Weekly Wonders: Eurhinodelphis

26 10 2009

Good tidings and well-wishes!

Due to the fact that over the past few weeks, this blog has essentially transformed into ‘Mark’s Ode To Phytosaurs’ (something which I seriously doubt that Dr. Hungerbuehler would have any sort of problem with), I’ve decided to dedicate this week’s ‘wonder’ to one of my beloved paleo-mammals.

Recently, my good friend and colleague Donny Price (another MCC paleo-student and research assistant with whom my long-time readers have already been acquainted on several occasions) were asked by Dr. Hungerbuehler’s wife, Simone, to create and present an hour-long lecture concerning the evidence for evolution for her high school students who have opted to take a special Mesalands biology class (yes, I know: this isn’t nearly enough time). When the time came to plan our specific examples, I couldn’t resist commenting on a growing trend I’ve observed in the science of paleontological evolution: cetaceans are the new avian theropods. Simply put, fossils which widen our knowledge of whale evolution are ‘hot’ right now, both in terms of press coverage and academic prestige, with entire websites dedicated to their study. Furthermore, many of the most prominent paleontology programs have taken at least one cetacean expert under their wing of late, including SUNY Stony Brook and the University of Michigan: a trend which is quite comparable to the hype surrounding individuals working on the early evolution of birds and bird-like theropods during the ‘dinosaur renaissance’ of the sixties and seventies. With this in mind, I insisted that we cover the information presented by the fossil record concerning this new study, a discussion for which I shall largely turn to the following video:

To best prepare myself for this scenario, I’ve been ‘boning’ up on fossil whales recently (okay, that pun even makes ME vomit…) and have stumbled across a rather bizarre critter: Eurhinodelphis sp., aka: the ‘sword-nosed dolphin’.

Eurhinodelphis skull reconstruction (hat-tip to Palaeos.com)

Eurhinodelphis bossi skull reconstruction (hat-tip to Palaeos.com)

In 1900, Frank Evers Beddard pointed out in his book creatively entitled “A Book Of Whales” that “the snout [of odontocetes, the ‘toothed whales’]… is very elongated, the degree of elongation varying from genus to genus. It is most developed, perhaps, in the extinct genus Eurhinodelphis, [(which he compares to a platanistid… more on this later)]. The toothed whales, in fact, embody the extremes of shortening and elongation of the facial regions of the skull.”

Before going into further ‘depth’ about the anatomy and lifestyle of this aquatic beast (I guess that pun wasn’t much better), a discussion of its phylogeny is in order. Eurhinodelphis is (unsurprisingly) utilized as an ambassador to the Eurhinodelphidae family which, according to the compendium “Prehistoric Mammals Of Australia And New Gunea: One Hundred Million Years Of Evolution” , is “an extinct group of medium- to long-snouted dolphins [k]nown around the world from the late Oligocene to the middle Miocene in marine deposits”. Remington Kellogg identified these animals by the following characteristics:

“Rostrum [(‘snout’)] excessively elongated, occupying in one case (Eurhinodelphis longirostrus) nine-elevenths of the length of the skull…premaxilla strongly attenuated, forming by itself, in E. longirostrus, much more than half of the rostrum; in E. cochetexui, it is, on the other hand, shorter than the rostral portion of the maxilla. Skull… either slightly convex (E. cochetexui, E. longirostrus) or with a transverse crest (E. cristatus). Maxilla and mandible alone bear teeth; maxilla with 37 to 60 conical teeth, single rooted in each maxilla; premaxilla edentulous [(‘toothless’)], with a rudimentary alveolar gutter with sharp borders, which extends to the anterior extremity of the rostrum [(‘forward-most part of the snout’)]… the symphysis of the lower jaw [(”the connection point between the two halves, or ‘mandibles’)] is very long, and the mandible is furnished with conical teeth, very close together, and single-rooted. Lachrymal free, separated from the jugal by a suture, but with age, sometimes anklyosed around it. Olfactory foramina are large. Supraorbital arch [(‘the arch above the upper half of the eye socket’)] convex. Maxillae, above the orbits, especially in E. cristatus, very thick… The form of the various bones in the skull, especially the squamosal, varies greatly in different individuals.”

Eurhinodelphis reconstruction.

Eurhinodelphis reconstruction.

Kellogg also notes that the cervical vertebrae of these animals are free, the scapula resembles that of modern oceanic dolphins, and the humerus is very similar to those found in modern sperm whales. Furthermore, unlike modern dolphins, Eurhinodelphis was a heterodont: meaning that its jaws contained differently-shaped teeth, with the anterior teeth generally being thinner than their posterior counterparts in addition to the former frequently pointing forward (most noticeably in E. cocheteuxi). On his personal page, Jayson Kowinsky writes that “Although Eurhinodelphis teeth are [more] complex [than those of modern dolphins], they are still tiny and peg-shaped… This means that Eurhinodelphis‘ diet was similar to that of today’s dolphins, [which consists] mainly [of] crustaceans and fish.”

Kowinsky holds an assemblage of Eurhinodelphis teeth.

Kowinsky holds an assemblage of Eurhinodelphis teeth.

He also compares the snouts of Eurhinodelphis and modern river dolphins (platanistoids) and points out that these creatures are unrelated (though somewhat comparable in size, as Eurhinodelphis reached lengths of six to seven feet or two to three meters, which is quite similar to those obtained by the extant Amazon river dolphins ), a fact solidified by the absence of premaxillary teeth in Eurhinodelphis (among other things). It’s been speculated that the long snouts of this creature was used for such things as digging for small, sand-dwelling organisms or as a bat with which to stun fish.

Just as the evolutionary transition between theropods and birds produced a number of oddballs, it would appear that cetaceans have had a few eccentric relatives of their own, many of which are doubtlessly awaiting discovery and research.

May the fossil record continue to enchant us all!

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6 responses

26 10 2009
Zach Miller

Whoa! I was totally unaware of this animal, so this was a fun read. It reminds me of the large ichthyosaur Eurhinosaurus (go figure, right?), and I just wonder what the heck it was doing with that elongated snout.

26 10 2009
tanystropheus

Your guess is as good as mine: though I personally lean towards the ‘battering ram’ idea because if these animals were ‘shovelers’, I’d imagine that their teeth would be more ‘heavy-duty’.

Convergent evolution = prehistoric copyright infringement.

29 10 2009
Brian Beatty

You should see the phocoenids with the elongate mandibular “rams” from southern California! Seriously, it is nice to hear cetaceans described as the “new avian theropods”. I totally love working on them, and it is nice to hear someone suggest they are popular. When you are in Long Island next, come by NYCOM to see some things. Aside from some interesting fossil cetacean specimens and CTs, we have a new cetacean evolution faculty in our department, Jonathan Geisler. So, although UMich and Stonybrook each have one, we have two! Gotta love NYCOM, I only wish we could have grad students (though that might be changing soon, at least an MS is a possible thing someday soon).

2 11 2009
tanystropheus

I knew you’d appreciate that comment, Brian. I’ll probably come to Long Island this July, having decided to go to Stony Brook and would absolutely love to see your specimens and facilities! It’d also be wonderful if this MS program becomes a reality as it’d be wonderful to be a NYCOM grad student.

16 11 2009
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[…] lecture to a high school biology class hosted by MCC and taught by Dr. Hungerbuehler’s wife, a fact which I briefly mentioned here. The main purpose of the presentation was to flesh out the fundamental concepts and implications of […]

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