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Wednesday, February 18, 2015

New Paper: Evolution of multicuspid teeth in a Triassic fish from Utah

the holotype of Hemicalypterus, USNM V 23425, composite image of the part and counterpart.

Just yesterday, my newest paper was published online in the journal The Science of Nature: Naturwissenschaften about a rather unusual fish from the Upper Triassic Chinle Formation of southeastern Utah. The fish, Hemicalypterus weiri, was a deep-bodied, disc-shaped fish, with enameled ganoid scales covering the anterior portion of its flank, and a scaleless posterior half, which presumably aided in flexibility while swimming. Although Hemicalypterus was first described in the 1960s (Schaeffer, 1967), recent collecting trips recovered many new specimens of Hemicalypterus, and I decided to reinvestigate this enigmatic fish as part of my dissertation research.

While cleaning specimens of Hemicalypterus at the University of Kansas Vertebrate Paleontology prep lab, I noticed rather unusual teeth on the lower jaw that I had exposed from the rock matrix. These teeth look like a mouthful of little forks, and there were at least six individual teeth on the lower jaw. As I prepared other specimens, I found that these teeth were also on the premaxillae. Each tooth has a long cylindrical base and a flattened, spatulate edge with four delicate, individual cusps. I hadn't seen anything like this before in other fossil fishes, and so I started searching the literature and talking to other ichthyologists.

The multidenticulate teeth on the premaxilla of one of the specimens

Well, as it turns out, this tooth morphology has evolved multiple times in several independent lineages of teleost fishes, and quite often fishes with similar dentition scrape algae off of a hard substrate. These teeth indeed act like little forks (or "sporks" might be more appropriate) for these herbivorous/omnivorous fishes. Examples of extant fishes with similar teeth include freshwater forms such as the algae-scraping cichlids and characiforms, as well as many marine forms that are key in controlling algae growth in coral reef environments, such as acanthurids (surgeonfishes, tangs) and siganids (rabbitfishes). Of course, these modern-day fishes also feed on other things (e.g., phytoplankton), but algae is often the primary staple, and these fishes use this specialized dentition for a specific feeding behavior.

The same teeth as above, but under fluorescent lighting


So while it is impossible to prove definitively what a species of fish that lived over 200 million years ago fed upon (without gut contents being preserved....or a time machine), it is still safe to infer that Hemicalypterus occupied an ecological niche space similar to algae-scraping cichlids or other modern-day herbivorous fishes and may have scraped algae off of a hard substrate, based on this unusual tooth morphology and its similarity to modern forms. 

The multidenticulate teeth of a modern-day algae-scraping cichlid, Labeotropheus

This discovery also extends evidence of herbivory in fishes clear back to the Early Mesozoic, whereas prior to this discovery it was assumed that herbivory evolved in the Middle Cenozoic in marine teleost fishes. Frankly, there was no evidence to say otherwise, as most Mesozoic fishes have general caniniform or styliform (peg-like) teeth, or they have heavy crushing or pavement-like teeth consistent with crushing hard-shelled organisms. The teeth of Hemicalypterus are very delicate, and wouldn't really do well with durophagy. This is the first potential evidence of herbivory in the Mesozoic, and in a non-teleost, ray-finned fish.

Original Source: Gibson, S.Z. 2015. Evidence of a specialized feeding niche in a Late Triassic ray-finned fish: evolution of multidenticulate teeth and benthic scraping in †Hemicalypterus. The Science of Nature — Naturwissenschaften 102:10. 

Also cited: Schaeffer, B. 1967. Late Triassic fishes from the western United States. Bulletin of the American Museum of Natural History 135: 289–342.

Friday, June 3, 2011

Super Popped

Field stationAt the field station

Looking at the collectionSurveying KU’s Entomology (insect) collection

Spencer print roomIn the Spencer print room

We sat in a classroom that smelled of mothballs. Drawers upon drawers of dead bugs lined the room, their bodies pinned to foam boards. It seemed the farthest place that one could possibly be from a jungle. The giant insects taunted us as we looked at them, mandibles frozen wide, and it seemed that we would never see them move.

It is now about 12 hours until we leave Lawrence, and the truth is hitting home. We’re about to see these giant insects, alive and gnashing, right in front of us in the Peruvian jungle. The Amazon.

The bags are packed, the plane tickets bought, the boots broken in, the checklist checked. We’ve had a whirlwind of preparation pre-departure, and it was a lot of fun. In that stuffy classroom, Dr. Chaboo talked about how insects fit into the tree of life, how they function, how they’re different from spiders, crabs, and worms, and about the group of insects that she studies, Chrysomelid beetles.

“We are descended, if you go back far enough, from the same ancestors that gave rise to insects. Your diaphragm is leftover segmentation,” she said, and I conjured an image of a human skeleton with its segment-like ribs and vertebrae. I certainly felt different from the shiny critters impaled on stainless steel spikes in front of me. But we’re related.

Relatedness is perhaps what our team is after. Half of us are trained in the arts and half are science-oriented, though we’ve all dabbled in both. If you’re interested in the training of the team, check out the Meet the Team post I did previously.

Our training has taken us to the Spencer Art Museum, the KU Natural History Museum, and KU’s field station just north of Lawrence. We looked at prints, drawings and paintings in the Spencer’s printroom, visited the Natural History Museum’s BugTown exhibit, and practiced collecting insects at the field station.

We will all assist Dr. Chaboo’ work on Chrysomelid beetles, but each student will also work on a project of their own. Art and writing students will craft creative works and biology students will conduct field research. But the idea is that we will be informed by the work done on both sides of the art/science divide. I hope to encourage these crossovers, catching them if they arise, and relate their ramifications on this blog in the days forthcoming.

Insects also take center stage in this endeavor, and I believe that it is important to convey their world, if possible. To bring them to the fore, I will strive to present them to the reader visually. Check out some close-ups of insects at the KU field station:

“It’s going to be a very physical experience,” Dr. Chaboo said, “The rain forest is not sexy because you will be covered in DEET!”

Preparation would be intimidating if she did not approach the study of insects with the energy and enthusiasm of an on-stage pop star.

“I’m super pumped!” said someone.

“Super popped?” asked Dr. Chaboo. Thus our pre-departure catch-phrase was born.

Tuesday, March 11, 2014

Tail Wagging the Ear?

Nancy Bixler concentrated on cleaning the impressive 6-foot moose today. She’s from Maine, so while she has seen these animals in the wild, it’s certainly a unique experience to walk carefully under and around one to clean the mount.

While carefully documenting the condition of the moose in the Panorama, the team discovered something strange in a moose’s ear: a tail. A tail of a moose, stuffed into its ear! Ron Harvey surmised that the moose lost its tail, and an employee decades ago thought it might get lost. So they stuffed it into the ear, and then years passed.

Other not so strange finds have included two dead bats. Once every few years, a bat sometimes crawls into the exhibit from the attic of Dyche Hall. These bats, which have probably always lived in the museum’s attic, are small brown bats about the size of an adult’s hand. At some point years ago, these two became stuck in the exhibit, and no one knew.