Top 10 Open Access Fossil Taxa of 2017: Eekaulostomus cuevasae

With the end of the year comes the end to our countdown of the winners of the Top 10 Open Access Fossil Taxa of 2017. We appreciate everyone that took the time to read all of the contenders this year and to vote in the contest!

At Number 1 is the armored trumpetfish Eekaulostomus cuevasae from the Paleocene of Chiapas, Mexico! Published in the Open Access journal Palaeontologia Electronica by authors Kleyton Magno Cantalice and Jesús Alvarado-Ortega, this unusual fish is related to modern-day trumpetfishes and represents the oldest-known representative of the acanthomorph fish superfamily Aulostomoidea.

I asked the lead author of this study, Dr. Kleyton Magno a few questions about this remarkable fish. Dr. Magno is currently a postdoctoral researchers at the Universidad Nacional Autónoma de México (UNAM).

PLOS Paleo: Tell me about the discovery of this fossil!

KM: In reality, this species was collected by Mr. Alberto Montejo, a local quarry worker and owner of the Belisario Dominguez paleontological site. In the annual expedition to Chiapas in 2010, he gave this specimen to Drs. Jesús Alvarado and Martha Cuevas, as a donation to the Paleontological National Collection (housed into the Instituto de Geología, Universidad Nacional Autónoma de México). This single specimen was found just at the end of a hard fieldwork day, when a tropical storm was about to start. Then, Mr. Montejo noted a shining small part of this specimen on a place away from the work area, where the unwanted flagstones are accumulated; it was almost covered by the fallen leaves of the rainforest jungle in Chiapas. A desperate search was undertaken to find the counterpart of this specimen; however, the force of rain and the night denied such a possibility.

At first glance, Dr. Alvarado though that this fish was an extinct representative of the seahorses or pipefishes due the armored trunk. He was ready to prepare and describe this fossil when I entered the scene. My involvement in this discovery began in 2016, when I joined the Instituto de Geología of Universidad Nacional Autónoma de México as postdoctoral researcher. The aim of my work is to describe the spiny fishes of different Mexican localities, manly those from the Paleocene outcrops near Palenque City. When I first saw this specimen I immediately identified some characteristics that could resemble a syngnathid, however, by its body shape and configuration of the unpaired fins it seemed more likely to be a  member of the group that includes cornetfishes and trumpetfishes (Superfamily Aulostomoidea). During this study, we began to discover the remarkable features of this fish, some of them never been seen in this group, such as two stout, paired spines on the dorsal and anal fins, few soft rays on fins, and the body and snout covered by rigid star-like scales.

As we went deeper into the study I felt very excited; this was my fist fossil fish described, and it was already revealing itself to be an important clue to understanding the natural history of the aulostomoids, as it extends the fossil record of the group up to the Paleocene. Extant aulostomoids members are easily distinguished from their relatives (i.e., shrimpfishes, pipefishes, and seahorses) by the absence of rigid dermal scutes on the external surface of the body, as well as other features, such as a long body with parallel dorsal and anal fins, and a somewhat deep caudal peduncle. However, our aulostomid fossil was entirely covered with stout scutes. The inclusion the new species Eekaulostomus cuevasae in a morphological phylogenetic analysis, previously proposed by Keivany and Nelson (2006) for extant groups corroborates our hypothesis that this species is the oldest member of the Superfamily Aulostomoidea. This evidence and the comparison of E. cuevasae with other fossil aulostomoid allow us to infer new insights about the evolutionary history of the Superfamily Aulostomoidea.

What does this fish tell us about the evolutionary history of Aulostomoidea?

Firstly, the Paleocene age of Eekaulostomus cuevasae represent an increment around 15 Ma on the origin and early diversification of aulostomoids, since the oldest forms were found in the middle Eocene of Europe (Pesciara of Monte Bolca, Italy). Furthermore, its geographical position is the first evidence of the Caribbean origin of aulostomoids with posterior diversification and currently worldwide distribution on tropical seas that still needs to better understood.

Eekaulostomus cuevasae is in the stem-group of aulostomoids. This allow us to say that the loss of dermal scutes, as well as stretching and tapering body, and the increment in the numbers of dorsal and anal soft rays are important morphological changes through the aulostomoid evolutionary history. We believed that these changes are morphological improvements on locomotion, buoyancy and adaptations to peculiar predatory behaviors present on extant aulostomoid species. The living species Aulostomus chinensis, for example, has the strategy to make reverse movements or maintain its body statically on the horizontal position, camouflaging between corals to opportunistically catch the prey.

What was the habitat and lifestyle of these fish? With their unusual heads, what did they feed on?

Unfortunately, little can be inferred about the habitat and lifestyle of this fish. Other fossils from the same locality of Eekaulostomus cuevasae are crabs, coprolites, fragments of turtles, carbonized plants, and a singular fauna of fishes that indicates a marine environment with some freshwater influence; however, more details about the paleoenvironment are still required. For now, what we can say is that E. cuevasae probably was a bad swimming, marine species that lived on marine shallow water, feeding on some crustaceans and small fishes using the peculiar method of prey suction through its feeding apparatus composed by small jaws and extreme elongated snout, like as in living aulostomoids forms.

The scales/scutes if this fish are really bizarre, and don’t look like fish scales at all! How did you recognize what you had? Do any other fish have scales like these?

As I mentioned previously, although living aulostomoid species do not have rigid body coverage, all close relatives have them. Nevertheless, the body coverage on these groups are composed of parallels bony plates that are quite distinct from the star-like scutes present on Eekaulostomuscuevasae. Its generic name is based on the shape of the scutes on this species. The prefix “Eek”, is a Mayan word that means “star” and, together with the word “aulos” (a kind if flute in Greek) and “stoma” (mouth in Latin) composes Eekaulostomus, in reference to a flute mouth fish with star-like scales.

Anything else you’d like to share with us about this fish?

We decided to honor our colleague Dr. Martha Cuevas Garcia naming this fish as Eekaulostomus cuevasae because of her initial impulse that allowed us to perform several of the paleontological projects that are currently developing in Chiapas. Although she is an archaeologist who has spent years of work on different archaeological themes related to the Palenque Maya site, after work together in the paleontological prospection works in the southeastern part of Mexico, now she claims her love for fossils.

Congratulations to the UNAM team on this fantastic discovery of this fantastic fish Eekaulostomus and being chosen as the #1 Open Access Fossil Taxa of 2017!

Reference:

Cantalice KM and Alvarado-Ortega J (2017) Eekaulostomus cuevasae gen. and sp. nov., an ancient armored trumpetfish (Aulostomoidea) from Danian (Paleocene) marine deposits of Belisario Domínguez, Chiapas, southeastern Mexico. Palaeontologia Electronica 19.3.53A: 1-24.
 doi:10.26879/682