Lucchi (1985) identified two groups within the ophiuroids she studied, one
related to the Malvinas (Falkland) Current and living at a depth greater than 60 m,
and the other related to warm waters and living at less a depth than 60 m.
Martínez (2008) identified two distributional patterns of ophiouroid and asteroid species. The first one comprises species with the southern end of their distributional range near Uruguay. This was divided in two sub-groups, depending on
whether their distribution extended across the Río de la Plata or not. Species whose
distribution is limited by the Río de la Plata, are affected by two main factors in
this area: temperature variation of the Subtropical Confluence Zone (ca. 308 to
458S, see Boltovskoy 1966 for example), where the cold Malvinas (Falkland) and
the warm Brazilian currents meet, and the strong variation in salinity and the
increase of turbidity of waters caused by fresh water discharge from the Rio de la
Plata (Piola et al. 2000, González-Silvera et al. 2004). The ‘‘salinity barrier’’ of the
Río de La Plata has been considered an explanation for the truncation of the
distribution of other organisms at the Rio de la Plata area, such as mollusks
(Scarabino 1977) or sand dollars (Martínez and Mooi 2005). The second group is
composed of species distributed within the area of the Argentinean or Patagonian
Province (ca. 438S and ca. 288S; Scarabino 1977; Boschi 2000), a unit characterized by a complex faunal composition. Tommasi (1970b; ophiuroids), Scarabino (1977; mollusks) and Martínez and del Río (2002; mollusks) suggested this
zone may be a true transition zone or ‘‘Provinciatone’’ between the adjacent
Magellanic and Brazilian Provinces.
The distribution of sand dollars was studied by Martínez and Mooi (2005) with
results and explanations comparable to the sub-groups of asterozoans that do not
cross the Rio de la Plata barrier.
10.3.2 Extinct Echinoderm Fauna
There are only eight species of echinoderms in the Uruguayan fossil record, one
crinoid species, one ophiuroid species, and six echinoid species. The crinoid and
ophiuroid species are from the Devonian.The echinoid species are from the
Cenozoic, being abundant in the Late Miocene. During those times (ca. 10 Ma.
ago) the Monophorasteridae (sister group of the Mellitidae) were particularly
abundant and diverse in what are today Uruguay and Argentina. Two species
(Mellita sp. and Encope sp.) are recorded only for the Quaternary and are still
extant in the area.
The following taxonomic arrangement of the fossil species. Suprageneric
classification is based on: Crinoidea, Ausich (1998); Holothuroidea, Pawson et al.
(2010); Ophiuroidea, Smith et al. (1995) and Shackleton (2005); Echinoidea: Kroh
and Smith (2010).
Class Crinoidea J.S.Miller, 1821
Subclass Camerata Wachsmuth and Springer, 1885
10 Echinoderm Research in Uruguay
351
related to the Malvinas (Falkland) Current and living at a depth greater than 60 m,
and the other related to warm waters and living at less a depth than 60 m.
Martínez (2008) identified two distributional patterns of ophiouroid and asteroid species. The first one comprises species with the southern end of their distributional range near Uruguay. This was divided in two sub-groups, depending on
whether their distribution extended across the Río de la Plata or not. Species whose
distribution is limited by the Río de la Plata, are affected by two main factors in
this area: temperature variation of the Subtropical Confluence Zone (ca. 308 to
458S, see Boltovskoy 1966 for example), where the cold Malvinas (Falkland) and
the warm Brazilian currents meet, and the strong variation in salinity and the
increase of turbidity of waters caused by fresh water discharge from the Rio de la
Plata (Piola et al. 2000, González-Silvera et al. 2004). The ‘‘salinity barrier’’ of the
Río de La Plata has been considered an explanation for the truncation of the
distribution of other organisms at the Rio de la Plata area, such as mollusks
(Scarabino 1977) or sand dollars (Martínez and Mooi 2005). The second group is
composed of species distributed within the area of the Argentinean or Patagonian
Province (ca. 438S and ca. 288S; Scarabino 1977; Boschi 2000), a unit characterized by a complex faunal composition. Tommasi (1970b; ophiuroids), Scarabino (1977; mollusks) and Martínez and del Río (2002; mollusks) suggested this
zone may be a true transition zone or ‘‘Provinciatone’’ between the adjacent
Magellanic and Brazilian Provinces.
The distribution of sand dollars was studied by Martínez and Mooi (2005) with
results and explanations comparable to the sub-groups of asterozoans that do not
cross the Rio de la Plata barrier.
10.3.2 Extinct Echinoderm Fauna
There are only eight species of echinoderms in the Uruguayan fossil record, one
crinoid species, one ophiuroid species, and six echinoid species. The crinoid and
ophiuroid species are from the Devonian.The echinoid species are from the
Cenozoic, being abundant in the Late Miocene. During those times (ca. 10 Ma.
ago) the Monophorasteridae (sister group of the Mellitidae) were particularly
abundant and diverse in what are today Uruguay and Argentina. Two species
(Mellita sp. and Encope sp.) are recorded only for the Quaternary and are still
extant in the area.
The following taxonomic arrangement of the fossil species. Suprageneric
classification is based on: Crinoidea, Ausich (1998); Holothuroidea, Pawson et al.
(2010); Ophiuroidea, Smith et al. (1995) and Shackleton (2005); Echinoidea: Kroh
and Smith (2010).
Class Crinoidea J.S.Miller, 1821
Subclass Camerata Wachsmuth and Springer, 1885
10 Echinoderm Research in Uruguay
351