This is Mazon Monday post #338.  What’s your favorite Mazon Creek fossil?  Tell us at esconi.info@gmail.com.

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The history of Mazon Creek paleontology is filled with fossils that have been reinterpreted as new species when new information became available. Animals have been moved from one group to another, species have been renamed, and some fossils once thought to represent animals have turned out to be something else entirely. There are even some, like Tullymonstrum gregarium, whose place on the tree of life is still being determined.

Another particularly interesting story is Howellitubus whitfieldorum. Howellitubus whitfieldorum was described by Eugene Richardson Jr. in the 1956 Fieldiana paper “Pennsylvanian Invertebrates of the Mazon Creek Area, Illinois – Marine Fauna”. Richardson described it as an annelid worm of class Chaetopoda and family Serpulidae.

The story begins in 1953 when the lone specimen was collected by Dr. Robert Whitfield, his wife Violetta, and their son Jon. The fossil was found at the Peabody Coal Company’s Pit 1, the current site of the Area No. 1 Club and Cinder Ridge Golf Club. You might remember Violetta from Mazon Monday #222, when we highlighted her collection of Mazon Creek Insects. Both Robert and Violetta are listed as Associates in the Department of Geology at the Field Museum from the 1947 until 1978. Robert is listed as a DDS (doctor of dental science).

The fossil inside the unusual concretion was a tapering, roughly circular structure about two inches long. It appeared to have a shell or tube surrounding a central core, or steinkern. Its outer surface was relatively smooth, while the inner surface displayed fine growth lines.

The specimen eventually came to the attention of Eugene S. Richardson Jr., Curator of Fossil Invertebrates at the Field Museum and one of the most important researchers in the history of Mazon Creek paleontology. In 1956, Richardson described the fossil as a new genus and species of polychaete worm, Howellitubus whitfieldorum. The specimen, Field Museum PE 150, became the holotype of a new species.

Richardson’s interpretation seemed reasonable at the time. Similar fossil worm tubes were known from the Upper Cretaceous of New Jersey and the Lower Cretaceous of England. Howellitubus subsequently found its way into the paleontological literature. It was included among fossil worms in the 1962 Treatise on Invertebrate Paleontology, and George Langford illustrated it in 1963. As late as 1977, Thompson and Johnson discussed Howellitubus in a paper on mineralized tubes of annelid worms.

Langford wrote the following on Page 15 of his second book “The Wilmington Coal Fauna and Additions to the Wilmington Coal Flora from a Pennsylvanian Deposit in Will County, Illinois.” Figure 13 is the same as seen above.

Figure 13. Howellitubus whitfieldorum Richardson. This rare
tube-building worm is known at present from only a single specimen, collected by Dr. and Mrs. Robert H. Whitfield and their son Jon, and deposited in Chicago Natural History Museum (No. PE150). The original description reads: “Straight or slightly bowed shell, composed of many layers arranged as cones one within the other, circular or sub-circular in cross-section; tapering, with increasing flare at apertural end; shell thick apically, thin aperturally.” Howellitubus presumably lived in the salt-water sea, but close to shore, in shallow water.

But Richardson wasn’t finished with Howellitubus.

He eventually returned to the original specimen and took another look. In 1980, nearly a quarter century after naming it, Richardson published a wonderfully direct, one-page paper titled “Howellitubus is not a worm tube.”

His conclusion was quite different from the one he had reached in 1956. According to a 1990 account by Andrew A. Hay, Richardson determined that the structure he had originally interpreted as the lumen of a worm tube “was not a worm tube but an indeterminate bone, most probably that of a fish.”

Abstract

Some years ago (Richardson, 1956, pp. 60-61), I described a single specimen in the Field Museum collection as a serpulid worm tube, Howellitubus whitfieldorum, new genus and species, from the Pennsylvanian Mazon Creek fauna of Illinois. So far as I know, the only subsequent references are those of Howell (1962, p. 157), Thompson and Johnson (1977, p. 472) and Thompson (1979, p. 171). Re-examining the specimen, I find that it is not a worm tube. It is in fact an indeterminate but clearly recognizable bone, probably of a fish. The lumen described as the home of a worm is the medullary cavity.

And just like that, one member of the Mazon Creek fauna vanished.

Andy Hay revisited the story in an October 1990 installment of “Creature Corner.” He summed up the situation nicely: Howellitubus had never really existed as an animal at all. It was a name based on the mistaken interpretation of a piece of bone.

CREATURE CORNER

In going over any list of plants and animals that have been discovered in concretions from the Mazon Creek, and subsequently described and classified, one cannot help but take note of the additions, deletions, and name changes that take place as the list is being updated. Various vertebrates, invertebrates, and flora have been restudied, reclassified, and renamed. Fossils once designated as myriapods have been reclassified as worms, several fossil “plants” are now recognized to be animal remains. Animals and plants are shifted from one order or family to another and renamed, etc. Changes such as these are the sign of an expanding, vibrant, alive branch of science.

Our Creature, Howellitubus, was collected in 1953, 2½ miles north of Braidwood. (A reminder at this date science was not yet aware of the paleontological cornucopia awaiting it just a few miles south –Pit 11.) The opened concretion revealed a tapering shell or tube, about 2 inchea long, roughly circular in cross section with one flared end. Parts of shell adhered to the portions of a steinkern. Outer surface of the shell was unornamented, inner surface displayed fine growth lines.

In 1956, the late Dr. Richardson described and classified the fossil as a worm tube, specimens quite similar to the Mazon Creek specimen having been found in the Upper Cretaceous clay of New Jersey and in a certain Lower Cretaceous strata of England. This Mazon Creek worm tube was given the name HOWELLITUBUS whitfieldorum.

Thompson and Johnson (1977) mentioned the mineralized worm tubes of the annelids Spirorbis and Howellitubus in an article describing Esconites. Richardson (1980) after restudying the concretion, stated the “lumen described as the home of a worm” was not a worm tube but an indeterminate bone, most probably that of a fish.

So, returning to the thrust of our article –Howellitubus never existed except as a name in several paleontological articles; a name to be deleted from Mazon Creek faunal lists.

– Andrew A. Hay

Interestingly, the original specimen still resides in the Field Museum’s collections as PE 150, the holotype of Howellitubus whitfieldorum. And references to Howellitubus can still be found in taxonomic databases and older lists of fossil worms. Without knowing about Richardson’s 1980 reassessment, it would be easy to assume that Howellitubus remains a recognized Mazon Creek polychaete.

Paleontology, as with all of science, is continually being revised as new information is uncovered. Sometimes, that new information is from a reexamination of old specimens. Richardson described Howellitubus, named it, and watched it become established in the scientific literature. Then, he had another look at the fossil and found his original interpretation was wrong. He then wrote a correction.

Howellitubus may no longer be a valid member of the Mazon Creek fauna, but its story is still very much a part of its history.

Specimen Photos

From the online Field Museum Geology Collection