Redescription and Systematics of the genus Torosteus (Arthrodira; Placodermi)

Author: Petar Tomic

  • Thesis download: available for open access on 5 Apr 2027.

Tomic, Petar, 2023 Redescription and Systematics of the genus Torosteus (Arthrodira; Placodermi), Flinders University, College of Science and Engineering

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Placoderms were a group of extinct armoured jaw vertebrates that were abundant in marine and estuarine environments, spanning a range from the Late Silurian (44.3.8-419.2ma) to the Late Devonian (419.2-359.3ma). Arthrodires were the most successful placoderm order with the eubrachythoracids being the most derived members of the group. Torosteidae was first erected by Gardiner & Miles (1990) alongside the genus Torosteus, though, the family would be synonymized into Plourdosteidae in Gardiner & Miles (1994). This would be reclassified back to Torosteidae by Carr (1996), after Plourdosteus was placed alongside Panxiosteus and Janiosteus into the Family Panxiosteidae. Torosteidae and subsequently Torosteus would be seldom used in future studies, leading to Torosteus becoming a wastebasket taxon where many undescribed specimens were placed within the group. This was due to the generalized nature of the diagnosis, poorly described or absent descriptions on key morphological structures on the gnathals and skull. This has led to the binomial uncertainty of both Torosteus species, leading to the discussion of which species fit within Torosteus and those that warrant the erection of a new species or genus. The systematics showed that the new structures and poorly described structures were morphologically important in distinguishing the Torosteidae, Torosteus and its species. The systematics discovered that the mesial tooth row of the inferognathal was present in adult specimens and the reduced posterior spine of the spinal, were key morphological indicators for the Torosteidae. The postocular process was a key indicator for Torosteus, whilst the dentition, parasphenoid and anterior ventrolateral were great species indicators. Specimens SAM P50606, WAM 01.11.09 and WAM 91.4.31 differed significant from Torosteus warranting the erection of a new genus with two species, as SAM P50606 differed significantly from the other two specimens. The original species described in Gardiner & Miles (1990) were viable being supported by the systematics, phylogeny and principal component analysis (PCA). Many of the new structures were present in most of the torosteids as well as other families from Gogo, therefore, necessitating the need to redescribe other taxa from the Gogo Formation.

Keywords: Placoderms, Devonian, Gogo Formation, Arthrodires, Palaeontology

Subject: Science, Technology and Enterprise thesis

Thesis type: Masters
Completed: 2023
School: College of Science and Engineering
Supervisor: Professor John Long