The smartest bony fish: Mormyridae

They say
that members of the clade Morymyridae (Figs. 1, 2) are the smartest fish based on their encephalization quotient (= brain volume divided by total volume). Wikipedia nests mormyrids with Osteoglossiformes like Osteoglossum. Several are electro-sensitive and can produce a very mild electric field in order to sense their environment in muddy river waters. They use their distended mouth parts to feed on small buried invertebrates.

By contrast
the large reptile tree (LRT, 1799+ taxa) nests mormyrids with the Brycon, the plant-eating piranha (Figs. 1, 2), and Serrasalmus, the flesh-eating piranha. Here are sample taxa close to the ancestry of two mormyrids, Mormyrops and Gnathonemus (Figs. 1, 2). In the LRT, Osteoglossiformes are in the OTHER bony fish clade, the one that includes all the placoderms, catfish, spiny sharks and lobefins.

Figure 1. Mormyrid evolution as told by sample taxa from their ancestry.

Figure 1. Mormyrid evolution as told by sample taxa from their ancestry. Arrows point to the vestigial pelvic  fins.

Note the gradual migration
of the anterior dorsal fin to the posterior position in this hypothetical sequence of ancestors to Gnathonemus, along with the reduction of the pelvic fin to a spine.

Figure 2. Mormyrid skull evolution as told by sample taxa from their ancestry. Note the layering of the green supratemporal atop the yellow-green intertemporal begins with Brycon.

Figure 2. Mormyrid skull evolution as told by sample taxa from their ancestry. Note the layering of the green supratemporal atop the yellow-green intertemporal begins with Brycon.

Adding taxa, like Mormyrops and Brycon,
(Figs. 1, 2) the newest additions to the LRT helped resolve the issue of where to place the very weird, very different, Gnathonemus. I could not have done it without Mormyrops. Adding characters would not have helped, despite entreaties from PhDs.

Figure x. Rayfin fish cladogram

Figure x. Rayfin fish cladogram

Brycon dentex 
(Müller and Troschel 1844; 80cm) is the extant South American trout or Sabalo barracuda. Here it nests between Serrasalmus (below) and Mormyrops, all descending from Salmo, the salmon (a type of trout) This omnivore eats fruit and seeds that fall into the water, along with small fish and invertebrates. The naris entrance is confluent with the exit. The teeth are robust and continue down the maxilla.

Mormyrops deliciosus
(Leach 1818, originally Mormyrops anguilloides Linneaus 1758; up to 1.5m in length) is the extant Cornishjack, a weakly electric river fish from Sub-Saharan Africa. The maxilla lacks teeth. The skull is extended due to an enlarged braincase. The teeth are robust, as in the ancestral Brycon.

Gnathonemus curvirostris
(Gill 1863) is the extant elephantfish, a member of the clade Mormyridae, ranging in size from 5cm to 1.5m. Traditionally considered a sister to Osteoglossum, here it nests as a sister to Mormyrops (above) and the piranha-sister, Brycon. Note the matching dorsal and anal fins. The cerebullum is greatly enlarged. The supratemporal appears as a ‘scale’ over the intertemporal. This slow, brackish water micro-predator uses electrical impulses to find tiny prey in cloudy waters convergent with electric eels, which evolved from pitch-black cave waters.


References
Brünnich MT 1788. Om en ny fiskart, den draabeplettede pladefish, fanget ved Helsingör i Nordsöen 1786. K. Danske Selsk. Skrift. N. Saml. 3: 398-407.
Gill TN 1863. Notes on the labroids of the western coast of North America. Proc. Acad. Nat. Sci. Phila. v. 15: 221-224.
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Müller JP and Troschel FH 1844. Synopsis generum et specierum familiae Characinorum. (Prodromus descriptionis novorum generum et specierum). Archiv für Naturgeschichte 10(1): 81-99 (Zu pag. 99 foldout).

wiki/Mormyridae
wiki/Brycon
wiki/Cornish_jack
wiki/Mormyridae
wiki/Gnathonemus

 

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.