| Trimucrodon | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Genus: | †Trimucrodon Thulborn,1973[1] |
| Species: | †T. cuneatus |
| Binomial name | |
| †Trimucrodon cuneatus Thulborn, 1973 | |
Trimucrodon is agenus ofornithischiandinosaur from theLate JurassicLourinhã Formation ofPortugal. The type, and currently only, species isT. cuneatus.[1]
Three isolated teeth found at thePorto Dinheiro (or Pinhiero) locality in theLisboa District of Portugal were given the name in1973 byRichard A. Thulborn, derived from theLatin words for "three" and a dagger point,tri- andmucro, and theAncient Greek wordὀδούς for "tooth". The only species in the taxon isTrimucrodon cuneatus, taken from the wedge shape of the teeth.[1] Though the unit the specimens came from was originally unnamed,[1] it was referred to theAlcobaça,[2] and thenLourinhã Formations, specifically the lateKimmeridgian Amoreira–Porto Novo Member.[3][4] The type specimen, uncovered between 1962 and 1967 by Germanzoologist andpaleontologist Georg Krusat, is distinguished by prominent denticles at the front and rear ends of the crown, and comes from an individual under 2 m (6.6 ft) long.[5][6][7] It is currently kept in the collections of theMuseu Geológico do Instituto Geológico e Mineiro inLisbon, Portugal, formerly having been kept in the collections of theFree University of Berlin.[7]
The holotype tooth ofTrimucrodon is 4.4 mm (0.17 in) wide, similar to some of the referred specimens, with the crown about as tall as wide. Other specimens have crowns as small as 1.5 mm (0.059 in) wide and only half as tall as wide. The crowns are of varying amounts of asymmetry, though each edge bears the same number of taperingdenticles.Tooth enamel is present of an equal thickness on both sides of the tooth crown, and both faces are smooth without ridges. The denticles increase in size away from the apex of the crown, ending with two widely divergent and sharply-pointed denticles at the front and rear ends of the base.[8]
Trimucrodon was originally referred to as a member of the ornithopod familyFabrosauridae by Thulborn in 1973, closest toEchinodon but also related toAlocodon andFabrosaurus.[1]Peter M. Galton retained it in the family in1978, though he noted that there were significant differences betweenTrimucrodon andEchinodon, and the Middle to Late Jurassic fabrosauridsAlocodon,Trimucrodon andEchinodon were representative of three independent and only distantly related branches of the family, withNanosaurus not preserving enough material to determine its relationships.[9] Given that the species was only represented by teeth,Trimucrodon was designated as anomen dubium in1990 byDavid B. Weishampel andLawrence M. Witmer, as an indeterminate member ofOrnithischia outside Ornithopoda.[10] While a basal ornithischian position outside Ornithopoda was retained byPaul Sereno in1991, it was considered a possibly valid taxon based on its prominent anterior and posteriormost denticles.[6] Galton revised his classification of the taxon in1994, considering it only referrable to Ornithopoda, and not closely related toEchinodon.[8]Trimucrodon was then compared favourable by Galton in1996 to the also Portuguese taxonTaveirosaurus, previously considered apachycephalosaur. With the later reclassifications ofTaveirosaurus as more similar tonodosaurids,Trimucrodon was identified by José Ruiz-Omeñaca in1999 to either be a member ofHeterodontosauridae alongsideEchinodon, or a member of Nodosauridae related toTaveirosaurus.[11] While the identity as a possible heterodontosaurid was upheld by Ruiz-Omeñaca and José Canudo in2004,[12] in the same year Weishampel, Witmer and colleagueDavid B. Norman followed their 1990 opinion onTrimucrodon, placing it as a dubious ornithischian, though they noted that further study could potentially support the validity of the taxon.[13]
Trimucrodon was found at the top of a cliff south of Porto Dinheiro, in the lower beds of the Lournihã Formation alongside a tooth referred to the ornithischianHypsilophodon, teeth fromrhamphorhynchoidpterosaurs, thecrocodylomorphsLusitanisuchus andGoniopholis, thechoristoderanCteniogenys, thelizardSaurillus, and over 800 teeth of various groups ofmammals.[3] Other deposits from the Amoreira–Porto Novo Member at Porto Dinheiro have contained material from thesauropodsZby andDinheirosaurus, thetheropodsLourinhanosaurus,Torvosaurus andCeratosaurus, ornithischian remains from thestegosaurMiragaia and an intermediate member ofIguanodontia, a possiblepleurosternidturtle, and scales from the fishLepidotes.[4]
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