On Giant Filter Feeders 170 Million Years

PERSPECTIVES

PALEONTOLOGY Massive ﬁ lter-feeding vertebrates have roamed the world’s oceans for the past On Giant Filter Feeders 170 million years. Lionel Cavin

he largest living marine verte- years ago), the diversity of mysticete whales these fi shes engulfed water by swimming brates—baleen whales and several was linked to the diversity of diatoms and to with an open mouth and sieved food while T lineages of sharks and rays—feed climatic variations (4 ). water escaped through the gill arches. directly on very small organisms (such as In the Jurassic (200 to 145 million years Giant reptiles roamed the Jurassic and plankton and small fi shes). Planktivorous ago) and the Cretaceous (145 to 65 million Cretaceous oceans, and some huge ray- sharks and rays collect food by fi ltering sea- years ago), ray-fi nned fi shes called pachy- fi nned fi shes—the ichthyodectiforms (bull- water through gill rakers (fi ngerlike pro- cormiforms lived in the oceans. These extinct dog fi sh and relatives)—emerged at the end jections on gill arches), whereas mysticete fishes are regarded as primitive teleosts, of the Cretaceous. But all these beasts were whales sieve small animals from seawater the group to which most living bony fi shes apex predators that fed on large preys, and through whalebone or baleen (comblike belong (5 ). A giant representative from the none had a fi lter-feeding diet. The newly keratin structures in their upper jaws) (1 , Middle Jurassic, Leedsichthys, was up to 9 discovered clade of massive fi lter-feeding 2). On page 990 of this issue, Friedman et m long and has been interpreted as a fi lter fi shes thus fi lls a large ecological niche. al. show that the fi rst known large pelagic feeder ( 6). This massive fi lter-feeding fi sh Marx and Uhen reveal how the taxonomic fi lter feeders, a group of ray-fi nned fi shes, has been regarded as an isolated and fl eeting diversity of another, younger type of mas- persisted between 170 and 65 million years evolutionary experiment. By reinterpreting sive fi lter feeder, the Tertiary baleen whales, ago (3 ). And on page 993, Marx and Uhen old fi ndings, analyzing new fossils, and run- was controlled by biological and environ- show that in the Tertiary (65 to 2.5 million ning phylogenetic analyses, Friedman et al. mental factors, rather than by the amount of show that this and other fossil fi shes form rock in which we might fi nd their fossils.

a clade of massive marine ﬁ lter feeders that Modern cetaceans (whales, dolphins, and on February 22, 2010 Department of Geology and Palaeontology, Natural His- tory Museum, Geneva, Switzerland. E-mail: lionel.cavin@ lived from 170 to 65 million years ago. As porpoises) fall into two groups: the baleen ville-ge.ch today’s planktivorous sharks and rays do (1 ), whales (Mysteceti) and the toothed whales

Marine environments Detritus 100 Primary production www.sciencemag.org

Detritus

10 Downloaded from

K/P boundary

Number of genera Mysticeti Mobulidae

Rhincodontidae

1 Suspension-feeding pachycormids Cetorhinidae

M. JURASSIC L. JURASSIC EARLY CRETACEOUS LATE CRETACEOUS PALEOGENE NEOGENE 161 145 100 65 23 Time (millions of years)

Past diversity of large filter feeders. The diversity of fi lter-feeding pachy- mysticete whales from ( 4). (Inset) At the Cretaceous–Paleogene boundary, the cormids is from (3 ); the dotted line shows the diversity, including ghost lin- food chains based on primary production collapsed, leading to the extinction of eages (which have no fossil record but are inferred to exist to comply with a large suspension feeders and large fi sh-eating fi shes (red), whereas costal and phylogenetic tree) [see supporting online material of (3 )]. The diversity of rays deep-ocean fi shes that relied more on detritus survived. and sharks (Mobulidae, Cetorhinidae, Rhincodontidae) is from (10 ) and that of

968 19 FEBRUARY 2010 VOL 327 SCIENCE www.sciencemag.org Published by AAAS PERSPECTIVES

(Odontoceti). The authors show that the or whether it was controlled by paleogeo- ing point for investigating major events in diversity of both groups can be explained by graphical factors. the history of life ( 3)—and not only an aim diatom diversity in conjunction with varia- What caused the gap between the Juras- per se, as happens too often with fossil fi sh tions in climate, as indicated by oxygen sta- sic/Cretaceous and the Tertiary episodes of studies—and that variations in the diversity ble isotope records. The results add to pre- the natural history of giant fi lter feeders? of life can be read directly from the fossil vious observations that have stressed the It is probably linked with the same event record if precautions are taken (4 ). importance of environmental parameters that caused a mass extinction at the Creta- (both geographic and oceanographic) in the ceous-Paleogene boundary on land. This References evolution of modern cetaceans (7 ). event affected only specific food chains, 1. S. L. Sanderson, R. Wassersug, in The Skull, vol. 3, J. Hanken, B. K. Hall, Eds. (Univ. Chicago Press, Chicago, The two papers change our view of the mainly those based on fresh plants ( 9). In IL, 1993), pp. 37–112. natural history of these evolutionary dis- the oceans, the phytoplankton-based food 2. T. A. Deméré, M. R. McGowen, A. Berta, J. Gatesy, Syst. tant organisms, which share similar trophic chains collapsed, whereas coastal and deep- Biol. 57, 15 (2008). 3. M. Friedman et al., Science 327, 990 (2010). resources (see the figure), and raise new ocean organisms that fed more on detri- 4. F. G. Marx, M. D. Uhen, Science 327, 993 (2010). questions about their evolutionary drivers. tus survived (see the fi gure, inset). The fi l- 5. J. Liston, in Mesozoic Fishes 3—Systematics, Paleo- For instance, it has been shown that marine ter-feeding pachycormiforms, relying for environments and Biodiversity, G. Arratia, A. Tintori, Eds. (Friedrich Pfeil, München, 2004), pp. 379–390. ray-fi nned fi sh diversity was positively cor- food on small organisms low in the trophic 6. D. M. Martill, N. Jahrb. Geol. Paläontol. 1988, 670 related with sea surface temperature in the chain, had the perfect profi le of a victim and (1988). Cretaceous, and that the Cretaceous fossil became extinct. The trophic niche was later 7. M. E. Steeman et al., Syst. Biol. 58, 573 (2009). fi sh record corresponds to a genuine bio- refi lled, fi rst with sharks and rays from ~56 8. L. Cavin, P. L. Forey, C. Lécuyer, Palaeog. Palaeoc. 8 Palaeoec. 245, 353 (2007). logical radiation ( ). Further evolutionary million years ago and then with modern 9. E. Buffetaut, Nature 310, 276 (1984). studies will help to determine whether the cetaceans from ~34 million years ago (see 10. H. Cappetta, in Handbook of Paleoichthyology, vol. 3B, diversity of the Jurassic/Cretaceous fi lter- the fi gure). H.-P. Schultze, Ed. (Friedrich Pfeil, München, 1987). feeder clade was related to climatic factors The two studies also show that phylo- and the diversity of primary producers, and/ genetic reconstructions can be the start- 10.1126/science.1186904 on February 22, 2010

PHYSICS Layer-by-layer growth provides a route to control the properties of complex interacting The Lowdown on Heavy Fermions electron systems.

Piers Coleman

ne of the quests of condensed matter between electrons that drives the development successful in preparing strongly correlated www.sciencemag.org physics is to discover materials with of new kinds of electronic behavior. When the electron materials. The fi rst is to fi nd layered O new types of collective electronic repulsion energy between electrons is small materials where the confinement of elec- properties, such as the giant magnetoresis- compared with their kinetic energy, electrons trons to two dimensions enhances their inter- tance materials ( 1) now used for memory move independently, but when the interactions. The other is to tune the material by storage or high-temperature superconductors actions are large, electron motions become some external parameter (e.g., pressure, mag- (2 ). Such “strongly correlated electron” mate- highly correlated, and may develop unexpect- netic or electric fi eld) to the brink of magnetic rials challenge our understanding and provide edly new types of collective behavior in order instability, a point in the phase diagram called Downloaded from the grist for future technologies. However, to try and lower the Coulomb energy. a “quantum phase transition” (4 , 5 ). Interac- identifying new kinds of electronic behav- Two strategies have proven particularly tions between electrons inside materials are ior is still serendipitous, largely because the materials structures A of greatest interest do not crystal- Exerting control. Electrons interact via the lize to order. On page 980 of this exchange of magnetic and electric fl uctuations issue, Shishido et al. (3 ) introduce that radiate outwards. Interactions decay more – a systematic approach based on Celn3 e– e slowly and are hence stronger in layered two- molecular beam epitaxy for the dimensional metals because they radiate in fewer directions. (A) Three-dimensional CeIn . (B) Layers preparation of complex interact- 3 of heavy-fermion CeIn made by MBE, as in the ing electron materials, thus open- 3D metal 3 study by Shishido et al., behave as a quasi–two- ing up the possibility of making dimensional metal, in which interactions decay available many new structures B more slowly, and are stronger. not currently accessible to direct chemical synthesis. Celn It is the Coulomb repulsion 3 Laln3 Celn3 Center for Materials Theory, Rutgers Uni- versity, Piscataway, NJ 08854–8019, USA. 2D metal E-mail: [email protected]

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