Jerry has recently noted a forthcoming book on the Cambrian by the infamous Stephen Meyer. There is a brand new book, The Cambrian Explosion, by the famous Douglas Erwin of the USNM and even more famous James Valentine of UC-Berkeley, that you might want to read if you really want to learn something about this period in the history of life.
Just published in January, you can see by the cover it’s got some great art work, and the publisher, Ben Roberts, has made chapter one and more of the art available at their website (after clicking, scroll down for art; it’s cheaper than Amazon there, too). Another fairly recent book on the Cambrian Explosion covers the very exciting recent discoveries in the Chengjiang of China, The Cambrian Fossils of Chengjiang, China by X.-Q. Hou and colleagues.
Lizards are far and away the most species-rich group of living reptiles, with over 7000 species. One of the first things you learn if you’re a little boy interested in such creatures is that snakes are lizards. One of the other things you learn is that snakes are not the only group of legless lizards. There are, in fact, many groups of lizards with reduced or missing legs, such as the European slow worm and American glass snakes (now preferably called glass lizards). Snakes are just the most evolutionarily successful such group of lizards, comprising 3000 or so of the species of lizards. One of the most distinctive of the non-snake legless lizards are the worm lizards, or amphisbaenians, a group of about 150, mostly tropical, burrowing species. Perhaps our greatest student of the group, the late Carl Gans, thought them so distinctive that he championed a classification in which they were ranked equally with lizards and snakes within the Squamata (the taxon which includes lizards and all their derivatives, including snakes and amphisbaenians), although most other workers did not accept this ranking.
Gans wrote in his Biomechanics (he was a functional morphologist and physiologist as well as a systematist) that:
Unfortunately, we lack fossils intermediate between the Amphisbaenia and other groups, and can only speculate what their ancestors looked like.
A paper published in Nature today by Johannes Muller and colleagues (abstract only) goes a long ways towards constraining our speculations. In the paper, they describe a new species of lizard from the Eocene Messel shale of Germany (Messel is a famous lagerstatte: a deposit with extraordinary fossil preservation) as a transitional form from ‘normal’ lizards to the amphisbaenians.
Ever since Charles L. Camp’s 1923 classic, “Classification of the lizards”, amphisbaenians have bounced around a bit in terms of who their closest relatives are (this proposal being the most heterodox), but recent molecular work (summarized here and here by Blair Hedges and Nicolas Vidal) has connected them to the Lacertidae, a group of typical-looking Old World lizards (‘lacerta’ is Latin for ‘lizard’). In describing the new species, known from a single, well-preserved, and nearly complete specimen, Muller and colleagues write that the species shows “a mosaic of lacertid and amphisbaenian anatomical characters”. The skull, like that of amphisbaenians, is strongly constructed, and evidently adapted for a semi-fossorial life, while the limbs, though well developed proximally, are fairly short and have miniaturized digits. The body is not elongated. Morphometric comparison to modern lizards show that Cryptolacerta was likely a cryptic, leaf litter dwelling form.
Thus, the burrowing head evolved before the fully fossorial life style, while the body was as yet unenlongated, and the limbs still fairly well developed. We should not be surprised to find limbs in a transitional form from the well-limbed lacertids, but it is also the case that three extant species of worm lizards, the members of the Mexican genus Bipes, retain short front legs. Though very short, the limbs are well-developed for mole-like burrowing.
The New York Times has a story on this, which gets the gist of the story right, but the headline (“Fossil Sheds Light on the Lizard-Snake Divide”) and lede (“The origin of snakes is a perplexing matter”) are way off: the paper concerns the origin of amphisbaenians, not snakes.
h/t: Matthew Cobb
UPDATE: Burrowing lizards seem to be all the rage this week, as alert readers Dominic and James C. Trager have pointed out two other burrowing lizard events in the comments below. First, a new species of blind skink, Dibamus, has been described by Thy Neang and colleagues in the journal Zootaxa (BBC piece here). There are about ten species of dibamids, which lack forelimbs, but have flap-like hindlimbs. Like amphisbaenians, they have bounced around a bit in their classification; the latest work (see papers by Hedges and Vidal below) places them as the earliest branch within the lizards. I’m not sure why this new species merited news coverage, except insofar as all new species are newsworthy. One of the authors of the new species is Lee Grismer, whose alpha taxonomic exploits we’ve noted here at WEIT before.
The second item is a paper by Steve McAlpin and colleagues at Macquarie University in Plosone, describing heretofore unknown complexity in lizard social behavior (NY Times piece here). I’ll let the abstract speak for itself:
Here we provide the first example of a lizard that constructs a long-term home for family members, and a rare case of lizards behaving cooperatively. The great desert skink, Liopholis kintorei from Central Australia, constructs an elaborate multi-tunnelled burrow that can be continuously occupied for up to 7 years. Multiple generations participate in construction and maintenance of burrows. Parental assignments based on DNA analysis show that immature individuals within the same burrow were mostly full siblings, even when several age cohorts were present. Parents were always captured at burrows containing their offspring, and females were only detected breeding with the same male both within- and across seasons. Consequently, the individual investments made to construct or maintain a burrow system benefit their own offspring, or siblings, over several breeding seasons.
Complex social behavior is well known in crocodilians and, of course, birds (which are glorified reptiles), but this is a unique case for squamates (so far). They don’t seem to be eusocial though, which, in addition to overlapping generations, requires cooperative care of the young (there is at least some indirect parental care here), and a reproductive division of labor. The skinks involved are burrowing, but well-limbed.
Camp, C.L. 1923. Classification of the lizards. Bulletin of the American Museum of Natural History 48:289-481. (pdf)
Hedges, S. B. and N. Vidal. 2009. Lizards, snakes, and amphisbaenians (Squamata). Pp. 383-389 in S. B. Hedges and S. Kumar, eds., The Timetree of Life, Oxford University Press, New York. (pdf)
McAlpin, S., P. Duckett and A. Stow. 2011. Lizards cooperatively tunnel to construct a long-term home for family members. Plosone 6(5):e19041, 4pp. (pdf link)
Muller J., C.A. Hipsley, J.J. Head, N. Kardjilov, A. Hilger, M.Wuttke and R.R. Reisz. 2011 Eocene lizard from Germany reveals amphisbaenian origins. Nature 473:364-367. (abstract)
Neang, T., J. Holden, T. Eastoe, R. Seng, S. Ith, and L.L. Grismer. 2011. A new species of Dibamus (Squamata: Dibamidae) from Phnom Samkos Wildlife Sanctuary, southwestern Cardamom Mountains, Cambodia. Zootaxa 2828:58-68. (abstract)
Vidal, N. and S. B. Hedges. 2009. The molecular evolutionary tree of lizards, snakes, and amphisbaenians. Compte Rendus Biologies 332:129-139. (pdf)
The New York Times is reporting some major media event at the American Museum of Natural History on Tuesday concerning a 47 million year old primate fossil from Germany. There’re reports of secrecy, exclusivity, and high priced documentaries. It seems a tad curious, since by available reports, the American Museum has nothing to do with the research or the fossil, which is in the collection of the Natural History Museum in Oslo, and the fossil was already reported on by the Timesa few days ago and by the Daily Mailover a week ago. The fossil is from the Messel shale an important lagerstatte. Keep an eye out for the reports later today.
(PS The American Museum has what seems to be a really neat new mammal exhibit, reviewed here. If you’re in New York, go see it.)
Update. The press conference has been held. The BBC has a few videos here. The specimen is a very well preserved, nearly complete, articulated skeleton, with remnants of fur and stomach contents (as is often the case in specimens from the Messel Lagerstatte), of a basal higher primate (i.e. near the ancestry of monkeys, apes, and man). The authors of the paper made a taxonomic faux pas in allowing the name of the new creature, along with a description, to be published prior to the appearance of their paper. The authorship of the name, and its date of publication, are now murky.
Update 2. As I feared, a big media roll out is not always conducive to getting the story right. Just now on the Rachel Maddow Show, the features reporter said that the new primate might be the missing link between man and ape. It is of course nothing of the sort, and the authors never said it was, but using the term “missing link” as the key descriptor of the find (see the Daily Mail link above for an example) was bound to lead to some such misunderstanding. He also stressed that it could be “upright”, which many may take to mean bipedal, but, of course, it wasn’t. Laelaps and PZ concur about the doleful effects of the media hype. More from Laelaps here. The hype is even more overheated than I realized: from the promoters: “WORLD RENOWNED SCIENTISTS REVEAL A REVOLUTIONARY SCIENTIFIC FIND THAT WILL CHANGE EVERYTHING | Ground-Breaking Global Announcement”. Money quote from Laelaps:
I have the feeling that this fossil, while spectacular, is being oversold. This raises an important question about the way scientific discoveries, particularly fossil finds, are being popularized. Darwinius is just the latest is a string of significant fossils to be hyped in the media before being scientifically described (or at least before that information is released to the public). Other recent examples include “Dakota” the Edmontosaurus, the pliosaur “Predator X“, and “Lyuba” the baby mammoth. I am glad that these finds are stirring excitement, but I am a bit put off by the way they are presented.
Update 3 (May 20).Carl Zimmer and Ed Yong add to the critical pile on. A sample of Ed Yong’s wonderful satirical evisceration:
Around the world, signs that everything has changed have already begun to appear. Jeanette Gould from Stoke-on-Trent was shocked to discover the outline of Darwinius emblazoned on her morning toast. “Well, it ruined breakfast,” said Ms Gould, failing to appreciate the detail of the creature’s stomach contents outlined in bread crumbs. “I couldn’t very well spread raspberry jam over the direct ancestor of my children, could I?”
There is a wonderful accompanying illustration of the piece of toast.
One of the most exciting developments in paleontology in the past ten years or so has been the discovery that many species of theropod dinosaurs had feathers. The earliest discoveries were quite controversial. At the 1997 meetings of the Society of Vertebrate Paleontology in Chicago, a paper was read criticizing the interpretation of the skin structures on these fossils as feathers. In response, Phil Currie, one of the team working on the fossils, presented an impromptu rebuttal paper later the same day, a rather unusual development for a normally tightly scheduled scientific meeting. I was not convinced they were feathers myself until a while later, when a number of fossils of the new forms were brought to the Field Museum, and I was able to see them for myself– they had feathers! One of the strangest of these feathered dinosaurs was Microraptor gui, which had both its forelimbs and hindlimbs modified into feathered wings. It seems to exemplify the remark of J.B.S Haldane, the British geneticist who was one of the founders of the modern synthesis, “that the universe is not only queerer than we suppose, but queerer than we can suppose.” Jerry highlights Microraptor in chap. 2 of WEIT, and notes a NOVA program on PBS, “The Four-winged Dinosaur”, that has a great website with interactives and videos, including the entire program. Originally airing last year, it was just recently shown again on my local PBS station, so check to see if it may be showing again in your area too.
Most of the specimens of feathered dinosaurs, as well as many true birds, have come from the fossil beds of Liaoning in northeastern China. The American Museum of Natural History has a nice website on the Liaoning fossil biota. The Liaoning deposits have become one of the most important and interesting of what are called Lagerstatten (singular: Lagerstatte), a German word for a fossil deposit with extraordinary conditions of preservation. Such deposits, because they reveal structures (such as soft parts like feathers) and organisms (those lacking hard parts) otherwise missing from the fossil record, are often of crucial importance in studying the history of life on Earth. Other famous Lagerstatten include the Pre-Cambrian Ediacara Hills of Australia, the Cambrian Burgess Shale in British Columbia and Chengjiang in China, and the Jurassic Solnhofen Limestone of Bavaria. These Lagerstatten have revealed, respectively, an early multicellular fauna, the Cambrian Explosion, including the earliest vertebrates, and Archaepoteryx, the first bird.