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El yacimiento de Atapuerca espera al Neandertal
El codirector de la campaña de excavaciones de Atapuerca,
Juan Luis Arsuaga, mostró ayer en Atapuerca su confianza en que
«pronto» aparezcan fósiles de la especie Neandertal en el yacimiento de
Cueva de las Estatuas, y confirmen la presencia de esta especie en la
sierra burgalesa, si bien es cierto que los trabajos «van en progreso» y
todo apunta a que «aparecerán». Según explicó el propio Arsuaga, en la
Galería de las Estatuas se trabaja en una serie de catas en las que se
puede afirmar que hay una ocupación de neandertales que apenas se ha
comenzado a excavar y de la que, con seguridad, saldrán nuevos datos en
nuevas catas que permiten hablar de una ocupación. Se trata de la
primera presencia de la especie Neandertal, una de las preocupaciones de
los especialistas que por causas geológicas no hallaron hasta este
momento ninguna cavidad de este estilo.
«Aquí no encontramos ninguna entrada al sistema pero
finalmente ha aparecido», aseguró Arsuaga. «Pronto publicaremos
resultados de la fauna y los ecosistemas y la industria, aunque los
fósiles humanos aparecerán cuando ellos quieran», remarcó. Por otro
lado, en la Cueva del Portalón se trabaja en los yacimientos holocenos,
en cuya parte inferior se encuentran restos del Pleistoceno a gran
profundidad. En este espacio, se han descubierto restos que permiten
conocer cómo fue la vida de los primeros agricultores y el ADN de las
primeras especies domésticas como el caballo.
Polémica con los ingleses
Del mismo modo, en la Sima de los Huesos y Cueva Mayor se
ha acumulado gran información en los últimos años por lo que Arsuaga
confía que sea este otoño cuando se saque una publicación –«en una
revista de primera línea»–, con todo lo que hasta ahora se ha ido
descubriendo. «La Sima será noticia a finales de otoño», apostilló.
Para este paleontólogo, la Sima de los Huesos es una
«colección única de fósiles humanos que permite estudiar una especie
desaparecida». Con esto quiso contestar a las declaraciones del profesor
inglés Chris Stringer, y la polémica en el periódico 'The Guardian',
que ponía en duda algunas de las dataciones sobre restos humanos
encontrados en estos yacimientos. «Si hubiéramos encargado esta
controversia, no lo habíamos hecho mejor», destacó Arsuaga, que añadió
que «es un jamón del que todo el mundo quiere sacar lonchas».
Arsuaga consideró que «la polémica no está realmente en
la cronología, aceptada por los profesionales, sino en la evolución».
Algunos investigadores quieren incluir la especie Homo Heidelbergensis
entre el Neardental y el Antecessor, como antepasado común del
Neardental y el Sapiens. Así, el científico insistió en que el debate
está en «en el último millón de años en Europa y eso está vinculado al
Homo Antecessor, o casi más, que a los fósiles de la Sima, que desde el
primer momento supimos que corresponde a una línea evolutiva que
corresponde a los neandertales».
Stringer manifestaba que los restos de la sima burgalesa
no tienen 600.000 años de antigüedad, sino 400.000; y que no se pueden
atribuir al Homo heidelbergensis, que el inglés considera una especie
previa a la hallada en Atapuerca, cuyos métodos de datación también
cuestiona en su artículo.
Por su parte, y en la misma línea que Bermúdez de Castro,
el tercer codirector Eudald Carbonell anotó que «cada vez que se hace
una reestructuración está pensada para obtener más eficiencia en los
registros». En el yacimiento de la Gran Dolina, donde aparecieron los
fósiles de Homo Antecessor, se podría encontrar un uso de la cueva mucho
más antiguo porque fósiles de animales y herramientas ya se han podido
conocer, «un fósil humano en estos niveles sería una gran noticia».
The Dinosaurs They are a-Changin’
The dinosaurs I met as a kid aren’t around anymore. I don’t mean to say that all the classic dinosaurs I saw in the late 1980s were sunk, synonymized or otherwise driven into a second extinction. “Brontosaurus” is the only major example of that (although Torosaurus and Anatotitan may soon follow). No, what I mean is that the tail-dragging, drab, stupid dinosaurs I was first introduced to have all been replaced by agile, brightly-colored, complex animals that were amazingly bird-like.
Our image of what a dinosaur is, and what dinosaur biology was like, has been changing ever since naturalists began scientifically describing creatures such as Megalosaurus and Iguanodon in the early 19th century. Dinosaurs have transformed from 100-foot-long lizards to bizarre creatures with a reptilian gloss, and only by the 1870s, when paleontologists started finding partial skeletons, did we start to get a picture of how unique dinosaurs were. Dinosaurs were re-envisioned as dynamic, bird-like animals by naturalists such as Edward Drinker Cope and Thomas Henry Huxley, only to have their hot-blooded dinosaurs replaced by sluggish swamp-dwellers that fully deserved the extinction that wiped them out. Thankfully, the “Dinosaur Renaissance” of the late 20th century sparked a dinosaur makeover and an interest in dinosaur paleobiology—dinosaurs were transformed into perplexing creatures that lived fast and died young, and the realization that birds are living dinosaurs gave paleontologists a new pool of information to investigate the details of dinosaur lives.
And now we’re in what paleontologist Thomas Holtz has called the “Dinosaur Enlightenment.” While the Dinosaur Renaissance was mostly an image change that raised a slew of questions about dinosaur biology, the Dinosaur Enlightenment is employing new techniques and ideas to approach long-standing questions about dinosaur biology. We’re finally starting to understand how dinosaurs grew up, how they might have mated and even what colors some dinosaurs were. But even the most basic aspects of dinosaur biology are open to revision—for example, paleontologists are trying to find ever-more-accurate and precise ways to estimate how heavy dinosaurs actually were.
Still, a complete and comprehensive perspective of dinosaur natural history remains far beyond our present knowledge. The more we discover, the stranger dinosaurs become. Our general picture of dinosaurs is more accurate than what has come before, but the details will undoubtedly continue to shift, especially as new discoveries are made and speculative ideas are tested. As paleontologist Paul Barrett recently wrote at the Guardian:
We are still in the dark when it comes to some aspects of dinosaur life: how exactly did they die out? Why did some of them prosper while others were short-lived? What were the functions of bizarre features, like Spinosaurus’s “sail”. And which factors led to their runaway evolutionary success? For now, there are still plenty of things we know nothing about – and scientists shouldn’t be afraid to say so.
Dinosaur mysteries will continue to pile up. In another Guardian editorial, paleontologist Dave Hone points out that dinosaurs were far more diverse and disparate than we often appreciate. Everyone knows Tyrannosaurus, Triceratops, Allosaurus, Diplodocus and other classic creatures found during the bone rush of the late 19th and early 20th centuries. These animals are dinosaurian royalty, the most famous of all, but they are only a tiny sampling of the vast array of forms dinosaurs evolved into. In fact, as Hone points out, paleontologists are naming new dinosaurs at an exceedingly rapid pace, and each new discovery adds a little bit more to our understanding of how weird and varied dinosaurs were. Hone writes:
The sheer number of species recovered may itself be notable, but the diversity of forms encompassed in that is probably also under-appreciated. Dinosaurs are famous not just for the huge sizes reached by many, but also their weird and wonderful body types. Animals like Diplodocus, Spinosaurus or Triceratops might seem odd, but there are other dinosaurs out there that stand out just as much compared with their relatives or are simply odd in their own right.
The feathery, ant-eating alvarezsaurs, and the pot-bellied, long-clawed herbivores called therizinosaurs are just two of several dinosaur lineages that paleontologists have only recently recognized, and these puzzling creatures have presented scientists with new, confounding questions about how such creatures lived and what pressures shaped their evolution. The more we learn, the more wonderful and mysterious dinosaurs become.
Diania cactiformis
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The fossil-rich Chengjiang deposits of Yunnan province, China, date from about 525 million years ago and are among lagerstätten that have preserved soft-bodied animals with amazing detail. Among the bizarre creatures inhabiting shallow Cambrian seas were the lobopodians, often described as legged worms. These are of evolutionary interest because of presumed, if enigmatic, relationships to velvet worms, water bears and arthropods. Both velvet worms and water bears have soft, segmented bodies and pairs of unstructured appendages – or lobopods – long seen as precursors to the segmented legs of arthropods.
An international team of Chinese and German scientists, led by Jiani Liu of Northwest University in Xi'an, has reported the discovery of a new genus and species of lobopodian that is the most arthropod-suggestive to date. Their description was based on three complete fossils and about 30 fragments. If their interpretations are correct, they suggest some controversial possibilities.
Their analysis of the new species, Diania cactiformis, places it close to the base of the arthropods and reinforces the notion that lobopodians are an artificial collection of early body plan experiments rather than a monophyletic lineage; that is, an evolutionary line that shares a unique common ancestral species.
Stated another way, their new species is claimed to be more closely related to arthropods than to other lobopodians.
D cactiformis does not immediately look like an animal to the untrained eye, contributing to its nickname: "walking cactus". The creature has robust and possibly hardened appendages that may possess articulated elements. Even more sensational is the suggestion that sclerotisation of limbs may have preceded that of the body on the march toward full-blown arthropod status.
The late palaeontologist and author Stephen Jay Gould talked about similarly improbable early body plans in his book about the Burgess Shale Formation, Wonderful Life. The foreign appearance of Dianiareminds me of Gould's take-home message: the contingency ofevolution. Had competition in the shallow Cambrian seas turned out differently, the living world today could well have looked completely different.
