Iniopteryx in situ preserves internal organs

Friday, January 19, 2024 20:41

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Here’s a Carboniferous fish fossil
that preserves a shark-like spiral intestine and other soft tissues. Unfortunately it is crushed in such a way that an accurate reconstruction is going to be difficult.

This is
Iniopteryx rushlani (PF6646) the first of the inopterygids to be described by Zangrel and Case 1973 (Fig 1). Their reconstruction diagram (Fig 1) was built as a chimaera of several specimens, as you’ll note in the apparent differences.

The authors wrote in 1973,
“The present understanding of the skull and visceral skeleton of this species is very unsatisfactory, in spite of the fact that a large number of skulls is at hand.”

Figure 1. Iniopteryx rushlandi (PF6646) in situ. Colors added here. Note the spiral intestine. The torso is twisted. This specimen does not preserve all the details shown in the Zangrel and Case diagram, a chimaera created from several specimens.

ResearchGate.net has no articles with Iniopteryx in the title.
So, apparently no other recent work has been done on this taxon. That means it is ready and ripe for a µCT scan!

Figure 2. Skull of the PF6645 specimen attributed to Iniopteryx rushlaui. It is wider than tall, distinct from the PF 6646 diagram in figure 1. Note the purported pectora fin here is made only of filamernts with no discernible robust anchor.

Another specimen attributed to this species
PF6645 (Fig 2) has a skull that bears little resemblance to the PF6646 specimen (Fig 1).

Note the robust and thorny pectoral fins
in figure 1. As in other iniopterygians those fins are anchored just behind the skull where the ancestral tabulars used to be. Yesterday we looked at similar taxa (e.g. Rainerichthys) and wondered if similar structures that had been fossilized closer to the parasagittal plane were also pectoral fins or transformed thoracic armor now serving as gill bars, as in another early shark, Ozarcus (Fig 3). Here (Fig 1) and elsewhere in Zangrel and Case 1973) the identity of these laterally directed elements is traditionally and universally considered high-set pectoral fins, as in extant remoras.

Figure 3. Carboniferous Ozarcus compared to Early Silurian Shenacanthus, which retains a carapace and plastron. Both of these split to become branchials in Ozarcus. Note the iniopterygian-like small, spiky tail.

Usually fossils that preserve soft tissue are easier to understand.
Iniopterygians appear to break that rule. Ancestors go back to tiny Early Silurian Shenacanthus (Fig 3), so iniopterygians had a long time to turn into a variety of remora-like sharks, all apparently with a spiky almost useless tail. Zangerl and Case thought iniopterygians swam by flapping their pectoral fins.

Have someone you know with access to these fossils µCT scan a few and let us know how it turns out after peer review and publication.

References
Zangerl R and Case GR 1973. Iniopterygia : a new order of Chondrichthyan fishes from the Pennsylvanian of North America. University of Illinois Urbana-Champaign. Chicago : Field Museum of Natural History.

wiki/Iniopteryx

Source: https://pterosaurheresies.wordpress.com/2024/01/20/iniopteryx-in-situ-preserves-internal-organs/