Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

First record of Ubaghsicystis (Eocrinoidea - Echinodermata) from the

Cambrian (Miaolingian, Wuliuan) of Sonora, Mexico:

Biostratigraphical and paleoecological considerations

Blanca Estela Buitrón Sánchez

Francisco Javier Cuen-Romero

Matilde Sylvia Beresi

Rogelio Monreal

1. Departamento de Paleontología, Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad

Universitaria, México; blancab@unam.mx

2. Departamento de Geología, Universidad de Sonora, Blvd. Luis Encinas y Rosales, Hermosillo, Sonora, México;

francisco.cuen@ciencias.uson.mx (*Correspondence).

3. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Consejo Nacional de Investigaciones

Científicas y Tecnológicas, Av. A. Ruiz Leal s/n, Parque General San Martín, Mendoza, Argentina;

mberesi@mendoza-conicet.gob.ar

Received 25-V-2020. Corrected 07-IX-2020. Accepted 15-IX-2020.

ABSTRACT

Introduction: The present work constitutes the first record of Ubaghsicystis Gil-Cid & Domínguez-Alonso

(Echinodermata-Eocrinoidea) in the El Gavilán Formation, exposed in the El Sahuaral Hill, a new Cambrian

locality of central Sonora, Mexico. The El Gavilán Formation is a sedimentary sequence mainly made up of

shale interbedded with limestone, with abundant invertebrate fossils, deposited in an open shelf marine environ-

ment. Objective: The main objective of this research work is to describe the species Ubaghsicystis cf. U. segu-

rae for the first time in Mexico, in addition to biostratigraphic and paleoecological considerations. Methods:

A composite stratigraphic section of the El Gavilán Fm. was measured in central Sonora, where samples corre-

sponding to eocrinods were collected, the material was examined in the Microscope Leica MZ10. Results: The

biotic association is composed of reticulosan sponges, chancelloriids (Chancelloria eros, Allonnia tintinopsis,

Archiasterella sp.), hyolithids, brachiopods, trilobites (Quadragnostus depressa, Peronopsis sp., Tonkinella

valida, and Elrathina sp.), and echinoderms (Ubaghsicystis cf. U. segurae). Regarding the age, the trilobite asso-

ciation establishes a chronostratigraphic position from the middle Cambrian (Miaolingian, Wuliuan), Altiocculus

Subzone, Ehmaniella Zone. The material studied is constituted by isolated echinoderm plates, which probably

represent various cycles of theca plates assigned to Ubaghsicystis cf. U. segurae. The genus Ubaghsicystis has

been scarcely recorded in a few Cambrian regions (e.g., Burgess Shale in Canada and Los Barrios de Luna in

Spain), so that the information about this taxon is limited. Conclusions: The Cambrian succession of Sonora,

where Ubaghsicystis occurred, was part of the border from the Laurentia craton during this period, located near

the Paleoequator during this period, where ideal conditions for increasing diversity and abundance of species

were developed, including echinoderms.

Key words: Eocrinoidea; Cambrian; biostratigraphy; paleoecology; Mexico.

Buitrón Sánchez, B.E., Cuen-Romero, F.J., Beresi,

M.S., & Monreal, R. (2021). First record of

Ubaghsicystis (Eocrinoidea - Echinodermata) from

the Cambrian (Miaolingian, Wuliuan) of Sonora,

Mexico: Biostratigraphical and paleoecological

considerations. Revista de Biología Tropical, 69(S1),

51-61. DOI 10.15517/rbt.v69iSuppl.1.46326

DOI 10.15517/rbt.v69iSuppl.1.46326

Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

Cambrian sedimentary rocks in Mexico

are characterized by being exposed in scarce

and isolated outcrops, but having a relatively

well-preserved biota, which has been studied

since the middle of the last century (Buitrón,

1992). The Cambrian in Sonora is exposed

in various isolated locations: Caborca, Cana-

nea, San José de Gracia, Mazatán, and Arive-

chi. These areas have been studied by several

authors (Lochman, 1948; Cooper et al., 1952;

Cooper et al., 1956; Stewart, McMenamin, &

Morales-Ramirez, 1984; González-León, 1986;

McMenamin, 1987; Almazán-Vázquez, 1989;

Vega-Granillo, 1996; Cuen-Romero et al., 2016;

Cuen-Romero et al., 2018; Cuen-Romero et al.,

2019; Beresi, Buitrón-Sánchez, Cuen-Romero,

& Palafox, 2019). The recent discovery of

Cambrian outcrops in central Sonora has been

the subject of several stratigraphic and paleon-

tological studies (Nardin, Almazán-Vázquez,

& Buitrón-Sánchez, 2009; Cuen et al., 2013;

Buitrón-Sánchez, Corona-González, Cuen-

Romero, Palafox-Reyes, & Ramírez-Guerrero,

2016; Buitrón-Sánchez, Cuen-Romero, Huerta-

Ruiz, & Montijo-González, 2017a; Buitrón-

Sánchez, Cuen-Romero, Montijo-González, &

Beresi, 2017b; Cuen-Romero et al., 2016; Cuen-

Romero et al., 2019). This research work was

carried out in a new Cambrian locality in the

central part of the state of Sonora, El Sahuaral

Hill, which has been scarcely studied but has an

abundant fossil biota. The first geologic work

of the Sahuaral Hill was carried out by Stewart,

Amaya-Martínez and Palmer (2002), who men-

tioned the presence of Cambrian rocks in the

area. Danzos-Acuña (2018) and Noriega-Ruiz

(2019), carried out a detailed biostratigraphic

study of the rocks in the region. However, the

first formal work carried out in the area is that by

Beresi et al. (2019), who documented the pres-

ence of reticulosan sponges and chancellorids.

Recently, Noriega-Ruiz et al (2019; 2020), car-

ried out a detailed stratigraphic study of the area.

The presence of echinoderms in Mexican

Cambrian rocks is scarce, with few isolated

elements documented for the country. Nardin et

al. (2009) reported isolated plates attributed to

the species Gogia granulosa, in the Cambrian

section of San José de Gracia, Sonora, Mexico.

Similarly, Buitrón-Sánchez et al. (2017b) stud-

ied to Gogia granulosa and Gogia sp. from the

same area, documenting the paleoecological

implications of these species as they are asso-

ciated with limestone, shale, and sandstone

strata, thus, showing great adaptability to dif-

ferent environments.

Regarding eocrinoids, Sprinkle (1973)

proposed the new subphylum Blastozoa

divided into four classes of extinct Paleo-

zoic “pelmatozoan” echinoderms: Eocrinoidea,

Paranlastoidea, Rhombifera, and Blastoidea.

Echinoderms of the subphylum Blastozoa are

characterized by a group often composed of

stalked echinoderms, lacking free arms but

with biserial brachioles with nutritional func-

tions, and with the presence of various respira-

tory structures in the theca. The main objective

of this research work is to describe the species

Ubaghsicystis cf. U segurae for the first time

for Mexico, in addition to biostratigraphic and

paleoecological considerations.

MATERIAL AND METHODS

A composite stratigraphic section of El

Gavilán Formation was measured at the south-

west flank of El Sahuaral Hill. Samples were

collected corresponding to carbonate and detri-

tal rocks. The paleontological material was

prepared in the Paleontology Laboratory at the

University of Sonora. Due to the conservation

of specimens, they do not show contrast when

dry, so the samples were wetted. The material

was photographed using a Nikon Camera D70S

and manipulated with Adobe Photoshop

Location of the study area: The pale-

ontological material studied comes from El

Sahuaral Hill, it is located 44 km northeast

of Hermosillo at geographical coordinates

29°21’5.58” N & 110°37’13.98” W, located 7

km north of the village of San José de Gracia,

in the central part of the Sonora state (Fig. 1).

Stratigraphy: Although in the study area,

exposed rocks vary in age from Precambrian to

Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

Holocene, the Cambrian rocks are best exposed,

and consists of the Proveedora, Buelna, Cerro

Prieto, and El Gavilán formations (Fig. 2).

Proveedora Formation: This formation

is composed of fine-grained quartzite, with

reddish spots due to oxidation, followed by

brown to dark gray quartzarenite with the pres-

ence of Skolithos isp. This unit is 216 m thick

and is exposed in most of the El Sahuaral Hill

(Noriega-Ruiz et al., 2020).

Buelna Formation: This formation is made

up of sandy limestone with fragments of hyo-

lithids, followed by limestone with oncolytic

algae, ending with dark-colored sandy lime-

stone. In the middle part of the unit, an oolitic

limestone bed is present. This unit is exposed

at the southwest side of the El Sahuaral Hill

with 64 m thickness. The lower and upper con-

tacts are conformable with the Proveedora and

Cerro Prieto formations, respectively (Noriega-

Ruiz et al., 2020).

Cerro Prieto Formation: This formation

consists of a cliff-forming dark gray oolitic

limestone with evidence of some dolomitiza-

tion. It is 53 m thick, being exposed to the

southeast side of El Sahuaral Hill. The lower

contact is conformable with the Buelna For-

mation, and the upper contact is conformable

with the El Gavilán Formation (Noriega-Ruiz

et al., 2020).

El Gavilán Formation: The lower part of

this unit is composed of a red-yellow colored

thin-bedded shale with reticulosan sponges,

chancellorids, brachiopods, and trilobites (Fig.

3). The middle part is made up of interbedded

red shale and gray limestone beds of vary-

ing thickness, with high fossiliferous content.

The upper part of the unit consists of yellow

sandstone. The real thickness of the unit has

not been determined due to folding. Also, this

unit is exposed in the valley, southwest of the

El Sahuaral Hill. The lower contact is conform-

able with the Cerro Prieto Formation, while the

upper contact is in angular unconformity with

the Miocene rhyolite-andesite volcanic rocks

(Noriega-Ruiz et al., 2020).

RESULTS

Systematic paleontology:

The nomenclature and morphological

terms used to describe the specimens are those

Fig. 1. Location of the study area, northeast of Hermosillo, Sonora, Mexico.

Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

proposed by Sprinkle (1973) and Gil-Cid &

Domínguez-Alonso (2002).

Phylum Echinodermata Bruguière, 1791

Subphylum Blastozoa Sprinkle, 1973

Class Eocrinoidea Jaekel, 1918

Family uncertain

Genus Ubaghsicystis

Gil-Cid & Domínguez-Alonso, 2002

Diagnosis: Eocrinoid with globose theca

formed by approximately 40 plates, epispires

present in the upper half and absent in the

lower part of the theca. Anal pyramid in lateral

position above the equator line of the theca.

Long, homeomorphic, and holomeric peduncle

with a distal fixation disc, the column is of

circular section, narrow lumen, and without

articular crenulations. Thin, biserial arms, with

cover plates and without brachioles (Modified

from Gil-Cid & Domínguez-Alonso, 2002).

Type species: Ubaghsicystis segurae Gil-

Cid & Domínguez-Alonso, 2002

Ubaghsicystis cf. U. segurae

Fig. 4A-4D

Occurrence: The El Gavilán Formation,

Sahuaral Hill, middle Cambrian (Miaolin-

gian, Wuliuan), Altiocculus Subzone,

Ehmaniella Zone.

Material: Two slabs with isolated plates

of the specimens USDG 354 and USDG 355.

The material is deposited in the Paleontological

Collection, Geology Department, University of

Sonora, Mexico.

Fig. 2. Stratigraphic column of the studied area. Where Sy. = System, Se. = Series, St. = Stage, Th. = Thickness, Fm. =

Formation. Modified after Beresi et al. (2019).

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Description: The specimens are incom-

plete and poorly preserved; only plates from

the lower and half part of the theca were recov-

ered. The plates are large of variable diameter,

with smooth edges (Table 1).

The specimen USDG 354 has four plates,

probably corresponds to the infralateral plates

of the cycle 2, as they are the largest, with

a smooth external surface and sometimes a

slight concavity. Over the cycle 2, the cycle

of lateral plates (cycle 3) is observed, display-

ing an irregular and curved polygonal contour.

Articulation concavity is observed in plates 2:

1-2: 2 and 2: 1-3: 2.

The specimen USDG 355 is incomplete

and poorly preserved, with seven plates that

correspond to 4 cycles. The plates are rounded

and smooth-edged. Plate cycle 1 is subrounded.

Cycle 2 (infralateral), plates are the largest and

have smooth edges, possibly articulated. Cycle

3 (lateral) plates are similar in size to cycle 1

plates but differ in the hexagonal edges (3:2).

Remarks: The infralateral plates of the

theca of the Mexican specimen are very similar

to those of Ubaghsicystis segurae, described

for the Ovielle Formation from the middle

Cambrian of Spain (Gil-Cid & Domínguez-

Alonso, 2002), in that they are the largest of

Fig. 3. Panoramic view of thin-bedded shale from the El Gavilán Formation.

TABLE 1

Specimens and plate cycles from the specimens studied

Specimen USDG 354

Plate cycles Dimensions (mm)

2:1 7,4

2:2 7,3

3:2 6,6

3:3 6,5

Specimen USDG 355

Plate cycles Dimensions (mm)

1:1 4,9

2:1 6,4

2:2 6,2

3:1 4,6

3:2 5,0

4:2 4,8

4? 4,0

Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

the theca and of smooth surface. The side plates

are similar to the same specimens, and they

have an irregular polygonal contour, and the

3:2 plate is presented in an almost hexagonal

shape. For the rest of the plate cycles (4), it is

not possible to make a comparison since this

cycle in U. segurae, is of irregular contour

plates without a defined pattern. However, as

in the Mexican specimen, they are smaller in

size, since they decrease in size as approaching

the oral region (Gil-Cid & Domínguez-Alonso,

2002). A notable difference between the Mex-

ico specimen and the example from Spain is

in terms of size, as the plates of the Mexican

specimen are considerably larger.

Ubaghsicystis segurae collected in beds

of the middle Cambrian area of the High Atlas

area of Morocco (Zamora, Clausen, Álvaro, &

Smith, 2010) is similar to the Mexican speci-

men in the polygonal and surrounded form of

Fig. 4. Isolated plates of Ubaghsicystis cf. U. segura. Scale line 5 mm. A. Specimen USDG 354. B. Specimen USDG 355.

Revista de Biología Tropical, ISSN electrónico: 2215-2075, Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

the plate cycles 2 and 3; however, it differs in

its smaller size.

Ubaghsicystis cf. U. segurae from Mex-

ico is very similar to ?Ubaghsicystis sp. from

the middle Cambrian Burgess Shale, Canada

(Sumrall & Zamora, 2015), especially in the

form of the plate cycles, for which the ones

from cycle 2 are also the largest and irregular

in size, however in terms of size, is also smaller

than the Mexican specimen.

DISCUSSION

Biostratigraphical considerations: The

trilobite fauna from the El Gavilán Forma-

tion of the El Sahuaral section is represented

by Quadragnostus depressa, Peronopsis sp.,

Tonkinella valida, and Elrathina antiqua. Alto-

gether, the trilobite fauna indicates a middle

Cambrian (Miaolingian, Wuliuan) chronostrati-

graphic position. The biotic content corre-

sponds to the Altiocculus Subzone, the upper

part of the Ehmaniella Zone, defined by Sund-

berg (1994), as an assemblage zone that occurs

above the Glossopleura Zone and below the

Bolaspidella Zone, dividing it into four sub-

zones: Proehmaniella, Elrathiella, Ehmaniella,

and Altiocculus.

For Gondwana, Ubaghsicystis is known

from the Cambrian of Spain and Morocco (Gil-

Cid & Domínguez-Alonso, 2002; Zamora et al.,

2010; Sumrall & Zamora, 2015). In Laurentia,

it had only been recorded in the Cambrian of

Burgess Shale (Sumrall & Zamora, 2015), and

we are reporting herein the first occurrence of

the genus in Mexico. In Spain, Ubaghsicystis

segurae has been documented from the Ovielle

Formation (Miaolingian, Wuliuan) of Barrios de

Luna, Province of León, Northern Spain (Gil-

Cid & Domínguez-Alonso, 2002). In Morocco,

it has been studied from the High Atlas, where

complete specimens of Ubaghsicystis segurae

were recovered, also from the middle Cam-

brian (Miaolingian, Wuliuan) (Zamora et al.,

2010). In North America ?Ubaghsicystis has

been documented from the Burgess Shale,

Canada, where poorly preserved specimens

were recovered, which are included in the

Ehmaniella Zone (syn. Bathyuriscus-Elrathina

Rasetti, 1951) of middle Cambrian (Miaolin-

gian-Wuliuan) age. As previously mentioned in

Mexico only isolated and disarticulated plates

of Ubaghsicystis have been collected from the

El Gavilán Formation in the El Sahuaral sec-

tion, central Sonora, where it is included, in

the upper part of the Ehmaniella Zone, middle

Cambrian (Miaolingian-Wuliuan).

Paleoecological and paleogeographic

considerations: For the study area, an abun-

dant fossil fauna has been documented con-

sisting of reticulosan sponges, chancelloriids,

linguloid brachiopods, trilobites (agnostids,

ptychopariids, corynexchids), as well as echi-

noderms. The faunal association constitutes a

typical middle Cambrian benthic marine com-

munity developed in an open shelf marine envi-

ronment over a soft substrate. The community

of El Sahuaral section is composed of different

trophic categories: A) suspension feeders, epi-

faunal-sessile: Porifera (Protospongia sp., and

Diagoniella sp.); Chancelloridae (Chancelloria

eros, Allonnia tintinopsis, and Archiasterella

sp.); Brachiopoda (Acrothele sp., Prototreta

sp., and Dictyonina sp.); Eocrinoidea (Ubagh-

sicystis). B) Detritus feeders, without vision

(slow-moving vagile): Trilobita-Agnostida

(Quadragnostus depressa and Peronopsis sp.).

C) Detritus feeders, with well-developed vision

(fast-moving vagile): Trilobita-Ptychopariida

(Elrathina antiqua). D) Carnivorous with well-

developed vision (fast-moving nektobenthic):

Trilobita-Corynexochida (Tonkinella valida).

Guilds were established according to the life

strategies of different organisms.

The ability of pelmatozoa to adapt to a

variety of marine environments was cited by

Zamora et al. (2010). Different morphological

innovations allowed them to adapt to soft, clay

offshore substrates, and sometimes to be able to

attach on shell fragments.

As mentioned above, the benthic commu-

nity of the middle Cambrian of the El Sahuaral

was developed in an open shelf marine envi-

ronment with a soft substrate. This is indi-

cated by the abundance of shale, related to the

Revista de Biología Tropical, ISSN electrónico: 2215-2075 Vol. 69(S1): 51-61, March 2021 (Published Mar. 30, 2021)

deposition of clay as fine material, along with

the presence of agnostid trilobites (Quadrag-

nostus depressa and Peronopsis sp.), which

have only been recorded in open shelf marine

environments (Robison, 1976; Liñán, 1996;

Cuen-Romero et al., 2019).

Concerning eocrinoids, they had a world-

wide paleogeographic distribution during the

Cambrian; for example, gogiids have been

documented in Spain, France, Morocco, United

States, Canada, and Mexico (Nardin et al.,

2009; Sumrall & Zamora, 2015; Buitrón et al.,

2017b). In the case of Ubaghsicystis, taking

into account the present work, it is known in

Morocco, Spain, Canada, and Mexico (Sumrall

& Zamora, 2015) (Fig. 5, Fig. 6).

The fossiliferous assemblage from the

middle Cambrian of the El Sahuaral sections

consists of complete chancelloriid sclerites

and fragments of scleritomes (bodies) partially

articulated of Chancelloria eros, together with

isolated sclerites belonging to Allonnia tintinop-

sis, and Archiasterella sp. (Beresi et al., 2019).

In the present report, chancellorids, hyo-

lithids, linguloid brachiopods, and trilobites

were also documented. This faunal content is

Fig 5. Distribution of common eocrinoids genera in the world: Ubaghsicystis, Gogia, Guizhoueacrinus, Eocystites,

Lepidocystis, Lichenoides, Lyracystis, Trachelocrinus, and Akadocrinus.

Fig. 6. Paleogeographic distribution of the genus Ubaghsicystis near to the Paleoequator.

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practically identical to the assemblage cited

from the type section of San José de Gracia,

Sonora, located 10 km to the south of the study

area (Fig. 1) (Cuen et al. 2013; Cuen-Romero

et al., 2016).

The El Gavilán Formation has yielded

a diverse faunal assemblage including small

shelly fossils as Chancelloria, Archiasterella,

and Allonnia. Numerous isolated complete

chancelloriid sclerites with central rays and

6-7 marginal rays belonging to Chancelloria

eros and diverse fragmentary shells of bra-

chiopods dominate most samples. Addition-

ally, eocrinoid remains, few hyolithids, and

trilobites are represented in the assemblage.

Few conical hyolithids are badly preserved on

bedding surfaces. Moreover, some brachiopods

as Lingulella sp. Acrothele sp., Prototreta sp.,

Dictyonina sp., and Linnarsonia sp. were found

at the type section of San Jose de Gracia of the

El Gavilán Formation (Cuen-Romero et al.,

2016), of which some are also present in the El

Sahuaral section.

Results demonstrate a wide distribution

and palaeobiological importance of the middle

Cambrian fauna in Sonora, Mexico as part of

the Laurentian shelf, characterized by carbon-

ates deposited in shallow and deeper shelf areas

under tropical conditions.

Ethical statement: authors declare that

they all agree with this publication and made

significant contributions; that there is no con-

flict of interest of any kind; and that we fol-

lowed all pertinent ethical and legal procedures

and requirements. All financial sources are

fully and clearly stated in the acknowledge-

ments section. A signed document has been

filed in the journal archives.

ACKNOWLEDGMENTS

The authors are gratefully to Frederick

A. Sundberg (Museum of Northern Arizo-

na, USA), who collected the material. The

authors thanks the financial support provided

by the project PRODEP UNISON-PTC-301:

“Paleoecología de los ecosistemas marinos del

Cámbrico de Sonora, México: Bioestratigrafía,

Paleobiogeografía y su relación con el cratón

de Norteamérica”. We also thank the Depart-

ment of Geology at the University of Sonora,

as well as the Instituto de Geología, UNAM,

for the support given to carry out this research.

RESUMEN

Primer registro de Ubaghsicystis

(Eocrinoidea - Echinodermata) del Cámbrico

(Miaolingio, Wuliuan) de Sonora, México:

Consideraciones bioestratigráficas y paleoecológicas

Introducción: El presente trabajo constituye el pri-

mer registro en México de Ubaghsicystis Gil-Cid &

Domínguez-Alonso (Echinodermata-Eocrinoidea) proce-

dente de la Formación El Gavilán, la cual aflora en el

Cerro El Sahuaral, una nueva localidad del Cámbrico

ubicada en la parte central del estado de Sonora, México.

La Formación El Gavilán es una secuencia sedimentaria

depositada en un ambiente marino de plataforma exterior,

la cual consiste principalmente de lutita intercalada con

caliza, conteniendo abundantes fósiles de invertebrados.

Objetivo: El principal objetivo del presente trabajo de

investigación es describir la especie Ubaghsicystis cf. U.

segurae por primera vez para México, así como indicar

las consideraciones bioestratigráficas y paleoecológicas.

Métodos: Una sección estratigráfica compuesta fue medi-

da para la Formación El Gavilán en Sonora central, donde

muestras correspondientes a eocrinoides fueron colectadas,

el material fue examinado en el Microscopio Leica MZ10.

Resultados: La asociación biótica está conformada por

esponjas reticulosas, chancellóridos (Chancelloria eros,

Allonnia tintinopsis, Archiasterella sp.), hiolítidos, bra-

quiópodos, trilobites (Quadragnostus depressa, Tonkinella

valida, Elrathina sp.), y equinodermos (Ubaghsicystis

cf. U. segurae). La asociación de trilobites confiere a

estas rocas una edad del Cámbrico medio (Miaolingiano,

Wuliuano), Subzona de Altiocculus, Zona de Ehmaniella.

El material estudiado está constituido por placas aisladas

y desarticuladas las cuales probablemente representen

varios ciclos de placas de la teca, las cuales son asignadas

a Ubaghsicystis cf. U. segurae. El género Ubaghsicystis

ha sido documentado previamente en otras localidades del

Cámbrico como Burgess Shale en Canadá y Los Barrios de

Luna en España, para los cuales existen escasos registros.

Conclusiones: La sucesión cámbrica de Sonora, donde

ocurre Ubaghsicystis, formó parte del borde del cratón de

Laurentia durante este período, el cual se localizaba cerca

del Paleo Ecuador, donde se generaron las condiciones

necesarias para una gran diversidad y abundancia de espe-

cies, incluyendo equinodermos.

Palabras clave: Eocrinoidea; Cámbrico; bioestratigrafía;

paleoecología; México.

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