Tiny Gregorius (Late Mississipian) revisited

As mentioned
yesterday, some changes have come to the basal vertebrates portion of the the LRT (Fig. 3). Here are the first of many highlights.

Gregorius rexi (Bear Gulch Fm. Serpukhovian, Latest Mississipian; Fig. 1) has not moved from its node in the large reptile tree (LRT, 1655+ taxa),
but the moray eel, Gymnothorax (Fig. 2), and the gulper eel, Eurypharynx, have moved to nest with goldfish-sized Gregorius.

Figure 1. Tiny Gregorius rexi nests basal to moray and gulper eels and also basal to all bony fish in the LRT.

Figure 1. Tiny Gregorius rexi nests basal to moray and gulper eels and also basal to all bony fish in the LRT. The yellow zone represents the pharyngeal bars that act as a second set of jaws in the related moray eel in figure 2. Shown life size.

Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Gregorius rexi (Lund and Grogan 2004; Bear Gulch Fm. Serpukhovian, Latest Mississipian) is traditionally considered a type of two-spined ratfish. In the LRT Gregorius is a late-surviving proximal outgroup to the Osteichthyes, the bony fish iincluding earlier placoderms, acanthodians and stem tetrapods. It retains the dorsal spines of its ancestor, Hybodus. It is not clear what sort of pectoral and pelvic fins Gregorius had due to matrix damage, but descendant taxa, like the moray eel, lack fins.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Gymnothorax afer (Bloch 1795, type genus; 2m) Gymnothorax funebris (Ranzani 1839) is the extant green moray eel, which has no limbs or fins and traditionally nests within the Teleostei. Here this ‘eel’ is derived from Gregorius, outside the major dichotomy that splits the Teleostei. Pharygneal jaws (former gill bars) race anteriorly to double capture prey and drag it back to the digestive system.

This is a novel hypothesis of interrelationships.


References
Bloch ME 1795. Naturgeschichte der ausländischen Fische. Berlin. v. 9. i-ii + 1-192, Pls. 397-429.
Lund R and Grogan E 2004. Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA. Recent Advances in the Origin and Early Radiation of Vertebrates 505-531.
Valliant LL 1882. Sur un poisson des grandes profondeurs de l’Atlantique, l’Eurypharynx pelecanoides. Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences, Série D, Sciences Naturelles 95: 1226-1228.

Gregorius_rexi.html
wiki/Eurypharynx
wiki/moray eel

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