8. Nov, 2017

After returning from my (20th?) visit to the Red sea, I here like to share some of my reflections on the trip. This was not an UW photo workshop,  so the emphasis was more on diving than on making  UW pictures.  I must confess that over the years diving  has  become less important for me:  I rather see it as a condition for making pictures than a purpose on its own. UW photography also requires  different  underwater skills than diving as a sportive event. Which implies that typical diving hazards like strong currents, navigating in murky water, and visiting deep wrecks are not my favorite and even have become  a reason to skip a dive.

Our itinerary went  a.o.  via Shab Abu Nuhas, Ras Muhammed, Jackson reef, Thistlegorm and the 'tile wreck' Chrisoulis K. The majority of divers on our live-aboard  Whirlwind came from the UK  on a trip organized  by Scuba Travel in London.  This meant pleasant company  and lots of laughter and jokes on the upper deck between the dives. The essence of which I (a Dutchman)  was no always able to follow. Regular diving trips  often imply that individual divers follow the group and  swim around a lot with insufficient time for the UW photographer to lag behind on interesting photogenic spots.  Nevertheless, the dive masters on our trip were aware of this problem and permitted me and Jack Bernstein (my diving companion from the US)  to dive apart from the group. At the end of the trip Subatravel had arranged for our group  one overnight stay in the Hurgada Hilton hotel prior to our flight home. Here we enjoyed  free drinks and meals, and were entertained with a never ending stream of classical music (mostly Mozart)  flowing  from the loudspeakers of the lobby and pool area.

Diving trips in the Northern Red sea are different from those  in the Southern Red sea, where shark encounters have become  the primary target.  Compared with my trips in the early 90-ties, the recent explosive growth of tourism and an the diving industry in northern Egypt does not seem to have substantially  changed the conditions of the Red Sea reefs. The only nuisance perhaps being the more crowded  dive sites where sevaral  live-aboards  are often lined up along the  reefs. With Ras Muhammed leading the list of favorite and busy sites. 

Egypt is still a country with a majority of underpaid or poor citizens. The military regime is often critisized by Western democracies, but   probably also guarantees that tourists can  still travel  safely and  enjoy their vacations in the Red sea area.  In the past  Egypts prosperity  and resources depended largely on the river Nile,  the reason why the Greek historian Herodotus called  Egypt a “Gift of the Nile".  Now,  almost  2500 year later  the Nile and its agricultural benefits seems to be not the only gift that the Gods had in mind for Egypt. Modern tourism industry has developed into the most important sector in the economy, in terms of high employment and incoming foreign currency.  This not only includes  historical attractions in Cairo, Luxor and Aswan, but also the Red sea resorts and diving trips. Hurghada and Sharm El-Sheikh now  collectively boast over 90,000 hotel rooms and provide jobs for half a million Egyptians. In the south, Marsa Alam is following the trend with similar wide scale investments. Charter flights allow citizens from various European countries, including Russia  and  more recently China to fly in to Hurghada in -say- five or six hours to profit from its relatively cheap hotels, resorts and splendid beaches. 

The investment  of billions of dollars spent in the last 30 years building a tourism industry with world-class resorts, beaches and hotels also created an awareness in Egyptians to protect  the Red Sea’s fragile marine ecosystem. A single major  oil spill  could  indeed cause economic disaster. In the northern Red Sea such could happen with oil platforms within striking distance of Hurghada and Sharm El-Sheikh. Luckily  the deep waters in  the central  Red Sea basin prevents building rigs further from the coast. But more  to the north, in the shallower waters of the Gulf of Suez, Egypt’s main oil producing area accounts for 80 percent of the country’s oil production. Over 180 offshore platforms siphon oil from the gulf’s maturing sub-sea fields, their gas flares illuminating the night sky.

The  northern Red Sea as we witness it today, still  offers interesting photogenic sites with healthy corals and many  fish species moving  around in their coral habitats. Lion-, butterfly-, soldier-, squirrel-, crocodile-, banner-fish and moray eels  are abundant, with occasional visits of a turtle or dolphins. Not to forget the snappers,  batfish, damselfish, blue spotted rays, groupers, and numerous anthias swarming along the drop offs. Sharks however have become rare visitors of the diving sites south of  the Sinai peninsula.

For fish-eye shooters many of these species are ideal targets to approach from a very close distance  against a blue background and with bright sunlight. Divers, or the diving boat on the surface can help to enhance the perspective. This wide angle mixed-lighting  technique* works very well on reef locations where  colorful fishes often linger in  their habitats, like a branch of soft coral expanding in the current or a stony  coral table.  My best pictures were actually taken  in shallow water under the boat were lionfish, butterflyfish and moray eels were willing to pose for me. The boat on the surface hid the sun but kept the sunrays spreading around the silhoutte of the boat. With a small aperture and the strobes set at half power this created a pleasant contrast between the bright strobe-lit fish on the foreground and the slightly darkish blue background (see picture at the front as an example). The resulting strong light-dark boundaries give the suggestion of clair-obscur, a suggestive effect often seen in in Dutch paintings of the 17th century. 

Another must for  northern Red sea divers are the wrecks.  Wreck dives are also  a challenge for UW photographers.  Our morning dive to  the famous  Thistlegorm wreck at Shab Ali near the SW point of the Sinai desert was quite hectic with strong currents and  low visibility on the wreck. The greatest challenge of visiting  the Thistlegorm are  the motorbikes and lorries, and swarms of smaller fish inside the holds. Another series of sunken ships can be found north of  Shab Abu Nuhas closer to Hurghada.  Here four wrecks are lined up in sequence:    Ghiannis D,  Carnatic, Chrisoula K. and Kimon M.  A strong wind and high waves made it difficult  to approach  Chrisoula K.  in the small ribs. A reason for the captain to cancel further visits to the wrecks and head for reefs closer to the coastline.

Overall, my feeling is that despite the beauty of the Red sea's underwater world, its diving hazards  should never be underestimated.  Strong winds, currents and high waves can create difficult conditions, especially for UW  photographers carrying heavy equipment.  When the big boat is not able to approach the diving site, a bumpy  ride with the ribs is the only option. Climbing aboard a rocking dinghy after handing over  camera and gear to the skipper in moving seas  is certainly  a physical challenge,  but not a pleasure for the less athletic or elderly divers. The same holds for deploying your surface marker buoy at the end of a dive, while holding the camera in one hand and  inflating the buoy with your free hand. 


Source and links:

*Underwater Photography Masterclass. Alex Mustard, Ammonite Press, 2016.



15. Oct, 2017

According to recent expert reviews (see: review1review2,review3) the new Nikon 8-15  fish eye lens seems to be a must for full frame UW photographers. The lens produces exceptional sharp images, great colors and offers a fully circular 180 deg image at  8mm (floating in a black background)  as well as a rectangular 180 deg diagonal view at 15 mm. A drawback might be that zooming in between  8mm and 15 mm will show a cut off circle with black corners.  Furthermore, a circular UW image may not be not everyone’s favorite, but it does promise spectacular creative images,  for example when taking over under shots of a sunset above a coral reef.

Left:  Tokina 10-17 and Nikon 8-15 fish eye's 

Interestingly, the new lens is  a 'hybrid'  that  can also  be used on DX cameras. On the zoom ring there is white marker placed at 11 mm, indicating the recommended zoom range for  cropped sensors: at 11 mm it will produce a 180 diagonal view and at 15 mm a 110 deg diagonal view (which is about the same range as the Tokina 10-17). At values lower than 11mm the image will show a cut off circle with black corners. That's  because the DX sensor is 1.5 factor smaller than that of a full frame FX camera.  So 10mm and 15 mm on a  DX camera would be equivalent to  15 mm and  22 mm on a full frame camera respectively.  

The question that remains if this new lens is worth  the big investment of around 1000 Euro.  DX users might say:  mmm.... maybe, but only if it will yield superior pictures on my DX than the Tokina  10-17. The ‘Tok’ is a much cheaper fish eye that  for many years has been the workhorse for many  cropped camera fish-eye adepts. Being one of those adepts, I am really looking forward to some comparative tests of both lenses on the D7200.

Another point to consider is  the minimal focusing distance. On the D7200/Tokina combo I use a 5inch Precision dome (virtual image about 18 cm) that  focuses on small objects at 10-15 centimeters in front of the dome. Which is a must for those that like to take CFWA or WAM shots. On my back-up 4/3 Olympus camera with a 4 inch dome (virtual image 15 cm) the  8mm fish eye lens (and small dome)  even allows me to get as close as  2 -5 cm to an object. While still preserving  a nice view of the background scenery. I am not sure if a full sensor camera equipped with the new Nikkon fish-eye lense and a larger dome can match such close focusing  distances.

A more general  question of course is if the advantages of more expensive new generation UW systems with high resolution cameras, advanced expensive  lenses, and a full frame sensor will outweigh those offered by older systems with low(er) resolution cameras, cheaper lenses and  a cropped sensor. The quality of future UW pictures will give  us the answer.   

16. Sep, 2017

One of  the most remarkable sea predators are the Seals. A more official name for these  semi aquatic marine mammals  is 'Pinnipeds', a composition of the Latin pinna "fin" and pes, pedis "foot. Although pinnipeds are widespread in the world, most species prefer the colder waters of the Northern and Southern Hemispheres. But unlike my British diving friends that have access to several diving areas near the British coast where the species are abundant, I have never had the opportunity  to visit them.   Often it takes a bumpy  ride in a small boat over a rough sea to reach the small islands that are their favorite habitat. One of which are the Farne Islands where colonies of grey seals are ready to play with UW photographers. Here the seals often come very close to the lense which

A group of elephant seals at Isla Guadalupe (Mexico)

allows close up shots of their head and open mouth displaying an impressive row of sharp teeth. But there are many more species of finfooters living in the Oceans of the world, and one gets easily confused by their great number and variety.

Classification To get some grip on it, it’s best to follow the top-down route:  family -->  genus --> species. The seals comprise three extant families, the Odobenidae (whose only living member is the walrus), the Otariidae (the eared seals), and the Phocidae (the earless seals, or true seals).  The eared seals consist of two big subfamilies: the sea lions and fur seals.  The earless seals in turn consist of many subfamilies with species  like the common, spotted, grey,  leopard and the elephant seals. According to an earlier theory the Pinnipeds would have  descended from two ancestral lines; walruses and otarids sharing a recent common ancestor  with bears, and phocids sharing an ancestor with mustlids  (e.g. the otter, weasel, badger). But more recent morphological and molecular evidence makes it more likely that they all descend from the same ancestor.

General characteristics There are clear physical and behavioral differences between the three families. Leaving the walruses with their prominent  tusks, whiskers,  tusks  and bulkiness aside,  the eared seals are better adapted to live on land than the earless seals.  They are  subdivided into the fur seals (Arctocephalinae  or bear heads) and sea lions (Otariinae) subfamilies, with the major distinction between them being the presence of a thick underfur layer in the former. Eared seals have a dog-like head and  are less adapted to an aquatic lifestyle than earless seals.  But because of their large flippers they can attain higher bursts of speed and have greater maneuverability in the water that the true seals. Their large fins also enable them to "walk" on land by rotating their hind flippers forward and underneath their big bodies. This is why they are so popular in aquaria and marine shows.

Earless seals in contrast  have small flippers, shuffle on their bellies on land, and lack visible ear flaps. Earless  seals are also  less social than their eared cousins. They spend more time in the water and often lead solitary lives in the wild, coming ashore together only once a year to meet and mate.  They forage much further in the sea to exploit prey resources, while otarids are more tied to zones close to breeding sites on land. They also swim by sideways movements of their bodies using the fore flippers for steering. The hind flippers are unsuited to walk with.

 A selection of  species The list of different seals  is almost endless.  So those who seek more details better click on one of the links in this article. I here focus on some species and characteristics that have received most interest  from divers and UW photographers. I shall start with the eared seals.

Sea lions The California sea lion (Zalophus californianus) is a popular eared seal native to western North America. It is one of five species of sea lions. Sea lions assemble in gregarious groups that can reach upwards of 1,500 individuals, often congregating  on the sand. They can also be found floating in the water in large groups called rafts.  Sea lions are characterized by external ear flaps, long foreflippers, the ability to walk on all fours,  short thick hair and a big chest and belly. Together with their cousins the fur seals they  are a common prey for  white sharks and killer whales. The agile and swift sea lion however also seems to enjoy outsmarting the great white and has even been filmed  biting the tail and fins of sharks before darting away back to the surface to breath. An easier prey for the great white are baby seals  that drift too far from the heard along the coastline. Steller sea lions (Eumetopias jubatus) from the northern Pacific look different from the California sea lion. They are the largest of the eared seals and much larger than the California sea lion. Males are further distinguished from females by broader, higher foreheads, flatter snouts, and thick mane of coarse hair around their large necks. Indeed, their Latin name translates roughly as "maned one with the broad forehead". Dive operators on Vancouver Island, British Columbia, offer dive trips to swim with Stellers at colony sites.

Fur seals Like sea lions fur seals have relatively long and muscular foreflippers and the ability to walk on all fours, but are generally smaller than sea lions.  Typically, they gather during the summer in large groups at specific beaches or rocky outcrops to give birth and breed. Many fur seal species were heavily exploited by commercial sealers, especially during the 19th century when their fur was highly valued. Some populations, notably the Guadalupe fur sealNorthern fur seal, and Cape fur seal, suffered dramatic declines but are now recovering. Fur seals  are also common prey for  white sharks, for example along Dyer island in South Africa a favorite habitat for numerous fur seals.

I now move on to the earless seals, that are found in southern as well as more northern seas. Worldwide two species in particular are now in the danger zone of survival; the Hawaiian monk seal is one of only two monk species extant, the even rarer Mediterranean monk seal  being the other. Here are some well known  and -luckily- less endangered species: 

The common seal  (Phoca vitulina), also known as the harbor seal, is found along temperate and Arctic marine coastlines of the Northern Hemisphere. The  seals are brown, silvery white, tan, or gray, with distinctive V-shaped nostrils. They are the most widely distributed species of pinnipeds that are found in coastal waters of the northern Atlantic and Pacific oceans, the Baltic and North Seas. In North Holland  the population is now estimated to be around 3500 species.

Grey seals The  earless grey seals (Halichoerus grypus) attract many divers from the UK, which is home to 40% of the world’s population.  The Farne Islands and Lundy Island are used to divers and regularly provide excellent photographic encounters. Grey seals can be very friendly and it is not unusual for them to push  their snouts and whiskers, or open mouth against the dome of the camera.

Elephant seals are large, ocean going earless seals in the genus Mirounga. The two species, the northern elephant seal (M. angustirostris; see picture above) and the southern elephant seal (M. leonina), were both hunted to the brink of extinction by the end of the 19th century, but the numbers have since recovered. The bull southern elephant seal is without rival the largest  and heaviest carnivorian alive. Elephant seals take their name from the large proboscis of the adult male (bull), which resembles an elephant's trunk.  The bull's proboscis is used in producing extraordinarily loud roaring noises, especially during the mating season. 

The leopard seal (Hydrurga leptonyx), also referred to as the sea leopard, is the second largest species of seals in the Antarctic, after the southern elephant seal. Its throat is whitish with the black spots that give the seal its common name. It is second only to the killer whale among Antarctica top predators.  While very few leopard seals have actually been measured, there have been reported lengths of around 3.8 metres from nose to tail. However, most leopard seals seen in the Antarctic Peninsula are much smaller, between 2.5 and 3 metres in length. Sometimes the hunting leopard seal likes to demonstrate his power by playing with the penguin in front of the camera. Although attacks on humans are rare, there are reports of leopard seals attacking  boats and even killing humans entering their territory.*

Source and links.

Berta, A.; Churchill, M. (2012). "Pinniped taxonomy: Review of currently recognized species and subspecies, and evidence used for their description". Mammal Review42 (3): 207–34

*Owen, James (August 6, 2003). "Leopard Seal Kills Scientist in Antarctica"National Geographic Society. Retrieved 2007-12-10







8. Sep, 2017

Coral reefs form a beautiful and important part of our ocean, made up of thousands of tiny animals—coral “polyps”—that are related to anemones and jellyfish. The polyp uses calcium and carbonate ions from seawater to build itself a hard, cup-shaped skeleton made of calcium. Some  stony corals of the family Acroporidae like Staghorn coral and Elkhorn coral can reach enormous proportions. Corals reproduce once a year, on cues from the lunar cycle and the water temperature. Entire colonies of coral reefs then simultaneously release their tiny eggs and sperm, called gametes, into the ocean. When a coral egg and sperm join together as an embryo, they develop into a coral larva, called a planula. Planulae float in the ocean, some for days and some for weeks, before dropping to the ocean floor. 

Comparison of coral areas near Key West (FL) identified on an old sea chart from 1775 (left) and a modern satellite chart (right) where the same coral is missing (adapted from McClenachan et al. 2017 *) 

Then, depending on seafloor conditions, the planulae may attach to the substrate and grow into a new coral colony at the slow rate of about 10 centimeters a year. Unfortunately, this wonderful subtle process of reproduction is also vulnerable and easily affected by external influences like tropical storms, changes in water temperature or environmental pollution. 

Decline of the coral reefs The ecology of coral reefs have been a matter of concern of  marine biologists, since their conditions deteriorated  considerably in the last 50 years. Anthropogenic causes of dying coral reefs are land erosion, fertilizers used in agriculture, draining of  swamps and mangroves, motor ways connecting chains of small island,  deforestation, building projects, cyanide fishing and release of waste and chemicals by the industries. Together they form a serious threat for survival of great reef formations, such as the Great  Barrier reef in NE Australia and the Coral Triangle in the Indo pacific Ocean. But also less spectacular reef formations in the Caribbean and Southern Florida regions have shown a decline,  which has made these reefs  a 'worst case scenario' in a recent IUCN report. The Elkhorn coral, one of the most important Carribean corals in terms of its contribution to reef growth, will be hard to find today.

Ghost reefs of Florida Humans have fundamentally  altered coastal ecosystems over the years. Deterioration of seawater quality goes hand in hand with damage of coral formation, and mostly so in coastal areas were effects of pollution tend to be more severe. Recently, a team of  American and Australian investigators discovered that in the last two centuries many coral formations along the southern Florida coastline had vanished, especially close to the shore (*). They had the ingenious idea to use 18th century British imperial charts of the Florida coast made by cartographer George Gauld. His precise sea charts have the reputation to provide useful  ecological information  especially with regard  to corals that are of interest as a navigational hazard. Using these charts they identified  143 coral formations on two charts that spanned from Key Largo to the Marquesas Keys.  Most of the observations fell into the three interior zones: the nearshore patch reef, the offshore patch reef, and the reef crest. Their overall findings were then  compared with modern satellite charts of the same region (the Millennium Coral Reef Mapping Project, the Benthic Habitats South Florida Map, and the Unified Florida Coral Reef Tract Map). 

This revealed that overall 52% of the corals on the seafloor around the Florida Keys was lost.  Strongest losses were in the Florida Bay and  nearshore areas were coral had declined  by 87.5% and 68.8% respectively (see picture above for an example), whereas offshore areas of coral had remained largely intact.  The investigators conclude that surveys  looking only at species within the know extant range may overlook loss of coral formation over a longer time range resulting in an overly optimistic view of the current conservation status. The danger of a shifting baseline syndrome is that not the orginal (forgotten) situation but the current or more recent situation is taken as a baseline to evaluate environmental changes. Another example is climate change and global warming, which could have started much earlier than normally assumed. Namely with the onset of industrial revolution some 250 years ago  when its  global manifestations were less conspicuous.  But the  Florida study also has some good news: it highlights the restoration potential of  coral species in nearshore areas  that hitherto were considered unsuited for coral growth.


*Loren McClenachan et al. Science Advances, 2017 6 September. Ghost reefs: Nautical charts document large spatial scale of coral reef loss over 240 years research article

J. B. C. Jackson, Reefs since Columbus. Coral Reefs 16, S23–S32 (1997).

20. Aug, 2017

Once upon a time, long before humans made their entry in the wold,  large and strange  animals were swimming in our oceans. They had  sharp teeth,  a long tail and a kind of paddles at the side of their body looking like hands and feet. Some had  tiny hind limbs and flipper-shaped fore limbs, others large  feet and  a long tail like crocodiles. These strange and fierce looking creatures  were the ancestors of our modern whales. These extinct whales or Archaeoceti  (‘ancient whales’)  lived in an period stretching from  the  early Eocene to the late Oligocene, 55 to 23 millions of years ago. Archaeoceti possessed land and mammal characteristics, demonstrating the evolutionary transition from land to sea. Many of them were descendants  from even-hoofed land animals called Artiodactyla, with long skuls and carnivorous teeth  related to our hippos, dear and pigs. Whales move their tales up and down, which is much like the undulating movements  of the vertebral column of running four legged mammals living on land.

Varieties The ancient whales consisted of five families with many subspecies, some of which paleontologists managed  to reconstruct out of their  bony parts and skulls.  Initially many must have lived in shallow near-shore environments such as estuaries and bays. Some species still lived on land, others were amphibious. Examples are Pakicetus, an extinct genus of amphibious cetacean of the Pakicetidae family, that had long slender legs, a long narrow tail, and could reach the size of a modern wolf. Rodhocetus from the Protocetidae family (see the artist impression inserted above)  also  lived amphibiously, while Protocetus  from the same family must have been fully aquatic. Ambulocetus  from the  Ambulocetids family discovered in Pakistan was able to  walk on land, but probably spent most of  its time in  ancient estuaries with brackish water. An important tool for scientists to determine if a sea animal lived most of its time in fresh or salt water -which it also drunk- are the different ratios of oxygen isotopes in its bones.

Overselling of whale evolution?  Some opponents of the evolutionist view have argued that the ‘evolution of whales’ scenario could be  but a fairy tale devoid of any scientific evidence*. For example, Ambulocetus could also have been a four-footed animal, similar to that of common wolves, found in a region containing fossils of such terrestrial creatures as snails, tortoises or crocodiles.  In other words, it could  have been  an isolated species of a land animal, not an aquatic -or transition to aquatic- one. In order to suggest a transition from land to water artistic retouches have drawn webbings on its front feet, which are hard to find on the fossile's skeleton. It is true that it has been hard to derive from fossile bones of certain land animals specific characteristics that signal a transitional stage to sea mammals. One example is the presence of sound transmission structures found in the lower jaws. Another are isotopes of oxygen in the bones that reflect in what kind of watery environment the creature lived. But these -admittedly- vague indications will probably  never convince the rigid creationist. I personally  do not see a contradiction between evolution and  (divine) creation. Whats wrong with the view that evolution provides a scientific basis of the creation of species, divine or not divine? Certainly, even a divine job could never  have been done in seven days.

Fosssile hotspots have  been discovered at  various places of the World,  not only in  India, Pakistan and Egypt, but surprisingly also in coastal waters of North-West Europe.  In Dutch-Belgian coastal waters, for example, an unique cemetry of buried bones of long lost mammals has recently been discovered.  In this specific region old soil layers of different ages are found very close to the shallow seabed.  The findings included among others numerous fossilized shark teeth, the remains of walruses from the last Ice Age (116.000-12.000 years ago) and vertebrae of primal whales from the warm Eocene period (40 million years ago). The whale vertebrae possibly belonged  to the family of Protocetidae. The fact that the bones were mostly intact and the finding of both males, females and young animals suggest that these sea giants had formed a local colony in the cold climate of the last Ice Age. The landscape in the widened estuary mouth of the river de Schelde  was then a tundra  with  large grazers  like woolly mammoth, woolly rhino, hippo, giant deer, forest elephant and steppe wisent.  

Adaptations  Later species had long snouts, large eyes, and a nasal opening located further up the head than in earlier archaeocetes. Which suggests that  they could breathe with the head held horizontally, similar to modern cetaceans — a first step towards a blowhole. Another typical area  present in the skulls of ancient wales is the ear region, which is surrounded by a bony wall just like in the now  living whales.  In a much later stage of their evolution the ancient whales split up in two cetacean suborders,  the Odontoceti (the toothed whales) and Mysticeti  (the baleen whales). So the Odonteci kept their teeth and developed into our toothed whales  which  include the porpoises, dolphins, killer wales  and the sperm wales. The other half,  the Mysticeti, changed their teeth for hairy curtains or baleenes, like in the humpback and blue whales. Reflecting that they must have gradually switched to suction feeding. This meant a more effective way of feeding on and filtering out  the tiney preys and large amounts of krill that drifted  abundantly in the colder parts of the oceans. Probably this transition went via an intermittent stage  when these whales possessed teeth and baleens at the same time. Other non cetacean filter feeders like  the whale and basking sharks do not use baleens but filtering plates.


Source and links

Bajpai, S; Thewissen, JG; Sahni, A (2009). "The origin and early evolution of whales: macroevolution documented on the Indian subcontinent" (PDF). J Biosci34 (5): 673–86. OCLC 565869881PMID 20009264

Thewissen, J. G. M.; Hussain, S. T.; Arif, M. (1994). "Fossil evidence for the origin of aquatic locomotion in archaeocete whales". Science263(5144): 210–212. PMID 17839179doi:10.1126/science.263.5144.210.


Cooper, Lisa Noelle; Thewissen, J. G. M.; Hussain, S. T. (2009). "New middle Eocene archaeocetes (Cetacea: Mammalia) from the Kuldana Formation of northern Pakistan". Journal of Vertebrate Paleontology. 94 (4): 1289–99. OCLC 506008976doi:10.1671/039.029.0423