Menaspis: a late placoderm and early catfish

Updated January 5, 2021
by the hypothesis that the head and gill chambers were missing in the holotype of Menaspis making it a spiny shark (Acanthodian) in the LRT (2107 taxa).

Previously we looked at several autapormorphic reconstructions
of fossil taxa, like Yi qi, Ambopteryx and various pterosaur bits and pieces.

Today’s weird-o: Menaspis aramata 
(Ewald 1848; Figs. 1-3), a Late Permian fish with head ‘spines.’ This taxon has been a headache for paleontologists trying to figure out its anatomy, phylogenetic placement and even its in situ exposure. Several prior workers (see list below) have been critical of the earlier workers. So that makes this taxon an official enigma.

Please note:
all those academic workers saw this fossil firsthand and still managed to disagree with one another. Maybe that aspect of paleontology is more common than everyone thinks.

Figure 1. Old lithograph of Menaspis with barbels raised like horns.

Figure 1. Old lithograph of Menaspis with barbels raised like spines. Since the fossil is preserved exposing the dorsal layer in ventral view, this freehand drawing in lateral view documents a fair amount of imagination and error.

Known as an intriguing German fossil for 171 years
the Late Permian (255 mya) fish with ‘spines’, Menaspis armada, was redescribed by Bendix-Almgreen (1971; Fig. 3) who wrote: “The two best preserved specimens of the Upper Permian fish Menaspis armata have been reinvestigated, resulting in new interpretations of a variety of anatomical features. The conclusion is reached that the menaspids cannot possibly be closely related to the chimaeriforms (myriacanthids, squalorajids, and chimaerids), nor to any of those better known bradyodonts (chondrenchelyids, helodontids or edestids) with which they were previously classified. As far as other elasmobranchiomorphs are concerned, the menaspids may be somehow related to, though surely not direct descendants of, the rhenanids, and it is conceivable that both these groups are derived from the same ancestral forms among the early arthrodires or the arthrodire predecessors.”

Figure 2. Menaspis armatas in situ. Colors added to bones and skin.

Figure 2. Menaspis armatas in situ. Colors added to bones and skin. This is an outdated interpretation based on the assumption that the skull was preserved, but the mouth and orbits were not identified. See figure 2b for an update.

Figure 2b. New reconstruction of Menaspis with the hypothesis that the skull and gil chambers are missing.

Figure 2b. New reconstruction of Menaspis with the hypothesis that the skull and gil chambers are missing.

Fifteen years later, Ortlam 1986 wrote:
(Google-translated from German) “Although the fossil has been known for almost 150 years, it has so far eluded a clearly recognized classification in the system of lower vertebrates. Many circumstances and new observations led to considerable doubts about the interpretation of numerous edits of the last hundred years. Only by the stereoscopic X-ray technique were observations made possible, which provided the knowledge that the fossils present from Berlin and Halle are seen from the ventral side and not from the dorsal side, as has been repeatedly assumed in the last hundred years. Surprisingly, this resulted in a complete agreement with the original description by Ewald (1848) of a ventral view.”

“The classification of Menaspis armata revealed numerous evidence for an arctolepid arthrodire, the last known arthrodire of the Paleozoic era. Previously, it was believed that this group of animals were extinct by the Lower Carboniferous (about 360 million years ago).”

Figure 3. Bendix-Almgreen 1971 dorsal view illustration of Menaspis with orbits misplaced. The actual fossil exposes the dorsal surface in ventral view with barbels descending, not ascending. 

Figure 3. Bendix-Almgreen 1971 dorsal view illustration of Menaspis with orbits misplaced. The actual fossil exposes the dorsal surface in ventral view with barbels descending, not ascending.

Six years later, Schaumberg 1992 wrote:
“Our knowledge of the anatomy of Menaspis armata Ewald has been extended by two newly found specimens of this holocephalian from the Upper Permian Kupferschiefer of Richelsdorf (Hessen) and Sangerhausen (Sachsen-Anhalt). New aspects concerning its body-form are discussed. Its classification as a holocephalian (= ratfish and kin) —repeatedly questioned in the past—is found to be correct.

In summary
some authors considered Menaspis a ratfish. Others thought it was a placoderm. The placement of the orbit has not been consistent. Individual bones have not been identified. The large semi-circular spines have never been interpreted as barbels.

Starting fresh, with a printed photograph,
a DGS tracing (Fig. 2b) revealed the skull and gill chambers were missing, likely bitten off. Everything else fell into place when that was realized (June 4, 2022).

Here,
in the large reptile tree (LRT, 1497 taxa then, 2106 taxa when revised) Menaspis nests with acanthodians (spiny sharks).


References
Bendix-Almgreen SE 1971. The anatomy of Menaspis armada and the phylogenetic affinities of the menaspid bradyodonts. Lethaia 4(1):21–49.
Ewald J 1848. Über Menaspis, eine neue fossile Fischgattung. Berichte Über die zur Bekanntmachung Geeigneten Verhandlungen der Königlich-Preussischen Akademie der Wissenschaften zur Berlin 1848:33-35.
Jäckel O 1890. Über Menaspis, nebst allgemeinen Bemerkungen über die systematische Stellung der Elasmobranchii. Sitzungsb. Ges. nature. Freunde, Berlin 1891: 115–131.
Ortlam D 1986. Neue Aspekte zur Deutung von Menaspis armata Ewald (Kupferschiefer, Zechstein 1, Deutschland) mit Hilfe der stereoskopischen Röntgentechnik. Geologisches Jahrbuch Reihe A, Band A 81.
Patterson C 1968, Menaspis and the bradyodonts. In: T. Ørvig, Current Problems of Lower Vertebrate Phylogeny. (Hrsg.): Nobel Symposium. Band 4. Almquist and Wiksell, Stockholm 1968, S. 171–205.
Schaumberg G 1992. Neue Informationen zu Menaspis armata Ewald. Paläontologische Zeitschrift 66:311.

wiki/Menaspis
Germanwiki/Menaspis
Menaspis as a ratfish digital model online – very autapomorphic
wiki/Catfish
wiki/Chimaeriformes
wiki/Bradyodonti
wiki/Cochliodontiformes
wiki/Rhenanida
wiki/Arthrodira
wiki/Arctolepidae

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