Rosenfeldia triasica Garassino, Teruzzi & Dalla Vecchia 1996

Rosenfeldia triasica Garassino, Teruzzi & Dalla Vecchia, 1996

Figs 1, 2N, 3

Rosenfeldia triasica Garassino, Teruzzi & Dalla Vecchia, 1996: 33–41, figs 6–10, 17–20.

Rosenfeldia triasica – Garassino & Schweigert 2006: 30. — Schweitzer et al. 2010: 43. — Feldmann et al. 2013: 3. — Audo et al. 2014a: 464, fig. 2E; 2014c: 500; 2017: 5, fig. 3M. — Audo 2016: 291, fig. 3M.

Diagnosis

See genus.

Material examined

Holotype

ITALY: MFSNgp 16178 (Fig. 1 A–B).

Paratypes

ITALY: 3 specimens (MFSNgp 16173, MFSNgp 16176, MFSNgp 16179).

Other material

ITALY: 35 specimens (MFSNgp 16110, MFSNgp 16122, MFSNgp 16139, MFSNgp 16151, MFSNgp 16152, MFSNgp 16155, MFSNgp 16171–16174, MFSNgp 16176–16179, MFSNgp 16181, MFSNgp 16183, MFSNgp 16185, MFSNgp 16186–16191, MFSNgp 16193–16194, MFSNgp 16198, MFSNgp 24712, MFSNgp 26783–26784, MFSNgp 27694, MFSNgp 27696, MFSNgp 32291, MFSNgp 34290, MFSNgp 34292, MFSNgp 40312) (Fig. 1 C–D).

Type locality

ITALY: northern side of mount Auda (Succhieve, Udine, Italy).

Type age

Late Triassic, Norian (after Garassino et al. 1996).

Emendation to description

SHAPE OF CARAPACE. Dorsoventrally flattened carapace, subquadratic in outline in dorsal view; concave frontal margin; anterolateral angle blunt, pointing slightly outward; spiny lateral margin with ocular, cervical, and postcervical incisions; U-shaped, almost semi-circular ocular incision; anterolateral margin slightly rounded posteriorly, oblique compared to longitudinal axis, poorly preserved; cervical and postcervical incisions opening in anterior half of lateral margin; cervical incision subtriangular; mediolateral margin shorter than anterolateral margin, rounded posteriorly; postcervical incision subtriangular, slightly deeper than cervical incision; posterolateral margin, slightly rounded, fringed by small spines; posterolateral angle round, short, not fringing pleonite 1; posterior margin slightly concave, wider than frontal margin.

CARAPACE GROOVES AND CARINAE. Postrostral carina not visible; postcervical carina well-marked in posterior half of carapace; very thin branchial carina, with anterior branch possibly incorporating (merged with) postorbital carina and extending on ⅓ of carapace length, posterior branch separated from anterior branch by cervical and postcervical grooves, extending to posterolateral angle; cervical groove poorly preserved, oblique, extending from cervical incision toward median line; postcervical groove poorly preserved, extending from postcervical incision toward median line, passing near cervical groove; branchiocardiac groove not visible; gastro-orbital groove thin, poorly preserved, extending obliquely from cervical groove toward median line.

PLEON AND TELSON. Pleon and telson slightly shorter than carapace; pleon narrower than carapace; pleonite 1 shorter and narrower than others; s2–s5 with subrectangular terga crossed by a pair of transverse grooves and an axial carina cutting the posterior transverse groove; s6 with subtrapezoidal tergum; s1 and s6 with narrow subtriangular tergopleura (also called “pleura” although it is structurally a part of terga); other tergopleura also subtriangular but wider than s1 and s6 tergopleura; telson rounded, strengthened by a pair of slightly oblique longitudinal carinae and with finely serrated margins.

EYE AND CEPHALIC APPENDAGES. Eye not protruding from ocular incision; antennula poorly preserved; antenna poorly preserved, with an ovoid scaphocerite strengthened by a median longitudinal carina; mandible with an asymmetric molar process (Fig. 1D) and an incisor process forming sharp irregular triangular teeth.

THORACIC APPENDAGES. Third maxilliped with kidney-shaped ischium carrying a few stocky podomeres; P1 slightly larger than others; P1 dactylus and pollex (= fixed finger) slightly curved; stocky P1 palm (portion of propodus excluding pollex), slightly longer than dactylus; P1 carpus short and subtriangular; P1 merus slightly longer than palm, with parallel margins; P2–P4 similar to P1, decreasing in size from the second to the fourth; P5 ending in a short dactylus, without claw in observed specimens.

PLEONAL APPENDAGES. Pleopods 1–5 poorly preserved, with subrectangular basipod; uropods with a stocky basipod carrying very rounded endopod and exopod, both with thin serration of their margins; uropodal exopod with no visible diaeresis.

ORNAMENTATION. Carapace and pleonites and first pereiopod propodus covered with coarse tubercles.

Occurrence

Only known from the type locality. Rosenfeldia triasica is among the oldest polychelidan lobsters discovered, being preceded only by? Coleia uzume Karasawa, Takahashi, Doi & Ishida, 2003 from the Carnian of Japan (Karasawa et al. 2003) and Tetrachela raiblana (Bronn, 1858) from the Carnian of Italy and Austria (Förster 1967).

Comments

Rosenfeldia triasica is known from 39 specimens. Most of these specimens are incompletely preserved, only appendages and pleon are often clearly visible. Among specimens which preserve the carapace, some appear to have a carapace that is longer than wide, such as in the holotype (Fig. 1 A–B), others exhibit a very wide carapace, such as in specimen MFSNgp 40312 (Fig. 1 C–D). As a result, R. triasica was reconstructed as very wide by Garassino et al. (1996: figs 6, 8A–B). Indeed, Garassino et al. probably considered the more abundant wide specimens to be typical. Alternatively, Audo (2016: fig. 3M) and Audo et al. (2017: fig. 3M), based upon the holotype only, represented R. triasica as narrower. Our reinvestigation of all available material leads us to affirm these reconstructions. Indeed, the specimens with an apparently wide carapace are undoubtedly exuvia. Their carapaces are split open (Fig. 1 C–D) and consequently seem superficially wider than they were (see also Audo 2016 for a short discussion of moulting in Polychelida). For this reason, we disagree with the reconstruction of R. triasica with a very wide carapace, proposed by Garassino et al. (1996). On the other hand, reconstructions by Audo (2016) and Audo et al. (2017) represent the carapace with indistinct cervical and postcervical incisions, which are, however, clearly represented by Garassino et al. (1996) and visible on some specimens (Fig. 1 C–D). Clearly, these reconstructions, based only upon the holotype, which does not preserve the lateral margins well, are inaccurate. We therefore propose an emended catalogue of the carapaces of all genera of fossil Polychelida, each based on its type species (Fig. 2), and a new, complete reconstruction of R. triasica (Fig. 3), both based on most of the available specimens. However, it should be noted that grooves on a carapace are rarely preserved, so their shape on the reconstruction is based on available information and comparison with other polychelidans.