Archive for July 29th, 2016

The work begins

July 29th, 2016

1 Wangs Corner 072916Rochester, Minnesota — Today we started collecting specimens and data for the Team Minnesota student Independent Study projects. We began with a long drive south to Decorah, Iowa, to measure a thick section of our Upper Ordovician target units at the Decorah-Bruening Quarry (N 43.29036°, W 91.76558°), but a patch of persistent and heavy rain lingered over the area all morning. We gave up and headed back north to the Rochester, Minnesota, region, where it was dry and sunny. Our first stop was at Wangs Corner (N 44.41047°, W 92.98338°) to collect fossils from the Decorah Formation for a taxonomic and paleoecological assessment. Rachel Wetzel and Nikki Bell are the Team Paleontologists for this work.

Wangs signWangs is a little crossroads in this part of the Minnesota prairie. (Photo by Nick Wiesenberg.)

2 Dean on WangsDean Thomas has a role at this outcrop as well. He will be doing a conodont biostratigraphy and paleoenvironmental study of the Decorah and units above and below. At Wang’s Corner he found a thin biosparite bed in the midst of the calcareous shale that he can use to help stratigraphically position this section of the Decorah, which has no visible upper or lower contacts.

3 Wangs carbonate bedThis bed is a beautiful nearly pure, coarse, well-cemented biosparite/grainstone in contrast to the argillaceous beds above and below. The orange patches in the top of the rock are burrows (likely Thalassinoides) filled with sediment from above. The traditional interpretation of these units is that they were formed by storms. Why they are so clay-poor is a mystery.

4 Turkey Run 072916Our last stop was the Turkey Run locality (N 44.38441°, W 92.91199°). Here the Decorah Formation is just barely exposed through the weeds. The students gamely collected fossils as the bright sun made us forget the disappointing morning rain.

Wooster’s Fossil of the Week: A new Late Ordovician bryozoan from Oklahoma

July 29th, 2016

1 Color brach Zigzagopora encrustedI am very pleased to introduce a new bryozoan genus and species recently described in the First View section of the Journal of Paleontology. Paul Taylor (Natural History Museum, London) and I present: “A new runner-like cyclostome bryozoan from the Bromide Formation (Sandbian, Upper Ordovician) of Oklahoma and its phylogenetic affinities”. The bryozoan is shown above encrusting the interior of an orthid brachiopod identified as Multicostella sulcata (thanks, Alycia Stigall!) in the Lower Echinoderm Zone of the Mountain Lake Member of the Bromide Formation near Fittstown, Oklahoma. We are particularly proud of its new scientific name. Here’s the abstract:

Zigzagopora wigleyensis n. gen. n. sp. is an Upper Ordovician (Sandbian, early Caradoc) cyclostome bryozoan from the Arbuckle Mountains of Oklahoma, USA. It has runner-type colonies characterized by a mostly uniserial, geniculate arrangement of monomorphic zooids that bud alternately left and right, producing a zig-zag pattern of growth. This new genus has calcified interior walls and non-pseudoporous exterior walls. It is thus most likely affiliated with the paleotubuliporine Family Sagenellidae, despite superficial similarities with the corynotrypid cyclostomes with which it co-occurs.”

You’ve got to love a job where you can coin a name like Zigzagopora wigleyensis. The fortuitous species name, by the way, refers to the Wigley Quarry in Oklahoma (below).

Slide08_052815Here is a pictorial guide to Zigzagopora wigleyensis, featuring Paul’s excellent Scanning Electron Microscope images:
2 Good zigs 0p20This is what we mean by a “uniserial, geniculate arrangement of monomorphic zooids that bud alternately left and right”. The zooids are the little skeletal tubes, each of which housed an individual bryozoan connected by soft tissue to the rest of the colony. Uniserial means that most series of zooids have just one branching from another. Geniculate means “bent abruptly” like a knee joint. Monomorphic refers to the shape of each zooid being about the same. The scale bar is 0.20 mm.

3 Zig zooid shape 0p10

It is this zig-zag shape that makes Zigzagopora distinctive. Scale bar is 0.10 mm.

4 Zig over Cory 0p20The abstract ends with “… superficial similarities with the corynotrypid cyclostomes with which it co-occurs.” In this scene Zigzagopora (Z) has overgrown a branch of the encrusting cyclostome bryozoan Corynotrypa (C). These bryozoans are obviously similar, but the geniculate (our new word!) nature of Zigzagopora sets it apart. This is significant beyond just the shape of the colony: it indicates a different kind of budding of one zooid from another. The scale bar is 0.20 mm.

5 Ancestrula Zig 0p06All bryozoans start from an initial zooid called the ancestrula. It is not always easy to find, but is critical for identification and systematics. The arrow points to the protoecium, the first chamber. The scale bar is 0.06 mm.

6 Pore in zooecium 0p03Inside a broken zooid we can see an interior wall surface and a tiny pore. Really tiny. This is likely an interzooidal pore connecting the soft parts of the zooids. Scale bar is 0.03 mm.

7 Extended zig 0p60Here, then, is Zigzagopora wigleyensis, new to science. It is a tiny new piece for the puzzle that is the evolution of cyclostome bryozoans. It is one of countless billions of species in the history of life, but unique nonetheless.

References:

Taylor, P.D. and Wilson, M.A. 1994. Corynotrypa from the Ordovician of North America: colony form in a primitive stenolaemate bryozoan: Journal of Paleontology 68: 241–257.

Wilson, M.A. and Taylor, P.D. 2016. A new runner-like cyclostome bryozoan from the Bromide Formation (Sandbian, Upper Ordovician) of Oklahoma and its phylogenetic affinities. Journal of Paleontology 90: 413-417.

UPDATE: Zigzagopora wigleyensis made the cover!

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