Dinosaur teeth uncover evolutionary secrets

UTM paleontologists search the past to learn how mammalian teeth evolved

Dinosaur teeth uncover evolutionary secrets

UTM paleontologists, professor Robert Reisz and former PhD student Aaron LeBlanc, published studies in PLOS One and the Proceedings of the Royal Society B that shed light on the complex evolution of teeth.

In PLOS One, Reisz and co-authors published an article that discusses Changchunsaurus parvus from the ornithopod family of dinosaurs. Ornithopods are herbivorous dinosaurs. Based on fossil records, ornithopods used their beaks to rip plants from the ground and had muscles to chew through coarse vegetation.

Reisz and LeBlanc explored the importance of this species in understanding the evolution of dentition in dinosaurs and a newfound form of teeth replacement.

LeBlanc’s study in the Proceedings of the Royal Society B located points of evolutionary change in mammalian dentition and delved into how mammalian dentition has evolved over the last 300 million years.

Both studies examined the fossil record by sawing off thin slices of tissue from the desired region. These slices were then polished to create transparent samples. The resulting slice was then subjected to three-dimensional analysis and subsequent computer configuration.

Herbivorous ornithopods are often studied due to the myriad of dental innovations they developed to cope with their diet. C. parvus was specifically studied, as it precedes major innovations in dinosaur dentistry and was thought to possess an ancestral version of previously investigated structures.

The thin sections examined confirmed the function of some components of the dental network. However, they also exhibited a novel form of tooth replacement, which was essential in herbivores due to the extensive pressures of a plant-based diet.

Reisz’s study also solidified that C. parvus had the earliest known occurrence of wavy enamel. This type of enamel was previously disassociated with the ornithopod family and its discovery in C. parvus opens their phylogenetic relationships for discussion.

The results are significant. C. parvus appears at a pivotal point in the evolutionary history of the tooth and understanding its dentition better will lead to a more complete understanding of teeth in general.

LeBlanc’s study examined tooth complexity.

Researchers previously believed that mammals had the most complex form of teeth, while reptiles possessed a simpler version. This was a result of mammals having a ligamentous attachment mechanism for teeth compared to the reptilian teeth being fused directly to the jaw.

But through observing thin sections of therapsid — early reptiles — teeth, Reisz and LeBlanc observed ligamentous structures similar to mammals.

Further study of thin sections from a variety of organisms implied that teeth ligaments developed before the divergence of mammals from reptiles, and that the reptilian fused teeth arrangement is in fact due to calcification — the accumulation of solid calcium deposits — of teeth over time.

Insight into dental history allows for a more comprehensive understanding of our teeth, and the resulting development of new theories, techniques, and explanations in dentition.

Blind as a bat

Visual constraints were necessary for the evolution of echolocation in bats

Blind as a bat


Believe it or not, Batman was not the first winged creature to use echolocation to hunt down his prey — ancestors of the modern bat began using echolocation, the process in which objects are located by reflected sound, between 65 million and 85 million years ago.

John Ratcliffe, an Assistant Professor of Biology at UTM, and his team used molecular phylogeny techniques to decode the evolution of echolocation in bats, reconstructing our perspective on how and why these creatures came to be sonar crusaders of the night.

Their study, recently published in Nature Communications, has built on an existing phylogenetic study to reveal that bats evolved advanced biosonar capabilities through ancient tradeoffs between vision and echolocation.

Bats are the second largest order of mammals in the world, with more than 1,300 species. The bulk of these species are carnivorous and nocturnal, hunting small insects in the night using echolocation.

The researchers used phylogenetic comparative methods to understand evolutionary relationships between sensory systems, neuroanatomy, and morphology in bats. The results of the study indicate that ancestral bats possessed insufficient visual capabilities to hunt small prey at night but had the neuroanatomical potential to echolocate. This proved that there was a pre-existing opportunity for echolocation to flourish into an advanced sensory system in future descendants.

Evolutionarily, bats have continuously exhibited processes of behavioural tradeoff: species with poor echolocation abilities tend to have better visual resolution, and vice versa.

They further found that modern bats that use echolocation of the weakest frequency had the best vision out of those in all other sensory frequency groups, demonstrating that this tradeoff can function in either direction. The non-echolocating pteropodid is an example of a family with this tradeoff.

Surprisingly, the pteropodids have auditory brain regions the same size as echolocators. This vestige confirmed that bats from this family were once capable of echolocating but have since lost the trait. This is in contrast to the alternative scenario that proposes they evolved independently of echolocators — instead they are descendants of the same group.

This study not only answers questions about the evolution of a key trait of one of the most diverse mammals in the world, but it also cements the importance of phylogenetic research.

“It’s like replaying the video of evolution under different scenarios,” said Jeneni Thiagavel, the primary author of the paper, who has been working in this area of research for the past four years. “That essentially gives users [of these comparative methods] the power to reconstruct what that was like.”

Streeters: are evolution and religion compatible?

Students weigh in on the roles religion and science play in their lives

At a meeting of the British Association in 1860, Samuel Wilberforce, the bishop of Oxford, and T.H. Huxley, a proponent of Darwinian evolution, engaged in a heated exchange about the validity of evolution.

The incompatibility of evolution and religion has had a long history. As science explains it, evolution is the process by which populations undergo genetic change over time. One of the agents of evolution is natural selection, which acts on the variation within a population. This variation must be heritable
(transmitted from parent to offspring) and must affect an organism’s ability to survive and reproduce in a given environment. 

Individuals with beneficial variants produce more offspring than those with deleterious ones because they are better able to survive and reproduce. Over time, the number of individuals with beneficial variants increase relative to those with deleterious ones. As a result, the population becomes better suited to its environment.

This week, The Varsity asked members of U of T to comment on whether evolution and religion are compatible. Here is what they said:

“From my perspective and knowledge regarding the subject matter, I am… confident to say that religion and evolution are intimately related to each other. They are simply different manifestations of the exact same phenomena that happened on earth a few million years ago. Looking back at every civilization, religion has always been around to serve as guidance for people as lost, and to offer an explanation for the magic of creation. On the other hand, evolution is the human way to regard this exact topic by crowning Homo sapiens at the top of the food chain. People could view this subject in whichever way that they are comfortable with, because the ‘truth’ shall never be altered [regardless of who] believes it… ” 

— Jessie Gao, third-year physics and math student

“Religion and evolution are completely compatible. Scientific evidence need not conflict with religion. Science and religion answer completely different questions. Science answers the ‘how and when’. and religion answers the ‘who and why’. A creator can therefore govern over evolution and have a hand in these processes. Nothing should surprise God, so when we discover a distant lineage of life that has implications for humans, that should not overturn religious doctrines but rather enable us to interpret them in new ways.”

— Adam Varro, fourth-year ethics, society, and law student

“For many Christians, it would never occur to them that a model for explaining nature’s development would be incompatible with a commitment to the truth or religious faith. The support for science and university, longstanding in the church, rises from conviction that there is one God and truth is united in him. That implies, however, that the Christian does not believe the universe is without a source or that life can be reduced to the physical realm and stripped of meaning and purpose.  For the believer, it is a fuller and truer description of life as we know and experience it.”

— The Rev. Canon Dr. Dean Mercer, instructor, Wycliffe College

“If, as many faiths teach, there is an all-powerful, omniscient Creator, the unfolding of scientific understanding can be seen as part of the divine plan and of the process of divine revelation, even if new scientific information — as in the developing study of evolution — challenges and transforms some previously-held beliefs.”

— The Rev. Andrea Budgey, Humphrys Chaplain, Trinity College and the University of Toronto

“Evolution as a theory was devised as a tool for us to … understand the world. It is supported by … evidence, but we are far from being able to claim that evolution is an accurate representation of the reality. In fact, no scientists claim their theories to be absolutely correct. That being said, sciences are not dogmas. Although the Bible may conflict with Darwin’s theory, this does not prevent religion from coexisting with sciences.”

— Dominic Li, third-year math and statistics student

“What does it mean to be compatible? In my personal opinion, if people are able to accept both religion and the theory of evolution then, by definition, the two are compatible. Nowadays, religion and science play two different roles in people’s lives. The primary role of a religion is more to give people comfort and relief. Before, people may have turned to religion to find the ‘truth’, but now that’s the role that science takes. If science and religion play two different roles in our lives, why shouldn’t they be compatible?”

— Mike Park, third-year math and physics student