While the range of physical diversity dogs show is often thought to be the result of intense breeding over the last 200 years, a new study – based on tracing 50,000 years of canid skull evolution – suggests domestic dogs began developing their distinctive forms thousands of years before humans started shaping modern breeds. Dogs at this time were shaped by early human influence, environmental shifts, and changing food sources. The origins and early diversification of domestic dogs are among the most debated topics in archaeology. Previous studies indicate that dogs first appeared during the Late Pleistocene, with major distinct genetic lineages appearing by at least 11,000 years before present. Because of their long association with humans, modern dogs exhibit an exceptional range of physical diversity, in both size and shape. It’s thought that much of this diversity is the direct result of intense breeding that happened in recent centuries. However, exactly when distinct dog variation first began to take shape is poorly understood and has been limited by the scarcity of Pleistocene specimens, the fragmentary condition of available remains, and the challenge of distinguishing early dogs from wolves based solely on skeletal morphology.

 

To trace how the physical forms of domestic dogs developed and diversified over time, Allowen Evin and colleagues used advanced 3D morphometric analysis to examine 643 canid skulls spanning 50,000 years, allowing them to measure subtle differences in skull shape and size with exceptional precision. By creating digital 3D models through laser scanning or photogrammetry, Evin et al. compared specific cranial features across ancient and modern dogs and their wild relatives. The findings show that distinct dog-like skull traits first appeared during the early Holocene, evidenced by 10,800-year-old remains recovered in Russia. Notably, all of the Ice Age canid skulls examined closely resembled wolves, suggesting that although visible domestication traits appeared only after 11,000 years ago, the process of domestication likely began earlier during the late Pleistocene, which is consistent with genetic evidence. The oldest known dogs from the Mesolithic and Neolithic possessed skulls that fell within the modern range of sizes but were typically smaller and less varied, lacking exaggerated traits that characterize many present-day breeds. Even so, their diversity was surprising; early Holocene dogs exhibited roughly half the morphological range seen in modern dogs and twice that of their Pleistocene wolf ancestors, suggesting that notable variation in dog form had already emerged millennia before modern breeding practices. The retention of wolf-like characteristics in some modern breeds highlights the gradual and complex evolution of the dog from their wild wolf ancestors. Evin et al. also found that ancient wolves were more varied in skull shape and size than they are today. “The domestication of dogs has captivated attention because of the close bonds that many humans share with dogs,” Melanie Fillios writes in a related Perspective. “[Evin et al.’s] research contributes to the wider understanding of domestication as a complex, multifaceted biological and cultural process in which thousands of years of human and animal history are intertwined.”

Just a few million years after the end-Permian mass extinction event (EPME), aquatic reptiles and other vertebrates had recovered to form thriving and diverse oceanic ecosystems, according to a study of an Early Triassic-age fossil site in the Arctic. The findings challenge previous assumptions of a slow and gradual establishment of mid-Triassic marine communities and suggest that vertebrate evolution paralleled the rapid resurgence of invertebrate life in the Early Triassic. The EPME, which occurred roughly 251.9 million years ago (Ma), wiped out upwards of 90% of all marine species on Earth. It has long been thought that recovery of ocean ecosystems following this event was slow, taking over eight million years. However, recent evidence indicates that, for some communities, such as invertebrates and bony fish, populations rebounded much more quickly than previously believed. The establishment and diversification of marine tetrapod communities – which first emerged in post-EPME oceans – is far less understood and is still considered to have been a long, gradual process with staged ecological complexification.

 

Here, Aubrey Roberts and colleagues describe new findings from the Grippia Bonebed (GBB), a mid-Early Triassic (~249 Ma) fossil site on the Arctic island of Spitsbergen in Svalbard, Norway. According to Roberts et al., the GBB fossil assemblage is notably rich, containing tens of thousands of fossils from an array of oceanic vertebrate species, and represents the earliest known marine tetrapod community from a stratigraphically constrained deposit. Using large-scale taxonomic comparisons and diversity analyses of the GBB fauna, the authors identified a highly diverse and complex marine community, composed of aquatic reptiles and amphibians, including apex-predator ichthyosaurs, smaller ichthyopterygians, durophagous ichthyosauriforms, semi-aquatic archosauromorphs, euryhaline temnospondyls, as well as a variety of fish species, all occupying multiple trophic levels. The findings suggest that many marine tetrapod lineages had already diversified and adapted to oceanic life soon after – or even before – the EPME.

As human groups migrated and settled across Holocene Eurasia, dogs often traveled with them, researchers report in a new genomic study – and sometimes dogs were traded among populations. The study reveals the integral role these animals played in culture and exchange. For at least the last 11,000 years, dogs and humans have lived side-by-side. However, the true antiquity of their association with humans remains elusive. Some evidence suggests that major dog lineages in different parts of the world appear to have diversified thousands of years earlier, suggesting that these dogs may have traveled with humans as they colonized different parts of Europe, Asia, and the Arctic, forming integral parts of the cultural and biological exchanges of early migrations. To explore how dogs and humans moved together, Shao-Jie Zhang and colleagues sequenced 17 ancient dog genomes dated between 9,700 and 870 years ago from sites across Siberia, the Central Eurasian Steppe, and northwest China, regions that experienced major shifts in human ancestry and culture during the Holocene. These new genomes were analyzed alongside 57 previously published ancient dog genomes, 160 modern dog genomes, and 18 ancient human genomes, which allowed Zhang et al. to explore how ancient dog lineages intersected with human migrations and cultural exchanges. The findings show that the movement of domestic dogs across the Eurasian Steppe, East Asia, and Eastern Siberia often coincided with the migrations of hunter-gatherers, farmers, and pastoralists, suggesting that dogs very commonly travelled alongside humans and were integrated into diverse societies. Some mismatches between dog genetic lineage and human population histories indicate that communities with different ancestries likely exchanged dogs with one another. This was particularly true for Arctic-lineage dogs, which were found among hunter-gatherer groups with differing ancestries across Eurasia.

HHMI Investigator Nicole King and Postdoctoral Researcher Jacob Steenwyk used large datasets and a combination of analyses to understand which organism roots the animal tree of life: the simple sponge or the more complex comb jelly.

The new research provides compelling evidence that sponges evolved first, suggesting that muscle-less and neuron-less organisms gave rise to more complex animals, including humans.

Knowing which animal is at the base of the tree of life helps researchers understand how organisms are related to each other and how complex features, like the nervous system, evolved.