Sunday, December 6, 2020

Antarctic Ichthyornis solved

So I've been doing some major updates to the Database for what will probably be a New Years upload, including the ornithuromorph section. One rather sad entry as it currently stands is the Antarctic Ichthyornis

I? sp. (Zinsmeister, 1985)
Late Cretaceous
Seymour Island, Antarctica
- Zinsmeister, 1985. 1985 Seymour Island expedition. Antarctic Journal of U.S. 20, 41-42. 

Now with Googling I found the original paper online, which allowed only a bit of improvement-

I? sp. (Zinsmeister, 1985)
Late Maastrictian, Late Cretaceous
Lopez de Bertodano Formation, Seymour Island, Antarctica

Material- several elements
- Zinsmeister (1985) states "several small bones tentatively identified as belonging to the Cretaceous bird Ichthyornis were discovered in the upper Cretaceous Lopez de Bertodano formation." 
Reference- Zinsmeister, 1985. 1985 Seymour Island expedition. Antarctic Journal of U.S. 20, 41-42.

So I saw that Zinsmeister worked with Chatterjee in the 80s, who found the Polarornis holotype in the same place two years before that.  I emailed Chatterjee about it, who replied-

"It was misidentified in the field. These were some shark teeth."

Mystery solved!  But can we do better?  Here's an Ichthyornis tooth-

Right eleventh dentary tooth of Ichthyornis dispar (YPM 1450) (after Field et al., 2018).

And here's the array of shark teeth from the Lopez de Bertodano Formation of Seymour Island (from a January 2011 expedition).  Can we find any easily confusable matches?

Chondrichthyan teeth from the Lopez de Bertodano Formation (scale 10 mm) (after Otero et al., 2014).

I think the circled 16 and 17 are pretty decent matches for a field identification, though much larger if compared directly.  Figures 6-17 are all identified as Odontaspidae indet., which covers any morphology similar to Ichthyornis.  Add in the fact that they were by far the most abundant teeth recovered (8 samples versus 1-3 for the other taxa), and I think we have a nice solution on our hands.

I wonder how many other weird records are out there that are based on initial misidentification but stay in the literature because nobody ever publishes a correction?

References- Otero, Gutstein, Vargas, Rubilar-Rogers, Yury-Yañez, Bastías and Ramírez, 2014. New chondrichthyans from the Upper Cretaceous (Campanian-Maastrichtian) of Seymour and James Ross islands, Antarctica. Journal of Paleontology. 88(3), 411-420.

Field, Hanson, Burnham, Wilson, Super, Ehret, Ebersole and Bhullar, 2018. Complete Ichthyornis skull illuminates mosaic assembly of the avian head. Nature. 557, 96-100.