# Polymorphodon

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Extinct genus of reptiles

Polymorphodon Temporal range: Middle Triassic, Ladinian PreꞒ Ꞓ O S D C P T J K Pg N Skeletal reconstruction and size comparison of the known remains Scientific classification Kingdom: Animalia Phylum: Chordata Class: Reptilia Clade: Archosauriformes Clade: Eucrocopoda Genus: Polymorphodon Sues et al., 2020 Type species †Polymorphodon adorfi Sues et al., 2020

***Polymorphodon*** is an [extinct](/source/Extinct) [genus](/source/Genus) of [*doswelliid*](/source/Doswelliidae) [archosauriform](/source/Archosauriform) reptile from the [Middle Triassic](/source/Middle_Triassic) of [Germany](/source/Germany). The only known species is ***Polymorphodon adorfi***, discovered in [Lower Keuper](/source/Lower_Keuper) ([Erfurt Formation](/source/Erfurt_Formation)) deposits at a quarry in Eschenau, Germany. *Polymorphodon* is notable for its [heterodont](/source/Heterodont) dentition, with long, conical [premaxillary](/source/Premaxilla) teeth followed by thin [maxillary](/source/Maxilla) teeth with large serrations. Maxillary teeth near the back of the mouth are short and leaf-shaped, similar to those of some living and extinct reptiles with a [herbivorous](/source/Herbivore) or [omnivorous](/source/Omnivore) diet. This may suggest that *Polymorphodon'*s diet included some plants, a rarity among [basal](/source/Basal_(phylogenetics)) archosauriforms, most of which are carnivores.[1]

## Discovery

*Polymorphodon* is named from a [holotype](/source/Holotype) specimen, [SMNS](/source/State_Museum_of_Natural_History_Stuttgart) 91343. This specimen is a disarticulated collection of bones from a single skeleton, including parts of the skull, a partial [braincase](/source/Neurocranium), [palatal](/source/Palate) fragments, sections of the lower jaws, bones of the hip and hindlimb, tail [vertebrae](/source/Vertebra), and potential hand bone fragments. Another specimen, SMNS 91400, consists of skull fragments. Although unique features can be recognized, many of the bones are distorted by crushing and [pyrite disease](/source/Pyrite_disease).[1]

The *Polymorphodon* specimens were found in 2010 at the Schumann limestone quarry on the outskirts of Eschenau, a village within [Vellberg, Germany](/source/Vellberg). The Eschenau quarry is one of the most fossiliferous sites preserving the [Ladinian](/source/Ladinian)-age Lower Keuper sequence, also known as the [Erfurt Formation](/source/Erfurt_Formation).[2] The specimens were specifically recovered from E6c-d, thin lake [mudstone](/source/Mudstone) beds near the top of the Untere Graue Mergel ("Lower Grey [Marl](/source/Marl)") subunit of the Lower Keuper.[1]

The unusual [heterodont](/source/Heterodont) dentition of *Polymorphodon* is the basis for its [generic name](/source/Generic_name_(biology)), which is derived from [Greek](/source/Greek_language) terms for "many shapes of teeth". The specific name honors Norbert Adorf, a fossil preparator whose work has been invaluable to the study of the local Triassic fauna.[1]

## Description

### Skull

Diagram of toothed snout bones

Although incomplete, the skull has been reconstructed as fairly short and deep, about 6.0 centimeters (2.4 inches) in length. The [premaxilla](/source/Premaxilla) is one of the most characteristic bones in the skull. Each premaxilla has five teeth, more than [euparkeriids](/source/Euparkeriidae), which have four. The teeth were smooth and conical, lacking serrations. The first three teeth were very long, with the second tooth being the longest. The largest component of the premaxilla is the posterodorsal process, a leaf-shaped prong of bone which extends behind the [nares](/source/Nares) (nostrils). Euparkeriids have a much smaller and more vertically-oriented posterodorsal process. Below the nares is a deep excavation known as a narial fossa. The [maxilla](/source/Maxilla) is fairly typical in shape, with a short anterior process (front branch), a slanted dorsal process (upper branch), a long posterior process (rear branch), and an [antorbital fenestra](/source/Antorbital_fenestra) defined between the dorsal and posterior processes. The anterior process has a notch at its front tip followed by a pit, as with a few other [archosauromorphs](/source/Archosauromorpha). The dorsal and posterior processes both taper rearwards like other early archosauriforms, and there may be a subtle antorbital fossa (depressed area) in front of the antorbital fenestra. The inner surface of the maxilla has an arched ledge overlooking broad [interdental plates](/source/Interdental_plate). The 11 maxillary teeth had [thecodont](/source/Thecodont_dentition) implantation and were more flattened in cross-section than the premaxillary teeth. The maxillary teeth were largest about 40% down the bone. Towards the rear of the maxilla, the tooth shape changes from long and recurved to short and leaf-shaped. Unlike the premaxillary teeth, there were large hook-shaped [serrations](/source/Serration) set at an angle on each maxillary tooth. The serrations decrease in size towards the [crown](/source/Crown_(tooth)) and extend closer to the [root](/source/Root) on the front edge of each tooth. The serrations (and the overall shape of teeth in the rear part of the maxilla) resembled those of [herbivorous](/source/Herbivore) or [omnivorous](/source/Omnivore) reptiles such as [iguanid](/source/Iguanidae) [lizards](/source/Lizard), [basal](/source/Basal_(phylogenetics)) [sauropodomorph](/source/Sauropodomorpha) dinosaurs, and *[Protecovasaurus](/source/Protecovasaurus)*.[1]

The presence of a Y-shaped [postorbital](/source/Postorbital_bone) indicates that *Polymorphodon* had a [diapsid](/source/Diapsid) skull. The postorbital had a blunt inner branch and curved rear and lower branches. The [frontal](/source/Frontal_bone) would have formed the upper edge of the [orbit](/source/Orbit_(anatomy)) (eye socket), but it is poorly preserved. The long front branch of the slender [jugal](/source/Jugal_bone) forms most of the lower edge of the orbit. The shorter rear branch of the jugal would have formed part of the lower edge of the [infratemporal fenestra](/source/Infratemporal_fenestra). The [quadrate](/source/Quadrate_bone) is straight, has a triangular pterygoid flange on its front edge, and generally resembles that of *[Euparkeria](/source/Euparkeria)*. The [pterygoid](/source/Pterygoid_bone) is slender, and it is unknown whether there were teeth on its lower surface. [Vomer](/source/Vomer) fragments are also preserved. The [braincase](/source/Neurocranium) was fairly typical by archosauriform standards, with a large [foramen magnum](/source/Foramen_magnum) surrounded by a variety of [occipital](/source/Occipital_bone) bones. The [foramen magnum](/source/Foramen_magnum) is edged by [exoccipitals](/source/Exoccipitals) which expand downwards but are separated by a [basioccipital](/source/Basioccipital) at the lower edge of the hole. This contrasts with [Erythrosuchidae](/source/Erythrosuchidae) (which have exoccipitals that meet at the bottom) but is similar to euparkeriids and *[Doswellia](/source/Doswellia)*. Also like *Euparkeria*, there is a deep and narrow [metotic foramen](https://en.wikipedia.org/w/index.php?title=Metotic_foramen&action=edit&redlink=1) (an area including the [jugular foramen](/source/Jugular_foramen) and inner ear) on the side of the braincase. However, the [parabasisphenoid](/source/Parabasisphenoid) is horizontally-oriented, similar to archosauriforms more basal than euparkeriids. Nevertheless, the basitubera of the parabasisphenoid are separated from each other, like derived archosauriforms. The lower jaw is represented by a low [dentaries](/source/Dentary) with parallel upper and lower edges. Preserved dentary teeth are variable in shape and serrated similarly to maxillary teeth.[1]

### Postcrania

There are several preserved [vertebrae](/source/Vertebra), most of them caudals (tail vertebrae) which are concave at both ends. Caudals closer to the base of the tail were shorter, while those near the tip of the tail were long, low, and simple. The vertebrae lack [notochordal](/source/Notochord) perforations and have neural spines fused to their centrum, indicating that the specimen was an adult. A few small and slender [manus](/source/Manus_(anatomy)) (hand) bones are preserved, indicating that the hand was small and had slightly curved claws. The hip and hindlimb were more complete. The [iliac](/source/Ilium_(bone)) has a slightly convex upper edge, a long postacetabular process (rear blade), and a small but distinct preacetabular process (front blade). A tentatively-identified [pubis](/source/Pubis_(bone)) has an expanded and leaf-shaped lower blade as well as an [obturator foramen](/source/Obturator_foramen) closer to its connection with the [ischium](/source/Ischium). A bone which may be the ischium is straight and flat. The [femur](/source/Femur) is slightly [sigmoid](/source/Sigmoid_function), with indistinct [condyles](/source/Condyle) and a ridge-like [fourth trochanter](/source/Fourth_trochanter). It generally resembles that of *Osmolskina*, as do the slightly shorter [tibia](/source/Tibia) and [fibula](/source/Fibula). [Pes](/source/Pes_(anatomy)) (foot) bones include a thick, hooked [metatarsal V](/source/Fifth_metatarsal_bone) and a straight, slender [metatarsal IV](/source/Fourth_metatarsal_bone), both of which are typical for archosauriforms. [Osteoderms](/source/Osteoderm) are missing in the fossil, though they may have been present in life.[1]

## Classification

*Polymorphodon* can be identified as an archosauriform thanks to several traits of the skull ([antorbital fenestra](/source/Antorbital_fenestra), serrated teeth) and hip (long, convex [iliac](/source/Ilium_(bone)) blade). The tapering posterior process of the [maxilla](/source/Maxilla) and the presence of [interdental plates](/source/Interdental_plate) suggest that it was a *[Euparkeria](/source/Euparkeria)*-[grade](/source/Evolutionary_grade) archosauriform, more derived than [Proterosuchidae](/source/Proterosuchidae) or [Erythrosuchidae](/source/Erythrosuchidae). When placed into the [parsimony](/source/Maximum_parsimony_(phylogenetics)) [phylogenetic analysis](/source/Phylogenetics) of [Ezcurra](/source/Mart%C3%ADn_Ezcurra) (2016),[3] *Polymorphodon* was found to be an unstable [eucrocopodan](/source/Eucrocopoda) in a [polytomy](/source/Polytomy) with [euparkeriids](/source/Euparkeriidae), [Proterochampsia](/source/Proterochampsia), [archosaurs](/source/Archosaur), and various other taxa. It was tentatively placed closer to archosaurs in a [bayesian analysis](/source/Bayesian_inference_in_phylogeny) of the dataset. A simplified strict consensus tree (average result) of the parsimony analysis is given below:[1]

Archosauriformes Proterosuchidae Fugusuchus Sarmatosuchus Cuyosuchus Erythrosuchidae Eucrocopoda Dorosuchus Polymorphodon Euparkeria Dongusuchus* Yarasuchus* Proterochampsia Archosauria

*Note: *Dongusuchus* and *Yarasuchus* have more recently been found to be [avemetatarsalian](/source/Avemetatarsalia) archosaurs in the group [Aphanosauria](/source/Aphanosauria).[4]

## References

1. ^ [***a***](#cite_ref-:0_1-0) [***b***](#cite_ref-:0_1-1) [***c***](#cite_ref-:0_1-2) [***d***](#cite_ref-:0_1-3) [***e***](#cite_ref-:0_1-4) [***f***](#cite_ref-:0_1-5) [***g***](#cite_ref-:0_1-6) [***h***](#cite_ref-:0_1-7) Sues, Hans-Dieter; Schoch, Rainer R.; Sobral, Gabriela; Irmis, Randall B. (2020-06-23). ["A new archosauriform reptile with distinctive teeth from the Middle Triassic (Ladinian) of Germany"](https://figshare.com/articles/journal_contribution/12848697). *Journal of Vertebrate Paleontology*. **40** (1) e1764968. [Bibcode](/source/Bibcode_(identifier)):[2020JVPal..40E4968S](https://ui.adsabs.harvard.edu/abs/2020JVPal..40E4968S). [doi](/source/Doi_(identifier)):[10.1080/02724634.2020.1764968](https://doi.org/10.1080%2F02724634.2020.1764968). [ISSN](/source/ISSN_(identifier)) [0272-4634](https://search.worldcat.org/issn/0272-4634). [S2CID](/source/S2CID_(identifier)) [221749201](https://api.semanticscholar.org/CorpusID:221749201).

1. **[^](#cite_ref-2)** Schoch, Rainer R.; Seegis, Dieter (2016-10-01). ["A Middle Triassic palaeontological gold mine: The vertebrate deposits of Vellberg (Germany)"](http://www.sciencedirect.com/science/article/pii/S0031018216302371). *Palaeogeography, Palaeoclimatology, Palaeoecology*. **459**: 249–267. [Bibcode](/source/Bibcode_(identifier)):[2016PPP...459..249S](https://ui.adsabs.harvard.edu/abs/2016PPP...459..249S). [doi](/source/Doi_(identifier)):[10.1016/j.palaeo.2016.07.002](https://doi.org/10.1016%2Fj.palaeo.2016.07.002). [ISSN](/source/ISSN_(identifier)) [0031-0182](https://search.worldcat.org/issn/0031-0182).

1. **[^](#cite_ref-3)** Ezcurra, Martín D. (2016-04-28). ["The phylogenetic relationships of basal archosauromorphs, with an emphasis on the systematics of proterosuchian archosauriforms"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4860341). *PeerJ*. **4** e1778. [doi](/source/Doi_(identifier)):[10.7717/peerj.1778](https://doi.org/10.7717%2Fpeerj.1778). [ISSN](/source/ISSN_(identifier)) [2167-8359](https://search.worldcat.org/issn/2167-8359). [PMC](/source/PMC_(identifier)) [4860341](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4860341). [PMID](/source/PMID_(identifier)) [27162705](https://pubmed.ncbi.nlm.nih.gov/27162705).

1. **[^](#cite_ref-Teleocrater17_4-0)** Nesbitt, Sterling J.; Butler, Richard J.; Ezcurra, Martín D.; Barrett, Paul M.; Stocker, Michelle R.; Angielczyk, Kenneth D.; Smith, Roger M. H.; Sidor, Christian A.; Niedźwiedzki, Grzegorz; Sennikov, Andrey G.; Charig, Alan J. (2017). ["The earliest bird-line archosaurs and the assembly of the dinosaur body plan"](https://web.archive.org/web/20200305125438/https://research.birmingham.ac.uk/portal/files/39495711/Nesbitt_et_al._in_press.pdf) (PDF). *Nature*. **544** (7651): 484–487. [Bibcode](/source/Bibcode_(identifier)):[2017Natur.544..484N](https://ui.adsabs.harvard.edu/abs/2017Natur.544..484N). [doi](/source/Doi_(identifier)):[10.1038/nature22037](https://doi.org/10.1038%2Fnature22037). [PMID](/source/PMID_(identifier)) [28405026](https://pubmed.ncbi.nlm.nih.gov/28405026). [S2CID](/source/S2CID_(identifier)) [9095072](https://api.semanticscholar.org/CorpusID:9095072). Archived from [the original](http://pure-oai.bham.ac.uk/ws/files/39495711/Nesbitt_et_al._in_press.pdf) (PDF) on 5 March 2020.

v t e Archosauromorpha Kingdom: Animalia Phylum: Chordata Class: Sauropsida Clade: Diapsida Clade: Sauria Clade: Archelosauria Sauropsida see Sauropsida Archosauromorpha see below↓ Archosauromorpha Archosauromorpha †Aenigmastropheus †Czatkowiella †Elachistosuchus? †Elessaurus †Malutinisuchus †Manistropheus †Mecistotrachelos †Prolacertoides †Protorosaurus †Rhombopholis †Vritramimosaurus †Tanysauria Jesairosaurus? Trachelosauridae Austronaga Dinocephalosaurus Fuyuansaurus? Gracilicollum? Protanystropheus Pectodens Sclerostropheus? Trachelosaurus Sharovipterygidae? Ozimek Sharovipteryx Tanystropheidae Akidostropheus Amotosaurus Augustaburiania Cosesaurus Fuyuansaurus? Gracilicollum? Gwyneddosaurus Langobardisaurus Luxisaurus Macrocnemus Raibliania Sclerostropheus? Tanystropheus Tanytrachelos Sharovipterygidae? Crocopoda †Boreopricea †Cryptovaranoides? †Tasmaniosaurus †Teyujagua †Allokotosauria see Allokotosauria †Rhynchosauria see Rhynchosauria †Prolacertidae? Kadimakara Prolacerta Archosauriformes see below↓ Archosauriformes Archosauriformes †Antarctanax †Cuyosuchus †Eorasaurus? †Kalisuchus †Koilamasuchus †Sarmatosuchus †Syntomiprosopus †Proterosuchidae Archosaurus Chasmatosuchus? Gamosaurus Jaikosuchus Proterosuchus Samsarasuchus Tsylmosuchus? Vonhuenia? †Protopyknosia Kranosaura Triopticus †Erythrosuchidae Bharitalasuchus Chalishevia Erythrosuchus Fugusuchus? Garjainia Guchengosuchus Shansisuchus Uralosaurus Eucrocopoda †Asperoris †Dorosuchus †Heteropelta †Litorosuchus †Marcianosuchus †Polymorphodon †Silescelida †Vancleavea †Euparkeriidae Euparkeria Halazhaisuchus Osmolskina †Proterochampsia see Proterochampsia Crurotarsi †Phytosauria see Phytosauria Archosauria Incertae sedis †Sikannisuchus? †Smok Avemetatarsalia see Avemetatarsalia includes birds Pseudosuchia see Pseudosuchia includes crocodilians Related topics Tooth taxa †Crosbysaurus †Lucianosaurus †Tecovasaurus †Palaeosaurus †Protecovasaurus †Uatchitodon †Zanclodon Nomina dubia †Albisaurus †Ankistrodon †Avipes †Blomosuchus †Collilongus †Exilisuchus †Fenhosuchus †Megacnemus †Microcnemus †Vjushkovisaurus †Wangisuchus Paraphyletic groups Proterosuchia Protorosauria Thecodontia Possible members Choristodera Drepanosauromorpha Kuehneosauridae Ichthyosauromorpha Sauropterygia Thalattosauria Category

Taxon identifiers Polymorphodon Wikidata: Q96623746 GBIF: 11114625

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