NEWSLETTER 05/2014 20.05.2014

The Manzano Ctenacanth: Godzilla Shark of New Mexico!

The Story

About 300 million years ago, in the Manzano Mountains east of Albuquerque, a shallow warm lagoonal estuary was home to a wide variety of plants and animals. Environmental conditions of the bottom of this lagoonal estuary suggest oxygen was extremely poor or not present. This prevented bacterial decomposition of organisms that died and sank to the fine- grained silts and muds to be preserved in relative completeness and in high detail. These conditions preserved thin plant cells, bone, cartilage, and soft tissues.

Paleontologists and geologists from the Smithsonian, Carnegie Museum, University of Kansas and the New Mexico Museum of Natural History and Science have researched the exquisitely preserved fossils from the Manzano Mountains since the late 1960’s. Fossils of plants, invertebrates, small fish, and small amphibians have been collected over the years. 

In 2013, during a paleontological conference day trip to the Manzano Mountains, shark paleontologist John-Paul Hodnett serendipitously came across the tip of the nose of a nine foot long ctenacanth (TEEN-uh-kanth) shark (Figure 1). Ctenacanth sharks have large spines in front of their dorsal fins and first appeared in the fossil record during the Late Devonian, about 380 million years ago, and survived until the Early Cretaceous, about 135 million years ago. Scientists in the past proposed that ctenacanths were direct ancestors of modern sharks. Current research, however, suggests ctenacanths might be more closely related to the extinct basal sharks rather than to their modern kin. Until this recent discovery in New Mexico, ctenacanth sharks were known only from two partial skeletons, a few partial skulls, and isolated teeth and dorsal spines. For a shark paleontologist the 2013 discovery was a dream come true…

The shark was exposed on its right side in a fine grained limestone. Due to its size the shark was removed in three sections to be preserved and re-assembled in the paleontology laboratory at the New Mexico Museum of Natural History and Science.  The top of the braincase and the right and left upper jaws of the skull, the dorsal fin spines, the vertebral column, and the pectoral and pelvic fins were exposed with mechanical preparation by museum staff. The tail is still being prepared.  It is currently under study by Hodnett, Dr. Spencer G. Lucas, and scientists from the American Museum of Natural History in New York and Northern Arizona University in Flagstaff.

What We Are Doing

• Using Computed Tomography (CT), we are scanning the head section of the “Manzano Ctenacanth”
• Scanning the head section we are looking at the composition of the braincase, the palatoquadrate (a single cartilage structure that is the cheek and upper jaw), and looking for the cartilages that make up the Meckel’s cartilages (the lower jaws) and the gill arches, which are not initially seen on the surface of the rock containing the specimen.
• We are CT scanning the full body skeleton of Cobelodus, a smaller shark and a relative of the “Manzano Ctenacanth”  found in the Manzano Mountains (Figure 1)
• For Cobelodus, we are looking for hidden structures that are hard to see or that are hidden by sediments to determine the morphology of the skull, visceral skeleton, the body column, and the fins

What We Know

• The “Manzano Ctenacanth” is presently the largest and most complete ctenacanth in the world
• It is presently the largest vertebrate fossil to be discovered at the fossil site in the Manzano Mountains
• It is approximately 85 to 90+% complete
• The lack of “claspers”, a skeletal sexual organ on the pelvic fins of male sharks, makes the “Manzano Ctenacanth” a female
• The size of the dorsal fin spines (which are almost two feet long) and the shape of the teeth suggest the “Manzano Ctenacanth” is a new species
• The body of the “Manzano Ctenacanth” was covered with small tooth-like scales, called dermal denticles
• Cobelodus is the most common shark from the fossil site in the Manzano Mountains
• Most of the specimens of Cobelodus are small, smaller than “adult specimens” from a similar aged locality in Indiana. These specimens have been proposed to be juveniles in the past.

Why CT Scanning Is Important

• Knowing the structure of the braincase and the visceral skeleton (jaws and gill arches) in the “Manzano Ctenacanth” and Cobelodus will help determine the relationship between these sharks to other extinct and modern cartilaginous fishes (Figure 2)
• The completeness of the “Manzano Ctenacanth” will allow us to use it as a keystone specimen to determine the missing data of other ctenacanth shark specimens around the world
• The “Manzano Ctenacanth”skull can be recreated in three dimensions from the CT data
• A three dimensional skull model can be used to determine how the jaws and gills operated and can help determine how strong of a bite force the “Manzano Ctenacanth” could produce
• A 3D skull of the “Manzano Ctenacanth” could be “printed” for study and display
• CT scanning the Cobelodus will allow us to test the hypothesis that the New Mexico sample represents juveniles in a marine nursery, or are small adults of a new species of Cobelodus, or a completely new shark
• The full skeleton of Cobelodus can be reconstructed three dimensionally from the CT data
• A skeletal model can be made to determine how the shark moved and hunted
• A 3D skeleton of Cobelodus could be “printed” for study and display

Figure 1:  bottom left, outline drawing of the “Manzano Ctenacanth”NMMNH P-68537 exposed to the surface; top left, reconstruction of the “Manzano Ctenacanth”; bottom right, outline drawing of NMMNH P-19182, a Cobelodusshark, from New Mexico Quarry; top right, reconstruction of Cobelodus . Both illustrations drawn to scale to a 5’10” male human (©New Mexico Museum of Natural History and Science/JP Hodnett)

Figure 2: “Shark Family Tree” by Ray Troll showing the branch where ctenacanth sharks are related to other cartilaginous fishes and “Bony” fishes (© Ray Troll, reproduced with permission, http://www.trollart.com/)

Sharks are in danger in most parts of the world, with a quarter of all sharks and rays now threatened with extinction. This ongoing collapse of shark populations has already hadfar-reaching effects on marine ecosystems. To arrest this trend we desperately need scientific data that effectively inform conservation management. But are we focusing our research effort in the right areas?

We looked at 20 years' worth of scientific papers on shark conservation to see if shark science is meeting the needs of conservation. Our results, included in a forthcoming book, suggest that the species most in need, and the places where most damage is done, aren’t getting the attention they deserve.

Are we looking in the right places?

For science to have the best chance of helping to protect sharks, it should be focused on places where the need for conservation is greatest. As fishing is the most serious threat to sharks, research efforts should therefore correspond to the places with the most fishing.

Pleasingly, our study found that although shark fishing has increased, scientific effort has also increased substantially in the past few decades. In 1992 only 2 peer-reviewed studies specifically on shark conservation and management were published, by 2011, 80 were published. However, the increase in scientific output is largely driven by two countries: Australia and the United States. In the countries where most shark landings occur (Indonesia, India, Taiwan and Spain) there is almost no research on shark conservation or management.

This lack of research effort is mirrored by the failure of these countries to implement national shark management plans along United Nations guidelines. There is therefore very little information on the conservation status of some of the world’s most vulnerable sharks, and few plans in place to improve the prospects of these populations.

Can we change the situation?

This geographic bias can be at least partly explained by wealth. Research is expensive, and countries that catch the most sharks are relatively poor. But as sharks are key players in marine ecosystems all over the world, we all have a vested interest in their conservation.

Moreover, many shark species are highly mobile. Sharks caught in one country’s waters may well have spent much of their lives elsewhere. That means that effective conservation in one region can be spoiled by poor management in a neighbouring country.

We suggest that countries that already invest heavily in conservation and management research have a powerful incentive to cooperate with those that cannot afford it.

For example, Indonesia catches more sharks than any other country in the world. If Australia were to focus some of its shark research on its nearest neighbour, the collaboration could deliver big gains in sustainable fishing management.

Are we doing the most effective science?

Australia publishes more studies on shark conservation research, per capita, than any other country. But we cannot afford to be complacent about the type of science that we do. Our study found major biases in which species of shark attracted the attention of researchers.

If conservation research is to be useful, it should prioritise species that are most at risk. Yet of 479 scientific articles on shark conservation and/or management published worldwide over the past 20 years, only 22 (less than 5%) focused on globally endangered species. And 16 of those were focused on a single species that is also of economic importance: the scalloped hammerhead. That leaves just six papers (on four species) in two decades which looked at all of the other globally endangered sharks (24 species).

More than 200 species (over 40%) of sharks are classified by the International Union for the Conservation of Nature as “data deficient”: we simply do not have enough data to make a call as to whether they are endangered or not. Yet, in the past two decades only 30 studies focusing on 14 data deficient species have been published. Many of these species are likely to be threatened or endangered but without hard data we just don’t know, so effective management is impossible.

Specifically referring to shark conservation, of the 20 most studied species, only the scalloped hammerhead is endangered and just two are listed as data deficient. We found that the vast majority of research is highly skewed towards species that are either economically important (such as the blacktip shark), or charismatic, such as the whale shark and the great white shark.

This skew may be explained by the advantages charismatic species confer in leveraging funding, combined with evidence that publishing in high-impact journals is easier with popular species, with obvious implications for researchers' careers.

Importantly, bycatch species are largely ignored, despite the fact that most sharks are caught as bycatch. This has serious consequences. In southeastern Australia, for example, no data on bycatch of deepwater sharks were available for many decades. By the time this data became available, some species – such as the now critically endangered Harrison’s dogfish – had declined by nearly 99%.

We have a long way to go to improve shark conservation science. While the research effort has increased over the last 20 years, it has done so in only a few countries and for a handful of species – and not always those most in need in either case.

If we want to ensure that sharks are properly managed right around the world, we need to start paying closer attention to the “where” and “what” of shark science.

Most fauna in the deep-sea rely upon a drizzle of particles of decaying animals and feces.  This marine snow is of low food quality as you might expect death and feces to be.  Occasionally, deep-sea buffets occur in the form of a large food fall, a nice way to a near complete carcass.  My work on chunks of wood on the deep-sea floor represents one type of these smorgasbords.  Other large food falls occur in the form of the well-known whale falls.  Natural food falls, i.e. scientist not tossing wood or a whales into the deep ocean, are rarely encountered.  Only nine vertebrate carcasses have ever been documented on the seafloor.  Add to that four more thanks to Nicholas Higgs, Andrew Gates, and Daniel Jones.

Off the Angolan African coast, these researchers document one whale shark and three ray carcasses at 1200 meters on the seafloor.  This is the first time any of these have been documented as deep-sea food falls and only recently have living whale sharks even been documented off Angola.

Despite one of the carcasses being covered in 54 eelpouts, a considerable amount of flesh still existed on the carcasses.

[in prior studies] When presented with elasmobranch and tuna bait on a baited camera trap, scavengers clearly preferred tuna and only consumed the elasmobranch once the tuna was gone…Repeated experiments in this region using [bony] fish as bait showed a 10-fold increase in scavenging rates compared to that when elasmobranch was used.

So why in a food desert like the deep sea would fresh meat not be consumed quickly?  Apparently, elasmobranch, i.e. shark and ray, flesh is bit unpalatable and tough to chew.  The tough, sand-paper-skin may prove a formidable barrier to scavenger jaws.  The high ammonia content of elasmobranch flesh may also be, to say the least, unappetizing.  The carcasses may also smell like death and deter other scavenging elasmobranchs.

Other uncharacterized chemicals that are found in rotting elasmobranch flesh (necromones) have been proven to strongly deter shark scavenging and invoke an alarm response, even among different species of elasmobranch. If this phenomenon extends to deep-sea scavenging elasmobranchs, it can be assumed that the Portugese dogfish, Centroscymnus coelolepis, would have been deterred from scavenging the elasmobranch carcasses. This will have severely hindered utilization of the carcasses by other species, since C. coelolepis is the dominant scavenger off the Angola margin.

Yet despite the smell of death and urine, a dead elasmobranch still provides an essential snack in the deep sea.  The researchers estimate that these elasmobranchs represent 4% of the total amount food that sinks to the seafloor off Angola in the form of marine snow.

Higgs, N., Gates, A., & Jones, D. (2014). Fish Food in the Deep Sea: Revisiting the Role of Large Food-Falls PLoS ONE, 9 (5) DOI: 10.1371/journal.pone.0096016

Top Canadian shark researcher Steven Campana, pictured here tagging a shark, said there's cause for hope. (Supplied)