Early Devonian Dialipina
(Figs. 2, 4,5) has been described as, ‘the oldest known actinopterygian’, Clement et al. 2018 nested Dialipina as the outgroup to the stem bony fish on their cladogram (Fig. 1). It was orignally considered a palaeonisciform, like Cheirolepis.
Prior authors have missed the many traits shared between this taxon and the extant coelacanth, Latimeria, (Fig. 3) perhaps because Dialipina fossils did not readily display distinct pectoral and pelvic lobe fins. The lobes are present (Figs. 4, 5), just not distinct. No one misses the coelacanth-like tail. Nor do they miss the muscular dorsal and anal fins.
The traditional view of bony fish systematics (Fig. 1):
“Osteichthyans comprise two divisions, each containing over 32,000 living species : Sarcopterygii (lobe-finned fishes and tetrapods) and Actinopterygii (ray-finned fishes).”
The LRT view of bony fish systematics (Fig. 6):
lobefins arose from fish without lobe-fins in the Late Silurian, documented by Dialipina in the Early Devonian.
Dialipina salgueiroensis (D. markae Schultze 1968; Schultze 1992; Schultze and Cumbaa 2001; Early Devonian. 420 mya) is the earliest known bony fish known from a complete skeleton. It is a sister to the extant coelacanth, Latimeria.
Latimeria chalumnae (Smithi 1939) is the extant coelocanth, a slow-swimming deep-water fish. The fins arise from long lobes. The postorbital is large. The supratemporal is absent. The maxilla is fused to the jugal and lacrimal. M maxillary teeth are absent.
Giles et al. 2015 reported,
“Dialipina was originally diagnosed as a actinopterygian based on scale morphology (Schultze, 1968), but more recent analyses have resolved it either as an stem actinopterygian (Giles et al., 2015b; Schultze and Cumbaa, 2001) or stem osteichthyan (Choo et al., 2017; Friedman and Brazeau, 2010; Giles et al., 2015c; Lu et al., 2016a; Qiao et al., 2016).”
Giles et al. 2015 reported,
“The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates).” According to the LRT, the foremost problem of Giles et al. only exists due to taxon exclusion.d
Clement AM et al. 2018. Neurocranial anatomy of an enigmatic Early Devonian fish sheds light on early osteichthyan evolution. Evolutinary Biology online here. eLife 2018; 7:e34349 DOI: 10.7554/eLife.34349
Giles S, Friedma M and Brazeau MD 2015. Osteichthyan-like cranial conditions in an Early Devonian stem gnathostome. Nature, 520 (7545): 82–85.
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