Austriocaris Glaessner, 1931

Genus Austriocaris Glaessner, 1931

Type species: Austriocaris carinata Glaessner, 1931 , by original designation, Reingraben formation, Austrotrachyceras austriacum Zone , Austrotrachyceras minor Biohorizon, Julian 2 Ib, Carnian, Upper Triassic, Polzberg, Austria.

Included species: Austriocaris sp. , Carnian, Upper Triassic, Slovenia ( Laville et al. 2024); Austriocaris secretanae Laville et al., 2023 , Callovian, Middle Jurassic, France.

Emended diagnosis. — Thylacocephala with an optic notch occupying only the ventral part of the anterior margin, presence of a straight dorsal midline and a sharp posterodorsal corner.

Remarks.—In their diagnosis of Austriocaris, Laville et al. (2023) erroneously mentioned the presence of a sharp posteroventral corner. In reality, it is the posterodorsal angle that is sharp and diagnostic for Austriocaris .

Stratigraphic and geographic range.—Carnian, Late Triassic of Austria.

Austriocaris carinata Glaessner, 1931 Figs. 3 – 5 View Fig View Fig .

1931 Austriocaris carinata sp. nov.; Glaessner 1931: 483, text-figs. 5, 6.

1969 Austriocaris carinata Glaessner, 1931 ; Rolfe 1969: R317, fig. 140.2.

1983 Austriocaris carinata Glaessner, 1931 ; Briggs and Rolfe 1983: 270, text-fig. 6C.

1990 Austriocaris carinata Glaessner, 1931 ; Dalla Vecchia and Muscio 1990: 41.

2014 Austriocaris carinata Glaessner, 1931 ; Schram 2014: 349.

2017 Austriocaris carinata Glaessner, 1931 ; Ji et al. 2017: 175.

2018 Austriocaris carinata Glaessner, 1931 ; Rak et al. 2018: 278, table 1. 2019 Austriocaris carinata Glaessner, 1931 ; Charbonnier et al. 2019: table 1.

2021 Austriocaris carinata Glaessner, 1931 ; Ji et al. 2021: table 1.

2021 Austriocaris carinata Glaessner, 1931 ; Laville et al. 2021: table 1. 2021 Austriocaris carinata Glaessner, 1931 ; Lukeneder and Lukeneder 2021: fig. 3L, table 1.

2023 Austriocaris carinata Glaessner, 1931 ; Lukeneder and Lukeneder. 2023: fig. 3Q, table 1.

Holotype: NHMW 1910 View Materials /0015/0041; sub-complete shield with well-preserved ornamentation.

Type locality: Polzberg near Lunz am See, Austria.

Type horizon: Reingraben formation, Austrotrachyceras austriacum Zone , Austrotrachyceras minor Biohorizon, Julian 2 Ib, Carnian, Upper Triassic.

Material.— Type material and 37 specimens: GBA 2021 / 002/0010, NHMW 1910 View Materials /0015/0001–0017, 0037–0039, 0040, 0044–0050; NHMW 2021 View Materials /0123/0002, 0203, 0764–0766; NHMW 2021 View Materials /0124/0108–0110. All from type locality and horizon.

Dimensions. —See Table 1.

Description.— Shield morphology: Sub-trapezoidal shield in lateral view, much longer than high ( Fig. 3A View Fig 1 View Fig , A 3 View Fig ). Maximal height reached around mid-length. Anterior margin made of an optic notch in its ventral part, sinuous and posteroventrally oriented in its dorsal part ( Fig. 3A–C View Fig ). Anterodorsal corner expressed as a sharp, short triangular rostrum ( Fig. 3B View Fig ). Straight and horizontal dorsal midline, divided into two branches near the posterodorsal angle and thus delimiting this later ( Fig. 4A View Fig 1 –A View Fig 3 View Fig ). Posterodorsal corner expressed as a spine ( Fig. 3D, E View Fig ). Short, straight and vertical posterior margin. Ventral margin divided into a straight posterior part, anteroventrally oriented, and a straight horizontal anterior part ( Fig. 3C View Fig ). Anterior part longer than the posterior one. Both parts merging approximately at the posterior third of the length. Rounded anteroventral corner. Marginal fold delimited by a shallow groove near all free margins ( Fig. 4D View Fig 1 View Fig , D 2 View Fig ).

Shield macro-ornamentation: Shield with a straight dorsolateral carina, slightly tilted posteroventrally ( Fig. 4D View Fig 1 View Fig , D 2 View Fig ). Dorsolateral carina converging with the dorsal midline at about one fifth of the length. Dorsolateral carina adorned with at least 30 tubercles, which might be remains of spines. Mediolateral carina located in the posterior half of the shield ( Fig. 3A View Fig ). Mediolateral carina divided into a posterior half, anteroventrally tilted, and straight horizontal anterior half. C-shaped ventrolateral carina, located in the anterior half of the shield ( Figs 3A View Fig , 4A View Fig 1 View Fig , A 2 View Fig , A 4 View Fig ). Concavity of the carina directed posteriorly. In some specimens, ventrolateral carina associated with a large oval bulge near its dorsal tip

Fig. 4C View Fig ). Short straight lateral carina dividing the rostrum into two parts ( Fig. 4B View Fig ). Fields of small punctuations visible between the anteroventral corner and the ventrolateral carina ( Fig. 4D View Fig 1 View Fig , D 3 View Fig ), and in the dorsal part of the shield, above the dorsolateral carina ( Fig. 4B View Fig ). High density of punctuations on the ventral branch of the ventrolateral carina, and on the part symmetrical to the ventral branch, in relation to the dorsal branch, giving the impression of having a third branch to the carina ( Fig. 3A View Fig ).

Posterior trunk: Posterior trunk made of at least five segments, visible by their lateral musculature in the posterior part of the shield ( Fig. 5).

Gills: Set of four gills located in the central part of the shield. Gills with an elliptic shape, becoming arcuate near the dorsal midline ( Figs. 4D View Fig 5, 5A 1 –A View Fig 3 View Fig ).

Other structures: Compound eyes and raptorial appendages not preserved.

Remarks.—In its original description of Austriocaris carinata, Glaessner (1931) had reversed the orientation of the specimens, the posterior part being at the front. This influenced his description, leading for example to describe the optical notch as a posterior notch, from which the abdomen came out. Rolfe (1969) and Forchielli and Pervesler (2013) later followed this orientation.

Since the original description, A. carinata has been recognised as a thylacocephalan, and new species of Austriocaris have been described ( Laville et al. 2023, 2024). This allowed to clarify the orientation of Austriocaris .

Two other morphological characters have also been misidentified in the past. The first is the anterior part of the ventral margin. Indeed, this structure is actually not anteroventrally tilted, as depicted by Glaessner (1931) and Rolfe (1969), but it is horizontal, as shown in Fig. 3C View Fig . The second character is the presence of a rostral plate. The posterodorsal spine delimited by the dichotomy of the dorsal midline has been interpreted as a rostral plate based on the comparison with phyllocarids. However, this spine neither is a rostrum and nor is articulated (absence of hinge) and thus is not movable as in phyllocarids.

With this redescription, we also provide new details that were previously unknown such as the presence of tubercles on the dorsolateral carina. A tuberculate dorsolateral carina was already known in one species of Austriocaris , Austriocaris secretanae Laville et al., 2023 . The most important character newly described is the soft-part-preservation. Indeed, several gills as well as the lateral musculature of some posterior trunk segments are reported here. This is the first record of soft part preservation in Polzberg thylacocephalans.

Stratigraphic and geographic range.—Carnian, Upper Triassic of Austria.