At the entrance of his office there is a caricature of José Luis Sanz (Pepelu, for friends) that says: Pepelusaurio. Although it is no longer the size of a dinosaur, because it has lost weight lately, that attitude of Sanz’s kind ancestral creature is true. He moves with familiarity among fossils and nothing from millions of years ago is alien to him. He displays his vocation, surrounded by dolls and posters of the lost world, boasting of being a specialist in dinosaur cinema, more than in dinosaurs. But his affability does not make us forget that he is the director of the most important site in Spain, Las Hoyas, in Cuenca, and a world authority on the origin of birds.
–What is of great interest in this Las Hoyas deposit?
-On the one hand, the time in which it is located, the lower Cretaceous, from 110 to 130 million years before the present. It is a particularly important moment in the history of life, because many organisms appear that are predominant in current systems, both plants and animals. To this must be added the exceptional conservation of the fossil remains, so good that it allows the appearance of feathers in birds, the venation of the wings of insects and the preservation of the integuments or soft parts of dinosaurs.
–And at the other site where you work, Bastús, in Lleida?
-It is very unique, because it contains a huge amount of dinosaur eggs, about 300,000 in a relatively small rocky body. We think that it is a laying place to which the dinosaurs would return on a recurring basis. In addition, the sediments in which the eggs are deposited belong to a beach from the Upper Cretaceous, that is, about 65 or 70 million years ago. Current orthodox dinosauriology admits that there were few relationships between dinosaur communities and marine environments, but this site suggests that some populations or species of dinosaurs may have used marine resources. This hypothesis was defended in the 1940s, but it had been abandoned, because most fossils appear in continental environments, such as river or lake sediments, and not in marine areas.
–However, 65 million years ago Bastús was the sea.
-Yes, there was a coastline, so you cannot think that there is trawling or transport. There are eggs that are practically whole, we have found them in the same place where the mother dinosaur laid them.
–I think last year they found a fossil chick, a baby.
-No, that calf comes from the deposits of the Sierra de El Montsec, in Lleida. It is similar in age to Las Hoyas and there are certain floral and faunal elements that are common to both sites. This little animal is a very young specimen that, among other things, is the first skull found in the Iberian Peninsula of a Mesozoic bird. It belongs to a group of primitive birds known by the name of Enantiornithes, which were typical inhabitants of the Cretaceous period and disappeared during the great Finicretaceous crisis. This specimen, on the one hand, has the structure of the skull still with teeth, which is more of a dinosaur than a bird character and also quite similar to the skull of the most primitive bird that we know of, Archeopteryx. But on the other hand, its postcranial skeleton is that of a fairly modern bird. So, compared to the structure of the skull that remains primitive for several million years, the skeleton rapidly evolves into a structure capable of flying much better than Archeopteryx. This little animal has something else: although we do not know how young it would be, we have observed that the growth of its bones is very similar to that of modern birds; an unexpected combination.
–Do all paleontologists think that birds evolved from dinosaurs?
– There are those who think that no, that they are related forms with the crocodiles or with much earlier animals. But the vast majority of paleontologists admit it. The phylogenetic definition of a bird is: a feathered, winged dinosaur that is capable of flight. In reality, the only thing people who oppose this origin, from my point of view, is to deny evidence, without giving other alternatives. For example, modern birds have a pectoral skeletal element, the furcula, which in chicken we call desire bone and is shaped like a fork. Well, the fact that birds come from dinosaurs was a hypothesis issued by Mr. Thomas Huxley at the end of the last century and later denied by a Swedish paleontologist named Heilmann because, according to him, dinosaurs lacked furcula. However, in recent years more and more theropod dinosaurs have been found that do. Specifically, the famous velociraptor had furcula. Even dinosaurs least related to birds, like ovirraptorosaurs, troodontians, even tyrannosaurs … they all have furcula.
–What can make a dinosaur fly?
-That is a very difficult question to answer and to contrast in all its terms. There are two non-reconcilable hypotheses, the first is called “from the trees down”, the Anglo-Saxons say “from the trees down”. He admits that between a terrestrial bipedal runner and a bird with flattened flight there would be a series of intermediate animals. These would be: a tree climber, a parachutist who glides from branch to branch and who millions of years later would make a smooth flight and would be sustained in the air. The other hypothesis is called “from the ground up”, that is, “from the ground up”. The initial ancestor would be the same, a biped runner who at a certain point would have a selective pressure that would drive him to develop protoflowers on the wings, with which he would be able to run faster and jump with greater agility, something very useful for catch insects on the fly and mislead predators. With the increase in the size of the proto-feathers, it would increase its airfoil, it would make greater and greater jumps and that would also lead it to move its wings, which would elongate. Both hypotheses admit an ancestral biped, but one of them requires an intermediate step, the climbing animal. And going back to the velociraptor, you have to ask yourself: would it be able to climb a tree? The answer is no.
–And what does this have to do with the discussion about the hot or cold blood of dinosaurs?
-The temperature is related to the origin of the feathers. There are two hypotheses: one considers them aerodynamic elements and the other, thermal insulation factors. For an endothermic (that is, warm-blooded) animal it is important to maintain an outer tegumentary layer that creates an air chamber between the epidermis and the external environment. Mammals developed the hairs that allow us to have this camera. Could the origin of bird feathers be similar? It is still not clear; Long ago I thought that the clearest selection pressure that feathers could have generated was of the aerodynamic type, but after the fossils found in China, which have tiny feathers that are not good for flight, maybe the conservation of heat is a good thing. reason.
–Could it be that some had hot blood and others cold?
-Sure. Dinosaurs are a group of very diverse shapes and sizes and would have different thermal regime solutions.
–Why do you think the subject of dinosaurs attracts most people’s attention so powerfully and is so fascinating?
-There are many answers, I think they form an alternative world of terrestrial animals that have nothing to do with those we now know and it produces a kind of vertigo to think that this planet was dominated many millions of years ago by them. In addition, the myth of the dragon is very widespread, both in Eastern and Western cultures. Another question is the size, there were some huge dinosaurs. Imagine a tetrapod that weighs 10 times more than a huge elephant. As an advertising phrase for the movie Godzila says: “size is important” (laughs). I know you have a lot of readings …
–Would you like to see a dinosaur?
-Of course, I would love to, the only way to see them now is in the cinema, and it is very pleasant, especially when they are well done, like in Spielberg’s films.
–I suppose this interest comes from a young age.
-Yes, I have been passionate about paleontology since I was a child. It began to fascinate me when I saw the films of the 50s, such as The Monster of Ancient Times, which is about an animal that comes out of the ice in the Arctic Ocean and arrives at the port of New York and organizes a brawl, begins by eating a police (laughs). These films left me shocked, and as a child, in Soria where I was born, I went to a site called El Mirón, where I used to collect marine fossils. He couldn’t get dinosaur bones, but at least he had animals that had witnessed that world.
–It is also fascinating to think of birds descending from them.
-Yes, I think that most of the people believed that these animals had disappeared. But it is shocking to think that some dinosaurs are not extinct, because they are birds. A few years ago, anyone wondered the reason for the extinction; what needs to be explained now is why some are extinct and others are not. On the other hand, it also makes us consider that dinosaurs (that is, birds) have been companions of humanity for millions of years and that they have great cultural and economic importance, due to food. In terms of biodiversity conservation, we realize that dinosaurs have two stages of crisis: the one 65 million years ago and the current one, since man is responsible for the extinction of many birds, that is, dinosaurs.
–And what is the answer? Why did some dinosaurs become extinct and others not?
-I think that the great finicretacic biotic crisis is much more complex than was believed until recently. The two classical approaches to the subject, which are the gradualist and the catastrophic, are real. For me there are three killers combined: a climate change, the fall of a large alien object and the volcanic eruptions of The Deccan, in India. The problem is to explain why non-avian dinosaurs disappear and birds, crocodiles, snakes or lizards remain. Nobody knows.
–At what level is Spanish paleontology currently?
-It is a discipline that has undergone an enormous renovation. I am not at all triumphalist nor do I expect to be pedantic if I assure that it is at the same high level as other countries, not only in fossil research, but also in conceptual and methodological development. This is proven by the increasingly common presence of Spanish paleontologists in the best international scientific journals.
Amelia Die
This interview was published in September 1998, in number 208 of VERY Interesting.
