Ianthodon

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Ianthodon
Temporal range: Pennsylvanian,
~304  Ma
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IanthodonReconstruction.png
I. schultzei cranial and skeletal reconstruction
Scientific classification OOjs UI icon edit-ltr.svg
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
Holotype KUVP 133735 Ianthodon schultzei 35.jpg
Holotype KUVP 133735

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. [1] 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. [2] The fossil of this organism was discovered in Garnett, Kansas. [2]

Contents

Description

Ianthodon was first named by Kissel & Reisz in 2004, [1] and a more detailed specimen was reevaluated in 2014. [2] 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, [3] during the same development stage. [1] [4] The specimen was easily distinguished from the skeletal element of Petrolacosaurus [5] 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 [6] [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 [5] 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. [6] 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. [7] [2]

Classification

Ianthodon belongs to the clade Sphenodontia within the clade Sphenacomorpha. It played an important role in understanding the initial evolution of sphenacodonts. [3] It also provided important evidence of the mammal origin. [8] The cladogram below follows a cladistic analysis by Spindler and colleagues, 2014. [2]

Varanopidae

Ophiacodontidae

Sphenacomorpha

Edaphosauridae

Sphenacodontia

Ianthodon schultzei

Haptodus garnettensis

Pantelosaurus saxonicus

Sphenacodontoidea

Cutleria wilmarthi

Sphenacodon spp.

Ctenospondylus spp.

Dimetrodon spp.

Therapsida

Biarmosuchus tener

Dinocephalia

Paleobiology and 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. [8] 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

Related Research Articles

<span class="mw-page-title-main">Synapsid</span> Clade of tetrapods

Synapsids are one of the two major clades of vertebrate animals in the group Amniota, the other being the sauropsids, which include reptiles and birds. The synapsids were once the dominant land animals in the late Paleozoic and early Mesozoic, but the only extant group that survived into the Cenozoic are the mammals. Unlike other amniotes, synapsids have a single temporal fenestra, an opening low in the skull roof behind each eye orbit, leaving a bony arch beneath each; this accounts for their name. The distinctive temporal fenestra developed about 318 million years ago during the Late Carboniferous period, when synapsids and sauropsids diverged, but was subsequently merged with the orbit in early mammals.

<span class="mw-page-title-main">Diadectomorpha</span> Extinct clade of tetrapods

Diadectomorpha is a clade of large tetrapods that lived in Euramerica during the Carboniferous and Early Permian periods and in Asia during Late Permian (Wuchiapingian), They have typically been classified as advanced reptiliomorphs positioned close to, but outside of the clade Amniota, though some recent research has recovered them as the sister group to the traditional Synapsida within Amniota, based on inner ear anatomy and cladistic analyses. They include both large carnivorous and even larger herbivorous forms, some semi-aquatic and others fully terrestrial. The diadectomorphs seem to have originated during late Mississippian times, although they only became common after the Carboniferous rainforest collapse and flourished during the Late Pennsylvanian and Early Permian periods.

<span class="mw-page-title-main">Edaphosauridae</span> Extinct family of synapsids

Edaphosauridae is a family of mostly large Late Carboniferous to Early Permian synapsids. Edaphosaur fossils are so far known only from North America and Europe.

<span class="mw-page-title-main">Sphenacodontidae</span> Extinct family of synapsids

Sphenacodontidae is an extinct family of sphenacodontoid synapsids. Small to large, advanced, carnivorous, Late Pennsylvanian to middle Permian "pelycosaurs". The most recent one, Dimetrodon angelensis, is from the late Kungurian or early Roadian San Angelo Formation. However, given the notorious incompleteness of the fossil record, a recent study concluded that the Sphenacodontidae may have become extinct as recently as the early Capitanian. Primitive forms were generally small, but during the later part of the early Permian these animals grew progressively larger, to become the top predators of terrestrial environments. Sphenacodontid fossils are so far known only from North America and Europe.

<span class="mw-page-title-main">Sphenacodontia</span> Clade of synapsids

Sphenacodontia is a stem-based clade of derived synapsids. It was defined by Amson and Laurin (2011) as "the largest clade that includes Haptodus baylei, Haptodus garnettensis and Sphenacodon ferox, but not Edaphosaurus pogonias". They first appear during the Late Pennsylvanian epoch. From the end of the Carboniferous to the end of the Permian, most of them remained large, with only some secondarily becoming small in size.

<span class="mw-page-title-main">Eupelycosauria</span> Clade of synapsids

Eupelycosauria is a large clade of animals characterized by the unique shape of their skull, encompassing all mammals and their closest extinct relatives. They first appeared 308 million years ago during the Early Pennsylvanian epoch, with the fossils of Echinerpeton and perhaps an even earlier genus, Protoclepsydrops, representing just one of the many stages in the evolution of mammals, in contrast to their earlier amniote ancestors.

<i>Petrolacosaurus</i> Genus of tetrapods

Petrolacosaurus is an extinct genus of diapsid reptile from the late Carboniferous period. It was a small, 40-centimetre (16 in) long reptile, and one of the earliest known reptile with two temporal fenestrae. This means that it was at the base of Diapsida, the largest and most successful radiation of reptiles that would eventually include all modern reptile groups, as well as dinosaurs and other famous extinct reptiles such as plesiosaurs, ichthyosaurs, and pterosaurs. However, Petrolacosaurus itself was part of Araeoscelida, a short-lived early branch of the diapsid family tree which went extinct in the mid-Permian.

<span class="mw-page-title-main">Caseasauria</span> Extinct clade of synapsids

Caseasauria is one of the two main clades of early synapsids, the other being the Eupelycosauria. Caseasaurs are currently known only from the Late Carboniferous and the Permian, and include two superficially different families, the small insectivorous or carnivorous Eothyrididae, and the large, herbivorous Caseidae. These two groups share a number of specialised features associated with the morphology of the snout and external naris.

Varanopidae is an extinct family of amniotes that resembled monitor lizards and may have filled a similar niche, hence the name. Typically, they are considered synapsids that evolved from an Archaeothyris-like synapsid in the Late Carboniferous. However, some recent studies have recovered them being taxonomically closer to diapsid reptiles. A varanopid from the latest Middle Permian Pristerognathus Assemblage Zone is the youngest known varanopid and the last member of the "pelycosaur" group of synapsids.

<span class="mw-page-title-main">Sphenacodontoidea</span> Superfamily of synapsids

Sphenacodontoidea is a node-based clade that is defined to include the most recent common ancestor of Sphenacodontidae and Therapsida and its descendants. Sphenacodontoids are characterised by a number of synapomorphies concerning proportions of the bones of the skull and the teeth.

<i>Haptodus</i> Extinct genus of synapsids

Haptodus is an extinct genus of basal sphenacodont, member of the clade that includes therapsids and hence, mammals. It was at least 1.5 metres (5 ft) in length. It lived in present-day France during the Early Permian. It was a medium-sized predator, feeding on insects and small vertebrates.

<i>Eothyris</i> Extinct genus of synapsids

Eothyris is a genus of extinct synapsid in the family Eothyrididae from the early Permian. It was a carnivorous insectivorous animal, closely related to Oedaleops. Only the skull of Eothyris, first described in 1937, is known. It had a 6-centimetre-long (2.4-inch) skull, and its total estimated length was 30 centimetres. Eothyris is one of the most primitive synapsids known and is probably very similar to the common ancestor of all synapsids in many respects. The only known specimen of Eothyris was collected from the Artinskian-lower.

<i>Limnoscelis</i> Genus of diadectomorphs

Limnoscelis was a genus of large diadectomorph tetrapods from the Late Carboniferous of western North America. It includes two species: the type species Limnoscelis paludis from New Mexico, and Limnoscelis dynatis from Colorado, both of which are thought to have lived concurrently. No specimens of Limnoscelis are known from outside of North America. Limnoscelis was carnivorous, and likely semiaquatic, though it may have spent a significant portion of its life on land. Limnoscelis had a combination of derived amphibian and primitive reptilian features, and its placement relative to Amniota has significant implications regarding the origins of the first amniotes.

<i>Palaeohatteria</i> Extinct genus of synapsids

Palaeohatteria is an extinct genus of basal sphenacodonts known from the Early Permian period of Saxony, Germany. It contains a single species, Palaeohatteria longicaudata.

"Haptodus" garnettensis is an extinct species of basal sphenacodont from the Late Carboniferous (Pennsylvanian) of Kansas, USA.

<i>Echinerpeton</i> Extinct genus of synapsids

Echinerpeton is an extinct genus of synapsid, including the single species Echinerpeton intermedium from the Late Carboniferous of Nova Scotia, Canada. The name means 'spiny lizard' (Greek). Along with its contemporary Archaeothyris, Echinerpeton is the oldest known synapsid, having lived around 308 million years ago. It is known from six small, fragmentary fossils, which were found in an outcrop of the Morien Group near the town of Florence. The most complete specimen preserves articulated vertebrae with high neural spines, indicating that Echinerpeton was a sail-backed synapsid like the better known Dimetrodon, Sphenacodon, and Edaphosaurus. However, the relationship of Echinerpeton to these other forms is unclear, and its phylogenetic placement among basal synapsids remains uncertain.

<i>Xyrospondylus</i> Extinct genus of synapsids

Xyrospondylus is an extinct genus of non-mammalian synapsids belonging to the Edaphosauridae. The type species, X. ecordi, was named in 1982; it was originally named as a species of Edaphosaurus in 1957.

<i>Acleistorhinus</i> Extinct genus of reptiles

Acleistorhinus (ah-kles-toe-RYE-nuss) is an extinct genus of parareptile known from the Early Permian of Oklahoma. It is notable for being the earliest known anapsid reptile yet discovered. The morphology of the lower temporal fenestra of the skull of Acleistorhinus bears a superficial resemblance to that seen in early synapsids, a result of convergent evolution. Only a single species, A. pteroticus, is known, and it is classified in the Family Acleistorhinidae, along with Colobomycter.

<i>Kenomagnathus</i> Extinct genus of synapsids

Kenomagnathus is a genus of synapsid belonging to the Sphenacodontia, which lived during the Pennsylvanian subperiod of the Carboniferous in what is now Garnett, Kansas, United States. It contains one species, Kenomagnathus scottae, based on a specimen consisting of the maxilla and lacrimal bones of the skull, which was catalogued as ROM 43608 and originally classified as belonging to "Haptodus" garnettensis. Frederik Spindler named it as a new genus in 2020.

References

  1. 1 2 3 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 7 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. 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. 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. 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
  6. 1 2 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.
  8. 1 2 Kemp, T. S.: Mammal-like Reptiles and the Origin of Mammals, Academic Press, New York, 1982
  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