Wretman, Liston and Kear 2020 bring us
their views on the Pachycormiformes, a clade named for Early Jurassic Pachycormus (Fig. 1). These are typically large fish (Fig. 2) with living relatives (Fig. 3) among the Osteoglossiformes (= bony tongues), like the arowana (Osteoglossum).
From the Wretman et al. abstract:
“Pachycormiforms are an extinct radiation of Mesozoic actinopterygian fishes that occupy a key transitional position along the Holostei-Teleostei stem.”
Figure 1. Pachycormus macropterus has a new skull reconstruction. Originally I did this without template or guidance. Now osteoglossiformes provide a good blueprint.
From the Wretman et al. abstract:
“The group first appears in the fossil record with an explosive diversification into two morphologically distinct lineages: ‘toothless’ suspension-feeders (SFP) including the famously gigantic Leedsichthys; and ‘tusked’ carnivorous pursuit predators, such as the superficially sword-fish like Protosphyraena (Fig. 2).
Figure 2. Protosphyraena museum mount. Length about 3m. Note the advanced placement of the pelvic fins.
From the Wretman et al. abstract:
“Pachycormiforms characteristically trended towards reduced ossification in the skeleton, especially amongst the larger-bodied suspension-feeding forms, which tend to be represented by fragmentary and enigmatic remains. Nevertheless, pachycormiform fossils have been recognized worldwide in strata of Early–Late Jurassic and Late Cretaceous age. In contrast, stratigraphically intermediate Early Cretaceous pachycormiforms are virtually unknown, with the exception of the Protosphyraena-like taxon Australopachycormus from the late Albian of Australia.”
Figure 3. Subset of the LRT focusing on fish. Here Pachycormiformes are highlighted.
From the Wretman et al. abstract:
“Here we report on a new Early Cretaceous pachycormiform taxon from the late Albian Allaru Mudstone of northwestern Queensland in Australia. Surprisingly, this specimen is edentulous and consists of a skull with the anterior half of the body, representing an individual of about 1.0-1.5 m SL — approximately equivalent in length to the Dresden juvenile specimen of Asthenocormus.”
“Significantly, the Allaru Mudstone pachycormiform is both the first SFP identified from Australia, and the first Early Cretaceous SFP globally. Moreover, while our multiple cross-referencing parsimony and Bayesian phylogenetic analyses decisively place it as a basally branching member of the suspension-feeding clade, the Allaru Mudstone pachycormiform possesses a curious character state mosaic incorporating traits that are more consistent with pursuit predator pachycormiform taxa of equivalent body-size.”
Figure 4. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.
From the Wretman et al. abstract:
“This observation raises questions about whether Cretaceous pachycormiforms manifested repeated convergence, or perhaps mask a more complex evolutionary history of secondarily-derived extreme feeding specializations.”
The living pachycormiform, Osteoglossum (Fig. 4), is a large (2m), slow-moving, surface predator, bony-tongue, not a suspension feeder. It is also a facultative air breather. So maybe the feeding strategy traditions of extinct taxa need to be reconsidered in this light.
Pachycormiforms/osteoglossiformes are some of the closest living relatives of spiny sharks (acanthodians). Note the sharp-pointed, bony pectoral fins of clade members (Figs. 1, 2, 4).
And that’s the last of the SVP abstracts.
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References
Wretman L, Liston J and Kear B 2020. First record of an edentulous suspension-feeding pachycormiform fish from the Lower Cretaceous of Australia. SVP abstracts 2020.
The Pterosaur Heresies 