Geosaurus suevicus, Sachs & Young & Abel & Mallison, 2021

Sachs, Sven, Young, Mark T., Abel, Pascal & Mallison, Heinrich, 2021, A new species of Cricosaurus (Thalattosuchia, Metriorhynchidae) based upon a remarkably well-preserved skeleton from the Upper Jurassic of Germany, Palaeontologia Electronica (a 24) 24 (2), pp. 1-28 : 22-23

Cricosaurus suevicus (Fraas, 1901) Young and Andrade, 2009

v* 1901 Geosaurus suevicus sp. nov. – Fraas, p.

410.

v 1902 Geosaurus suevicus (Fraas) – Fraas p.

41, figure 7 Taf. 5-8.

v1 973 Geosaurus suevicus (Fraas) – Steel, p.

44, figure 18 (2-3).

v 2005 Geosaurus suevecicus (Fraas) – Mueller-Töwe, p. 211. [sic]

v 2009 Cricosaurus suevicus (Fraas) comb. nov. – Young and Andrade, p. 557, figure 6.

v 2010 Cricosaurus suevicus (Fraas) – Young et al., p. 802, figure 1, figure 5.

v 2019 Cricosaurus suevicus (Fraas) – Sachs et al., p. 1.

Lectotype. SMNS 9808 : complete skeleton preserved in limestone ( Figures 9D , 10B ).

Type locality. Nusplingen, Baden-Württemberg,

Germany.

Type formation. Nusplingen Formation.

Type horizon. Lithacoceras ulmense Subzone ,

Hybonoticeras hybonotum Tethyian ammonite

Zone, lower Tithonian, Upper Jurassic.

Etymology. ‘Swabian ring lizard’.

Referred specimens. SMNS 90513: almost complete skeleton preserved in limestone ( Figure 9 );

GPIT-PV-31380: incomplete skeleton; GPIT-PV-

31381: largely complete skeleton ( Figures 8D , 9A ).

All referred specimens are from the Nusplingen

Formation.

Geological range. Upper Jurassic. Lithacoceras ulmense Subzone , Hybonoticeras beckeri Tethyian ammonite Zone, upper Kimmeridgian.

Emended diagnosis. A member of Cricosaurus with the following unique combination of characters (proposed autapomorphic characters are indicated by an asterisk *): bicarinate dentition, lacking conspicuous enamel ornamentation; tooth crowns in the premaxilla, maxilla and dentary show distinct labiolingual compression (shared with C. albersdoerferi BMMS-BK 1-2, C. bambergensis NKMB-PWatt14/274 and C. elegans SNSB-BSPG AS I 504); lack of pronounced, or regular shallow, reception pits on the lateral margins of the middle maxilla and dentary (shared with C. elegans SNSB-BSPG AS I 504 and C. medius SNSB-BSPG AS VI 2); all the neural spines of the dorsal vertebrae are rectangular when see in lateral view, a flat dorsal margin is the most prevalent (shared with C. albersdoerferi BMMS-BK 1-2), and the neural spines of adjacent vertebrae are in close proximity to one another*; estimated to have approximately 50, or more, caudal vertebrae; morphology of the tail displacement unit: the distal-most seven preflexural vertebrae have neural spines that are oriented very strongly posteriorly, with their posterior margin lying on top of the prezygapophyses of the adjacent vertebra; the distal-most three preflexural neural spines appear almost rod-like in lateral view*; the three vertebrae anterior to them have a similar morphology, but the neural spines are raised such that they do not overlap the prezyapophyses of the vertebrae immediately posterior*.

Cricosaurus suevicus shares the following synapomorphy with C. elegans (SNSB-BSPG AS I 504), C. medius (SNSB-BSPG AS VI 2) and C. albersdoerferi (BMMS-BK 1-2): 1) the maxillary tooth row terminates anterior to, or approximately level to, the anterior-margin of the orbits.

Cricosaurus suevicus shares the following tail fluke synapomorphies with C. albersdoerferi (BMMS-BK 1-2): 1) the distal-most preflexural vertebra (also identifiable as it has a verticalized neural spine) has a dorsoventrally deep hemapophysis, with a midline flange (i.e., it does not have a ‘rod-like’ hemapophysis as in C. bambergensis NKMB-P-Watt14/274 and Rhacheosaurus gracilis NHMUK PV R 3948); 2) the five-six proximal-most flexural vertebrae have strongly anteriorly oriented neural spines (much more so than C. bambergensis NKMB-P-Watt14/274, R. gracilis NHMUK PV R 3948 and Thalattosuchus superciliosus GPIT-PV-31379); 3) the flexural hemapophyses contact one another along their posteroventral-anterodorsal margins (not their posterior-anterior margins as in C. bambergensis NKMB-P-Watt14/274, R. gracilis NHMUK PV R 3948 and T. superciliosus GPIT-PV-31379); and 4) the distal-most post-flexural hemapophyses retain their dorsoventrally deep profile (i.e., they do not return to a ‘rod-like’ morphology, as in C. bambergensis NKMB-P-Watt14/274 and R. gracilis NHMUK PV R 3948).

Figures

FIGURE 8. Strict consensus topologies of Metriorhynchinae found in the parsimony analyses. A, unweighted topology; B, strongly down-weighted topology (k=1); C, all other weighting analyses topology (k=3, 7, 10, 20, and 50).

FIGURE 9. Comparison of crania of Late Jurassic Cricosaurus specimens from southern Germany. (A) BMMS-BK 1-2, holotype of Cricosaurus albersdoerferi sp. nov.; (B) NKMB-P-Watt14/274, holotype of Cricosaurus bambergensis; (C) SNSB-BSPG AS I 504, holotype of Cricosaurus elegans; (D) SMNS 9808, lectotype of Cricosaurus suevicus; (E) GPIT-PV-31381, referred specimen of Cricosaurus suevicus and (F) SMNS 7322, referred specimen of Cricosaurus suevicus. Scale bars equal 50 mm.

FIGURE 10. Comparison of tail bends of Late Jurassic Cricosaurus specimens from southern Germany. (A) BMMS-BK 1-2, holotype of Cricosaurus albersdoerferi sp. nov.; (B) SMNS 9808, lectotype of Cricosaurus suevicus; (C) GPIT-PV- 31381, referred specimen of Cricosaurus suevicus; (D) NKMB-P-Watt14/274, holotype of Cricosaurus bambergensis. No scale bars intended.