Graduation Date

Spring 2021

Document Type



Master of Science degree with a major in Biology

Committee Chair Name

John Reiss

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Sharyn Marks

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Mihai Tomescu

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Paul Bourdeau

Fourth Committee Member Affiliation

HSU Faculty or Staff


Lepidosiren, Ascaphus, Dicamptodon, Gill, Protopterus, Morphology, Homology

Subject Categories



Vertebrate gills may be either external (protruding from the body surface) or internal (enclosed in a chamber). Among living amphibians, external gills are found in salamander larvae and neotenes, early frog larvae, and caecilian embryos; internal gills are found only in later-stage frog larvae. Evidence for internal gills has also been found in stem tetrapods, and amphibian-like external gills have been found in some fossil temnospondyls and anthracosaurs. Gill homology among these groups and life stages has long been questioned. To address this, scanning electron microscopy, vascular casting, and paraffin sectioning were utilized to study the morphology of gills and associated vessels of four sarcopterygian species: the basal frog Ascaphus truei, the salamander Dicamptodon tenebrosus, and the lungfishes Lepidosiren paradoxa and Protopterus sp. In all studied species, blood flows from the heart through four pairs of afferent branchial arteries, through the gill lamellae (when present), and drains through efferent branchial arteries into the dorsal aorta. In D. tenebrosus and A. truei no gill lamellae are found on the fourth branchial arch; instead, the afferent branchial artery supplies blood to the lung. In the external gill of D. tenebrosus the afferent arteries travel posterolaterally within an elongation of the interbranchial septum and protrude dorsolaterally from the body, supplying blood to the paired, digit-like lamellae via a single vascular loop per lamella. Ascaphus truei, unlike most anuran larvae, never develops external gills, but only internal gills. These extend directly from the ventral side of the branchial arches. Each unpaired lamella has multiple club-like branches, each housing a vascular loop. Protopterus sp. possesses internal gills on the hyoid arch and branchial arches III-V, with the hyoid and branchial arch V developing unpaired primary lamellae. The lamellae of all arches possess secondary lamellae. No gill lamellae were found in the studied larval Lepidosiren paradoxa. The external gills of Dicamptodon tenebrosus show some remarkable similarities to the internal gills of basal sarcopterygians, possessing paired primary lamellae (though they never develop any secondary lamellae), and provide further evidence that the external gills of amphibians are homologous to the internal gills of fishes. The evolutionary significance of the internal gills of frogs is less clear, but the morphology of the basal Ascaphus truei provides evidence suggesting that the internal gills of frogs are an independently evolved character, rather than a retained ancestral feature. These findings shed light on the morphology and evolution of gills within sarcopterygians.

Citation Style


Included in

Evolution Commons



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