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The return of Zapsalis, plus Tripriodon is not Paronychodon



When you hear the names Zapsalis and Tripriodon, what do you think of? "Junior synonyms of Paronychodon", I bet. That's what I thought until I looked into the matter for use on my website, but it seems the current consensus is wrong.


Zapsalis, a valid dromaeosaurine

Estes (1964) included all theropod teeth with ridges and a flattened lingual side in Paronychodon, including those with serrations. Currie et al. (1990) later restricted Paronychodon to the unserrated forms, and believed the serrated ones were growth abnormalities of named genera- Dromaeosaurus, Saurornitholestes and Troodon. Baszio (1997) included these in his Paronychodon discussion, referred to them as Paronychodon-like teeth. Sankey et al. (2002) separated the Paronychodon-like teeth with Dromaeosaurus-like serrations as ?Dromaeosaurus morphotype A. In addition to their ridges and flat lingual side, they differ from Dromaeosaurus albertensis in being shorter and labiolingually narrower, and having a straight distal edge. They argued complete D. albertensis tooth rows are known, so the morphology of morphotype A teeth is not due to positional variation. Furthermore, they have a different stratigraphic distribution than D. albertensis, being present in the Late Maastrichtian unlike the latter species. This makes a pathological explanation unlikely.

The holotype of Zapsalis abradens is a tooth which is flat lingually, with no mesial serrations and 3 distal serrations per mm (Cope, 1876). There are three lingual ridges and four labial ones. The length is 12 mm, the FABL 6.5 mm, and the BW 3 mm. It was synonymized with Paronychodon lacustris by Estes based on its flat lingual side and ridges, which has been followed in the literature without comment ever since. However, Zapsalis falls outside the current concept of Paronychodon in having serrations, and is more robust than teeth of that genus as well. Yet Zapsalis does match ?Dromaeosaurus morphotype A, which are lingually flat with ridges on both sides, and serrations which can occur on both carinae (3-4/mm). The proportions also match, with an average length of 12.4 mm, FABL of 6.3 mm, and BW of 3.4 mm. Thus Zapsalis is here used as the valid name for these teeth.


Tripriodon, junior synonym of the multituberculate Meniscoessus

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 here, after Olshevsky (1991).


References- Cope, 1876. On some extinct reptiles and batrachia from the Judith River and Fox Hills Beds of Montana. Proceedings of the Academy of Natural Sciences, Philadelphia. 28, 340-359.
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
http://home.myuw.net/eoraptor/Home.html