For a long time now, we have known modern birds evolved from certain lineages of dinosaurs that lived millions of years ago. This has led researchers to look to dinosaurs to explain some of the features unique to birds, for example, feathers, bone structure and so on. But there’s something special about the wings of birds in particular that piqued the interest of researchers at the University of Tokyo’s Department of Earth and Planetary Science.

“At the leading edge of a bird’s wing is a structure called the propatagium, which contains a muscle connecting the shoulder and wrist that helps the wing flapping and makes bird flight possible,” said Associate Professor Tatsuya Hirasawa. “It’s not found in other vertebrates, and it’s also found to have disappeared or lost its function in flightless birds, one of the reasons we know it’s essential for flight. So, in order to understand how flight evolved in birds, we must know how the propatagium evolved. This is what prompted us to explore some distant ancestors of modern birds, theropod dinosaurs.”

Theropod dinosaurs, such as Tyrannosaurus rex and Velociraptor, had arms not wings. If the scientists could find evidence of an early example of the propatagium in these dinosaurs, it would help explain how the modern avian branch of the tree of life transitioned from arms to wings. However, it’s not so simple, as the propatagium is made up of soft tissues which do not fossilize well, if at all, so direct evidence might not be possible to find. Instead, the researchers had to find an indirect way to identify the presence or lack of a propatagium in a specimen.

“The solution we came up with to assess the presence of a propatagium was to collect data about the angles of joints along the arm, or wing, of a dinosaur or bird,” said Yurika Uno, a graduate student at Hirasawa’s lab. “In modern birds, the wings cannot fully extend due to the propatagium, constraining the range of angles possible between connecting sections. If we could find a similarly specific set of angles between joints in dinosaur specimens, we can be fairly sure they too possessed a propatagium. And through quantitative analyses of the fossilized postures of birds and nondinosaurs, we found the telltale ranges of joint angles we hoped to.”

Based on this clue, the team found that the propatagium likely evolved in a group of dinosaurs known as the maniraptoran theropods, including the famous Velociraptor. This was backed up when the researchers identified the propatagium in preserved soft tissue fossils, including those of the feathered oviraptorosaurian Caudipteryx and winged dromaeosaurian Microraptor. All the specimens they found it in existed prior to the evolution of flight in that lineage.

This research means it’s now known when the propatagium came into being, and it leads researchers on to the next question of how it came to be. Why these particular theropod species needed such a structure to better adapt to their environment might be a harder question to answer. The team has already begun exploring possible connections between the fossil evidence and embryonic development of modern vertebrates to see if that will shed any light on it. The team also thinks some theropods might have evolved the propatagium not because of any pressure to learn to fly, as their forelimbs were made for grasping objects and not for flying.

“Dinosaurs portrayed in popular media are becoming more and more accurate,” said Hirasawa. “At least now we get to see features like feathers, but I hope we can see an even more up-to-date representation soon where theropods have their propatagium too.”

Maltreatment during childhood is an especially serious risk factor for health problems in the exposed individual, as it brings a host of lifelong consequences. Among the impacts are physical, mental, behavioral, and social ramifications that can continue through pregnancy and parenthood. As a result, adverse experiences during the parents’ childhood can affect their own children’s development and health.

Higher risk of asthma, ADHD, autism, and depression

In the newly published study, a team of researchers headed by Dr. Claudia Buss, a professor at the Institute of Medical Psychology at Charité, shows that health problems are more common in children of mothers who experienced maltreatment themselves as children. The researchers define maltreatment as physical, emotional, or sexual abuse or neglect by a parent or guardian leading to physical or emotional harm or the threat of harm to a child. They analyzed data on more than 4,300 American mothers and their children from 21 long-term cohorts. Mothers reported on their childhood experiences and provided information on health diagnoses in their biological children up to the age of 18, or this information was collected during visits conducted as part of the study. This valuable trove of data extending across two generations of the same family allowed researchers to identify meaningful connections.

They found that children of mothers who reported adverse experiences were at higher risk of asthma, attention-deficit/hyperactivity disorder (ADHD), and autism. These children also have a higher incidence of symptoms and behaviors associated with depression and anxiety disorders, which are known as “internalizing” disorders. Daughters of mothers in this group are also at higher risk of obesity than their sons. “All of these connections are independent of whether the mother has the same diagnosis,” explains Buss, the study’s lead author. “That suggests that the risk of that particular health problem is not being transmitted genetically.”

First study to cover multiple health outcomes

Researchers have not yet fully decoded the exact mechanisms by which the risk is passed on to the next generation. There are indications that adverse childhood experiences could affect maternal biology during pregnancy, as for example stress hormones. This can affect fetal development in a way that the offspring become more vulnerable for impaired health. There is evidence that biological changes like these are more pronounced in mothers who have developed mental health problems, such as depression, as a consequence of their traumatic experiences. If the mother’s mental health is affected by her childhood experiences, this may also impact on how she interacts with her child once it is born, which is likely to be just as important a factor in these multigenerational effects.

“To our knowledge, this is the first study to examine multiple health problems at once in relation to early trauma in mothers in a large, sociodemographically and ethnically diverse sample. That has been done primarily for individual diseases in the past,” explains Dr. Nora Moog, also from the Institute of Medical Psychology at Charité and first author of the publication. In keeping with this approach, the researchers showed that children of mothers exposed to early trauma are at greater likelihood of developing multiple physical and mental health problems. The risk is also greater the more serious the mother’s childhood experiences were. “At the same time, I should stress that our findings do not mean that all children of mothers with adverse childhood experiences automatically end up with health problems,” Buss says, providing context for the group’s findings. “The risk is elevated, but it doesn’t necessarily lead to a specific health problem.”

Early identification and support for those affected

“I assume that appropriate support for mothers who suffer from the consequences of childhood maltreatment can have a positive effect on their health and well-being and that of their children. That means it’s very important to identify these mothers and children early on,” Buss points out. One way to do this would be to have doctors address parents’ own childhood experiences during prenatal or pediatric checkups and provide information on how to contact various support programs or counseling services. This kind of early intervention could help two generations: the parent, who experienced maltreatment and may be suffering from health consequences; and the child, who could be prevented from developing health problems.

Developing new, targeted therapeutic measures will depend on better understanding the exact mechanisms by which the elevated risk of health problems is passed on to the next generation. The research team is currently working on that. The researchers also plan to conduct follow-up studies to investigate which children remain resilient, meaning they do not suffer consequences beyond one generation: What makes them, their mothers, and their social environment different? Beyond that, the father’s childhood experiences have received relatively little attention so far, but there are indications that these experiences can also be passed on to the next generation, albeit in some cases by different mechanisms than those involved in mother-child transmission. The researchers plan to explore these research questions in further detail in future projects as well.

About the study

The international team of researchers analyzed the data of 4,337 American mothers from 21 long-term cohorts with an eye to the mothers’ childhood experiences. They also examined information on health diagnoses in the mothers’ biological children up to the age of 18. The cohort data were provided by a research program named Environmental influences on Child Health Outcomes (ECHO). ECHO encompasses 69 cohorts in the United States. It is supported by the National Institutes of Health (NIH). Dr. Claudia Buss, a professor at the Institute of Medical Psychology at Charité and adjunct professor at the Department of Pediatrics at the University of California Irvine, led the study. She is a principal investigator of a research group within the ECHO consortium and has furthermore received a Starting Grant from the European Research Council (ERC) and funding from the German Research Foundation (DFG) and the German Federal Ministry of Education and Research (BMBF).