After an asteroid slammed into Earth 66 million years ago, now called the Cretaceous-Paleogene (K-Pg) extinction, fish in the fossil record went dark for about 10,000,000 years. When they have been found again, any species that look different than those that came before, leaving scientists to wonder what evolutionary paths fishes took between about 66 and 56 million years ago. A new paper describes marine fishes dated to 62.2 million years ago, helping to fill that interval, including the earliest known fossil skeletons of jack, a type of sportfish, moonfish and pipefish, the family to which seahorses belong.

In total, they discovered 21 kinds of fishes across nine orders of fish. Most of the fishes are percomorphs, a major group in today's oceans but which were relatively uncommon during the age of dinosaurs

The researchers also wondered what their findings meant in the broader context of the fossil record early after the K-Pg extinction. Comparing their findings to information from other fossil deposits, the researchers found that most of the percomorphs found just after the extinction event were mostly in the tropics. There appeared to be fewer percomorphs in higher latitudes. Only long after the extinction did percomorphs seem to become common everywhere.

The researchers say there could be many reasons why the 10-million year gap has occurred. One reason could be that the majority of paleontological work has been concentrated in Europe and North America, missing valuable deposits that might be present elsewhere.

Citation: Sanaa El-Sayed et al., Rise of modern marine fishes captured in an early Paleocene Lagerstätte.Sci. Adv.12,eaec8978(2026). https://www.science.org/doi/10.1126/sciadv.aec8978

Laser-assisted electron scattering (LAES) is a tool for understanding how electrons interact with matter under the influence of strong fields. When electrons are fired at atoms or molecules, they are scattered in all directions; the presence of strong light can change the way in which the scattering takes place due to an exchange of energy with the surrounding light field. The amount of energy exchanged is precisely governed by quantum mechanics and yields characteristic shifts in the energies held by scattered electrons.

Now, researchers have succeeded in detecting laser-assisted electron scattering using circularly polarized light for the first time. The use of circularly polarized light promises valuable insights into how atomic scale “helicity” impacts how electrons interact with matter and light. Using synchronized femtosecond laser pulses and electron pulses directed at argon atoms, they succeeded in detecting a  laser-assisted electron scattering  signal showing excellent agreement with theory.
 

Recent experiments have used LAES measurements to show how strong electromagnetic fields can fundamentally change the behavior of matter. Examples include “light-dressing,” where strong laser light modifies the distribution of electrons around atoms.

A key challenge in recent work on LAES is the use of circularly polarized light. As a wave of oscillating electric and magnetic fields, light can have a “polarization” direction in which the electric fields oscillate. In circularly polarized light, the polarization direction rotates as the wave propagates forward. Since it has a characteristic “handedness,” of whether it rotates left or right, the way in which it interacts with matter may be sensitive to any intrinsic “chirality” in the structure, the “handedness” of the structure itself. Importantly, measuring the difference between left and right-handed light in LAES gives access to the “phase” of scattered electrons, an inaccessible quantity using linearly polarized light. However, the gold standard measurement of LAES using circularly polarized light in single atoms has not yet been achieved.

The team successfully demonstrated LAES in argon using femtosecond circularly polarized laser pulses in the near-infrared range, and simultaneous electron pulses. They were able to measure the energy and angular distributions of electrons scattered by argon in the presence of femtosecond laser pulses, finding peaks characteristic of the LAES process. While the signal was weaker than with linearly polarized light, the scattering signal agreed with a form expected from seminal extensions to LAES theory (Kroll-Watson theory). At this point, they were unable to measure the minute difference between LAES with left and right-handed light.

While there is further work to be done to improve detection efficiency and statistical accuracy, the team’s work demonstrates how LAES with circularly polarized light might illuminate new aspects of electron-matter interaction in strong fields.