Friday, February 19, 2010

Citipati or IGM 100/42?

Another mini-post.  Everyone's familiar with IGM 100/42, that oviraptorid that was the classic example of its family through the 80's and 90's.  It's known from an almost complete skeleton first mentioned by Barsbold in 1981.

Skull of IGM 100/42, courtesy of Auditore.

Everyone's also familiar with Citipati osmolskae, the nearly complete specimen that was named in 2001 and whose skull was described by Clark et al. (2002).  The most famous nesting oviraptorid Big Mama (Clark et al., 1999) and the stil undescribed Big Auntie have been assigned to this species as well, as has the most famous oviraptorid embryo (Norell et al., 2001).

Citipati osmolskae holotype (copyright AMNH)

Now these specimens are similar, and may indeed be congeneric, but this hasn't been demonstrated yet.  While Osmolska et al. (2004) found IGM 100/.42 to be the sister taxon of Citipati osmolskae in their cladistic analysis, Lu (2004) found that it was the sister taxon to Oviraptor or Conchoraptor (depending on taxa included) using Maryanska et al.'s (2002) characters.  The point of this post is that some phylogenetic analyses have been quite sloppy in regard to exactly which oviraptorid they are coding.  The first phylogenetic analysis to include either was the TWG analysis, which started with Norell et al. (2001).  They called it Oviraptorid IGM 100/42.  Note the progression of what this OTU is labeled as the TGW analysis is modified in future works-

Norell et al., 2001 (Ostrom volume) Oviraptorid IGM 100/42
Clark et al., 2002 (Mesozoic Birds) Oviraptorid IGM 100/42
Hwang et al., 2002 (Microraptor) IGM 100/42
Xu et al., 2002 (Incisivosaurus) IGM 100/42
Xu et al., 2002 (Sinovenator) IGM 100/42
Makovicky et al., 2003 (Byronosaurus) Citipati osmolskae
Hwang et al., 2004 (Huaxiagnathus) Citipati osmolskae
Lu, 2004 (thesis) Citipati osmolskae
Makovicky et al.; Makovicky and Norell; Norell and Makovicky, 2004 (Dinosauria 2) Citipati osmolskae
Xu and Norell, 2004 (Mei) Citipati osmolskae
Kirkland et al., 2005 (Falcarius) Citipati
Makovicky et al., 2005 (Buitreraptor) Citipati osmolskae
Mayr et al., 2005 (Archaeopteryx) IGM 100/42
Novas and Pol, 2005 (Neuquenraptor) Citipati osmolskae
Gohlich and Chiappe, 2006 (Juravenator) Citipati
Norell et al., 2006 (Tsaagan) Citipati osmolskae
Hwang, 2007 (enamel thesis) Citipati
Martinelli and Vera, 2007 (Achillesaurus) Citipati osmolskae
Senter, 2007 (coelurosaurs) Citipati osmolskae* (see below)
Turner et al., 2007 (Shanag) Citipati osmolskae
Turner et al., 2007 (Mahakala) Citipati osmolskae
Xu et al., 2007 (Gigantoraptor) Citipati osmolskae
Novas et al., 2008 (Orkoraptor) Citipati osmolskae
Xu et al., 2008 (Anchiornis) Citipati osmolskae
Zhang et al., 2008 (Epidexipteryx) Citipati osmolskae* (see below)
Makovicky et al., 2009 (Beishanlong, Xiongguanlong) Citipati osmolskae
Zanno et al., 2009 (Nothronychus graffami) Citipati osmolskae
Zheng et al., 2009 (Tianyuraptor) Citipati osmolskae* (see below)

You can see it changed inexplicably in 2003.  For unknown reasons, it was dropped from the Graciliraptor and Pedopenna versions, which I assume to mean it's absent in Xu's (2002) thesis.  You might say this kind of relabeling is harmless, but I find it misleading.  If someone didn't follow the sequence of permutations of the TWG matrix, they could think the codings were based on specimens described in the literature.  After all, Citipati's holotype is a complete skeleton, though it remains undescribed except for the furcula.  Lu (2004) referred to it as Citipati osmolskae in his revisions of the TWG matrix, but coded IGM 100/42 and Citipati separately for his versions of Maryanska et al.'s matrix.  So one of his Citipati's was not comparable to his other Citipati.  Even worse, Senter (2007) used the IGM 100/42 codings as Citipati osmolskae, then coded IGM 100/42 as a separate taxon!  So really his matrix has two copies of IGM 100/42.  Oddly, there are coding differences and they are not sister taxa.  Zhang et al. (2008) copied this in their Epidexipteryx analysis, as did Zheng et al. (2009) in their Tianyuraptor analysis.  So this problem can worm its way through the literature unnoticed.

In conclusion, if anyone is going to use the TWG matrix (and I know you are), please label your OTU IGM 100/42.  Or else defend the assertion IGM 100/42 belongs to Citipati osmolskae.  Taxonomy via data matrix should be avoided.

1 comment:

  1. So this problem can worm its way through the literature unnoticed.