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Actuotaphonomic model of the mollusk fauna

of Laguna de Mandinga, Veracruz, Mexico

F. Raúl Gío-Argaez

*, Catalina Gómez-Espinosa

& Saraí Romero

1. Universidad Nacional Autónoma de México, Instituto de Ciencias del Mar y Limnología, Ciudad de México, México;

raulgio@cmarl.unam.mx

2. Universidad Autónoma de Guerrero, Escuela Superior de Ciencias de la Tierra, Taxco el Viejo, Guerrero, México;

c_gomez@ciencias.unam.mx

3. Universidad Veracruzana, Posgrado de la Facultad de Ciencias Biológicas y Agropecuarias, Tuxpan de Rodríguez

Cano, Veracruz, México; iamsara@ciencias.unam.mx

*Correspondence

Received 03-VI-2020. Corrected 12-XI-2020. Accepted 18-XI-2020.

ABSTRACT. Introduction: The taphonomic attributes of a faunal assemblage provide information about which

agents affect the distribution and preservation of ancient or newly formed biogenic materials during depositional

and post-depositional processes. Actuotaphonomy thus is a valuable tool for reconstructing fossil communities

because it establishes analogies between observable processes in the present and those that happened in the past.

Objective: The taphonomic attributes of a marginal marine environment were analyzed to assess the origin of

fragmentation, bioerosion, and encrustation processes and the role of these characteristics in the deterioration of

current sediment accumulations of mollusks (gastropods and bivalves). Methods: The material studied was col-

lected from a shell-remain accumulation called “El Conchal” in the Laguna de Mandinga, Veracruz, a lagoonal

complex located in the Gulf of México. Taphonomic analysis included fragmentation, bioerosion, and encrusta-

tion features on recent gastropods and bivalve’s shells. The categories of each attribute were classified in three

degrees: poor, regular and good. The analysis was performed only in complete shells. Results: A bulk sample

of 1 697.9 g was processed, recovering 1 165 complete specimens, of which 5 genera of bivalves and 4 genera

of gastropods were identified. The fragmentation and bioerosion were classified as regular (grade 1), this may

be the results of the water energy in the environment, that permits a constant rework, and exhumation of the

remains at the lagoon’s water-sediment interface; meanwhile, three eroders were identified to ichnogenus level:

Entobia, Oichnus, and Caulostrepsis, being Caulostrepsis the least abundant. The encrustation was classified as

poor (grade 2); the result can be interpreted based on the ecosystem intrinsic conditions that do not allow many

encrusting organisms to develop properly. The encrusters are represented by calcareous organisms including

bryozoans, serpulids tubes, and barnacles. The results yielded an actuotaphonomic model that could be appli-

cable to analogous ecosystems in Laguna de Mandinga (Mandinga Lagoon), in Veracruz, Mexico. Conclusions:

In marine marginal environments as in lagoon areas the encrustation does not have an important role in the

preservation or destruction of shelly assemblages, being taphonomically more important than fragmentation and

bioerosion as potentially destructive agents that can be a source of loss of fidelity in the fossil record.

Key words: actuotaphonomic model; fragmentation; bioerosion; encrustation; lagoon; mollusk.

Gío-Argaez, F.R., Gómez-Espinosa, C., & Romero, S. (2021).Actuotaphonomic model of

the mollusk fauna of Laguna de Mandinga, Veracruz, Mexico. Revista de Biología

Tropical, 69(1), 207-217. DOI 10.15517/rbt.v69i1.38916

ISSN Printed: 0034-7744 ISSN digital: 2215-2075

The taphonomic attributes of a faunal

assemblage provide information about which

agents affect both the distribution and pres-

ervation of ancient or newly formed biogenic

materials during their depositional and post-

depositional processes. These processes are

regulated by the surrounding environmental

conditions and the life habits of the organisms

DOI 10.15517/rbt.v69i1.38916

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that constitute such assemblages (Callender

et al., 2002; El-Sorogy, 2015; Gómez-Espi-

nosa, Gío-Argáez, Farinati, Aliotta, & Salga-

do-Souto, 2018). Thus, actuotaphonomy is a

valuable tool for reconstructing fossil commu-

nities because it establishes analogies between

observable processes in the present and those

that happened in the past. Actuotaphonomy

helps elucidate the events that lead to preserva-

tion of organic remains, which in turn assists in

interpretation of sedimentological and ecologi-

cal conditions that gave rise to the formation

of a fossil deposit (Gómez-Espinosa & Gío-

Argáez, 2009).

Kowalewski, Flessa, and Hallman (1995)

proposed a triple classification graphical

approach to taphonomic interpretations, using

a diagram called “ternary taphograms,” in

which a taphonomic signature is assigned to

a specific degree of alteration. With this clas-

sification assigned according to the percentage

of shell coverage, it can be “good” (extensive

or abundant coverage), “medium” (moderate

coverage), or “poor” (little or no coverage).

Mollusks are major components of many

current and fossilized marine ecosystems, and

thus have been frequently incorporated into

taphonomic analyses, with a special focus on

gastropods and bivalves (Gómez-Espinosa et

al., 2018). The in situ study of preserved mol-

lusk assemblages is essential for understanding

the taphonomic processes involved in the pres-

ervation or destruction of shell remains before

their burial (Erthal, Korsian, & Simoes, 2013).

For this reason, actuotaphonomic studies are

particularly useful for predicting and estimat-

ing the physiochemical and/or biological pro-

cesses that prevailed in a given environment,

as well as speculating about the capability pre-

serving mollusk assemblages in each environ-

ment (Kowalewski & Labarbera, 2004).

Different characteristic conditions may

lead to taphonomic losses that affect the pres-

ervation of remains in a taphonomically active

zone (TAZ), where the greatest dissolution,

destruction, or taphonomic alteration of shells

occurs. Among these conditions are the per-

manence of the organisms on the surface, the

energy of the system, currents, salinity, and

anthropogenic activity (Parsons-Hubbard et

al., 1999; Olszewski, 2004; Gordillo, Bayer,

Boretto, & Charó, 2014).

The objective of the present study was to

analyze the different degrees of taphonomic

alteration that might enhance either the preser-

vation or destruction of a gastropod and bivalve

assemblage in the present marine marginal dep-

ositional environment of the Laguna de Mand-

inga, Veracruz, Mexico. By characterizing the

fragmentation, bioerosion, and encrustation on

both gastropod and bivalve shells, along with

the subsequent construction of ternary tapho-

grams for each of these taphonomic attributes,

we generated an actuotaphonomic model that

may be applicable in analogous ecosystems.

MATERIALS AND METHODS

Study site: Laguna de Mandinga is locat-

ed in the state of Veracruz, Mexico (19º00’00”-

19º06’00” N & 96º02’00”- 96º06’00” W), 18

km South of Veracruz Port (Fig. 1). One of the

main coastal lagoons along the Gulf of Mex-

ico (Krutak, 1971; Reguero & García-Cubas,

1994), Laguna de Mandinga is a sedimentary

environment of the Quaternary made of a flu-

vial accumulation of fine to very fine particle

size, consisting of sand, silt, and clay overlying

sandy and alluvial sediments. In some areas,

it emerges with the gravel derived from the

accumulation of mainly molluscan shells (Con-

treras, 1985). The fact that Laguna de Mand-

inga generates high concentrations of organic

remains makes it a suitable location for tapho-

nomic studies. The samples for this study were

collected in a shell-remain accumulation called

“El Conchal” located in “Laguna Redonda”.

At present, Mandinga is recognized as a

tourist location with the development of com-

mercial fishing. This status has meant that the

lagoon and the channels that connect it to the

Jamapa River have been regularly dredged

since 1980 (Heimo, Siemens, & Hebda, 2004).

Sediment sampling and processing: A

total of 1 697.9 g of sediment was collected

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from the ends and core from a shell mound

known locally as “El Conchal”, following

the sieving method described by Anderson,

McBride, Taylor, and Byrnes (1998). The

sample was processed in the Laboratory of

Environmental Micropaleontology, ICMyL,

UNAM. Only complete specimens were

included in the present taphonomic analysis,

defined as retention of more than 70 % of the

original shell or valve surface. Among those

with a smaller preservation percentage, we

retained gastropod specimens that still had a

last whorl and/or columella and bivalves that

still had a hinge. A total of 1 165 specimens

were evaluated, of which 173 were gastropods

and 922 were bivalves.

Taxonomic identification, taphonomic

attributes, and ternary taphograms: All

bivalves and gastropods sampled, along with

bioeroding and encrusting organisms associ-

ated with them, were taxonomically identified

according to the illustrated catalogs of García-

Cubas and Reguero (2004, 2007) for bivalve

mollusks and gastropods from the Gulf of

Mexico and the Caribbean Sea. The identifica-

tion of ichnogenus and encrusting was carried

out following the ethological classification

of Seilacher (1964) and the World Regis-

ter of Marine Species platform (http://www.

marinespecies.org/). The compared taphonom-

ic attributes considered were fragmentation,

bioerosion, and encrustation, assessed using

ternary diagrams based on Kowalewski, Flessa

and Hallman (1995).

RESULTS

Taxonomic identification: From the ana-

lyzed sample (N = 1 165), we identified five

genera of bivalves (N = 922): Anadara Gray,

1847; Crassostrea Sacco, 1897; Ischadium

Jukes-Browne, 1905; Mulinia Gray, 1837, and

Rangia Desmoulins, 1832. We also identified

four gastropod genera (N = 173): Bailya Smith,

1944; Cerithideopsis Thiele, 1929; Nassarius

Duméril, 1805; and Neritina Lamarck, 1816

(Fig. 2). Among the bioeroding organisms

Fig. 1. Location of the study area “Laguna de Mandinga” Veracruz, close up mark with a star “El Conchal” shell

remain accumulation.

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found in the sample, three types of perforations

were identified related respectively to ich-

nogenus Entobia Bronn, 1937; Caulostrepsis

Clarke, 1908; and Oichnus Bromley, 1981. The

specimens presented either one or more types

of perforations per individual.

Ethological classification:

Domichnia Seilacher, 1964

Ichnogenus Entobia Bronn, 1837

Type ichnospecies Entobia cretacea

Portlock, 1843

Description: Most of the perforations were

small, rounded, and widely distributed (Fig.

2A, Fig. 2B, Fig. 2C, Fig. 2D). Some perfora-

tions were so strongly marked that they caused

shells to lose their shape because of fragmenta-

tion. Perforation was more commonly found in

bivalves than in gastropods, possibly because

of the greater surface area of bivalves.

Ichnogenus Caulostrepsis Clarke, 1908

Type ichnospecies Caulostrepsis taeniola

Clarke, 1908

Description: This ichnogenus was the least

common in the sample. It was observed only in

the outer layers of bivalves, exhibiting a wider

diameter at the beginning of the perforation

than at the end. C. taeniola was found in the

gastropod shell towards the apex, manifesting

as shallow elongated perforations (Fig. 2E, Fig.

2F, Fig. 2G, Fig. 2H).

Ethological classification:

Praedichnia Seilacher, 1964

Ichnogenus Oichnus Bromley, 1981

Fig. 2. Identification of bioerosive traces. A-D. Entobia perforations. E-F. Caulostrepsis perforations,

I-L. Oichnus perforations.

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Type ichnospecies Oichnus simplex

Bromley, 1981

Description: This perforation was the sec-

ond most abundant type in the sample, appear-

ing in both bivalves and gastropods, although

more commonly in bivalves. Perforations were

frequently located at the umbo of bivalves and

at the last whorl of gastropods but were seen

towards the apical region of some specimens

(Fig. 2I, Fig. 2J, Fig. 2K, Fig. 2L).

Regarding the encrusting specimens

detected, we identified calcareous serpulid

polychaete tubes and calcareous bryozoan and

barnacle skeletons. The polychaete tubes were

the most common of the three. Serpulid poly-

chaetes were found in both the dorsal and ven-

tral surfaces of the bivalve shells analyzed (Fig.

3A, Fig. 3B, Fig. 3C, Fig. 3D), as well as the

external surface of gastropods (Fig. 3C).

Bryozoans from the Order Cheilostoma-

tida Nusk, 1852 were identified in four bivalves

in the sample, either on the ventral surface of

the valves or on top of other encrusting serpu-

lids and barnacles (Fig. 3D, Fig. 3E, Fig. 3G).

Barnacles of the genus Amphibalanus Pitombo,

2004 were recognized on the ventral surface of

two bivalve specimens, at the umbo region of

this location, and it is inferred that encrustation

happened postmortem (Fig. 3F, Fig. 3G).

Taphonomic attributes and ternary

taphograms: Table 1 represents the tapho-

nomic attribute percentage according to the

coverage degree of the shells, based on the

number of specimens observed in each sample.

Fragmentation was observed in 58.1 %

of the total sample; bivalves were the most

affected group. While bioerosion appears in

a great number (47 %) of mollusk specimens

analyzed and encrustation is quite scarce (5 %)

in the sample.

Fig. 3. Presence of encrusting organisms on mollusk shells. A-D. Serpulid polychaetes.

D-E, G. Bryozoan colony. F-G. Barnacles.

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Analysis of the results of ternary tapho-

grams (Fig. 4) for bivalves showed medium-

grade (< 50 % shell coverage) fragmentation

and bioerosion (Fig. 4A, Fig. 4B), according

to Kowalewski, Flessa and Hallman (1995).

The gastropod fragmentation also was medium

grade (Fig. 4A), but the bioerosion was poor

(Fig. 4B). For both groups, encrustation (Fig.

4C) was poor (absent attribute).

Among bivalves, fragmentation was

present in 58.1 %, bioerosion in 47 %, and

encrustation in 5 %. Within the gastropods,

fragmentation was present in 42.2 %, bioero-

sion in 48 %, and encrustation in 0.6 %. Of the

total, fragmentation was present in 55.7 %, bio-

erosion in 47.1 %, and encrustation in 4.4 %.

Based on the taphonomic analysis, bivalves

were the most affected group (Table 2).

DISCUSSION

Modern marine environments offer infor-

mation about past geological processes and

conditions that affected organisms and their

eventual burial. However, the fossil record in

brackish water bodies, such as coastal lagoons,

has a lower diversity of representation com-

pared to the marine record because of how

organisms are preserved and the ephemeral

nature of the habitats (Adomat, Gishler &

Oschmann, 2015). For this reason, actuota-

phonomic studies in brackish water bodies are

TABLE 1

Total number of specimens and taphonomic attributes analyzed (fragmentation, bioerosion, and encrustation)

Bivalves (N = 992) Gastropods (N = 173)

Taphonomic attribute Poor (Grade 2) Regular (Grade 1) Good (Grade 0) Poor (Grade 2) Regular (Grade 1) Good (Grade 0)

Fragmentation 416 (41.9 %) 489 (49.3 %) 87 (8.8 %) 100 (57.8 %) 57 (32.9 %) 16 (9.3 %)

Bioerosion 526 (53 %) 440 (44.3 %) 26 (2.7 %) 90 (52 %) 65 (37.6 %) 18 (10.4 %)

Encrustation 942 (9 %) 48 (4.8 %) 2 (0.20 %) 172 (99.4 %) 1 (0.06 %) -

TABLE 2

Organisms exhibiting bioerosion and encrustation according to their taphonomic degree and taxonomic group

Bivalves Gastropods

Poor Regular Good Poor Regular Good

Bioeroders

Entobia

181 17 28 12

Caulostrepsis

83 7

Oichnus

109 1 18

Entobia/Caulostrepsis

29 5 2

Entobia/Oichnus

35 3 1

Caulostrepsis/Oichnus

2 11 4

Entobia/Caulostrepsis/Oichnus

Encrusters

Barnacles 1

Bryozoans 3

Serpulids 43 1 1

Barnacles/Bryozoans 1

Serpulids/Bryozoans 1

Poor (Grade 2) = absent attribute; regular (Grade 1) = < 50 % coverage of the shell; good (Grade 0) = > 50 % coverage of

the shell.

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relevant to understanding the past extrinsic and

intrinsic conditions of these ecosystems.

Different factors regulate the abundance

and composition of fossil deposits, such as

susceptibility to modification and destruction

by organisms, taphonomic conditions exposed

in the environment, and the time scale accu-

mulation (Behrensmeyer & Kidwell, 1985).

These factors are clearly observable in current

marine-marginal environments, where ecologi-

cal interpretations of the species can be made

based on the factors that influence the transport

of the organic remains.

In order to study a recent mollusk assem-

blage in a marine marginal environment, just

as the ones that are developed in coastal

lagoons, requires consideration of the ener-

gy rates, environmental interactions, and tro-

phic relationships of the system under study.

These factors regulate molluscan communi-

ties and are crucial tools in interpreting their

taphonomic attributes.

Taphonomic interpretation: The sample

position in each ternary taphogram expresses

the variation of taphonomic characteristics,

which may result from the different conserva-

tion environments (hydrodynamic regime, bio-

logical activity, degree of subaerial exposure),

variation in size, and architecture of the shells

(Kowalewski, Flessa, & Hallman 1995). The

use of taphograms saves space and allows a

quick comparison of the taphonomic character-

istics among samples.

Fragmentation was observed in 58.1 % of

the total sample, and bivalves were the most

affected group. This characteristic is associated

not only with high environmental energy but

Fig. 4. Ternary taphograms. Global representation of the taphonomic attributes analyzed. Fragmentation and bioerosion

exhibit a regular degree, while encrusting presents a poor degree. A. Bivalve and gastropod fragmentation, regular. B.

Bivalve bioerosion, regular; gastropod bioerosion, poor. C. Bivalve and gastropod encrustation, poor.

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also with biological interactions. The origin of

the fragments could depend on different stages

of taphonomic processes (depredation, biotur-

bation, and biostratinomic processes), system

energy, and anthropogenic action (opening of

canals) that provokes constant cycles of rework

and exhumation of organic remains (Kidwell,

Fürsich, & Aigner, 1986; Zuschin, Stachow-

itsch, & Stanton, 2003).

Because of the nature of the encrusting

organisms and bioeroders, it is believed that

they developed in underwater conditions, so

that the shells were deposited and accumulated

in islets called “conchales”. Bioerosion was

present in a great number (47 %) of mollusk

specimens collected from Laguna de Mand-

inga, but encrustation (5 %) was quite scarce.

Such scarcity might arise from the considerable

sediment reworking and exhumation that char-

acterize the study site. Both the burial and the

frequent subaerial exposure may have protect-

ed the shells from bioeroders and encrusting

organisms (Lescinsky, Edinger, & Risk, 2002).

Most of the organisms responsible for

the perforations identified in our sample were

clionid sponges (Porifera), which produce the

ichnogenus Entobia. To a lower degree, there

were carnivorous gastropods that produce the

ichnotrace Oichnus and the serpulid poly-

chaetes that produce the ichnogenus Caulo-

strepsis. All three ichnogenera were present in

both bivalves and gastropods, but their inci-

dence was higher in bivalves. The same ichno-

fossils and their higher prevalence on bivalves

were registered on recent shell assemblages

from a siliciclastic beach on the Gulf of Mexico

(Gómez-Espinosa et al., 2018).

Given the relatively high percentage of

bioerosion detected in the Laguna de Mandinga

sample (47 %), it can be inferred that a great

number of the analyzed organisms spent con-

siderable time in the TAZ, where bioeroding

organisms could settle on the exposed surface

of the mollusk shells (Davies, Powell, & Stan-

ton, 1989; Walker, Parson-Hubard, Powell,

& Brett, 1998).

Encrusting organisms were found in only 5

% of the specimens, and all but one individual

were bivalves. Most encrustations were located

on the ventral surface of the valves, suggesting

a postmortem occupation, most likely to gain

protection (McKinney, 1996). A large number

of encrusting bryozoans were observed colo-

nizing the surface of other encrusting organ-

isms (i.e., serpulid polychaetes and barnacles),

so that the first arrivals could be considered as

secondary colonizers capable of inhabiting sur-

faces with varying degrees of roughness and/or

curvature (Gherardi & Bosence, 1999; Gibson,

1992; Taylor & Wilson, 2003). The encrusting

bryozoans did not have a preference regarding

substrate specificity, and differences were relat-

ed to the variable physical stability of the shells

exhibiting different frequencies of circumrota-

tory growth (Jackson, 1984; McKinney, 1996).

The high rate of fragmentation and low

degree of biogenic processes calculated for

Laguna de Mandinga imply that the taphonom-

ic processes occurring in mollusk assemblages

are primarily driven by a high sedimentation

rate and a constant reworking of the skeletal

concentrations in the area. These conclusions

agree with inferences from the models of fossil

concentrations by Kidwell (1986) and Kidwell,

Fürsich, and Aigner (1986).

In some cases, the bioerosion and encrus-

tation contributed to the deterioration of the

remains, producing the subsequent fragmen-

tation of the shells. These effects would be

expected to inhibit the conservation of the

shells and could be the cause of their loss from

the fossil record.

Several factors may be responsible for the

low fouling density of mollusks. Among these

are a relatively short exposure period before the

burial (Brett et al., 2011); low nutrient levels

(Lescinsky et al., 2002), constant movement of

the rests or rapid wear of scales, and decreases

in biological activity because of high turbidity

(Parsons-Hubbard, 2005).

Formation of skeletal concentrations: In

the fossil record, evidence of disturbance prior

to burial can be used to infer peculiarities of

the burial history or the life habits of the organ-

isms (Brett & Baird, 1986). This association

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can be inferred in the present work thanks to

the taphonomic analysis, in which cause–effect

relationships of processes observed in Mandin-

ga Lagoon could be established and contrasted

with observations in the obtained sample.

Kidwell et al. (1986) recognized three

types of processes responsible for skeletal

concentration formations: sedimentological,

biogenic and diagenetic. In Laguna de Man-

dinga, the taphonomic processes in mollusks

are determined by a high rate of sedimenta-

tion and a constant reworking of skeletal

concentrations. These conditions produce a

high rate of fragmentation and a low degree of

biogenic processes.

The formation of different biotopes (islets)

in the lagoon traces to the constant dragging

of sediments and dead organisms, which after

a certain time are associated with a death

assemblage (thanatocoenosis) with high sedi-

mentation rates. Thus, as a result of constant

reworking and high sedimentation rates, the

encrusting organisms would rarely fossilize

because of the long periods of time they

require to become established on the remains

(Asch & Collie, 2008).

Death assemblage represents the first step

in the formation of a fossil assemblage, so our

results represent a useful tool for biological and

paleontological studies aimed at understanding

the ecological, geological, and taphonomic

processes that occur in marine-marginal envi-

ronments with similar characteristics.

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

We thank Miriam Moranchel, Bachelor

in Earth Sciences, for her contributions and

review of texts in English. At the same time,

we thank the biologist Brenda Martínez Villa

for her support in this project.

RESUMEN

Modelo actuotafonómico de la fauna de moluscos

de Laguna de Mandinga, Veracruz, México. Introduc-

ción: Los atributos tafonómicos de los conchales proveen

información acerca de cuáles agentes afectan la distri-

bución y preservación de la acumulación de materiales

biogénicos recientes o fósiles, especialmente durante las

etapas deposiconales y postdeposicionales. La actuotafo-

nomía es una herramienta valiosa para la reconstrucción

de las comunidades fósiles, para establecer analogías

entre los procesos observables en el presente con los que

ocurrieron en el pasado. Objetivos: Evaluar el impacto de

los rasgos tafonómicos y su papel en la formación de los

conchales en ambientes de lagunas costeras Métodos: El

material estudiado fue recolectado en una acumulación

de restos de conchas llamado “El Conchal” en la Laguna

de Mandinga, Veracruz, un complejo lagunar ubicado en

el Golfo de México. El análisis tafonómico incluye las

características tafonómicas de fragmentación, bioerosión

e incrustación en conchas de gasterópodos y bivalvos

recientes. Las categorías de cada atributo se clasificaron en

tres grados: pobre, medio y alto. El análisis fue realizado

solo en conchas completas. Resultados: Se procesaron

1 697.9 g de sedimentos, recuperando 1 165 ejemplares

completos, de los cuales se identificaron 5 géneros de

bivalvos y 4 géneros de gasterópodos. La fragmentación

y bioerosión se clasificaron como un “grado regular”, esto

puede ser el resultado de la energía del agua en el ambiente,

que permite el constante retrabajo y la exhumación de los

restos en la interfase agua-sedimento en la laguna; en tanto

que, se identificaron tres erosionadores a nivel de género,

estos corresponden a los icnogéneros: Entobia, Oichnus y

Caulostrepsis, siendo Caulostrepsis el menos abundante.

La incrustación mostró un “grado pobre”; el resultado

puede interpretarse basado en las condiciones intrínsecas

del ecosistema que no permiten que muchos incrustantes

se desarrollen de la manera adecuada. Los incrustantes

están representados por organismos calcáreos incluyendo

briozoarios, tubos de serpúlidos y balanos. Se analizaron

los atributos tafonómicos para generar un modelo actuota-

fonómico que pueda ser aplicable a ecosistemas análogos

en el registro fósil. Conclusiones: En ambientes marino

marginales como son las áreas lagunares la incrustación no

tiene un papel importante en la preservación o destrucción

de los conchales, siendo tafonómicamente más importante

la fragmentación y bioerosión como agentes potencialmen-

te destructivos que pueden ser un recurso de pérdida de la

fidelidad en el registro fósil.

Palabras clave: modelo actuotafonómico; fragmentación;

bioerosión; incrustación; laguna; moluscos.

216

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