When I was little, my big brother would take me fossil-hunting on a quest for trilobites, marine arthropods that have been extinct for around 250 million years. Occasionally we'd find lone specimens but never a bunch of them in a conga line as seen above. Paleontologists at France's Université Claude Bernard Lyon 1 studied lines of nearly two dozen trilobytes from Moroccan fossil beds to gain insight into the origins of collective social behavior. From the New York Times:

These trilobites lived during the Great Ordovician Biodiversification Event, a period defined by a dramatic increase in the variety and complexity of marine life. It was the evolutionary sequel to the first major diversification event, the so-called Cambrian explosion, which established most animal groups in the fossil record some 541 million years ago.

Before the Cambrian, there is “no evidence for group behavior” in animals, (paleontologist Jean) Vannier said, because Precambrian life-forms lacked sophisticated nervous systems.

Ampyx trilobites, in contrast, had an anatomy that could have enabled chemical communication and sensory stimulation. Though they were visually blind, the trilobites had long spikes protruding from their rear ends. These appendages clearly overlap and link individuals in the fossilized chains, and perhaps allowed tactile or pheromone signals to be exchanged.

This week, French paleontologists unearthed a two-meter long dinosaur femur in southwestern France. From Reuters:

The... femur at the Angeac-Charente site is thought to have belonged to a sauropod, herbivorous dinosaurs with long necks and tails which were widespread in the late Jurassic era, over 140 million years ago.

“This is a major discovery,” Ronan Allain, a paleontologist at the National History Museum of Paris told Reuters. “I was especially amazed by the state of preservation of that femur.”

“These are animals that probably weighed 40 to 50 tonnes.”

Engineers digging to lay water pipes in Oxfordshire, England turned up more than two dozen 3,000-year-old human skeletons, some of which were likely killed in sacrifices. From CNN:

The remains of 26 people from the Iron Age and Roman periods were found, including a woman with her feet cut off and her arms bound behind her head, and another person with their skull placed by their feet...

Archaeologists inspecting the remains believe the people found were from the same community involved in creating the Uffington White Horse, a prehistoric chalk sculpture on a nearby hill...

The findings "provided a glimpse into the beliefs and superstitions of people living in Oxfordshire before the Roman conquest," said Neil Holbrook, chief executive of Cotswold Archaeology. "Evidence elsewhere suggests that burials in pits might have involved human sacrifice."