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Ianthodon Temporal range: Pennsylvanian, ~304 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
I. schultzei cranial and skeletal reconstruction
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Eupelycosauria
Clade:	Metopophora
Clade:	Haptodontiformes
Genus:	†Ianthodon Kissel & Reisz, 2004
Type species
†Ianthodon schultzei Kissel & Reisz, 2004

Ianthodon is an extinct genus of basal haptodontiform synapsids from the Late Carboniferous about 304 million years ago. The taxon was discovered and named by Kissel & Reisz in 2004. The only species in the taxon, Ianthodon schultzei, was found by separating it from a block that also contained the remains of Petrolacosaurus and Haptodus. The evolutionary significance of the taxon wasn't realized until a publication in 2015. The fossil of this organism was discovered in Garnett, Kansas.

Description

Ianthodon was first named by Kissel & Reisz in 2004, and a more detailed specimen was reevaluated in 2014. This single juvenile skeleton with delicate bones has an estimated skull length of around 10 cm, which is similar to other taxa, such as Haptodus, during the same development stage. The specimen was easily distinguished from the skeletal element of Petrolacosaurus by the position and the proportion of foreman and supinator process in the humeri.

Skull

It can be distinguished from Haptodus by its narrower skull and dentition. The higher number of precaninie maxillary teeth and the more rectangular shape of the humerus distinguish the holotype of H. garnettensis from that of Ianthodon. The teeth of Ianthodon have wide bases but slender crowns, unusual among contemporary amniotes and indicating that Ianthodon occupied a different trophic niche from the bulbous-crowned Haptodus to which it was closely related. Like other sphenacodonts, Ianthodon has a tall lacrimal bone, and so would have had a proportionally taller snout than more basal synapsids such as varanopids and eothyridids.

Classification

Ianthodon belongs to the clade Sphenacodontia within the clade Sphenacomorpha. Ianthodon has been considered the basalmost known sphenacodont. The cladogram below follows a cladistic analysis by Spindler and colleagues, 2014.

See also

• List of pelycosaurs
• List of therapsids

References

1. ^ Kissel, R. A. & Reisz, R. R. Synapsid fauna of the Upper Pennsylvanian Rock Lake Shale near Garnett, Kansas and the diversity pattern of early amniotes. In G. Arratia, M. V. H. Wilson & R. Cloutier (eds.). Recent Advances in the Origin and Early Radiation of Vertebrates. Verlag Dr. Friedrich Pfeil, 2004.
2. ^ Spindler, F.; Scott, Diane; Reisz, Robert (October 2014). "New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance". Fossil Record. 18: 17–30.
3. ^ Currie, P. J.: A new haptodontine sphenacodont (Reptilia: Pelycosauria) from the Upper Pennsylvanian of North America, J. Paleontol., 51, 927–942, 1977
4. Reisz, Robert R.; Heaton, Malcolm J.; Pynn, Bruce R. (1982). "Vertebrate Fauna of Late Pennsylvanian Rock Lake Shale near Garnett, Kansas: Pelycosauria". Journal of Paleontology. 56 (3): 741–750. JSTOR 1304403.
5. ^ Roger B. J. Benson (2012) Interrelationships of basal synapsids: cranial and postcranial morphological partitions suggest different topologies, Journal of Systematic Palaeontology, 10:4, 601-624, DOI: 10.1080/14772019.2011.631042
6. ^ Laurin, Michel (1993). "Anatomy and Relationships of Haptodus garnettensis, a Pennsylvanian Synapsid from Kansas". Journal of Vertebrate Paleontology. 13 (2): 200–229. doi:10.1080/02724634.1993.10011501. JSTOR 4523501.
7. Fröbisch, Jörg; Schoch, Rainer R.; Müller, Johannes; Schindler, Thomas; Schweiss, Dieter (March 2011). "A New Basal Sphenacodontid Synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany". Acta Palaeontologica Polonica. 56 (1): 113–120. doi:10.4202/app.2010.0039. ISSN 0567-7920.

v t e Synapsida
Kingdom: Animalia Phylum: Chordata Superclass: Tetrapoda Clade: Amniota Tetrapodomorpha see Tetrapodomorpha Reptiliomorpha see Reptiliomorpha Synapsida see below↓
Synapsida Synapsida †Diadectomorpha? †Caseasauria? Eothyrididae Asaphestera? Eothyris Oedaleops Vaughnictis Caseidae Alierasaurus Angelosaurus Arisierpeton Callibrachion Casea Caseoides Caseopsis Cotylorhynchus Datheosaurus Ennatosaurus Eocasea Euromycter Lalieudorhynchus Martensius Oromycter Phreatophasma Ruthenosaurus Trichasaurus Eupelycosauria †Varanopidae? Apsisaurus Archaeovenator Ascendonanus Eoscansor Dendromaia Nitosaurus? Pyozia Thrausmosaurus Mesenosaurinae Anningia Cabarzia Elliotsmithia Heleosaurus Mesenosaurus Microvaranops Varanodontinae Aerosaurus Mycterosaurus? Ruthiromia Tambacarnifex Varanops Varanodon Watongia Metopophora see below↓ Incertae sedis †Dimacrodon †Driveria †Gorgodon †Knoxosaurus †Mastersonia †Protoclepsydrops?
Metopophora †Ophiacodontidae Archaeothyris Baldwinonus Clepsydrops Echinerpeton Ophiacodon Stereophallodon Stereorhachis Varanosaurus Haptodontiformes †Ianthodon †Milosaurus †Edaphosauridae Bohemiclavulus Edaphosaurus Glaucosaurus Gordodon Ianthasaurus Lupeosaurus Melanedaphodon Ramodendron Remigiomontanus Xyrospondylus Sphenacodontia †Cutleria †Haptodus †Hypselohaptodus †Kenomagnathus †Tetraceratops †Palaeohatteriidae Palaeohatteria Pantelosaurus Sphenacodontoidea †Shashajaia †Sphenacodontidae Cryptovenator Ctenorhachis Ctenospondylus Cutleria? Dimetrodon Eosyodon Macromerion Neosaurus Secodontosaurus Sphenacodon Steppesaurus? Tappenosaurus? Tetraceratops? Therapsida see below↓
Therapsida Therapsida †Raranimus †Biarmosuchia see Biarmosuchia †Dinocephalia see Dinocephalia †Anomodontia see Anomodontia includes dicynodonts †Gorgonopsia see Gorgonopsia Eutheriodontia †Therocephalia see Therocephalia Cynodontia see Cynodontia includes mammals Incertae sedis †Dinosaurus †Kamagorgon †Niaftasuchus
See also: Pelycosauria Phthinosuchia Theriodontia Category

• Sphenacodonts
• Carboniferous synapsids of North America
• Fossil taxa described in 2004