Horseshoe crabs now date back to 445 MYA

"A remarkable new fossil horseshoe crab, Lunataspis aurora gen. et sp. nov., from recently discovered Upper Ordovician (c. 445 Ma) shallow marine Konservat-Lagerstätten deposits in Manitoba (Canada)."

See Rudkin, DM, GA Young & GS Nowlan, 2008. The oldest horseshoe crab: a new Xiphosurid from late Ordovician Konservat-Lagerstätten deposits in Manitoba, Canada. Palaeontology, 51(1): 1-9. and "Oldest Horseshoe Crab Fossil Discovered," by Jeanna Bryner. LiveScience.com, 28 Jan 2008.

This pushes back evidence for the mysterious horseshoe crabs by almost 100 million years, from 350 million to 445 million years ago. Having survived multiple extinction events during its geological existence, but habitat loss and marine pollution have seen significant localised loss of population numbers in some countries.

Present day horseshoe crabs appear to be similar to such fossils and we refer to them as "living fossils". In Singapore, Mandai mangroves appear to be a significant refuge for them. Let's hope we can extend their impressive record a little longer.

Deforestation in Brazil declining... or not?

The Brazilian government has announced a fall in the rate of deforestation in the Amazon for the third year running, ending July 2007. But environmental groups say that this is a 'past achievement' and that rates of deforestation are rising again. And as common sense will tell you, a fall in the rate of deforestation means that deforestation is still going on, just a bit slower.... Read more...

Giant Sea Scorpion!

We usually think of invertebrates as small animals, and arthropods in particular as being limited by the structural engineering of an exoskeleton, which is less capable of supporting large body sizes than an endoskeleton. A new fossil discovery however should creep out anyone who thinks that crabs and lobsters are already bigger than a decent invertebrate should be.

From a 43 cm long claw of the fossil eurypterid (sea scorpion) species Jaekelopterus rhenaniae found in Germany, researchers extrapolated the length of the animal's body to be between 233 to 259 cm, using claw size to body length ratios from other sea scorpinons. Eurypterids are members of the extinct subclass Eurypterida within the class Merostomata of the subphylum Chelicerata, i.e. they were chelicerates (like spiders and scorpions) most closely related to the horseshoe crabs.

Eurypterids were aquatic and the buoyancy conferred by water may help explain structurally their large size, but what about the problem of gaseous diffusion to tissues? They presumably had an open circulatory system like other arthropods which is less efficient than the closed circulation of vertebrates. The authors hypothesise that the higher oxygen levels in the atmosphere in the past could have helped them attain their large size, or that it was driven by an evolutionary arms race with their prey.

Some questions to think about:

• Why is extrapolation using data from other sea scorpions a valid means of predicting the body length of the animal from only its claw?
  
• Among the extant (still living) chelicerates, how do the methods of gas exchange differ between the aquatic and terrestrial groups?
  
• What can we infer about its mode of feeding and possible prey?
  
• How can we explain why such giant arthropods are no longer extant today?
  

Yangtze River Dolphin extinct?

An intensive survey carried out to locate remaining individuals of the critically endangered Yangtze River Dolphin, or baiji, a freshwater dolphin endemic to that river and the only surviving representative of its family, has not been able to find any of the dolphins. According to IUCN criteria, however, this species cannot be formally classed as extinct because Red List rules stipulate that 50 years must have passed since the last verified sighting of the organism. However, very few surveys of such detail have been carried out for the Yangtze River Dolphin, so the IUCN Red List's entry on this dolphin is probably too optimistic in its estimates, and the baiji is probably either gone for good, or with too few numbers in the wild to survive for very much longer.

Numbers of baiji have always been low; estimates in the 1980s ranged from 100 - 400, with sightings of the animals usually in groups, but a more recent survey in 1997-9 sighted just over 20 individuals. This present survey covered the 1669 km length of the Yangtze between Yichang and Shanghai twice, using visual and acoustic methods. The authors point out that the baiji is primarily a victim of 'incidental mortality', unlike other recently extinct or endangered animals, such as the dodo and tiger, which are victims of hunting and trapping. What killed off the dolphin population was a combination of pollution and habitat degradation, as well as accidental killing from booming river shipping traffic and fishing activity.

The fact is that 'even large charismatic and nominally protected animals are still in grave danger of being lost', and just because an animal is on the Red List, is widely known, and is discussed at international meetings or in the media, doesn't mean that anything concrete is being done about its death and decline. In this respect it reminds me of the case of the Indian tiger and how its wild populations may have been systematically underestimated for years, while illegal poaching and trade in tiger parts has still persisted even in supposedly protected wildlife reserves. Furthermore, while the death of a big mammal is a tragic and dramatic wake-up call, it's clear that the extinctions that we're not aware of are still proceeding unabated and will continue to do so even if governments enforce conservation laws more strictly.

Reference: Turvey, S.T. et al. 2007. "First human-caused extinction of a cetacean species?" Biology Letters, 3(5): 537-540; published online: doi:10.1098/rsbl.2007.0292.

Indirect Dependence and Extinction

Something new that was highlighted in Science Daily:

Neighbors gone, sex gone, fruits gone, species gone. This is the ultra-short conclusion of the findings in a study by Dennis Hansen, Heine Kiesbüy, and Christine Müller from Zurich University, and Carl Jones from the Mauritian Wildlife Foundation, who found that an endangered plant in Mauritius depends on a neighboring plant to provide a safe home for its pollinator, a day-active gecko.