Fossilized ambergris from the Pleistocene of Italy: tales of marine taphonomy 1

I’ve wanted to somewhat regularly cover marine taphonomy on this blog for a while now, and with the recent publication of Baldanza et al. (2013), I thought that now is as good a time as any to start. It’s been a pretty busy last couple of weeks, but I’ve just delivered a department talk and have also spent the past few days recouping from a nasty cold, and now have some spare time again. So, here's installment 1 of a new series, tales of marine taphonomy. I'll occasionally cover papers discussing some of the weirder and less familiar aspects of marine taphonomy - and the taphonomy of marine vertebrates in particular. To be honest, it's not a subject that has been given much attention any way (so many "regular" concepts will probably be foreign to terrestrial workers), and many studies have butchered the subdiscipline altogether.

The last couple of weeks have seen some exciting advances in paleontology, but while everyone on the paleo-part of the internet was busy discussing the two papers reporting on new Jurassic mammals – in the same issue – but disagreeing whether or not they were mammals or something further down the stem – a new discovery was published that is actually interesting (and not just controversial from the standpoint about cladistic disagreements, which – no offense – can be horribly dull). Fossilized ambergris was reported by Baldanza et al. (2013) in the journal Geology from the Pleistocene of Italy. This is pretty damn neat, as it’s something I never had much hope in being preserved in the fossil record.

 

An atrociously humongous slab of ambergris. From pbs.org

First off, what is ambergris? Ambergris – or gray amber – is a waxy substance formed from bile secretions in the digestive tract of sperm whales. It is often found with embedded squid beaks, and is thought to be a sort of protective lining that forms along the sides of the intestinal wall to protect against the sharp beaks. Ambergris can be expelled as fecal matter, or if too large it may be regurgitated. In the days of whaling, ambergris could be found within the intestines of freshly killed whales. It is often picked up by beachcombers along the shoreline (and beachcombers often pick up all sorts of other goodies that they think is ambergris). Ambergris is buoyant, and will float all the way to shore. Unlike cetacean feces – which has the consistency of greek yogurt and rapidly disaggregates once pooped out – ambergris is formed as somewhat consolidated chunks. Ambergris is perhaps most famous for its smelly qualities: although the soft, fatty and white precursor to ambergris (unsurprisingly) retains a strong fecal smell (how pleasant), once aged properly (apparently by sustained floating in the ocean) it can become quite hard and will produce a sweet smell, often compared to rubbing alcohol. The smell itself is of course not fantastic or of serious note, but it is rather its potency as a fixative for odors that makes it desirable for perfumes. It’s currently illegal to own or sell ambergris in the United States, and has long been rendered obsolete by synthetic fixatives; it is still possible to find perfumes made with ambergris in some European countries.

In their new paper, Baldanza et al. (2013) report about 25 coprolites from early Pleistocene (~1.75 Ma) marine rocks in Italy. These coprolites were calcareous, equidimensional to oval/lozenge shaped, up to 1 meter in length, and discolored relative to the background sediment; they were found to occur within only ~1200 square meters. A series of concentric ring traces are present, which argues against these structures representing things like recently described lungfish burrow traces. Occasionally, some specimens showed longitudinal wrinkles, which in modern in situ ambergris specimens occur on conical parts tapering towards the anus. Most damning of all, many of the coprolites were filled with squid beaks – oddly enough, mostly lower beaks, and upper beaks were rare and poorly preserved. Several chemical analyses were undertaken, and liquid chromatography analysis detected the presence of lipid derived organic compounds, and cholic acids which might be related to mammalian gastric activity were also found. Traces of eight amino acids were also detected, and relate to the decomposition of squid beaks.

Some ambergris coprolites - from Baldanza et al. (2013).

Some interesting hypotheses have been proposed to explain the occurrence of these ambergris coprolites. What’s strange is that they all occur in a single stratum in a small area (1200 square meters – approximately 35 by 35 meters, or just less than ¼ the area of an American football field), which is a pretty high density of ambergris. Baldanza et al. (2013) argued that their ambergris masses represent remains present within dead sperm whales, rather than coprolites naturally excreted in life – although, based on what information, I am unaware. Baldanza et al. (2013) suggest that the presence of whale fall mollusks in the vicinity are suggestive of a mass mortality event – and the carcasses were apparently preserved elsewhere. They further suggested that the paleogeography of the area may have served as a ‘natural trap’ for pods of sperm whales pursuing squid into shallow waters.

Some more ambergris specimens. From Baldanza et al. (2013).

I am certainly happy with the discovery of fossil ambergris – that is surprising enough. However, I don’t really think it’s at all necessary to invoke some sort of catastrophic interpretation for an assemblage that cannot really even be called a death assemblage, because there isn’t any evidence of death. There aren’t even any skeletons – the analogy would be digging up a vault toilet at a summer camp and identifying it as a mass grave. If there’s no body, it’s hard to claim that a murder has taken place. What mechanism would there be for removing the skeletal remains, but leaving instead coprolites with a far lower preservation potential? I can’t really think of one, save for a bunch of whales defecating at death and having the presumably easier to transport ambergris chunks transported elsewhere on the seafloor.I think a far more plausible hypothesis would be as follows: the locality was sort of a paleogeographic ‘eddy’ where ambergris floated and concentrated by surface currents, eventually becoming waterlogged and sinking to the seafloor.

Now, why was I never very optimistic about cetacean coprolites? Here's a youtube clip showing what happens when a dolphin defecates (it's not really that gross):

Ambergris, on the other hand, is a bit more cohesive and solid, so to speak. It probably won't be so diffusive upon its exit from the body. What hopes can we have for finding ambergris in older parts of the rock record? It mostly rests on two questions: 1) is ambergris restricted to the extant sperm whale Physeter? and 2) how far back does the fossil record of Physeter extend? According to Rice (2009), the answer to the first question is 'yes'. Answering the second question is a bit more difficult, as Physeter doesn't really have much of a fossil record, although Physeter-like sperm whales were around during the early Pliocene (Whitmore and Kaltenbach 2008), and a close relative that already had adaptations for teuthophagy is known from the middle Miocene of California (Aulophyseter).

Baldanza, A., Bizzari, R., Famiani, F., Monaco, P., Pellegrino, R., and Sassi, P. 2013. Enigmatix, biogenically induced structures in Pleistocene marine deposits: a first record of fossil ambergris. Geology doi:10.1130/G34731.1
 
Rice, D.W. 2009. Ambergris. Encyclopedia of Marine Mammals, 2nd addition. p.28-29.

Whitmore, F.C., and J. A. Kaltenbach. 2008. Neogene Cetacea of the Lee Creek Phosphate Mine, North Carolina. Virginia Museum of Natural History Special Publication 14:181-269