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might have been different in the Early and

Middle Triassic ( 12 ). If ocean productivity

was crucial for fueling the rise of today’s

giants ( 3 ), was it not for ichthyosaurs, too? 

Sander et al. provide insight into how

Triassic ocean ecosystems promoted and

maintained vertebrate gigantism. C. youn-

gorum was one of several species of ichthyo-

saurs recovered from the same strata of rocks

in Nevada. The fossil invertebrate fauna from

the site is dominated by ammonoids—now-

extinct shelled cephalopods—which repre-

sented the likeliest diet for ichthyosaurs. By

modeling the energy flux through this eco-

system, Sander et al. show that there was

enough food in the open ocean to support

large predators and that the marine food web

was stable, populated by pelagic conodonts

(extinct, eel-like jawless vertebrates), am-

monoids, and small ichthyosaurs as prey for

larger predators. One possibility that should

be explored further is whether conditions in

the open oceans in the Proto-Pacific were bet-

ter for promoting gigantism than the hotter,

shallower oceans in the Tethys Sea, where the

Chinese early ichthyosaurs are found.

Regardless of pace, do ocean giants share

similar pathways to gigantism? The com-

parison of ichthyosaurs to whales leads to

even more questions about the patterns and

processes of these parallel evolutionary in-

novations: When and how did ichthyosaurs

evolve key adaptations for live birth under-

water, a stable body temperature, crucial

feeding strategies, and new ways to swim?

We are used to thinking of ichthyosaurs as

the dolphins of the Mesozoic, but that might

cloud important and interesting differences.

For example, Triassic ichthyosaurs such as

Cymbospondylus had longer necks, torsos,

and tails and were probably more “lizard-

like,” with different foraging and behavioral

ecologies compared with the more iconic ich-

thyosaurs from the Jurassic ( 13 ).

The largest whales today are threatened

with extinction in large part because of their

extreme size, which makes them dependent

on ephemeral food resources, and because of

human activities. For ichthyosaurs, the early

innovation of gigantism may also have car-

ried extinction risk, but the history of body

size in this group is complex. Ichthyosaurs

were top ocean predators for three times as

long as whales have even existed. The group

survived the Triassic-Jurassic mass extinc-

tion event, which reduced their diversity in

size and feeding ecology, 50 million years

after the appearance of C. youngorum ( 13 ).

Ichthyosaurs then survived more than 100

million years longer until finally going ex-

tinct in the Cretaceous period, possibly be-

cause of climate change ( 14 ).

It remains unclear whether ichthyosaurs

were ecosystem engineers in the way that

some large species of whales are ( 11 ), but it

is clear that sunken ichthyosaur carcasses

served as a substrate for seafloor communi-

ties in the way that whalefalls do today ( 15 ).

Ichthyosaur history tells us that ocean giants

are not guaranteed features of marine ecosys-

tems, which is a valuable lesson for all of us

in the Anthropocene, especially if we want to

sustain the presence of the surviving ocean

giants among us that contribute to our own

well-being ( 11 ). j

REFERENCES AND NOTES

1. J. A. Goldbogen et al., Science 366 , 1367 (2019).


2. N. D. Pyenson, G. J. Vermeij, Biol. Lett. 12 , 20160186
   (2016).


3. G. J. Slater, J. A. Goldbogen, N. D. Pyenson, Proc. Biol. Sci.
   284 , 20170546 (2017).


4. R. Motani, G. J. Vermeij, Biol. Rev. Camb. Philos. Soc. 96 ,
   1769 (2021).


5. N. P. Kelley, N. D. Pyenson, Science 348 , eaaa3716
   (2015).


6. P. M. Sander et al., Science 374 , eabf5787 (2021).


7. R. Motani et al., Nature 517 , 485 (2015).


8. V. S. Engelschiøn et al., Norwegian Journal of Geology 98 ,
   239 (2018).


9. B. C. Moon, T. L. Stubbs, Commun. Biol. 3 , 68 (2020).


10. N. D. Pyenson, Curr. Biol. 27 , R558 (2017).


11. M. S. Savoca et al., Nature 599 , 85 (2021).


12. C. P. A. Smith et al., Sci. Rep. 11 , 19657 (2021).


13. P. M. Thorne, M. Ruta, M. J. Benton, Proc. Natl. Acad. Sci.
    U.S.A. 108 , 8339 (2011).


14. V. Fischer, N. Bardet, R. B. J. Benson, M. S. Arkhangelsky,
    M. Friedman, Nat. Commun. 7 , 10825 (2016).


15. S. Danise, R. J. Twitchett, K. Matts, Nat. Commun. 5 , 4789
    (2014).

10.1126/science.abm3751

Million years ago

Triassic Jurassic Cretaceous Cenozoic

252* 201* 145 ~94 66* 0*

Enters

water

Gigantism reached

in <3 million years

Ichthyosaur

extinction

Enters

water

Gigantism reached

after 50 million years

Ichthyosaurs Cetaceans

*Mass extinction events

MAGNETISM

Magnetic

control in the

terahertz

Strong magnon-phonon

coupling may help develop

superfast optical drives

By Dominik M. Juraschek1,2

and Prineha Narang^1

M

agnetic materials are central to in-

formation storage devices, with on-

going research seeking to develop

faster and more energy-efficient

systems. The individual bits of

data, written as 1’s and 0’s, can be

stored as different orientations of magnetic

moments. Conventionally, an electromag-

netic head is used to flip these bits between

1 and 0, and the read and write speeds using

this method are currently limited to giga-

hertz frequencies. A substantial amount of

energy is used to drive electric currents that

generate the magnetic fields. Instead of ma-

nipulating magnetic moments with slow or

static magnetic fields, an intriguing alterna-

tive involves coupling light from a laser to

their quantum mechanical states. On page

1608 of this issue, Mashkovich et al. ( 1 ) re-

port the coupling of light, magnetism, and

the crystal structure of a material, which

opens new possibilities for controlling the

magnetic state of materials on very short

time scales.

Over the past two decades, researchers

have explored the use of laser pulses to

modify magnetism and push the boundar-

ies of read-write speeds to the terahertz and

even petahertz range. When a laser is shone

onto a magnetic material, the electromag-

netic field of the incident light interacts

with the spins of the atoms and can trigger

collective precessions of the spins around

their equilibrium orientation. These preces-

sions form quantized quasiparticles, collec-

tive interactions of atoms that act as single

particles, that are called “magnons.” If the

amplitude of these precessions becomes

large enough, entire magnetic domains in

the material may change their orientation,

(^1) Harvard John A. Paulson School of Engineering and Applied
Sciences, Harvard University, Cambridge, MA 02138, USA.
(^2) School of Physics and Astronomy, Tel Aviv University,
Tel Aviv 69978, Israel. Email: [email protected];
[email protected]
24 DECEMBER 2021 • VOL 374 ISSUE 6575 1555
Two stories of ocean gigantism, eras apart
Ichthyosaurs were the first ocean giants, and the discovery of Cymbospondylus youngorum narrows the
window for how fast they evolved extremely large body sizes. Although ichthyosaurs evolved whalelike sizes
in the first 1% of their evolutionary history, it later took cetaceans nearly 90% of their evolutionary history to
evolve similarly large sizes.