Page 2 - A_new_subtropical_temperate-Borghi2016
P. 2
2 E. Borghi and V. Garilli
Downloaded by [vittorio garilli] at 22:43 08 June 2016 A further, more interesting case is that of the still extant brooding echinoids and to the reliability of the assumed
family Temnopleuridae Agassiz, 1872, which disappeared relationship between their reproductive strategy/sexual
from the eastern Atlantic domain in the very Early Pleisto- dimorphism and their morphology.
cene and has never been recorded in the Mediterranean
area to date. Species of this family are characterized by a Palaeoclimatic framework
plate ornamentation with pits going deep down into the
test surface. Some temnopleurid species exhibit morpho- The Pliocene (ZancleanÀPiacenzian) and the Pleistocene
logical differences that are commonly related to sexual (GelasianÀTarantian) epochs, from about 5.3 Ma to 0.012
dimorphism. These species are supposed to be marsupiate, Ma, span an interval of global climate changes. Periods of
with a brooding strategy that might increase their adapt- warmth with low-amplitude variability transitioning to
ability to cold high latitudes and, in general, to environ- high-amplitude variability, associated with the initiation
mental conditions of marked physical stress (see Blake & of Northern Hemisphere glaciation, at about 3.6 Ma
Zinsmeister 1991, and Gillespie & McClintock 2007 for (Mudelsee & Raymo 2005), were followed by the onset of
an overview on brooding in echinoids). It is still contro- marked alternations of warmer and colder phases, which
versial whether fossil Temnopleuroidea Kroh & Smith, had their peak in the Middle to Late Pleistocene 100 kyr-
2010, having a large apical disc forming more than two- controlled ‘Ice Ages’ (Raymo 1994; Zachos et al. 2001;
thirds of the upper surface, are actually female specimens. Raymo & Nisancioglu 2003; Lisiecki & Raymo 2005;
In some cases, on the basis of this morphological feature, Dowsett & Caballero Gill 2010; Dowsett et al. 2013). The
marsupialism and reproduction involving sexual dimor- early Pliocene is considered to have been almost globally
phism and parental brooding have been inferred for fossil characterized by a warm climate, and a much warmer
taxa of this group whose apical system structure is palaeoclimate is recorded in the mid-Piacenzian (previ-
unknown (Dudicourt et al. 2005; Pereira 2010). Con- ously mid-Pliocene) warm period with a thermal regime
versely, the statistical dataset assembled on Australian comparable to that projected for the year 2100 (Haywood
Tertiary temnopleuroids by Jeffery & Emlet (2003) sug- & Valdes 2004; Meehl et al. 2007; Dowsett & Caballero
gests that the presence of a large apical disc does not nec- Gill 2010; Dowsett et al. 2013; De Shepper et al. 2014).
essarily indicate dimorphism; however, this matter has However, at northern latitudes of the eastern Atlantic,
never been addressed exhaustively. Within Recent temno- palaeoclimatic reconstructions for the late early Pliocene
pleuroids, the marsupiate condition has been detected in Coralline Crag Formation are conflicting (Johnson et al.
the family Trigonocidaridae Mortensen, 1903 only in the 2009; Williams et al. 2009 with references). There is evi-
genus Hypsiechinus Mortensen, 1903 (Philip & Foster dence that the climate at these latitudes became warmer
1971; Jeffery & Emlet 2003). Since Thomson (1878), during the mid-Piacenzian (Dowsett et al. 1992) and dete-
brooding in echinoids has been a debated topic of interest riorated when long-term cooling started in the late Piacen-
as it is difï¬cult to state whether just single or multiple zian, with marked steps related to the major changes in
driving factors, or a general environmental factors Northern Hemisphere ice sheets (Lawrence et al. 2010). A
(stressed or stable), may select for this mode of reproduc- mid- to warm-temperate climate has been inferred for the
tion (Gillespie & McClintock 2007 with references). One Early Pleistocene Red Crag Formation in eastern England
interpretation is that marsupialism and brooding are (Waltononian Red Crag), with cooling at c. 2.7 Ma
particularly adapted to climatic cooling and/or to cold- (Wood 2009) and c. 2.5 Ma (Head 1998). This setting
temperature settings (Poulin & Feral 1996, 1998; changed to a subpolar climate by 2.0 Ma, as recorded at
Neraudeau et al. 2003). A different interpretation consid- DSDP site 548 in the north-east Atlantic (Loubere &
ers environmental stability, especially in nutrient supply, Moss 1986).
and the life-history strategies as the main drivers in select-
ing marsupiate echinoids, and in triggering their At the southernmost latitudes, during the Zan-
biogeographical dynamics (McNamara 1994). cleanÀmid-Piacenzian interval, subtropical conditions
occurred in the mid-Atlantic Mondego Basin (Silva et al.
Here we report on abundant and well-preserved 2010; see also Monegatti & Rafï¬ 2007), when the Medi-
echinoid fossils collected from several Italian deposits terranean Basin was experiencing warmer conditions with
that formed at a key time in the Early Pleistocene. These a tropical climate (Monegatti & Rafï¬ 2001). From that
echinoids share original and undescribed features within time on, even the Mediterranean progressively underwent
the family Temnopleuridae and are described as Placenti- climatic deterioration with major cooling events at c. 3.0,
nechinus davolii gen. et sp. nov. We discuss the occur- 2.5 and 2.1 Ma (late PiacenzianÀGelasian) as indicated
rence of this family in the Mediterranean, and attempt to by changes in mollusc settings (Monegatti & Rafï¬ 2001).
outline the palaeoenvironmental factors that caused its These events are also recognized in the formation of char-
southward shift and its enigmatic disappearance from the acteristic sequences with shallow-water calcarenite bod-
European domain. This contributes to the controversial ies, which are exposed in northern (Emilia Romagna) and
explanation of the Cenozoic migration and evolution of
