Bitubulites: Yeah, Nach

Several months back, I published a post on a decidedly obscure tubular fossil by the name of Serpularia: once described, completely forgotten. Is it possible to top that for inconsequentiality?

You betcha, because the subject I drew for today's post, Bitubulites irregularis, never even got a sketchy diagram to illustrate it. And once again, we have an early German palaeontologist to thank. In 1820, Ernst Friedrich, Freiherr von Schlotheim, published a book called Die Petrefactenkunde auf ihrem jetzigen Standpunkte durch die Beschreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzenreichs der Vorwelt erläutert, because they don't write book titles like they used to. As far as I can tell, the title basically translates as Got Some Great Fossils Here, Wanna See? As with Münster's Beiträge zur Petrefakten-Kunde that provided the source for the Serpularia post, Schlotheim's publication was basically a description of some of the fossils held in his own collection. His comments on B. irregularis appeared on p. 376, and were as follows:

Bitubulites irregularis.
Aus dem Muschelflötzkalk der Gegend von Weimar.
Einzelne cylinderförmige Stücke, von der Dicke eines mäſsigen Fingers, mit gröſstentheils concaven Durchschnittsflächen, auf welchen sich gewöhnlich ins Dreyeck gestellte kleine Öffnungen zeigen, welche mit durchgehenden Nervenröhren in Verbindung zu stehen scheinen. Äuſserlich ist die Oberfläche fein puncktirt.
Da sich mehrere übereinstimmende Stücke finden, so läſst sich nicht erwarten, daſs wir ein bloſses Naturspiel vor uns hätten. Zuweilen sind auch vier, aber alsdenn noch unregelmäſsiger gestellte Öffnungen, vorhanden. Bis jetzt haben sich, meines Wissens, noch keine ganz vollständigen und recht gut erhaltenen Exemplare aufgefunden.

And I'll be honest, I have very little idea what any of that means, because I don't read German beyond chucking stuff into Google Translate. The genus Bitubulites had established in 1803 by another German scientist, Johann Friedrich Blumenbach, for a different fossil, B. problematicus. Bitubulites problematicus was composed of two small conjoined tubes that Blumenbach illustrated thus:

Schlotheim's B. irregularis was presumably similar to Blumenbach's original; as far as I can work out, each tube was cylindrical and about the thickness of a finger. Small openings down the sides of the main tubes indicated the presence of smaller connecting tubes ("nerve-tubes") between them; the entire outer surface was finely punctate. The second paragraph of Schlotheim's states that he possessed several examples, indicating that the association between the tubes was not a mere accident. I think he says that the tubes were sometimes associated in fours rather than in pairs, but the overall confirmation remained the same. The "Muschelflötzkalk" refers to a Middle Triassic formation; both the two Bitubulites species came from the same formation.

Blumenbach had called his original fossil 'problematicus' because he had little idea what type of animal it represented. Schlotheim was none the wiser, listing Bitubulites among unclassifiable forms with no close analogues in the modern fauna. He did tentatively compare it to a couple of fossil mollusks, such as the straight-shelled cephalopods or the reef-forming hippuritid bivalves. And there Bitubulites lay for over a century, more or less forgotten by all except the most pedantic of cataloguers (ahem...)

In 1962, Walter Häntzschel included Bitubulites in his chapter on problematica for the Treatise on Invertebrate Paleontology. It was tucked away in the end, in a list of "Unrecognized and Unrecognizable "Genera"" that Häntzschel felt largely deserved nothing more than to be cast forever into the outer darkness. Nevertheless, he did suggest a possible identity for Bitubulites: Rhizocorallium, a fossil that can be found in deposits dating from the Cambrian all the way to the present, commonly looking like this (copyright Manuel Flöther):

Rhizocorallium is a trace fossil, a structure created by the activity of some animal and preserved in the geological record. Rhizocorallium takes the form of a U-shaped burrow, with the two arms of the burrow connected by fine cross-lines or fractures referred to as Spreiten (German for "spread"). The Spreiten are the result of the animal digging its burrow further into the substrate, with sediment being taken from the outer side of the tube and packed on the inner side. The burrows often run more or less parallel to what would have been the original surface of the sediment; they may have been primarily dwelling burrows, or they may have been feeding burrows extended as the animal searched for buried organic matter. Rhizocorallium-type burrows were probably made by many different types of animal, such as worms or arthropods, and their presence in a deposit is more indicative of environmental conditions than faunal composition.

At the time that Blumenbach and Schlotheim were writing their books, no-one had yet twigged what these kind of trace fossils were; neither author would have been alone in mistaking a burrow for a body fossil. Many structures that are now recognised as traces were described as fossil algae. It was not until the late 1800s that a Swedish and an American palaeontologist independently noted the similar between a number of these 'algae' and the structures left by marine organisms as they went about their daily life. Even today, this earlier misunderstanding has left its mark in the tradition of referring to particular trace fossils by binomial names, as trace 'genera' and 'species'. Nevertheless, trace fossils often provide us with a window into the past over and above what we can learn from body fossils alone, and they are an invaluable tool in developing a truly rounded understanding of life in ages past.

REFERENCES

Blumenbach, J. F. 1803. Specimen Archaeologicae Telluris terrarumque inprimis Hannoverarum. Henricum Dieterich: Göttingen.

Häntzschel, W. 1962. Trace fossils and problematica. In: Moore, R. C. (ed.) Treatise on Invertebrate Paleontology pt W. Miscellanea: Conodonts, Conoidal Shells of Uncertain Affinities, Worms, Trace Fossils and Problematica pp. W177-W245. Geological Society of America, and University of Kansas Press.

Schlotheim, E. F. von. 1820. Die Petrefactenkunde auf ihrem jetzigen Standpunkte durch die Beschreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzenreichs der Vorwelt erläutert. Becker'schen Buchhandlung: Gotha.