Class Echinoidea Leske, 1778

Subclass Cidaroidea Smith, 1984

Family Miocidaridae, Durham and Melville, 1957

Type genus—Miocidaris Döderlein, 1887

Other genera—Eotiaris Lambert, 1900, Couvelardicidaris Vadet, 1991, Procidaris Pomel, 1883

Genus Eotiaris Lambert, 1899

Type species—Cidaris keyserlingi Geinitz, 1848, from the Wuchiapingian Zechstein of Germany and England.

Diagnosis—Miocidarid with small test. Interambulacral plates imbricate adapically. Areoles confluent only at and below ambitus. Spines with spinules, clavate to bulbous.

Occurrence—Upper Permian of Germany, the U.K. and now Guadalupian of Texas, USA.

Remarks—The name Eotiaris is used instead of Miocidaris as the type material of the type species of Miocidaris is indeterminate. The name Miocidaris was first used by Döderlein25 who failed to explicitly name a type species for the genus. Bather26 then designated Cidaris klipsteini Desor, 1855 as the type species, renaming it Miocidaris cassiani since it was preoccupied by C. klipsteini Agassiz & Desor, 1847. M. cassiani, itself, however, is a junior objective synonym of C. ampla Desor, 1858, a name proposed by Desor in the Addendum to his synopsis when he realized that his C. klipsteini was preoccupied27. Bather’s lectotype26 consists of just fragmentary interambulacral plates28, which are indeterminate at the generic level and are best left restricted to the type material. Geinitz29 and King30 described the taxa Cidaris keyserlingi Geinitz and Cidaris verneuiliana King from the Wuchiapingian of the UK and Germany. King31 then placed Cidaris verneuiliana into Archaeocidaris, however this taxon does not have the four interambulacral columns that characterize Archaeocidaris. Desor32 furthermore placed Cidaris keyserlingi into Eocidaris however, this genus is strictly indeterminate, being based solely off of disarticulated interambulacral plates. Lambert then proposed the name Eotiaris keyserlingi for the material described by Geinitz. We follow Bather26 and Smith and Hollingworth19 in synonymizing Cidaris keyserlingi Geinitz and Cidaris verneuiliana King. Because the type of Miocidaris, however, is indeterminate, the genus should only be restricted to the type species, Miocidaris ampla (Desor) from the Carnian St. Cassian beds. Lambert’s name Eotiaris is thus the oldest available name for the material described by Geinitz and King and is used herein.

Eotiaris guadalupensis Thompson n. sp.

1959 Spine Kier 1958a p. 889 Plate 114 Fig. 3.

1965 Miocidaris sp. Kier 1965 p. 456.

Type—Holotype is USNM 610600, paratypes are USNM 610601-610605.

Diagnosis—Eotiaris with straight, clavate and bulbous spines covered in numerous spinules arranged helically around the shaft.

Derivation of name—guadalupensis from the Guadalupe Mountains of west Texas, from where the type material was collected.

Description—Test regular and small, known only from disarticulated interambulacral columns. Columns range in width from 4.2 mm to 9.3 mm (Fig. 1A,B,D,E,G). Modern cidaroids have an interambulacral ambital width about 45% of their test diameter19, thus estimated E. guadalupensis test diameters about 9.4 mm to 20.6 mm. Apical system unknown and adapical interambulacral plates are not preserved articulated to the interambulacral columns of the test. Adapical interambulacral plates likely imbricate whereas ambital and adoral interambulacral plates rigidly sutured (Fig. 1E). Peristomial plates unknown, however apophyses are present on most oral interambulacral plates (Fig. 1G,H). No buccal notches present.

Figure 1 Eotiaris guadalupensis n. sp. (A) Paratype USNM 610604. Interambulacral area fragment first mentioned in Kier24 from Roadian of the Glass mountains. Note two column interambulacral area structure indicative of crown group echinoids. (B) Holotype USNM 610600. Interambulacral area fragment and associated spine. Note crenulate tubercles. (C) USNM 610605a. displaying clavate, bulbous spine morphology. (D) Paratype USNM 610604. Internal view of interambulacral fragment showing apophyses at adoral end. (E) Paratype USNM 610601. Interambulacral fragment of larger specimen. Note at least six plates in ambulacral columns and crenulate tubercles with sunken areoles. Plates rigid at least below adapical plates. (F) Paratype USNM 610605b. Spine displaying less clavate morphotype and spinules. (G) Internal view of interambulacral area of paratype USNM 610602. Note apophyses, which identify this species as a cidaroid and denticulate adambulacral plate margin indicative of beveling. (H) Close up of apophyses of USNM 610602. All scale bars represent 2.5 mm. Full size image

Lantern and teeth unknown. Ambulacra unknown, although likely beveling under interambulacral plates as interior adradial interambulacral plate edges are denticulate.

Interambulacral plating arranged into two rows. First four to six plates usually rigidly sutured with more adapical plates disarticulated (Fig. 1D,E). Plates pentagonal, about 1.3 to 1.6 times as wide as high. Primary tubercles large, sunken and confluent below ambitus (Fig. 1A,E). Areoles at ambitus on specimen USNM 610601 about 2.6 mm wide and 2.6 mm high. Boss crenulate with mamellons undercut and perforate. At ambitus, one row of secondary tubercles on each plate separates tubercles. Above ambitus, multiple rows of secondary tubercles separate ambitus on large specimens. On large specimens, about four rows of secondary tubercles between the edge of each tubercle and the perradial suture at ambitus (Fig. 1E). About three rows of secondary tubercles between primary tubercles and adradial suture at ambitus. Adorally, this is reduced to two rows and eventually one row on the most adoral plates. On smaller specimens, the number of secondary tubercles arranged laterally to the primary tubercles are reduced to one. Interior of interambulacral plates slightly concave with seven or eight denticles per plate at ambitus.

Spines ranging in morphology from straight (Fig. 1F) to clavate to bulbous (Fig. 1C). Proximal fourth to third of spine shaft smooth, ending in diagonally oriented ridge, which contains the first row of spinules. Spinules oriented diagonally, along this raised ridge with more distal rows parallel to first row. Spine morphology variable, with some maintaining constant width and others tapering distally. Others ending in large clavate bulb covered in spinules. It is likely that spines varied aborally to orally, as is present in some archaeocidarids22 and recent cidaroids such as Eucidaris clavata33. Although this variability exists, all spines of differing morphologies contain diagonally oriented ridge bearing first row of spinules. Acetabulum of spine bearing perforation and faint crenulations. A single non-clavate spine is found associated with an interambulacral fragment which is 5.0 mm in length (Fig. 1B). The interambulacral fragment is 7.6 mm wide indicating a probable test diameter of 16.8 mm. This would indicate that the spines were likely less wide than the diameter of the test. Spines have a prominent milled ring proximally. Bulbous spines hollow distally in bulb and non-bulbous spines hollow distally. Secondary spines and pedicellariae unknown.

Remarks—This taxon has been mentioned previously by Kier23,24 from the Roadian and Wordian of west Texas, albeit as a single disarticulated interambulacral area and as misidentified cidarid secondary spines respectively. The inclusion of more material and the association of the spines with the test of this species allow for a more thorough description herein. All new specimens of this taxon are known from the Lamar Member of the Bell Canyon Formation from the Guadalupe Mountains of west Texas, however, previously described specimens, now assigned to this taxon, indicate its stratigraphic range expands into the Roadian. The spines of this taxon are known from the Word Formation23 of the Glass Mountains, however, they were originally incorrectly described as secondary spines of a larger cidarid. These spines were collected from in between the Willis Ranch and Appel Ranch members of the Word Formation, which are lower Wordian in age34. Furthermore, Kier24 attributed a specimen from the Road Canyon Formation of the Glass Mountains to Miocidaris sp. This specimen (Figs 1A and 2D) is herein assigned to Eotiaris guadalupensis. This extends the stratigraphic range of this taxon into the Roadian, as the Road Canyon Formation is Roadian to Kungurian in age34,36,37. All of the material described herein has been silicified.

Figure 2 New divergence date of the divergence of cidaroid and euechinoid clades based on the Roadian occurrence of Eotiaris guadalupensis n. sp. Thick lines represent fossil range and thin lines represent inferred range based on phylogenetic relationships. The establishment of E. guadalupensis as the oldest known cidaroid in the fossil record also extends the inferred range of euechinoids, as the oldest known euechinoids, Diademopsis herberti, and Hemipedina hudsoni are first found in the fossil record in the Norian, 40 Ma years later. Phylogenetic relationships are from Kroh and Smith1 and Kroh35 modified with information regarding phylogenetic placement of E. guadalupensis from Supplementary Figure S2. Full size image

Morphologically, E. guadalupensis is very similar to Eotiaris keyserlingi from the Zechstein of the UK and Germany, differing significantly only in the morphology of its spines. Both bear rigidly sutured tests with plate imbrication adapically, sunken tubercles with multiple rows of scrobicular tubercles and crenulate and perforate tubercles. The spines of E. keyserlingi, which are well known19, are smooth and have much smaller spinules than those of E. guadalupensis19. They lack the clavate spine morphotype of E. guadalupensis and are much shorter. E guadalupensis also differs significantly from E. connorsi24. The test of E. connorsi is composed entirely of imbricate, non-rigid plates, while the tests of E. guadalupensis and E. keyserlingi are rigid except for adapically. The interambulacral plates in E. connorsi are also much wider and do not display densely packed scrobicular tubercles, as is the case in E. guadalupensis or E. keyserlingi.

Occurrence—Specimens are known from the Lamar Member of the Bell Canyon Formation of the Guadalupe Mountains and the Road Canyon Formation and Word Formations of the Glass Mountains of west Texas. They are thus Roadian-Capitanian in age.

Localities are USNM 725e, 728p and 738b from Cooper & Grant38 see supplementary information.