We have a sign: there are reports
of a new video from Tsunemi Kubodera of an Architeuthis—unfortunately, I haven’t been able to find a copy of the video online anywhere yet. If anyone finds it, let me know!
There’s a small and rather grainy copy of the video on the BBC website!
The copy at CNN is of much higher quality.
Oh, man, I feel for the kids nowadays. When I was an itty-bitty dinosaur-happy tyke, it seemed like there was a manageable amount of Latin nomenclature you had to memorize to keep up with the dinosaur clan. Now it’s like there’s a new one added every week, and you’ve got to be a freakin’ genius to be able to follow them all. Kids do still go wacky over dinosaurs, right? We haven’t gone so far down the tubes that the little nerds are neglecting their paleontology, have we?
Anyway, there’s a new one out of Spain, Turiasaurus riodevensis, an old school sauropod, and it’s a big one. Pictures below the fold…
I’ve just read the article on the parthenogenetic Komodo dragons in Nature, and it’s very cool. They’ve analyzed the genetics of the eggs that have failed to develop (the remainder are expected to hatch in January) and determined that they were definitely produced without the aid of a male.
We analysed the parentage of the eggs and offspring by genetic fingerprinting. In the clutches of both females, we found that all offspring produced in the absence of males were parthenogens: the overall combined clutch genotype reconstructed that of their mother exactly. Although all offspring were homozygous at all loci, they were not identical clones. Parthenogenesis was therefore confirmed by exclusion (clutches had different alleles from potential fathers) and by the fact that the probability of obtaining a clutch of homozygous individuals after sexual reproduction was very low (P<<0.0001). Sungai’s resumption of sexual reproduction confirmed that parthenogenesis was not a fixed reproductive trait (that is, it is facultative) and that asexual reproduction is likely to occur only when necessary.
That line about “all offspring were homozygous at all loci, they were not identical clones” might need a little more explanation. Mama Dragon is heterozygous at some loci, but the meiotic mechanism that produces a diploid egg means that one cleavage (most likely the second meiotic cleavage) was suppressed, so both homologous chromosomes in the resultant ovum were derived from the same replicated DNA strand. They are not clones of the mother, because they are all homozygous while she was heterozygous; they are not identical, because which of each of the paired homologous chromosomes was passed on to an individual is random.
(I’m a little confused by the statement that they offspring are homozygous at all loci, though; that would imply that there was no crossing over at all in meiosis I, which doesn’t sound right. There ought to be reduced heterozygosity but not complete homozygosity, unless reptiles are weirder than I thought.)
The other useful snippet of information is that sex determination in these reptiles is of the WW/WZ type, where the females are the heterogametic sex. Since all of the progeny of parthenogenesis are homozygous, they are all of the homogametic genotype, and therefore male.
Parthenogenesis can also bias the sex ratio: in Varanus species, females have dissimilar chromosomes (Z and W), whereas the combination ZZ produces males10, so the parthenogenetic mechanism can produce only homozygous (ZZ or WW) individuals and therefore no females.
This has theological implications, obviously. We can now understand how a female could give rise to a male by parthenogenesis: Mary Mother of God must have been a heterogametic reptoid. David Icke will be so pleased.
Watts PC, Buley KR, Sanderson S, Boardman W, Ciofi C, Gibson R (2006) Parthenogenesis in Komodo dragons. Nature 444:1021-1022.
What are the key ingredients for making a multicellular animal, or metazoan? A couple of the fundamental elements are:
A mechanism to allow informative interactions between cells. You don’t want all the cells to be the same, you want them to communicate with one another and set up different fates. This is a process called cell signaling and the underlying process of turning a signal into a different pattern of gene or metabolic activity is called signal transduction.
Patterns of differing cell adhesion. But of course! The cells of your multicellular animal better stick together, or the whole creature will fall apart. This can also be an important component of morphogenesis: switching on a particular adhesion molecule (by way of cell signaling, naturally) can cause one subset of cells to stick to one another more strongly than to their neighbors, and mechanical forces will then sort them out into different tissues.
These are extremely basic functions, sort of a minimal set of cellular activities that we need to have in place in order to even begin to consider evolving a metazoan. Fortunately for our evolutionary history, these are also useful functions for a single celled organism, and while the metazoa may have elaborated upon them to a high degree, there’s nothing novel about the general processes in our make-up. The principles of signaling and transduction were first worked out in bacteria, and anyone who has a passing acquaintance with immunology will know about the adhesive properties of bacteria, and their propensity for modulating that adhesion to build complexes called biofilms.
So let’s take a look at the distribution of signaling and adhesion molecules in single-celled organisms, multicellular animals, and most interestingly, a group that is close to the division between the two (although more on the side of multicellularity), the sponges.
Let me tell you a story.
Depending on the point of view, it’s either a bit of daily routine, or a tragedy.
(via My Confined Space)
This sad jumble of bones is all that remains of Volaticotherium antiquus, a small rat-sized mammal that was recently dug up in China. There are two particularly outstanding things about this creature.
One is that browner layer in the rock: that isn’t an artifact, it’s a bit of soft tissue that was preserved, called a patagium. A patagium is a thin membrane stretched between the limbs, and is used for…flying! This animal probably lived much like a modern flying squirrel (although it is definitely not a squirrel), gliding from tree to tree.
The second surprise is the age. This is a Mesozoic mammal, from Chinese beds that are roughly dated to somewhere around the mid Jurassic to early Cretaceous—it was a contemporary of the dinosaurs. I’m tickled to imagine a diplodocid stretching up its long neck to strip the foliage from a tree branch, and this little guy squeaking angrily and leaping off to fly to the next tree.
Now one more thing we need, but are extremely unlikely to find, is a Mesozoic moose.
Mang J, Hu Y, Wang Y, Wang X, Li C (2006) A Mesozoic gliding mammal from northeastern China. Nature 444:889-893.
It’s a strange thing to care about a dog I’ve never met…
Isn’t she pretty? This is Promachoteuthis sloani, a new species of deep water squid trawled up out of the North Atlantic.
Many more photos of this creature are available online, and you can also download the paper describing it.
