RE: Various other papers of interest in the latest Palaeontology

[Michael Mortimer <mickey_mortimer111@msn.com>]

Tim Williams wrote-

> (1) None of these nomenclatural acrobatics qualify yet as a formal 
> synonymization?

Correct.

> (2) The above paragraph implies that the _Tripriodon caperatus_ holotype is a 
> dinosaur (theropod) tooth after all, rather than from a mammal - correct?

Correct-

Tripriodon was based on teeth assigned to two species by Marsh (1889)- the 
genotype T. coelatus, and T. caperatus. The former is a junior synonym of the 
multituberculate Meniscoessus robustus (as first shown by Osborn, 1891), while 
the second belongs to Paronychodon (as first shown by Estes, 1964). Estes was 
incorrect in synonymizing Tripriodon itself with Paronychodon however, as T. 
caperatus is only a referred species. This also prevents Marsh's 
Tripriodontidae from being a theropod family.

In more detail....

Marsh (1889) originally described Tripriodon caperatus based on several teeth 
and tooth fragments, including supposed lower incisors. The holotype is often 
listed as YPM 11853, but is 11852 in the YPM online catalog. Although Marsh 
states the specimen came from Laramie beds, the Laramie Formation has not 
yielded dinosaurs in Wyoming, and the YPM online catalog confirms it was 
actually found in the Lance Formation. Marsh viewed T. caperatus and the 
genotype T. coelatus as belonging to a new family Tripriodontidae in his 
Allotheria, most closely related to Stereognathus (now recognized as a 
tritylodontid). Tripriodon coelatus is based on a molar which is now thought to 
belong to Meniscoessus robustus, a species of multituberculate. This was first 
recognized by Osborn (1891), who believed T. caperatus were lower incisors of 
Meniscoessus. Osborn also recognized supposed lower incisors of Selenacodon 
brevis (YPM 10630) and Tripriodon coelatus (YPM coll.) have the same morphology 
as T.
 caperatus. Selenacodon brevis is now viewed as a junior synonym of the 
multituberculate Cimolemys gracilis. Estes (1964) incorrectly believed T. 
caperatus to be the genotype, and was the first of many authors to synonymize 
Tripriodon with Paronychodon. He referred the T. caperatus holotype and YPM 
10630 to Paronychodon lacustris. Currie et al. (1990) mistakenly listed 
Dipriodon caperatus, but Dipriodon is another genus now viewed as a synonym of 
Meniscoessus.

The holotype tooth seems nearly identical to the Paronychodon holotype except 
for having a shorter crown. It clearly matches tooth type A of Sankey et al. 
(2002). Baszio (1997) notes these Lance Formation teeth are larger than 
Paronychodon lacustris from the Milk River, Dinosaur Park, Frenchman and 
Horseshoe Canyon Formations, with more pronounced wrinkles. They are retained 
as Paronychodon caperatus on my (currently offline) website, after Olshevsky 
(1991).


Marsh, 1889. Discovery of Cretaceous mammalia. American Journal of Science, 3rd 
series. 38, 81-92.

Osborn, 1891. A review of the "Discovery of the Cretaceous Mammalia". The 
American Naturalist. 25(295), 595-611.

Estes, 1964. Fossil vertebrates from the Late Cretaceous Lance Formation, 
eastern Wyoming. University of California Publications in Geological Sciences. 
49, 1-180. 

Currie, Rigby and Sloan, 1990. Theropod teeth from the Judith River Formation 
of southern Alberta, Canada. in Carpenter and Currie (eds.). Dinosaur 
Systematics: Perspectives and Approaches. Cambridge University Press, New York. 
pp. 107-125. 

Olshevsky, 1991. A Revison of the Parainfraclass Archosauria Cope, 1869, 
Excluding the Advanced Crocodyila. Mesozoic Menanderings #2 (1st printing). iv 
+ 196pp. 

Baszio, 1997. Investigations on Canadian dinosaurs: systematic palaeontology of 
isolated dinosaur teeth from the Latest Cretaceous of south Alberta, Canada. 
Courier Forschungsinstitut Senckenberg. 196, 33-77. 

Sankey, Brinkman, Guenther and Currie, 2002. Small theropod and bird teeth from 
the Late Cretaceous (Late Campanian) Judith River Group, Alberta. Journal of 
Paleontology. 76(4), 751-763. 

Mickey Mortimer