Eospongilla morrisonensis Dunagan, 1999

Pronzato, Roberto, Pisera, Andrzej & Manconi, Renata, 2017, Fossil freshwater sponges: Taxonomy, geographic distribution, and critical review, Acta Palaeontologica Polonica 62 (3), pp. 467-495 : 476-477

Eospongilla morrisonensis Dunagan, 1999

Fig. 11. Type horizon: Morrison Formation , Upper Jurassic .

Type locality: Fort Collins (Highway 287 roadcut, 40°40.432’N, 105°11.319’W), Colorado, USA .

References: Waldschmidt and LeRoy 1944: 1097; Yen 1952: 31; Dunagan 1999.

Description (emended from Dunagan 1999).—Spiculite with two massive accumulation of spicules, small (10–15 mm), low domical to cylindrical. Megascleres dominant strongyles and oxeas (180–300 × 20–35 μm) with smooth surface, spineless. Microscleres, gemmuloscleres and gemmules not detected.

Remarks. —The most important evidence, stressed by Dunagan (1999), is the very rare discovery of two entire fossil specimens of freshwater sponges. Unfortunately, as it can be judged from published photos, it is clear that we deal not with specimens of sponges with original spicules arrangements, but rather artificial accumulation of spicules (spiculite) most probably within a burrow. Dunagan (1999) highlights in the discussion the morphological differences of Eospongilla morrisonensis vs. Palaeospongilla chubutensis considering in the latter species the presence of microscleres and prevailing oxeas (megascleres) as morphotraits supporting the erection of a new taxon. No other extant or fossil taxa were taken into account. The erection of the new taxon is based on the supposed absence of microscleres (thus, a negative character), in opposition to the case of P. chubutensis , but first of all the preservation of the material is very different in the two cases. In the case of Palaeospongilla the rock is silicified and spicules are preserved in situ, while E. morrisonensis is embedded in carbonate matrix that facilitates dissolution of silica spicules (also the megascleres are substituted with calcium carbonate). Thus the absence of microscleres may be just a taphonomic effect, for example, winnowing of smaller spicules. Their absence cannot be used as taxonomic character justifying erection of a new taxon. It is not really possible to conclude whether microscleres and gemmules were really absent or present in this sponge. Indeed, gemmules may be absent both due to taphonomical effect, as well as the fact that sponges were fossilized (if we accept interpretation of the material as real sponges, not artificial aggregation of spicules) in a period in which gemmulating sponges are devoid of gemmules (vegetative phase). Thus any taxonomical conclusion based on presented material must be limited to the statement that we deal with freshwater sponges, without more precise attribution, and the taxon E. morrisonensis should be considered as nomen nudum.