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1. Introduction
Alexander Agassiz (1874) created the order Clypeasteroida to include the burrowing flat sea urchins, commonly named sand dollars. These costal worldwide inhabitants have an important fossil record along the Cenozoic, including some important index species (Mooi, 1987). The origin and composition of clypeasteroids has been debated for decades.
Durham (1955) and Seilacher (1979) pointed out that the family Fibulariidae, previously named by Duncan (1889), includes the oldest clypeasteroids; hence, the order Clypeasteroida arose in the Early Cretaceous (Table 1). Contrary, Kier (1962), and later Smith (1984), thought that the late Paleocene genus TogocyamyusOppenheim, 1915, from West Africa, was the first clypeasteroid representative; consequently, this order is entirely restricted to the Cenozoic.
Table 1 Order Clypeasteroida according to different authors, showing inconsistencies between approaches.
| DURHAM (1955) | KROH & SMITH (2010) | SMITH & KROH (2011) |
|---|---|---|
| Suborder Clypeasterina | Stem group Clypeasteroida | Stem group Clypeasteroida |
| Family Clypeasteridae | † Family Faujasiidae, (+ †Stigmatopyginae) | †Family Plesiolampadidae |
| Family Arachnoididae | †Family Plesiolampadidae | †Family Conoclypeidae |
| Suborder Laganina | †Family Conoclypeidae | †Family Oligopygidae |
| Family Fibulariidae | †Family Oligopygidae | Crown group Clypeasteroida |
| Family Laganidae | Crown group Clypeasteroida | Suborder Clypeasterina |
| Suborder Scutellina | Family Clypeasteridae (+ Clypeasterinae; Ammotrophina; Arachnoidinae) | †Family Fossulasterinae(includes †Scutellinoididae) |
| Family Scutellidae | †Family Fossulasterinae(+ †Scutellinoididae) | Suborder Scutellina |
| Family Protoscutellidae | Suborder Scutellina | Stem group Scutellina |
| Family Eoscutellidae | Stem group Scutellina | †Family Scutellinidae |
| Family Dendrasteridae | †Family Scutellinidae | Infraorder Laganiformes |
| Family Echinarachniidae | Infraorder Laganiformes | Family Fibulariidae (includes Echinocyamidae) |
| Family Monophorasteidae | Family Fibulariidae (+ Echinocyamidae) | Family Laganidae (includes Laganinae; †Neolaganinae) |
| Family Mellitidae | Family Laganidae (+ Laganinae; †Neolaganinae) | Infraorder Scutelliformes |
| Family Astriclypeidae | Infraorder Scutelliformes | Family Taiwanasteridae (incertae sedis ) |
| Family Abertillidae | Family Taiwanasteridae (incertae sedis ) | Stem group Scutelliformes |
| Family Scutasteridae | Stem group Scutelliformes | †Family Protoscutellidae |
| Family incertae cedis | †Family Protoscutellidae | Crown group Scutelliformes |
| Suborder Rotulina | Crown group Scutelliformes | Family Echinarachniidae |
| Family Rotulidae | Family Echinarachniidae | †Family Scutellidae |
| Suborder incertae cedis | Family Dendrasteridae | †Family Eoscutellidae |
| Family Rotulidae | †Family Scutasteridae | |
| †Family Scutellidae | Family Dendrasteridae | |
| †Family Eoscutellidae | †Family Abertellidae | |
| †Family Scutasteridae | Family Rotulidae | |
| †Family Abertellidae | Family Astriclypeidae | |
| Family Astriclypeidae | †Family Monophorasteridae | |
| †Family Monophorasteridae | Family Mellitidae | |
| Family Mellitidae |
The paleontological age estimates, based on older fossils for the origin of order Clypeasteroida using molecular clocks (Smith et al., 2006), are 100-105 Ma (Albian, Cretaceous). This statement supports the study of the post-Paleozoic echinoids phylogeny (Kroh and Smith, 2010), which reveals the monophyletic nature of Clypeasteroida, including 4 and 17 taxa as stem and crown families, respectively. Here again, the origin of this order is pulled back to the Cretaceous because the extinct family Faujasiidae, erected by Lambert, 1905 (now involving the family Stigmatopyginae Smith and Wright, 2000), includes Cenomanian representatives (Table 1).
The composition and relationships of the Clypeasteroida have not been fully determined constitute problematic and unfinished tasks. Kroh and Smith (2010) published the most comprehensive phylogenetic study of this group. These authors claimed, although weakly supported, that the Faujasiidae represents a stem family of the order Clypeasteroida. Other less-extensive studies, performed with more restricted scopes, suggest alternative taxonomical compositions of this order, in which the Faujasiidae is excluded (e.g., Durham, 1955; Kier, 1982; Smith, 1984).
Currently, it is desirable to contrast these different ideas about the taxonomical composition of the order Clypeasteroida. However, any effort in that direction goes beyond the aim of this work. Therefore, here the family Faujasiidae is considered part of the order Clypeasteroida as it was concluded by Kroh and Smith (2010).
Cretaceous marine sediments of Mexico bear a potentially important fossil record of clypeasteroids, whose taxonomy must be updated following the latest studies (Wang, 1984; Mooi, 1987; Mooi, 1989; Kroh and Smith, 2010; Smith and Kroh, 2011). Nieto and García (2006) published a brief review of the Mexican echinoids, which was only based in a literature search without the direct review of the available specimens; that study enlists the occurrence of 65 echinoids species in different Cretaceous localities throughout Mexico, 20 regular and 45 irregular echinoids, including the following clypeasteroids: Clypeaster, Encope L. Agassiz, 1840, HaimeaMichelin, 1851 and Astrodapsis.
The aim of this work is to review the Cretaceous fossil record of Clypeasteroida from Mexico based on a careful anatomical review of the specimens deposited in different national or foreign paleon-tological collections, as well as to sort, recover, and update their taxonomic and geologic data.
2. Materials and Methods
2.1. Institutional abbreviations
The fossils of clypeasteroids from the Mexican Cretaceous referred in this study are deposited in different collections, whose abbreviations are the following:
IGM, Instituto Geológico de México (previous name of the Instituto de Geología, UNAM) that houses the Colección Nacional de Paleontología (CNP) in its Museo María del Carmen Perrillat Montoya, Ciudad Universitaria, Mexico City, Mexico.
MNHN, Muséum National d’HistoireNaturelle, Collection des échinodermes fossiles, Paris, France.
USNM-PAL, National Museum of Natural History, Paleotological Collection, Smithsonian Institute, Washington, USA.
2.2. Observed specimens
This work includes the review of specimens belonging to order Clypeasteroida deposited in different collections: Astrodapsis bajasurensis Squires and Demetrion IGM 5926-5932, Clypeaster pileus Israelsky IGM 2553, Clypeaster rogersi (Morton) IGM 2554, Encope grandis subsp. inezana Durham IGM 2825-2827, Encope loretoensis Durham IGM 8150-8151, Encope michoacanensis Durham IGM 7057-7061, Encope perspective Agassiz IGM 7062, Encope shepherdi Durham IGM 2822-2824, Encope tatetlaensis Böse IGM 147-148 and IGM 7154, Haimea bajasurensis Squires and Demetrion IGM 5934-5937, Hardouinia aequorea (Morton) USNM-PAL 464465-464466, 464468, 464470-464473, USNM-PAL, Hardouinina potosiensis Lambert MNHN F.J01116 and Petalobrissus burckhardti Lambert USNM-PAL 108380. One specimen of Hardouinia aequorea from the Regional Collection (CNP, IGM, UNAM) was determined, described, and illustrated. The taxonomical identities of the specimens studied were redetermined using the criteria of Kroh and Smith (2010) and Smith and Kroh (2011).
3. Results
3.1. Paleontological systematics
Class Echinoidea Leske, 1778
Order Clypeasteroida A. Agassiz, 1872
Stem group Clypeasteroida
Family Faujasiidae Lambert, 1905
Subfamily Stigmatopyginae Smith and Wright, 2000
Genus Hardouinia Haime in d’Archiac and Haime, 1853
Synonymous. Hardouinia Haime in d’Arvhiac and Haime, 1853, p. 214. Pomel, 1883, p. 65. Cooke, 1942, p. 6; 1953, p. 19.
EchinanthusDesor, 1858, p. 295.
GonioclypeusEmmons, 1858, p. 309.
AustralanthusBittner, 1892, p. 20. H.L. Clark, 1946, p. 357. Mortensen, 1948, p. 222.
Cassidulus (Hardouinia) Gregory, 1891, p. 436. Procassidulus (Hardouinia) Lambert and Thiéry, 1921, p. 362.
Type species. Pygorhynchus mortonisMichelin, 1851, p. 240 by monotypy (Cooke, 1953).
Stratigraphic range. Upper Cretaceous (Turonian to Maastrichtian, Smith and Kroh, 2011).
Hardouinia aequorea (Morton, 1834)
Synonymous. Cassidulus aequoreusMorton, 1834, p. 76, fig. 3.14.
Type material. Specimen from the ferruginous sand, Prairie Bluff, Alabama, USA, with no cata-log number available, illustrated by Morton (1834, fig. 3.14). Probably deposited in the Philadelphia Academy of Natural Sciences.
Description. Test subpentagonal, elongated. Aboral surface convex, oral surface flat and slightly sunken toward the peristome. Ambulacra narrow and continue toward the peristome. Phyl-lodes surrounding the peristome. Interambulacra wide and covered with small tubercles. Periproct aboral, sunken in a furrow, covering one third of the posterior diameter. Peristome pentagonal, sur-rounded by a floscele.
Examined material. USNM-PAL 464465, 464466, 464471 and 464472, from the Upper Cretaceous (Maastrichtian) sediments of Prairie Bluff Chalk, Alabama, USA. USNM-PAL 464468, 464470 and 464473, from Upper Cretaceous (Maastrichtian), Prairie Bluff Chalk, Mississippi, USA.
Distribution. Cárdenas Formation, San Luis Potosí, Mexico. Lagunar system, with low energy and storm deposits (Sánchez-Rodríguez, 1997). It has been reported in Navesink Marl, Group Monmouth, New Jersey and Ripley Formation (Upper Cretaceous), Alabama, USA (Sánchez-Rodríguez, 1997).
Hardouinina aequorea (Morton, 1834) IGM 6259
Figure 1 Hardouinia aequorea IGM 6259. Length: 52.18 mm; height: 22.06 mm; width: 42.41 mm. Late Cretaceous. Cárdenas, San Luis Potosí (21°38’22’’ N, 99°38’22’’ W). Collected by Ralph L. Myers, 1966. A. Aboral view, B. Oral view, C. Petaloid ambulacra, D. Posterior view, E. Lateral view (right), F. Phyllodes.
Table 2 Morphometric data (mm) of Hardouinia aequorea IGM 6259.
| Length | Width | Height | |
|---|---|---|---|
| Test | 52.2 | 22.1 | 42.4 |
| Ambulacrum I | 18.2 | 5.6 | * |
| Ambulacrum II | 17.2 | 7.1 | * |
| Ambulacrum III | 20.6 | 5.3 | * |
| Periproct | 7.7 | 3.0 | * |
Description. Aboral surface rounded. Apical system monobasal, slightly anterior, concurring with the apex; with four genital pores, G3 towards the front. Petaloid ambulacra with similar length; ambulacra III close to ambitus. Petaloids with internal pores elliptical and external pores slit-shaped, connected by a slightly shallow channel. Ambulacra with outer pore elongated transversely; no visible pores beyond ambulacra. Periproct aboral, visible from the top, almost reaching the ambitus; triangular, elongated vertically, sunken in a furrow. Oral surface slightly sunken longitudinally. Peristome slightly anterior, pentagonal, surrounded by a floscele. Bourrelets tooth-like, projecting into and over the peristome. Phyllodes, wide, single pored; the inner series straight, with rounded small pores; the outer series arranged in a broad arc, with elliptical pores.
Observations. Hardouinia aequorea differs from Australanthus and Petalobrissus by having flat test and elongated ambulacra. It also diverges from Hardouinia potosiensis in the position of the periproct. In H. potosiensis the petaloids do not reach the periproct, contrary to the posterior petaloids in H. aequorea. The holotype has a subconical test, but without specimens to compare, this could be either a regular shape or the result of the fossilization process. Locality. IGM-locality 956. Cárdenas, San Luis Potosí (21°38’22’’N, 99°38’22’’W); Upper Cretaceous, Campanian-Maastrichtian (Ferrusquía-Villafranca et al., 2016). Collected by Ralph L. Myers, 1966.
Hardouinina potosiensisLambert, 1936
Figure 2 Upper Cretaceous Faujasiidae from Mexico. Hardouinia aequorea (Morton, 1834); USNM-PAL 464465. A. Aboral view, B. Oral view, C. Lateral view (left), D. Posterior view. Hardouinina potosiensis Lambert, 1936 (Holotype MNHN F.J01116, Credits MNHN, 2017). E. Aboral view, F. Oral view, G. Posterior view. Petalobrissus burckhardtiLambert, 1936 (USNM-PAL108380). H. Aboral view, I. Oral view, J. Lateral view (left), K. Posterior view.
Type species. Echinobrisus setifensisCotteau, 1866, p. 151 by original designation (Kier, 1962). Stratigraphic range. Upper Cretaceous (Turonian to Maastrichtian, Smith and Kroh, 2011).
Type material. Holotype MNHN L.19.773. Coniacian (Upper Cretaceous) sediments of the Cárdenas Formation, San Luis Potosí, Mexico (Lambert, 1936, pp. 5-6, figs. 1.2-1.4)
Description. Test large, oval, rounded at the anterior rear, slightly elongated. Aboral surface subconic. Apical system anterior, with four genital pores. Petaloid ambulacra, narrow, short, lanceo-late and distally closed; posterior ambulacra not reaching the periproct. Periproct elongated and pointy. Oral surface slightly concave towards sub-central peristome. Oral area with bourrelets and phylodes.
Examined material. Holotype MNHN F.J01116. Cárdenas Formation, San Luis Potosí, Mexico. Upper Cretaceous, Campanian-Maas-trichtian (Ferrusquía-Villafranca et al., 2016).
Distribution. Cárdenas Formation, San Luis Potosí, Mexico. (Lambert, 1936; Myers, 1968).
Genus PetalobrissusLambert and Thiéry, 1921
Petalobrissus burckhardtiLambert, 1936
Synonymous. Phyllobrissus cubensisCooke, 1953, p. 17, figs. 17.11-17.14.
Type material. Holotype MNHN L.19.775. Cretaceous, Ocozocuautla, Chiapas, Mexico.
Description. Test oval, slightly wider at the posterior rear. Aboral surface slightly inflated. Oral surface flat, slightly concave at the peristome. Pet-aloid ambulacra short, reaching half the distance between the apical system and the ambitus. Apical system anterior, with four genital pores and a central large madreporite (Cooke, 1953).
Examined material. Phyllobrissus cubensis USNM-PAL 108380. Ocozocuautla, Chiapas, Mexico. Cretaceous, Senonian.
Distribution. Ocozocuautla, Chiapas (Cooke, 1953). Cretaceous, Upper Senonian (Kier and Lawson, 1978).
4. Discussion
Families Faujasiidae, Echinarachniidae, Clypeasteridae, and Mellitidae are wrongly included in the most recent revision on Cretaceous Echinoids in Mexico (Nieto and García, 2006). The specimens exist in the referred collection, but do not correspond to Cretaceous localities (Table 3).
Table 3 Species of clypeasteroids reported in the most recent revision of Cretaceous echinoids in Mexico (Nieto and García, 2006). *Species present in the National Collection of Paleontology (IGM).
| Family | Species |
|---|---|
| Clypeasteridae | |
| Clypeaster pileus Israelsky, 1924* | |
| Clypeaster rogersi Morton, 1834* | |
| Echinarachniidae | |
| Astrodapsis bajasurensis Squires and Demetrion, 1993* | |
| Haimea bajasurensis Squires and Demetrion, 1994* | |
| Faujasiidae | |
| Hardouinia potosiensis Lambert, 1936 | |
| Mellitidae | |
| Encope grandis subsp. inezana Durham, 1950* | |
| Encope loretoensis Durham, 1950* | |
| Encope michoacanensis Durham, 1994* | |
| Encope perspectiva L. Agassiz, 1841* | |
| Encope shepherdi Durham, 1950* | |
| Encope tatetlaensis Böse, 1906* |
Genus Astrodapsis is included in family Echinarach-niidae, and genera Clypeaster and Encope in family Mellitidae. Both families are classified in the crown group of infraorder Scutelliformes Haeckel, 1896. Family Echinarachniidae has been reported from the middle Eocene to present, with recent species reported in North Pacific (from Japan to California, USA) (Kroh and Smith, 2010; Smith and Kroh, 2011). Family Mellitidae originated during early Miocene (Kroh and Smith, 2010) and includes recent species reported in Central and South America and the Caribbean Sea (Smith and Kroh, 2011).
Durham (1994) described Encope michoacanensis using invalid catalog numbers from the National Paleontological Collection (IGM). We include the catalog numbers used in the original references and the corrected catalog numbers used in the National Paleontological Collection (Table 4).
Table 4 Data of the clypeasteroids reported in Nieto and García, 2006 with amendments in catalog numbers. NA: Information not Available.
| Catalog | Family | Species | Formation | Locality | Age | Type | Invalid num. |
|---|---|---|---|---|---|---|---|
| IGM 2553 | Clypeasteridae | Clypeaster pileusIsraelsky, 1924 | NA | La Catalina Mine, Simojovel, Chiapas, Mexico. | Oligocene | ||
| IGM 2554 | Clypeasteridae | Clypeaster rogersi (Morton, 1834) | NA | Teapa River, Ixtapangajoyac, Chiapas, Mexico. | Oligocene | ||
| IGM 5926 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Holotype | |
| IGM 5927 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5928 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5929 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5930 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5931 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5932 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5933 | Echinarachniidae | Astrodapsis bajasurensisSquires and Demetrion, 1993 | Isidro | Near San Juanico, Baja California Sur, Mexico. | Middle Miocene | Paratype | |
| IGM 5934 | Echinarachniidae | Haimea bajasurensisSquires and Demetrion, 1994 | Tepetate | La Paz, Baja California Sur, Mexico | Lower Eocene | Holotype | |
| IGM 5935 | Echinarachniidae | Haimea bajasurensisSquires and Demetrion, 1994 | Tepetate | La Paz, Baja California Sur, Mexico. | Lower Eocene | Paratype | |
| IGM 5936 | Echinarachniidae | Haimea bajasurensisSquires and Demetrion, 1994 | Tepetate | La Paz, Baja California Sur, Mexico. | Lower Eocene | Paratype | |
| IGM 5937 | Echinarachniidae | Haimea bajasurensisSquires and Demetrion, 1994 | Tepetate | La Paz, Baja California Sur, Mexico. | Lower Eocene | Paratype | |
| IGM 2822 | Mellitidae | Encope grandis inezanaDurham, 1950 | NA | Santa Ines Bay, Mulegé, Baja California Sur, Mexico. | Pleistocene | Paratype | |
| IGM 2823 | Mellitidae | Encope grandis inezanaDurham, 1950 | NA | Santa Ines Bay, Mulegé, Baja California Sur, Mexico. | Pleistocene | Paratype | |
| IGM 2824 | Mellitidae | Encope grandis inezanaDurham, 1950 | NA | Santa Ines Bay, Mulegé, Baja California Sur, Mexico. | Pleistocene | Paratype | |
| IGM 8150 | Mellitidae | Encope loretoensisDurham, 1950 | Salada | Los Cabos, Baja California Sur, Mexico. | Upper Pliocene | Paratype | |
| IGM 8151 | Mellitidae | Encope loretoensisDurham, 1950 | Salada | Los Cabos, Baja California Sur, Mexico. | Upper Pliocene | Paratype | |
| IGM 7057 | Mellitidae | Encope michoacanensisDurham, 1994 | Ferrotepec | Near La Mira, Michoacán, Mexico | Lower Miocene | Holotype | IGM 2939 |
| IGM 7058 | Mellitidae | Encope michoacanensisDurham, 1994 | Ferrotepec | Near La Mira, Michoacán, Mexico | Lower Miocene | Paratype | IGM 2940 |
| IGM 7059 | Mellitidae | Encope michoacanensisDurham, 1994 | Ferrotepec | Near La Mira, Michoacán, Mexico | Lower Miocene | Paratype | IGM 2941 |
| IGM 7060 | Mellitidae | Encope michoacanensisDurham, 1994 | Ferrotepec | Near La Mira, Michoacán, Mexico | Lower Miocene | Paratype | IGM 2942 |
| IGM 7062 | Mellitidae | Encope michoacanensisDurham, 1994 | Ferrotepec | Near La Mira, Michoacán, Mexico | Lower Miocene | Paratype | IGM 2943 |
| IGM 7061 | Mellitidae | Encope perspectivaAgassiz, 1841 | NA | Santa Cruz, Santa María Huatulco, Oaxaca, Mexico. | Pliocene- Pleistocene | IGM 2944 | |
| IGM 2822 | Mellitidae | Encope shepherdiDurham, 1950 | Marquer | Marquer Bay, Carmen Island, Baja California Sur, Mexico. | Upper Pliocene | Paratype | |
| IGM 2823 | Mellitidae | Encope shepherdiDurham, 1950 | Marquer | Marquer Bay, Carmen Island, Baja California Sur, Mexico. | Upper Pliocene | Paratype | |
| IGM 2824 | Mellitidae | Encope shepherdiDurham, 1950 | Marquer | Marquer Bay, Carmen Island, Baja California Sur, Mexico. | Upper Pliocene | Paratype | |
| IGM 147 | Mellitidae | Encope tatetlaensisBöse, 1906 | NA | Santa María Tatetla, Veracruz, Mexico | Pliocene | Sintype | |
| IGM 148 | Mellitidae | Encope tatetlaensisBöse, 1906 | NA | Santa María Tatetla, Veracruz, Mexico | Pliocene | Sintype | |
| IGM 5174 | Mellitidae | Encope tatetlaensisBöse, 1906 | NA | Santa María Tatetla, Veracruz, Mexico | Pliocene | Sintype |
5. Conclusions
We report three species of clypeasteroids for the Cretaceous in Mexico: Hardouinia aequorea, Hard-ouinia potosiensis, and Phyllobrissus burckhardti. These species are classified in the family Faujasiidae, part of the stem group of clypeasteroids, with origin in the Campanian (Cretaceous). The records of families Echinarachniidae and Mellitidae (Nieto and García, 2006) are incorrect. These results support the phylogenetic hypothesis on the origin of the order Clypeasteroida proposed by Kroh and Smith (2010).
The correct revision and tracing of the taxonomic information in the paleontological collections allows us to correct catalog numbers of the National Paleontological Collection (IGM) assigned wrongly and published by Durham (1994).
Continuous reviews of the data deposited in biological and paleontological collections are needed in order to study and propose a robust phylogenetic hypothesis for the family Faujasiidae and to update and amend taxonomic information to eliminate mistakes.
