A fresh look at Cladarosymblema narrienense, a tetrapodomorph fish (Sarcopterygii: Megalichthyidae) from the Carboniferous of Australia, illuminated via X-ray tomography

Abstract

Background The megalichthyids are one of several clades of extinct tetrapodomorph fish that lived throughout the Devonian–Permian periods. They are advanced “osteolepidid-grade” fishes that lived in freshwater swamp and lake environments, with some taxa growing to very large sizes. They bear cosmine-covered bones and a large premaxillary tusk that lies lingually to a row of small teeth. Diagnosis of the family remains controversial with various authors revising it several times in recent works. There are fewer than 10 genera known globally, and only one member definitively identified from Gondwana. Cladarosymblema narrienense Fox et al. 1995 was described from the Lower Carboniferous Raymond Formation in Queensland, Australia, on the basis of several well-preserved specimens. Despite this detailed work, several aspects of its anatomy remain undescribed. Methods Two especially well-preserved 3D fossils of Cladarosymblema narrienense, including the holotype specimen, are scanned using synchrotron or micro-computed tomography (µCT), and 3D modelled using specialist segmentation and visualisation software. New anatomical detail, in particular internal anatomy, is revealed for the first time in this taxon. A novel phylogenetic matrix, adapted from other recent work on tetrapodomorphs, is used to clarify the interrelationships of the megalichthyids and confirm the phylogenetic position of C. narrienense. Results Never before seen morphological details of the palate, hyoid arch, basibranchial skeleton, pectoral girdle and axial skeleton are revealed and described. Several additional features are confirmed or updated from the original description. Moreover, the first full, virtual cranial endocast of any tetrapodomorph fish is presented and described, giving insight into the early neural adaptations in this group. Phylogenetic analysis confirms the monophyly of the Megalichthyidae with seven genera included (Askerichthys, Cladarosymblema, Ectosteorhachis, Mahalalepis, Megalichthys, Palatinichthys, and Sengoerichthys). The position of the megalichthyids as sister group to canowindrids, crownward of “osteolepidids” (e.g.,Osteolepis and Gogonasus), but below “tristichopterids” such as Eusthenopteron is confirmed, but our findings suggest further work is required to resolve megalichthyid interrelationships.

A new elpistostegalian from the Late Devonian of the Canadian Arctic

“…b , Majority-rule tree from undated Bayesian analysis with posterior probabilities. Both analyses recover a basal polytomy; Megalichthys is shown as the outgroup, consistent with other studies 9 , 23 , 25 , 36 . …”

“…a, Strict consensus tree from the maximum parsimony analysis with Bremer decay (D) and bootstrap support values.b, Majority-rule tree from undated Bayesian analysis with posterior probabilities. Both analyses recover a basal polytomy; Megalichthys is shown as the outgroup, consistent with other studies9,23,25,36 .…”

“…Analyses were run for five million generations with four runs of four chains sampling every 5,000 generations and a burn-in of 20%. Megalichthys was designated as an outgroup, consistent with other studies 9 , 23 , 25 , 36 .…”

“…(b) Majority rule tree of maximum parsimony analyses with bootstrapping (500 replicates). In all panels, Megalichthys is plotted as the outgroup consistent with previous phylogenetic analyses of early tetrapods 9 , 23 , 25 , 36 , although basal polytomies are recovered. (c) Unambiguous character changes recovered on the strict consensus tree using the command ‘apolist’ from PAUP* 38 .…”

Investigating the dentoalveolar complex in archaeological human skull specimens: Additional findings with large volume micro‐CT compared to standard methods

“…The LV micro‐CT scanning system has been used in research for oral surgery (Beetge et al, 2018; Stan et al, 2019; Theye et al, 2018), biomedical (Grace et al, 2022; Kusins et al, 2019; Wearne et al, 2022) and medical research (Hutchinson et al, 2016; Kramer et al, 2019; Main et al, 2021; Smit et al, 2020; Tan et al, 2022; Welsh et al, 2020), paleontology (Clement et al, 2021), and forensic investigations (Alsop et al, 2022, Braun et al, 2022, Nikolova et al, 2019, Rutty et al, 2012). The non‐invasive nature of this type of micro‐CT scanner, as well as its technical capabilities, suggests that it could be of great value for the investigation of rare, delicate, and valuable archaeological human remains.…”