User:Sclerotized/Platylomaspis

Platylomaspis is an extinct genus of polybranchiaspiform galeaspid known from the Telychian age (Llandovery, Silurian) of the Tataertag Formation (Kalpin County, Xinjiang, northwest China).

Etymology
The generic name is derived from the Greek words πλατύς platús (broad) %etc.%, thus the name can be translated as "broad brim shield", chosen "in reference the broad ventral rim of head-shield".

Description
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The head shield of Platylomaspis takes a broad pear shape with a dome-shaped depression at its centre surrounded by a wide flattened marginal band that tapers rostrally into a long rostral process. The shield could reach a maximum width of 60-70 mm at the middle point and a length of 70–80 mm excluding the rostral process. It is ornamented by coarse-granular tubercles and bears along its lateral marginal 5-6 serrations every 10 mm.

The rostral process of both specimens is only proximally preserved, but it is possible to interpret an anterior tapering of the same into a rod-like structure.

The flattened ventral region of the body, the ventral rim, is diagnostic in Platylomaspis for its dimension. It accounts for approximately one-fourth of the head-shield length at 20.0 mm. This is exceptionally broad for polybranchiaspiformes, which typically have it account for one-tenth.

The central dome-shaped depression is expected, based on material from close species, to have bored two orbital fenestras, where the eyes would be located, and a mediodorsal fenestra, through which the water intake would occur [citation needed], although they are not preserved. It encloses the oralo-branchial chamber that connects to the exterior by the oralo-branchial fenestra, a ventral opening embraced by the ventral rim. This fenestra is anteriorly composed of a subtriangular form, the anterior oral fenestra, that posteriorly widens into a large suborbicular shape, the posterior branchial fenestra, with 5–7 successive notches, the external branchial openings. In this way, Platylomaspis does not display the polybranchic condition seen in many extinct jawless fishes (i.e., that of bearing a considerable number of gills).

Phylogeny
2 ramos s/ ramificacoes:

2 ramos, 1º c/ ramificacoes:

2 ramos, 2º c/ ramificacoes:

2 ramos com ramificações:

3 ramos: