Ianthodon

{{Automatic taxobox

| fossil_range = Pennsylvanian,
~{{fossil_range|304}}

| image = IanthodonReconstruction.png

| image_caption = I. schultzei cranial and skeletal reconstruction

| taxon = Ianthodon

| authority = Kissel & Reisz, 2004

| display_parents = 3

| type_species = {{extinct}}Ianthodon schultzei

| type_species_authority = Kissel & Reisz, 2004

}}

File:Ianthodon schultzei 35.jpg

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.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. The only species in the taxon, Ianthodon schultzei, was found by separating it from a block that also contained the remains of Petrolacosaurus and was initially thought to contain elements of Haptodus. The evolutionary significance of the taxon was not realized until a publication in 2015. The fossil of this organism was discovered in Garnett, Kansas.{{cite journal |last1=Spindler |first1=F. |last2=Scott |first2=Diane |last3=Reisz |first3=Robert |date=October 2014 |title=New information on the cranial and postcranial anatomy of the early synapsid Ianthodon schultzei (Sphenacomorpha: Sphenacodontia), and its evolutionary significance |url=https://www.researchgate.net/publication/280961968 |journal=Fossil Record |volume=18 |pages=17-30}}

Description

Ianthodon was first named by Kissel & Reisz in 2004; elements on the holotype slab reidentified as Ianthodon provided more details 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,Currie, P. J.: A new haptodontine sphenacodont (Reptilia: Pelycosauria) from the Upper Pennsylvanian of North America, J. Paleontol., 51, 927–942, 1977 during the same development stage.{{Cite journal|last=Reisz|first=Robert R.|last2=Heaton|first2=Malcolm J.|last3=Pynn|first3=Bruce R.|date=1982|title=Vertebrate Fauna of Late Pennsylvanian Rock Lake Shale near Garnett, Kansas: Pelycosauria|jstor=1304403|journal=Journal of Paleontology|volume=56|issue=3|pages=741–750}} The specimen was easily distinguished from the skeletal element of PetrolacosaurusRoger 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 by the position and the proportion of foramen and supinator process in the humeri.

= Skull =

It can be distinguished from Haptodus{{Cite journal|last=Laurin|first=Michel|date=1993|title=Anatomy and Relationships of Haptodus garnettensis, a Pennsylvanian Synapsid from Kansas|jstor=4523501|journal=Journal of Vertebrate Paleontology|volume=13|issue=2|pages=200–229|doi=10.1080/02724634.1993.10011501}} by its narrower skull and dentition. The higher number of precanine 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.{{Cite journal|last=Fröbisch|first=Jörg|last2=Schoch|first2=Rainer R.|last3=Müller|first3=Johannes|last4=Schindler|first4=Thomas|last5=Schweiss|first5=Dieter|date=March 2011|title=A New Basal Sphenacodontid Synapsid from the Late Carboniferous of the Saar-Nahe Basin, Germany|journal=Acta Palaeontologica Polonica|volume=56|issue=1|pages=113–120|doi=10.4202/app.2010.0039|issn=0567-7920|doi-access=free}}

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.

{{Clade|{{clade

|1=Varanopidae

|2=Ophiacodontidae

|label3=Sphenacomorpha

|3={{clade

|1=Edaphosauridae

|label2=Sphenacodontia

|2={{clade

|1=Ianthodon schultzei

|2={{clade

|1=Haptodus garnettensis

|2={{clade