The sawfish, Pristis, enters the LRT

Continuing with long-nosed basal chondrichthyans
the large reptile tree (LRT, 1772 taxa; subset Fig. 4) would not be complete without a sawfish.

Figure 1. The sawfish (Pristis pristis) in vivo.

Figure 1. The sawfish (Pristis pristis) in vivo.

Pristis pristis 
(Linck 1790; up to 7.6m) is the extant sawfish, a sister to the guitarfish (Rhinobatos, Fig. 5)) in the LRT. That’s no surprise. All prior workers have this in their hypotheses of interrelationships.

The nasal dermal denticles are larger than the teeth. They become worn with age and are not replaced. As in sister taxa the rostrum is a huge sensory organ for finding buried prey. The saw is also used to swipe and incapitate swimming fish and pin fish against the sea floor. Prey are swallowed whole.

The prefrontals (brown) contribute to the width of the skull. Gills and nares are ventral.

Figure 2. Pristis the sawfish from Digimorph.org, used with permission and colorized here.

Figure 2. Pristis the sawfish from Digimorph.org, used with permission and colorized here.

Both the guitarfish and sawfish
are derived from the dogfish shark, Squalus, which is also basal to another clade of bottom-feeding taxa, the chimaera or ratfish.

Figure 3. Ventral view of Pristis micro don. Note the ventral gills, nares and flat surface.

Figure 3. Ventral view of Pristis micro don. Note the ventral gills, nares and flat surface.

The addition of the Prisitis, the sawfish,
provoked a reexamination of Rhinobatos, the guitarfish (Fig. 5).

Figure 5. Updated image of Rhinobatos showing a lateral expanded prefrontal (brown) on top of the nasal (pink). Apologies for the earlier misunderstanding. I'm learning as I go and no prior studies attempt to color shark skulls with tetrapod homologs.

Figure 5. Updated image of Rhinobatos showing a lateral expanded prefrontal (brown) on top of the nasal (pink).

Figure 4. Subset of the LRT focusing on sharks.

Figure 4. Subset of the LRT focusing on sharks.

Bone identities in the guitarfish, Rhinobatos
(Fig. 5) were modified today. Apologies for the earlier misunderstanding. I’m learning as I go and no prior studies have attempted to color shark skulls with tetrapod homologs.


References
Linck HF 1790. Versuch einer Eintheilung der Fische nach den Zähnen. – Magazin für das Neueste aus der Physik und Naturgeschichte 6 (3): 28-38. Gotha.
Welten M et al. 2015. Evolutionary origins and development of saw-teeth on the sawfish and sawshark rostrum (Elasmobranchii; Chondrichthyes). Royal Society Open Science 2(9):150189.

wiki/Pristis
wiki/Sawfish

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