.S.A. The new species is represented by a nearly complete, articulated skull (ANSP 23748) and additional cranial bon...

New material from the Upper Devonian (Famennian) Catskill Formation of Pennsylvania, U.S.A., indicates the presence of a new species of Megalichthys. A large collection of complete and well-preserved fossil material from the Red Hill field locality enables a thorough anatomical description that is not commonly available in Megalichthyidae. The cran...

We describe new material of the tristichopterids cf. Langlieria socqueti and cf. Eusthenodon wangsjoi and other unassignable tetrapodomorph remains from the upper Famennian locality of Strud, Belgium. Because of recent improvements in our tristichopterid knowledge, a new phylogenetic analysis is presented in addition to a paleobiogeographic analysi...

Hyneria lindae is one of the largest Devonian sarcopterygians. It was found in the Catskill Formation (late Famennian) of Pennsylvania, USA. The current study focuses on the palaeohistology of the humerus of this tristichopterid and supports a low ossification rate and a late ossification onset in the appendicular skeleton. In addition to anatomica...

Thomson (1968, Postilla 124:1–13) described and diagnosed the tristichopterid Hyneria lindae from parts of a disarticulated skull and isolated scales recovered from the Upper Devonian (Famennian) Catskill Formation of Pennsylvania, U.S.A. Since the publication of that description, knowledge of the tristichopterid clade has grown significantly, with...

New material from the Upper Devonian (Frasnian) Nordstrand Point Formation of Ellesmere Island, Nunavut, Canada, represents the largest known species of antiarch and the first described from the Nordstrand Point Formation. Bothriolepis rex, sp. nov., is additionally remarkable for the thickness and compactness of its dermal skeletal plates. The new...

Discovery of the Late Devonian fish, Tiktaalik roseae, provides a new opportunity to examine the environmental context of the fish-tetrapod transition. Here we present the stratigraphic framework for the 30 m above and below the T. roseae-bearing portion of the Fram Formation. The Fram was described by Embry and Klovan (Bull. Can. Pet. Geo., 1976)...

The study of morphological rules, or trends, offered classical biologists the opportunity to address the mechanisms underlying the evolution of anatomical designs. Regularities in evolution suggested that common functional or developmental rules governed the transformation of structures. Parallelism is one such example. Journal Article

The stratigraphically earliest and the most primitive examples of vertebrate skeletal mineralization belong to lineages that are entirely extinct. Therefore, palaeontology offers a singular opportunity to address the patterns and mechanisms of evolution in the vertebrate mineralized skeleton. We test the two leading hypotheses for the emergence of...

The monospecific genus Ageleodus is a primitive chondrichthyan known exclusively from isolated Late Devonian and Carboniferous teeth. Due in part to the paucity of material, dental variation in Ageleo dus has not been fully recognized. This paper reports on a large new sample of Ageleodus pectinatus teeth (382) from the Catskill Formation (Late Dev...