Ianthodon

Ianthodon
Temporal range: Pennsylvanian 305.9–303.4 Ma
↓
Ianthodon schultzei cranial and skeletal reconstruction
Scientific classification
Kingdom:Animalia
Phylum:Chordata
Clade:Sphenacodontia
Genus:†Ianthodon
Kissel & Reisz, 2004
Type species
†Ianthodon schultzei
Kissel & Reisz, 2004
Species

†Ianthodon schultzei Kissel & Reisz, 2004

Introduction

Ianthodon schultzei holotype KUVP 133735

Ianthodon[1] is an extinct genus of basal sphenacodont synapsids from the Late Carboniferous about 306-303 million years ago, the taxon Ianthodon was discovered and named by Kissel & Reisz in 2004,[1] the only species in the taxon Ianthodon schultzei was found by separating from a block that contains the remains of both Petrolacosaurus and Haptodus. The evolutionary significance of the taxon wasn't realized until the new publication in 2015,[2] it was known from the Garnett locality of Kansas.[2]

Taxonomy

The Ianthodon belongs in Sphenodontia clade which is within the clade of Sphenocomorpha, it played an important role in understanding the initial evolution of Sphenacodonts,[3] it provided us with precious evidence of early reptilian-mammal transition.[4]

Description

Humeri

Ianthodon was first name by Kissel & Reisz in 2004[1], as a more detailed specimen was reevaluated in 2014[2], this single juvenile skeleton with delicate bones has an estimate skull length of around 10 cm, and this was similar to other taxon like Haptodus[3] during the same development stage.[1][5] The specimen was easily distinguished from the skeletal element of Petrolacosaurus[6] by the position and the proportion of foreman and supinator process in the humeri.

Skull

Ianthodon was identified as the basalmost known sphenacodont.[2] It can be distinguished from Haptodus[7][3] 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[6] 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.[7] 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.[8][2]

Classification

Ianthodon belongs to the clade of Spenacodontia, replacing Haptodus as the basalmost taxon in the clade. The taxon placement on this parsimonious tree results from the evaluation of the bootstrap values between the taxons.

 

 

Varanopidae

 
 

 

Edaphosauridae

 
 

 

Ianthodon schultzei

 
 

 

Haptodus garnettensis

 
 

 

Dimetrodon spp

 
 

 

Biarmosuchus tener

 
 

Dinocephalia

 
 
 
 
 
 
 

Paleobiology & Evolutionary significance

The clear morphological evidence of the new material initialize the finalization of the understanding of the radiation of the Sphenacomorpha,[9] and the evolution of that led to the emergence of mammal.[4] So based on the information, it was concluded that basal Sphenacomorphs came from a generalist form with a great potential for adaptions.[2] However, the understanding of Ianthodon and basal Sphenacodonts are still relatively limited by the number of the specimen available for study and further excavation of Garnett fauna is required, despite the present evidence suggests that Ianthodon represents the primitive condition of sphenacodont evolution,[10] more studies are require for a better understanding of this particular stage of synapids evolution.

See also

References

  1. 1 2 3 4 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. 1 2 3 4 5 6 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".
  3. 1 2 3 Currie, P. J.: A new haptodontine sphenacodont (Reptilia: Pelycosauria) from the Upper Pennsylvanian of North America, J. Paleontol., 51, 927–942, 1977
  4. 1 2 Kemp, T. S.: Mammal-like Reptiles and the Origin of Mammals, Academic Press, New York, 1982
  5. ↑ 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.
  6. 1 2 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
  7. 1 2 Laurin, Michel (1993). "Anatomy and Relationships of Haptodus garnettensis, a Pennsylvanian Synapsid from Kansas". Journal of Vertebrate Paleontology. 13 (2): 200–229. JSTOR 4523501.
  8. ↑ Fröbisch, Jörg; Schoch, Rainer R.; Müller, Johannes; Schindler, Thomas; Schweiss, Dieter (2011-03). "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. Check date values in: |date= (help)
  9. ↑ Osborn, H. F.: The reptilian subclasses Diapsida and Synapsida and the early history of the Diaptosauria, Memoirs of the American Museum of Natural History, 1, 449–507, 1903
  10. ↑ Reisz, R. R., Berman, D. S., and Scott, D.: The cranial anatomy and relationships of Secodontosaurus, an unusual mammal-like reptile (Synapsida: Sphenacodontidae) from the early Permian of Texas, Zool. J. Linn. Soc.-Lond., 104, 127–184, 1992
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