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PeerJ
2019 Jan 01;7:e7361. doi: 10.7717/peerj.7361.
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Echinoids from the Tesero Member (Werfen Formation) of the Dolomites (Italy): implications for extinction and survival of echinoids in the aftermath of the end-Permian mass extinction.
Thompson JR
,
Posenato R
,
Bottjer DJ
,
Petsios E
.
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The end-Permian mass extinction (∼252 Ma) was responsible for high rates of extinction and evolutionary bottlenecks in a number of animal groups. Echinoids, or sea urchins, were no exception, and the Permian to Triassic represents one of the most significant intervals of time in their macroevolutionary history. The extinction event was responsible for significant turnover, with the Permian-Triassic representing the transition from stem group echinoid-dominated faunas in the Palaeozoic to Mesozoic faunas dominated by crown group echinoids. This turnover is well-known, however, the environmental and taxonomic distribution of echinoids during the latest Permian and Early Triassic is not. Here we report on an echinoid fauna from the Tesero Member, Werfen Formation (latest Permian to Early Triassic) of the Dolomites (northern Italy). The fauna is largely known from disarticulated ossicles, but consists of both stem group taxa, and a new species of crown group echinoid, Eotiaris teseroensis n. sp. That these stem group echinoids were present in the Tesero Member indicates that stem group echinoids did not go extinct in the Dolomites coincident with the onset of extinction, further supporting other recent work indicating that stem group echinoids survived the end-Permian extinction. Furthermore, the presence of Eotiaris across a number of differing palaeoenvironments in the Early Triassic may have had implications for the survival of cidaroid echinoids during the extinction event.
Figure 1. Geographic position of the Tesero section within (A) Italy and within (B) the Fiemme Valley, Trento Province.
Figure 2. Stratigraphic column of the Tesero succession containing the formational and (supposed) erathem boundaries and the stratigraphic ranges of conodonts and brachiopods.The duration of the extinction interval is from Posenato (2010); the extinction peak (EP) refers to the extinction of the lagenide foraminifers at a confidence interval of 96% (from Groves et al., 2007). The echinoids studied herein were collected from beds CNT6 to CNT11A. Abbreviations: Orthothet., Orthothetina; Comelic., Comelicania; Hi., Hindeodus (modified from Posenato, 2009).
Figure 3. Photos of specimen MPL 8651-1 of Eotiaris teseroensis.Photos of specimen MPL 8651-1 of Eotiaris teseroensis. (A-D) show the same specimen, with different angles and amounts of lighting. Note the crenulate tubercles, and confluence of areoles. The specimen in (D) has been coated with ammonium chloride prior to photography. Photo credit for A-C to Jeffrey Thompson and D to Renato Posenato.
Figure 4. Plates and lantern elements attributed to Eotiaris teseroensis or indeterminate.(A) Specimen MPL 8651-2, a disarticulated hemipyramid. Note the shallow foramen magnum indicated with arrow. (B) Specimen MPL 8652, disarticulated spine from E. teseroensis. (C) Specimen MPL 8659, disarticulated spine from E. teseroensis. Photo credit to Jeffrey Thompson.
Figure 5. Disarticulated echinoid interambulacral plates and spines from the Tesero Member of the Werfen Formation.Interambulacral plates (A–D) and spines with distinct milled ring (E–L) are attributed to Eotiaris teseroensis, while spine fragments (M–R) are indeterminate. (A) Specimen MPL 8653-1, disarticulated interambulacral plate. (B) Specimen MPL 8656-2, fragmentary interambulacral plate from sample. (C) Specimen MPL 8656-1, fragmentary interambulacral plate; note non-confluent areole. (D) Specimen MPL 8657-5, interambulacral plate; note crenulate tubercle. (E) specimen MPL 8654-2, fragmentary spine; note prominent milled ring. (F) Specimen MPL 8655-1, spine; small spinules on distal tip of spine. (G) Specimen MPL 8653-5, fragmentary spine. (H) Specimen MPL 8653-3, incomplete spine; note small spinules along spine shaft. (I) Specimen MPL 8657-4, spine base and proximal shaft. (J) Specimen MPL 8657-3, spine. (K) Specimen MPL 8658-5, spine base and proximal spine. (L) Specimen MPL 8657-6, spine; note slightly fusiform morphology of spine. (M) Specimen MPL 8657-2, spine fragment. (N) Specimen MPL 8654-3, spine fragment. (O) Specimen MPL 8658-4, spine fragment. (P) Specimen MPL 8653-4, spine fragment. (Q) Specimen MPL 8658-2, spine fragment. (R) Specimen MPL 8658-7, spine fragment. All scale bars one mm. Photo credit to Jeffrey Thompson.
Figure 6. Disarticulated echinoid Aristotle’s lantern elements and spines from the Tesero Member of the Werfen Formation.Lantern elements are indeterminate (A–G), while spines are attributed to stem group echinoids (H–L). (A) Specimen MPL 8654-1, disarticulated rotula from sample TCn 10. (B) Specimen MPL 8657-8, disarticulated rotula from sample CNT11A . (C) Same as B. (D) Specimen MPL 8658-1, disarticulated rotula from sample CNT6. (E) Same as D. (F) Specimen MPL 8658-8 disarticulated hemipyramid from sample CNT6. (G) Specimen MPL 8657-1, disarticulated hemipyramid from sample CN T11A. (H) Specimen MPL 8653-2, disarticulated spine. (I) Specimen 8657-7. (J) Specimen MPL 8658-6, disarticulated spine from sample CNT6. (K) Specimen MPL 8655-2, disarticulated spine. (L) Specimen MPL 8658-3, disarticulated spine from sample CNT6. In spines attributed to stem group echinoids (H-L) note lack of milled ring and rounded, smooth acetabulum. All scale bars 1 mm. Photo credit to Jeffrey Thompson.
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