Dialipina: an overlooked coelacanth (clade: Actinistia)

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.

Figure x. This is a traditional cladogram, from Clement et al. 2018, lacking appropriate outgroup taxa.

Figure 1. This is a traditional cladogram, from Clement et al. 2018, lacking appropriate outgroup taxa. Dialipina is the outgroup here. Latimeria is not listed here.

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.

Wikipedia does not list Dialipina in their list of coelacanths (clade: Actinistia).

Figure 2. Dialipina skull in situ and reconstructed.

Figure 2. Dialipina skull in situ and reconstructed. The slender lacrimal, maxilla and jugal fuse in Latimeria (Fig. 3).

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.

Figure 4. Latimeria updated. Note the fusion of the jugal, lacrimal and toothless maxilla into one bone. Compare to Dialipina in figure 2.

Figure 3. Latimeria updated. Note the fusion of the jugal, lacrimal and toothless maxilla into one bone. Compare to Dialipina in figure 2.

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.

Figure 3. Dialipina overall in situ. Two specimens. Note the very Latimeria-like tail, and the lobe portion of the lobefins were overlooked in prior studies.

Figure 4. Dialipina overall in situ. Two specimens. Note the very Latimeria-like tail, and the lobe portion of the lobefins were overlooked in prior studies.

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.

Figure 6. Dialpina in situ.

Figure 5. Dialpina in situ with DGS applied. This small Early Devonian lobefin was not recognized as one, despite so many traits shared with Latimeria

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., 2015bSchultze and Cumbaa, 2001) or stem osteichthyan (Choo et al., 2017Friedman and Brazeau, 2010Giles et al., 2015cLu et al., 2016aQiao et al., 2016).”

Figure x. Updated subset of the LRT, focusing on basal vertebrates = fish.

Figure 6. Updated subset of the LRT, focusing on basal vertebrates = fish. Here Dalipina nests with Latimeria closer to the bottom of this diagram than to the top.

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


References
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.
Lund R and Lund W 1984. New genera and species of coelacanths from the Bear Gulch Limestone (Lower Carboniferous) of Montana (U.S.A.). Geobios. 17 (2): 237–244.
Schultze H-P 1968. Palaeoniscoidea-Schuppen aus dem Unterdevon Australiens und Kanadas und aus dem Mitteldevon Spitzbergens. Bulletin of the British Museum (Natural History) 16: 343–376.
Schultze H-P 1973. Crossopterygier mi heterozerker Schwanzfloss aus dem Oberdevon Kanadas, nebst einer Beschreibung von Onychodontida-Resten aus dem Middledevon Spaniens und aus dem Karbon der USA. Palaeontograhica A 143:188–208.
Schultze H-P 1992. Early Devonian actinopterygians (Osteichthyes, Pisces) from Siberia. Pp. 233–242 in Mark-Kurik, E.: Fossil Fishes as Living Animals. Academy of Sciences of Estonia.
Schultze H-P, and  Cumbaa SL 2001. Dialipina and the characters of basal actinopterygians, p. 315–332. In: Major Events in Early Vertebrate Evolution: Palaeontology, Phylogeny and Development. Ahlberg PE (ed.). Systematics Association Special Volume 61, Taylor and Francis, London.

Finding Our First Fish

wiki/Dialipina
wiki/Latimeria
wiki/Miguashaia

wiki/Actinistia
wiki/Coelocanth

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