view of the best preserved book gill of O. augusti'' Only the
alimentary canals of a few species of eurypterids, such as
Carcinosoma newlini,
Acutiramus cummingsi and
Eurypterus lacustris, have been described. However, the excellent levels of preservation of the
O. augusti fossils have allowed the description of what most likely was the anterior portion of the
gut. Between the two coxal (from the
coxa, the point of union with the appendages)
muscle masses of the swimming leg, a spiral-shaped structure was found. A similar structure in the stylonurine
Hibbertopterus wittebergensis, in which a spiral valve has been found near the posterior zone of the prosoma, has been reported. These valves have developed independently in certain groups of
fishes in response to the need to increase the absorptive area of the gut, so Braddy, Aldridge and Theron considered the case was the same for the eurypterids. Nevertheless, the presence of this valve may have depended on the
digestion and absorption requirements of each eurypterid, in turn depending on factors such as the feeding
habitats or the size of the animal. The appendages of
H. wittebergensis suggest it was a
sediment feeder, using its valve to extract food from the soil and increase the absorptive capacity of the gut. It is possible that the spiral structure of
O. augusti had a similar function, acting as a valve for the
mesenteron (midgut, formed by the
stomach and
intestines), thus increasing the absorptive area of this region. Apart from this spiral structure, the pretelson of the paratype preserves a faint impression that expanded posteriorly to a depression in the
medial area, representing an
anal opening. Its great preservation has also allowed the examination of the internal muscular structure of the swimming leg. The coxal muscles were elongated towards an anterolateral orientation. This suggests the legs were maintained in a posterolateral position to walk in order, thus allowing sufficient stability at the animal's
center of gravity, The eurypterid
ichnospecies (a species based on fossil prints)
Palmichnium capensis is thought to have belonged to
O. augusti. This ichnospecies was found in the Table Mountain Sandstone and dates from the
Ordovician, coinciding with
O. augusti. Its
trackways were medium-sized (largest track wide) and consisted of several symmetrical series of four tracks and individual typically oval or tear-shaped marks with small impressions on the sides, sometimes bilobed and intermittent. A
median line was occasionally displayed. Several factors support that
P. capensis represents the tracks of
O. augusti; the average external width of
P. capensis is comparable to that of fossils of
O. augusti, the distal spines of the swimming leg of
O. augusti could have caused such bilobed marks and
Onychopterella represents the only Ordovician eurypterid from those
deposits. In addition, the median line could have been produced by the telson touching the
substrate.
O. augusti would have been able to make incursions to the
terrestrial surface, but it would have been uncomfortable for it, performing an undulatory
gait and keeping its telson in regular contact with the ground, hence the median line. But nevertheless, this can not be completely proven unless a specimen of
O. augusti is found alongside similar tracks. ==Paleoecology==