Re: What's cookin', Doc?

[David Marjanovic <david.marjanovic@gmx.at>]

Robert J. Asher, Meng Jin, John R. Wible, Malcolm C. McKenna, Guillermo W. 
Rougier, Demberlyn [sic] Dashzeveg & Michael J. Novacek: Stem Lagomorpha and 
the Antiquity of Glires, Science 307, 1091 -- 1094 (18 February 2005)

Abstract:
"We describe several fossils referable to *Gomphos elkema* from deposits 
close to the Paleocene-Eocene boundary at Tsagan Khushu, Mongolia. *Gomphos* 
shares a suite of cranioskeletal characters with extant rabbits, hares, and 
pikas but retains a primitive dentition and jaw compared to its modern 
relatives. Phylogenetic analysis supports the position of *Gomphos* as a 
stem lagomorph and excludes Cretaceous taxa from the crown radiation of 
placental mammals. Our results support the hypothesis that rodents and 
lagomorphs radiated during the Cenozoic and diverged from other placental 
mammals close to the Cretaceous-Tertiary boundary."

More quotes:
"*G. elkema* was first described as a paramyid-like rodent on the basis of 
lower-cheek teeth from deposits overlying Paleocene rocks at Gashato, 
Mongolia".
Sort of like *Carcharodontosaurus*.

"It differs from extant rodents and lagomorphs in having two pairs of 
mandibular incisors but is similar to extant lagomorphs in having two pairs 
of upper incisors [...]"

Cladistic analysis: 68 taxa, 225 morphological characters, five genes!

"The most parsimonious trees (MPTs) we recovered from the combined data set 
(Fig. 3) show Gomphos on the stem leading toward Lagomorpha and 
zalambdalestids outside the crown radiation of Placentalia. This signal was 
stable despite changes in character ordering (fig. S1), assumptions 
regarding anterior incisor homology (fig. S2), exclusion of characters (fig. 
S3) and taxa (fig. S4) with less than 75% representation in our anatomical 
data set, and treatment of third positions in our DNA data set (fig. S5). In 
addition, analysis of the morphological data set constrained to agree with a 
recent molecular topology of Glires [...] also supported Gomphos on the stem 
to Lagomorpha, as well as Cretaceous eutherians outside of Placentalia (fig. 
S6)."
Everything that starts with S is in the supplementary information.

"Placing zalambdalestids as the sister taxon to Glires requires an 
additional 27 steps in the equally weighted NONA analysis; a 
zalambdalestid-duplicidentate clade requires 54 additional steps. As 
measured by Wilcoxon rank sum tests (Table 1), both alternatives can be 
rejected with a high level of significance."

The supp. inf. lists 18 unambiguous autapomorphies for Placentalia excluding 
*Zalambdalestes* and friends.

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