KEY, LINNAEUS, 1758

Macaluso, Loredana, Wencker, Lukardis C M, Castrovilli, Maria, Carnevale, Giorgio & Delfino, Massimo, 2023, A comparative atlas of selected skeletal elements of European urodeles (Amphibia: Urodela) for palaeontological investigations, Zoological Journal of the Linnean Society 197 (3), pp. 569-619 : 612-614

IDENTIFICATION KEY

Otic–occipitum complex

1. Smooth otic–occipitum complex, with no parietal crest and no parotic crest and process .... Speleomantes

- Different from above ..........................................................................................................................................2

2. Middle depression with small foramina at the bottom and tuberculum at the posterior end of the prominentia semicircularis anterioris .................................................................................... Salamandrina

- Different from above ..........................................................................................................................................3

3. Middle depression among prominentiae occupied by a fourth small prominentia ..................... Chioglossa

- Different from above ..........................................................................................................................................4

4. In ventral view, fenestra basicranialis posterioris entirely covered by crista retrosellaris...........................5

- Fenestra basicranialis posterioris visible in ventral view...............................................................................6

5. Ventral spine present anterior to basicapsular commissure....................................................... Pleurodeles

- Ventral spine absent .................................................................................................................... Salamandra

6. Crista retrosellaris covering the anterior half of the fenestra basicranialis ............................ Mertensiella

- Crista retrosellaris absent.................................................................................................................................7

7. In lateral view, parotic process ventrally concave and small fenestra ovalis ............................... Calotriton

- In lateral view, parotic process not ventrally concave and wide fenestra ovalis ............................................8

8. Middle depression with small foramina at the bottom................................................................... Euproctus

- Smooth middle depression ................................................................................................................................9

9. In ventral view, low or absent medial crest ............................................................................... Ichthyosaura

- In ventral view, medial crest high...................................................................................................................10

10. Parotic process rectangular in anterior and posterior views, minimally laterally extended...... Lissotriton

- Parotic process laterally extended and sub-triangular in anterior and posterior views .............................11

11. Low parotic crest, equally high throughout its length............................................................ Ommatotriton

- High parotic crest, generally higher close to the parietal crest ........................................................ Triturus

Atlas+

1. Strongly dorsoventrally compressed confluent occipital joints, with reduced horizontal odontoid process dorsal to them ....................................................................................................................................... Proteus

- Different from above ..........................................................................................................................................2

2. Neural bulge or two articular surfaces instead of neural crest.......................................................................3

- No neural bulge or articular surfaces (walls of neural arch fused).................................................................4

3. Articular surface of the odontoid process unseparated ........................................................ Salamandrella

- Articular surface of the odontoid process clearly separated.................................................... Speleomantes

4. High neural crest, posteriorly forked with lateral eversion .................................................. Salamandrina

- Different from above ..........................................................................................................................................5

5. Horizontal dorsal edge of the neural arch in lateral view and neural crest low or absent...... Mertensiella

- Different from above ..........................................................................................................................................6

6. Dorsal portion of the neural arch with several small foramina in posterior view ..................... Pleurodeles

- Different from above ..........................................................................................................................................7

7. Triangular neural canal .............................................................................................................. Salamandra

- Circular neural canal.........................................................................................................................................8

8. Low neural crest, neither posteriorly enlarged nor forked (or absent)...........................................................9

- Low neural crest, posteriorly enlarged ...........................................................................................................10

9. Neural spine present**..................................................................................................................... Euproctus

- Neural spine absent......................................................................................................................... Calotriton

10. Low or absent secondary crests ............................................................................................... Ommatotriton

- Marked secondary crests.................................................................................................................................11

11. Articular facets of odontoid process not contacting each other (large groove between them) Ichthyosaura

- Articular facets of odontoid process contacting each other or slightly separated (narrow groove between them)..................................................................................................................................................12

12. Blade-like neural and secondary crests marked in anterior view .................................................... Triturus

- Neural and secondary crests not marked in anterior view .......................................................... Lissotriton * Chioglossa is not included in the key because the only available atlas is too incomplete. **In one specimen (MDHC 507) the neural spine is not present; the diagnosis is identical to the one of Calotriton .

Precaudal vertebrae

1. Amphicoelous vertebrae ....................................................................................................................................2

- Opisthocoelous vertebrae ..................................................................................................................................4

2. No ventral crests and keels ...............................................................................................................................3

- Wide ventral crests and ventral keel................................................................................................... Proteus

3. Foramen on the lateral wall of the neural arch present.......................................................... Speleomantes

- Foramen on the lateral wall of the neural arch absent ........................................................ Salamandrella

4. High, forked neural crest (with lateral lips)........................................................................... Salamandrina

- Different from above ..........................................................................................................................................5

5. Dorsoventrally compressed vertebra (only one-fifth of the vertebra height formed by the neural arch dorsal to postzygapophyses), with low anterior zygapophyseal crests poorly visible in lateral view ......................6

- Different from above ..........................................................................................................................................8

6. Length approximately equal to width of the vertebra ............................................................... Salamandra

- Elongate vertebrae.............................................................................................................................................7

7. Prezygapophyses not markedly laterally extended from the neural arch................................... Chioglossa

- Prezygapophyses laterally projecting from the neural arch (vertebra with an overall hourglass-shape) ...................................................................................................................................................... Mertensiella

8. Anterior zygapophyseal crests contacting parapophyses or lamina of transverse processes or ventral half of diapophysis................................................................................................................................. Pleurodeles

- Anterior zygapophyseal crests contacting dorsal half of diapophyses............................................................9

9. In anterior view, foramen at the base of parapophyses wide ................................................. Ommatotriton

- In anterior view, foramen at the base of parapophyses small .......................................................................10

10. Dorsoventrally compressed vertebra (only one-fifth of the vertebra height formed by the neural arch dorsal to postzygapophyses) ........................................................................................................................... Triturus

- One-third of the vertebra formed by neural crest/arch dorsal to postzygapophyses ...................................11

11. Wide, equidimensional prezygapophyses (circular or quadrangular)........................................... Calotriton

- Elliptical prezygapophyses..............................................................................................................................12

12. High, posteriorly forked neural crest and condyle visible for most of its length in dorsal view .. Euproctus

- Different from above ........................................................................................................................................13

13. In dorsal view, medial edges of the prezygapophyseal facets generally anteriorly diverging........ Ichthyosaura

- In dorsal view, medial edges of the prezygapophyseal facets generally parallel......................... Lissotriton

Caudal vertebrae

1. Amphicoelous vertebrae ....................................................................................................................................2

- Opisthocoelous vertebrae ..................................................................................................................................4

2. Posterior, dorsal bulge present ..........................................................................................................................3

- Dorsal bulge absent, and forked posterior edge of the neural arch ................................................... Proteus

3. Transverse processes expanded in dorsal view and slightly dorsally concave in anterior view .................................................................................................................................................... Speleomantes

- Transverse processes sub-rectangular in dorsal view and ventrally pointing in anterior view ................................................................................................................................................. Salamandrella

4. Low and wide neural arch dorsal to postzygapophyses (neural arch dorsal to postzygapophyses flattened) ............................................................................................................................................................................5

- High and narrow neural arch dorsal to postzygapophyses (neural arch dorsal to postzygapophyses not flattened) ............................................................................................................................................................6

5. High neural and haemal crest .................................................................................................... Mertensiella

- Low haemal crest, and neural crest high only in its mid-length............................................... Salamandra

6. M-shaped transverse processes and anterior and posterior ventral crests forming an angle <130° in lateral view........................................................................................................................................... Salamandrina

- Different from above ..........................................................................................................................................7

7. Posterior area of the dorsal surface of the neural arch and of the ventral surface of the haemal arch perforated ....................................................................................................................................... Pleurodeles

- Different from above ..........................................................................................................................................8

8. Wide foramen on the lateral surface of the haemal arch ................................................................................9

- Small foramen or no foramen on the lateral surface of the haemal arch .....................................................10

9. Height/length ratio ~1.3–1.4, and transverse processes in lateral view, laminar and anteroventrally inclined ...................................................................................................................................... Ommatotriton

- Height/length ratio <1.3, and transverse processes different from above ....................................... Triturus

10. Transverse processes triangular in anterior view .......................................................................... Euproctus

- Transverse processes different from above ....................................................................................................11

11. Transverse processes posteriorly concave in lateral view ............................................................. Calotriton

- Transverse processes different from above ....................................................................................................12

12. Height/length ratio> 1.4 ................................................................................................ Lissotriton Uulgaris

- Height/length ratio ~1.3–1.4 ............................................................. Ichthyosaura /other Lissotriton spp.