Category: fossils

When did modern placental mammals diversify?

February 3, 2014 • 1:36 pm

by Greg Mayer

Almost exactly a year ago, I reported in two posts here at WEIT on a paper in Science by Maureen O’Leary and colleagues on the radiation of placental mammals. Placentals are one of three major groups of living mammals, the others being the marsupials (dominant in Australia, plus a fair number in South and Central America, and a few in North America) and the monotremes (the egg-laying playtpus and spiny anteaters: a handful of Australasian species). Placentals are by far the most species rich and abundant of the mammals, including the cats, dogs, cattle, deer, and us that are the dominant land animals of our world today.

What O’Leary et al. argued for was a view of placental evolution called the “Explosive Model” (see figure below). In fact, they argued for an ‘extra-explosivey’ model, since they thought the common ancestor of the modern placental orders of mammals arose after the extinction of the dinosaurs (i.e. in the Paleogene, not the Cretaceous); in the figure below by Ken Rose, the ‘explosive’ evolution begins at the very end of the Cretaceous).

Models of placental mammal radiation (Rose, 2006).
Models of placental mammal radiation (Rose, 2006); the thicker lines represent extant orders of placental mammals..

The O’Leary et al. study was widely misinterpreted by the press, which said they had discovered the common ancestor of mammals, a beast called Protoungulatum. This interpretation is completely wrong, and not what O’Leary et al. claimed. My earlier posts emphasized correcting this misinterpretation.

I also noted that O’Leary et al. used the fossil record in a quite literal way to infer dates of lineage splitting. But fossils only provide a minimum date of separation of lineages, and there may be a considerable unrecorded history predating the earliest known fossil. A new paper in Biology Letters (open access), a Royal Society publication, takes O’Leary and colleagues to task on precisely this issue.

Mario dos Reis and colleagues use various approaches to calibrate the molecular clock of placental divergence and accounting for the imperfections of the fossil record. Under all three methods they use (a, b, and c in the figure below), the divergence of the modern orders begins in the Cretaceous, their estimates ranging from 72 to 107 mya (the former, though, not very far from O’Leary et al’s 65 mya). O’Leary’s view is shown in panel d of the figure.

dos Reis et al. 2014, Figure 1.
dos Reis et al. 2014, Figure 1. a, b, and c are the estimates they contemplate; d is the view of O’Leary et al.

So, who’s right here? The first thing I would note is that although the Cretaceous-Paleogene boundary has great psychological weight (and is when a lot of things went extinct, including the dinosaurs), Rose’s depiction of the “Explosive” model had divergence beginning in the Late Cretaceous, and 72 to 107 mya is still Late Cretaceous (or very close to it). So while dos Reis et al. strongly object to O’Leary’s methodology, the results of the two papers are not very different: O’Leary has the most recent explosion, dos Reis has a somewhat earlier explosion, and both bracket the time of divergence depicted by Rose. dos Reis’s timing does have biogeographic implications differing from O’Leary’s, since an extra 25 million years allows for greater influence of plate tectonic events on mammalian distribution.

The second thing to note is that a defender of O’Leary’s might make the empirical retort that we have a fair number of Late Cretaceous mammal fossils, and none of them are clearly progenitors of the modern placental orders. Absence of evidence is not evidence of absence, unless, of course, you’ve looked where the evidence should be, and that’s what an O’Leary defender could argue.

And a third issue is that dos Reis et al. rely heavily on Bayesian statistics to make their inferences. It would be a very long and dry argument to explore this here, but suffice it to say that I find Bayesian statistics, in most cases, to be logically unjustified, and thus I’m not entirely sanguine about dos Reis’s inferences. It’s a fairly arcane issue in the logic of scientific inference, so I’ll just point in the references below to two sources (Royall and Sober) that I have found helpful.

In one of my original posts, I asked

[I]sn’t using the literal fossil record a pretty crude way of determining ages of taxon splits, since such ages are always minimum ages? And shouldn’t the richer information available in molecular sequence data that is time-calibrated by securely known fossil dates be used? Well, the critics will answer “yes” to both questions, and will also point out that the fossil record is imperfect, so to say we don’t have any fossils dated to the Cretaceous is different from saying no such animals existed then. O’Leary et al. might reply that all molecular dating requires geological calibration, so that the fossil data is primary, not the molecular extrapolation; and that we have lots of Cretaceous mammal fossils, and none of them are obviously the varied precursors of the Cenozoic placental radiation.

And concluded by asking

Who’s right? I don’t know. But that’s what the upcoming arguments will be about.

Indeed, dos Reis et al. have made a sharp statement in this ongoing argument.

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dos Reis, M.,  P.C.J. Donoghue, and Z. Yang. 2014. Neither phylogenomic nor palaeontological data support a Palaeogene origin of placental mammals. Biology Letters 10. pdf

O’Leary, M.A., et al. 2013. The placental mammal ancestor and the post-K-Pg radiation of  placentals. Science 339:662-667. (abstract)

Rose, K.D. 2006. The Beginning of the Age of Mammals. Johns Hopkins University Press, Baltimore. (Google Books)

Royall, R. 1997. Statistical Evidence: A Likelihood Paradigm. Chapman & Hall, London. (Google Books)

Sober, E. 2002. Bayesianism — its scope and limits. in R. Swinburne, ed., Bayes’ Theorem, Proceedings of the British Academy 113:21-38. pdf

Tiktaalik had hind limbs!

January 14, 2014 • 9:46 am

by Greg Mayer

In a paper in press in the Proceedings of the National Academy of Sciences, Neil Shubin, Ted Daeschler, and the late Farish Jenkins describe the pelvis and partial hind limb of Tiktaalik roseae, the lobe-finned fish from the Canadian high arctic that they discovered in 2004 and described in Nature in 2006. Tikataalik is a transitional form from fish to tetrapods, and presents such a suite of advanced (for a fish) features that Neil dubbed it the “fishapod”. The newly reported finds show that Tiktaalik had a very substantial pelvic girdle and limb, which must have had a significant role in locomotion.

Of course, it’s not a surprise that Tiktaalik had hind limbs– most vertebrates do– but  the nature of the hind limbs in this, the most tetrapod-like of fish, is of especial interest. It’s been known for a while that Neil et al. had found the hind limb, and their publication on it has been eagerly awaited. The most important find, a pelvis and part of the associated limb, was actually found on the original holotype specimen (the one from which the species was described) found in 2004; four other isolated pelvises were found in later years. Since the first publication, preparator Fred Mullison has been working to free all the bones from the encasing rock.

Comparison of the girdles of Tiktaalik to those of Eusthenopteron (a 'standard' lobe finned fish) and Acanthostega (one of the earliest known amphibians)
Comparison of the girdles of Tiktaalik to those of Eusthenopteron (a ‘standard’ lobe finned fish) and Acanthostega (one of the earliest known amphibians)

So, what have we found out? The pelvis is robust, with an ilium and pubis, and a large acetabulum for receiving what must have been a substantial femur. There’s no ischium (the third bone in a typical tetrapod pelvis). The Tiktaalik website has 3D scans of the pelvis which you can rotate to see the full morphology.

Tiktaalik pelvis from below: ilium on left, the rounded acetabulum for reception of the head of the femur, pubis on right. The pubis is directed laterally.
Tiktaalik pelvis from below: ilium on left, the rounded acetabulum for reception of the head of the femur, pubis on right. The pubis is directed medially.

Only a portion of the hind limb was preserved: the intermedium, two radials, and several bony fin rays (lepidotrichia). We can tell from the acetabulum though that the femur must have been robust.

Hind limb of Tiktaalik from Shubin et al. 2014. The thin rays are lepidotrichia; the upper rectangular bone is the intermedium, the lower pair are radials.
Hind limb of Tiktaalik from Shubin et al. 2014. The thin rays are lepidotrichia; the upper rectangular bone is the intermedium, the lower pair are radials.

Here’s how the team summarized their findings:

Although no femur was found, Tiktaalik‘s fin rays and several other bones suggest the hind fin was comparable in size and complexity to the front fin. The shape and size of the hip socket reveal that the fin was capable of a wide range of movements, from swimming to supporting weight and rotating more like a tetrapod limb. But the overall structure of the pelvis is still more fish-like. Whereas tetrapods have a pelvis made of three parts, Tiktaalik‘s pelvis is still made of one, like fish. …

Overall, the mix of fish and tetrapod characteristics show us that the structures and mechanisms necessary for the invasion of vertebrate life on land evolved in the water first. Not only that, but before this discovery, we thought the front fins held the key to how vertebrates began to walk on land. The “front wheel drive” theory that fish dragged themselves out of the water with strong front fins and puny hind fins no longer holds. It appears that an “all-wheel” or even a “rear-wheel drive” system is a more appropriate analogy as the hind fins were just as important and may have even been involved in a walking behavior first.

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Shubin, N.H., E.B. Daeschler and F.A. Jenkins, Jr. 2014. Pelvic girdle and fin of Tiktaalik roseae. Proceedings of the National Academy of Sciences in press. pdf

First two Images from the Tiktaalik website 2014 New Discovery page.

Much ado about something

September 27, 2013 • 1:39 pm

by Greg Mayer

In a paper in press in Nature, Min Zhu and colleagues describe a new species of placoderm from the Silurian period of China. Placoderms are an extinct group of (usually) heavily armored jawed fishes that lived in the Silurian and Devonian. The new species is based on a beautifully preserved 3-D specimen, and is interesting, but it is being widely misreported in the press.

The holotype of the new species, a three-dimensionally preserved specimen with head and trunk armour in anterolateral (a), lateral (b), anteroventral (c) and dorsal (d) views. A small part of the left trunk armour was accidentally sawed off as extraneous material and repositioned in b. Scale bars, 1 cm. e, Life restoration.

To understand why this new species is interesting requires some background information. First, we need to know that while most modern vertebrates (backboned animals such as ourselves) have jaws, and are called gnathostomes (“jaw mouths”), not having jaws is the primitive condition (jawless vertebrates, represented today only by hagfish and lampreys, are called agnathans). The origin of jaws is thus a key episode in the vertebrate story.

Second, we need to know that there are four great groups pf gnathostomes, the placoderms, the acanthodians (another extinct group, often called ‘spiny fish’), chondrichthyans (cartilaginous fish: sharks, rays, and their relatives), and osteichthyans (bony fish: tuna, gars, goldfish, etc.; the tetrapods are descended from osteichthyans, and for our purposes can be included with them).

And finally, we need to know that the vertebrate skull is a composite of bones from three different sources: the chondrocranium, bones preformed in cartilage that surround the brain, the splanchocranium, bones preformed in cartilage that support the gill arches, and the dermatocranium, bones that ossify directly and cover most of the outside of the skull. Gnathostome jaws are formed by the anteriormost bones of the splanchocranium (the palatoquadrate in the upper jaw, and Meckel’s cartilage in the lower jaw), which are often covered over or replaced by dermal bones in development. (Chondrichthyans, lacking bone, have only the first two components in their skulls.)

Chondrocranium, blue, splanchocranium green, dermatocranium labeled ‘dc’. From https://ecovertanatomy.wikispaces.com/Properties+of+Bone+and+Cartilage+and+Regions+of+the+Cranial+Skeleton.

Okay, so what’s interesting? Placoderms have jaws, including the palatoquadrate and Meckel’s cartilage, which are accompanied by dermal bones that have usually been thought not to correspond very precisely to the dermal bones of osteichthyans. In the new fossil, Zhu and colleagues identify some dermal bones as being the same as in osteichthyans, most prominently the maxilla in the upper jaw and the dentary in the lower jaw (see first figure above). This is what’s interesting, because if true, it would mean that the osteichthyan condition is more widespread than previously known, and thus perhaps change some of our ideas on the relationships of the various gnathostome groups.

Another thing Zhu and colleagues do is a phylogenetic analysis of 75 taxa with 253 characters, but unfortunately for them the results are quite muddled, with no clear evidence that the ‘maxilla’ or other dermal jaw bones of the new placoderm are homologous to those of osteichthyans. These large data set analyses rarely produce convincing results, because it is the interpretation and analysis of the individual characters that most strongly influence the results, and these individual analyses are usually de-emphasized (or as in this case, hidden in the online supplement).

So where has the press gone wrong? First, some commentary, especially by scientists, has been directed toward the differing trees gotten by Zhu and colleagues, versus the one obtained by Davis et al. (2012) last year using essentially the same data set. This is inside baseball– the relationships among the four great gnathostome groups is quite interesting, but this paper does not resolve the question.

Popular media have been implying that jaws were not previously known in placoderms or fish in general, or that we would not expect jaws in fish this primitive or early. None of this is right. Placoderms are jawed fish, they are not the oldest known jawed fish, and the bones in this specimen do not apparently show a new or previously unknown condition (rather, the claim is that the condition in this fish resembles an already known condition). There is definitely something of interest here, but it’s not quite all that the media are portraying it as.

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Davis, S. P., Finarelli, J. A. & Coates, M. I. 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486: 247–250.

Zhu, M., X. Yu, P.E. Alberg, B. Choo, J. Lu, Q. Qu, W. Zhao, L. Jia, H. Blom and Y. Zhu. 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature in press.

More about turtles

June 4, 2013 • 3:26 am

[JAC: In response to my own and other readers’ questions about turtle morphology and evolution, Greg kindly put up another post to clarify matters.]

by Greg Mayer

To really appreciate what turtles have done with their shells, it helps to see into one. So here’s a view into a turtle’s shell. The shell has been cut parasagitally, to the right of the midline, so we can see the vertebrae, but the rest of the skeleton– head, neck, limbs, girdles, and tail– are left intact so we can see their relation to the shell. (As Turtle Dundee once said, “That’s not an evolutionary novelty– that’s an evolutionary novelty.”)

Inside a turtle.
Inside a turtle.

Note that the shoulder and pelvic girdles are both within the dome of the carapace. And in turtles, the shoulder girdle is a bigger affair than it is in mammals. Turtles not only have a scapula, but also a coracoid as a major bony element, plus turtle scapulas are two pronged affairs with an acromial process nearly as big as the main part of the scapula itself, so that the whole girdle is a tri-radiate structure.

The shell itself is composed of epidermal, dermal, and deeper skeletal elements, and all three can be seen in this view. The horny scutes on the exterior of the shell, made of the same material as scales and fingernails, are epidermal, with a layer of live cells between the scutes and the bone.  The bony part composes parts of the deeper axial skeleton: the vertebrae and ribs, which are preformed in cartilage during development; and the more superficial dermal bones, that ossify directly in the dermis without being preformed in cartilage. The plastron (bottom shell) consists of just epidermal and dermal elements. The plastral bones may be homologous to some of the dermal bones of the shoulder girdle (clavicle and interclavicle) and the gastralia of other reptiles.

As mentioned in the previous post, what the new paper by Lyson and colleagues (see previous turtle post for references) has especially done is to try to interpret the disputed turtle precursor Eunotosaurus in terms of the developmental processes proposed to underlie the evolution of the shell as seen in the undoubted turtle precursor Odontochelys and more derived turtles. Much of that recent developmental work has come from the Laboratory of Evolutionary Morphology at the RIKEN  Center for Developmental Biology in Japan, especially this 2009 paper by Hiroshi Nagashima and colleagues (see additional figures in RIKEN’s press release; and a nice review by Shigeru Kuratani and colleagues from 2011).

"[T]he amniotes' ribs and muscle plate grow together ventrally and make a single layer in body, outside of which the scapula is situated. In turtles, ribs grow laterally and are confined dorsally. However muscle plate is folded at the tip of ribs and runs inside the scapula as in other amniotes, showing basic topology between the elements is not changed both in turtles and other amniotes." From RIKEN.
“[T]he amniotes’ ribs and muscle plate grow together ventrally and make a single layer in body, outside of which the scapula is situated. In turtles, ribs grow laterally and are confined dorsally. However muscle plate is folded at the tip of ribs and runs inside the scapula as in other amniotes, showing basic topology between the elements is not changed both in turtles and other amniotes.” From RIKEN.
Lyson and colleagues integrate Eunotosaurus into Nagashima and colleagues’ developmental scenario by proposing that the rib broadening seen in Eunotosaurus is homologous with that in Odontochelys and Proganochelys. One problem that I see with this attempt is that, if I’m interpreting Eunotosaurus correctly, the distal ends of its ribs curve ventrally and tuck in around the lateral edge of the body, while in turtles the ribs grow out straight to the sides towards a feature in the embryo called the carapacial ridge; this is how, in fact, the scapula gets inside the ribs. It could be argued, though, that this straightness is a later evolved feature, although it’s the straight lateral growth that is associated with getting the cartilaginous ribs associated withe bone-producing dermis that produces the broad plates of bone.

Figure 4 from Lyson et al. 2013.
Figure 4 from Lyson et al. 2013 (click to see enlarged view).

To stress again how profound are turtles’ morphological changes in skeletal and soft tissues, and how they ramify throughout its physiology, ecology and behavior, let me quote from the famous morphologist and paleontologist Rainer Zangerl (1969; and who, in the quoted paper, also refers to the development of the turtle shell as “astounding”):

This shell did not merely cover the pre-existing anatomical structures of the body, but it modified them profoundly. The drastic alteration was probably the consequence of an intimate involvement of the dermal shield with parts of the axial skeleton (vertebrae and ribs) and with dermal portions of the primary skeleton (clavicles, interclavicle and gastralia). The restructuring had far reaching morphological, physiological, evolutionary, and ecological consequences . Anatomically, the presence of a rigid shell led to extensive modification of the structure of the body wall, and to the differentiation of the locomotor apparatus, of the neck region and of the copulatory mechanism, to mention just a few . Functionally it necessitated changes in the mode of respiration ; it impaired locomotion, especially on the ground, and restricted aquatic locomotion to the “paddle types” ; it delimited the storage capacity of the body for air, food, water, fats (oil in the shell bones of sea turtles), and waste materials . It probably affected the permeability of the body wall and hence modified the capacity of the animal to retain water . It drastically modified the behavioral pattern of the animal.

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Kuratani, S., S. Kuraku, and H. Nagashima. 2011. Evolutionary developmental perspective for the origin of turtles: the folding theory for the shell based on the developmental nature of the carapacial ridge Evolution & Development 13:1-14. abstract 

Nagashima, H. et al. 2009. Evolution of the turtle body plan by the folding and creation of new muscle connections Science 325: 193-196. pdf

Zangerl, R. 1969. The turtle shell. Biology of the Reptilia 1: 311-339. pdf

Turtle origins

June 2, 2013 • 12:30 pm

by Greg Mayer

In a paper soon to be published in Current Biology (abstract), Tyler Lyson and colleagues propose a model for the origin of turtles, using the Permian (ca. 260 mya) fossil Eunotosuarus as a transitional form.

GraphicalAbstract-finalThe origin of turtles is a fascinating and important area of study, although one that is perhaps generally underappreciated (Burke 2009). The reason for its importance is that the turtle shell is probably the most novel and highly derived of all skeletal structures in the vertebrates. Nothing in human evolution, for example, compares. What do we have that’s distinctive? A really short tail? It’s been done to death, and just involves some reduction in size and number of bones. Bipedality? Also done many times. A large cranium? Just a few bones getting bigger.

What have turtles done? They’ve moved their shoulder and pelvic girdles inside their rib cages! If you want to appreciate what this means, reach behind your back and touch your shoulder blades, then reach down and touch your hip bones. Now feel your ribcage, front and back. And now imagine getting your shoulder blades and hips inside your rib cage– that’s what turtles have done.

Understanding of the origin of turtles has been hampered by the lack of a good fossil record. For many years the earliest known turtle was Proganochelys from the Late Triassic (ca. 210 mya), which, while primitive in various respects, had a full shell, both top (carapace) and bottom (plastron). The first fossil breakthrough came in 2008, when Li and colleagues described Odontochelys, a Late Triassic turtle a bit older than Proganochelys, but in which the plastron was well formed, but the carapace (top) consisted of only neural bones above the vertebrae, and enlarged ribs.

Lyson and colleagues extend the model of shell origins, incorporating further data on shell ontogeny in modern turtles, and, most significantly adding Eunotosaurus as an early ancestral turtle, which has a proto-carapace of expanded ribs. They also point to Milleretta, another Permian reptile, as a possible very first step in the direction of turtles. (At this point, we pause for Snappy to say hello, so readers don’t forget what the object of our discussion is.)

"Snappy", Chelydra serpentina, Somers, WI
“Snappy”, Chelydra serpentina, Somers, WI

There are two phylogenetic controversies that are involved in this scenario of turtle origin. First, although Eunotosaurus has long been bandied about as a turtle precursor, the consensus has long been that it is not, although Lyson and colleagues (2010) have argued it is. Second, there is great debate about where turtles fit in amongst reptiles in general. Because of the generally primitive nature of their skulls (lacking any openings or fenestrations), turtles have often been linked with one or another of various early reptile groups, and Lyson and colleagues favor this view. There is an almost equally old hypothesis, however, that turtles, despite lacking any skull openings, are nonetheless members of the Diapsida, the great group of two-fenestra reptiles (and their modern feathery descendants) that includes Archosaurs (crocodiles and birds among living taxa, dinosaurs and pterosaurs among the extinct) and Lepidosaurs (tuatara, lizards and snakes among living taxa, mosasaurs among the extinct).

Recent molecular data, including two new genome studies (Wang et al. 2013, Shaffer et al. 2013; see Gilbert and Corfe 2013), have supported earlier molecular studies (including one of my own) in placing turtles among the Diapsida, and indeed, well within the Diapsida, as the sister group of the extant archosaurs.  Although the resolution of these latter debates will have bearing on the full turtle origin story, one thing that I think is now clear is the stepwise origin of the turtle shell, with the various components having been assembled sequentially.

h/t P

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Burke, A.C. 2009. Turtles… …again. Evolution & Development 11:622-624.

Gilbert, S.F. and I. Corfe. 2013. Turtle origins: picking up speed. Developmental Cell 25:326-328.

Kirsch, J.A.W. and G.C. Mayer. 1998. The platypus is not a rodent: DNA hybridization, amniote phylogeny and the palimpsest theory. Philosophical Transactions of the Royal Society B 353:1221-1237. pdf

Li, C, X.-C. Wu, O. Rieppel, L.-T. Wang and L.-J. Zhao. 2008. An ancestral turtle from the Late Triassic of southwestern China. Nature 456:497-501. abstract

Lyson, T.R., G.S. Bever, B.S. Bhullar, W.G. Joyce, and J.A. Gauthier. 2010. Transitional fossils and the origin of turtles. Biology Letters 6:830-833. pdf

Lyson, T.R., G.S. Bever, T. M. Scheyer, A.Y. Hsiang, and J.A. Gauthier. 2013. Evolutionary origin of the turtle shell. Current Biology in press. abstract

Shaffer, H.B. et al. 2013. The western painted turtle genome, a model for the evolution of extreme physiological adaptations in a slowly evolving lineage. Genome Biology in press. pdf

Wang, Z., et al. 2013. The draft genomes of soft-shell turtle and green sea turtle yield insights into the development and evolution of the turtle-specific body plan. Nature Genetics 45 701-706. pdf

Books on the Cambrian worth buying

April 17, 2013 • 11:30 am

by Greg Mayer

Jerry has recently noted a forthcoming book on the Cambrian by the infamous Stephen Meyer. There is a brand new book, The Cambrian Explosion, by the famous Douglas Erwin of the USNM and even more famous James Valentine of UC-Berkeley, that you might want to read if you really want to learn something about this period in the history of life.

Erwin & Valentine The Cambrian Explosion

Just published in January, you can see by the cover it’s got some great art work, and the publisher, Ben Roberts, has made chapter one and more of the art available at their website (after clicking, scroll down for art; it’s cheaper than Amazon there, too).  Another fairly recent book on the Cambrian Explosion covers the very exciting recent discoveries in the Chengjiang of China, The Cambrian Fossils of Chengjiang, China by X.-Q. Hou and colleagues.

Hou Cambrian book

The Chengjiang is especially exciting for me, because it has revealed a variety of chordates, which are much less diverse in the previously best known Cambrian locality, the Burgess Shale of British Columbia. There are some older books about the Burgess Shale, including The Fossils of the Burgess Shale, by Derek Briggs and colleagues, with great photos by Chip Clark, and The Burgess Shale by Harry B. Whittington, the late dean of Burgess Shale studies. There are also the more polemical Wonderful Life by Steve Gould, and The Crucible of Creation by Simon Conway Morris.

Goings on at the Dinosaur Discovery Museum, Kenosha, Wisconsin

March 17, 2013 • 9:52 pm

by Greg Mayer

The Dinosaur Discovery Museum in Kenosha, Wisconsin, is becoming a hotbed of evolutionary activity. I already posted about their Darwin Day celebrations, and now I want to announce an upcoming event in their Spring Lecture series: Life and Death in a Cretaceous Coastal Swamp by my colleague, Prof. Chris Noto. The lecture is this Wednesday, March 20, at 6 PM, and is free and open to the public. His topic will be his work at the Arlington Archosaur Site in Texas, and I’m sure he’ll include a discussion of his work on the feeding habits of giant Cretaceous crocodiles, which we’ve remarked upon here at WEIT before.

Cretaceous crocodile crunching critter (artist's conception)
Cretaceous crocodile crunching critter, by Jude Swales.

The previous event at the Museum was Women in Science Day, which I unfortunately neglected to announce until the day of the event. There was a good turnout nonetheless, as many people, including lots of kids, came to meet the women scientists and see the special exhibits they had set up. My colleagues Drs. Summer Ostrowski and Natalia Taft , joined by MaryRuth Kotelnicki (a trilobite enthusiast who is an adjunct professor at Edgewood College in Madison) entertained and educated the visitors.

Dr. Summer Ostrowski talks with a visitor on Women in Science Day. Her shirt reads "This is what a scientist looks like."
Dr. Summer Ostrowski talks with a visitor on Women in Science Day. Her shirt reads “This is what a scientist looks like.” Note field gear to left, fossils, and a fine selection of plastic extinct animals. How many can you identify?
Dr. Natalia Taft standing next to her exhibi,t which featured the "fishapod" Tiktaalik, which she studied during a postdoctoral fellowship.
Dr. Natalia Taft standing next to her exhibit, which featured the “fishapod” Tiktaalik, which she studied during her postdoctoral fellowship.
A young visitor momentarily glances up from the giant ornamented trilobite she had been examining.
A young visitor momentarily glances up from the giant ornamented trilobite she had been examining.

I was pleased to find that some WEIT readers were able to attend Darwin Day, so perhaps with a less tardy notice than for Women in Science Day, some might have a chance to make the upcoming Cretaceous coastal swamp lecture. Kenosha is close to both Milwaukee and Chicago. I’m also glad to report that the cartoon Charles Darwins from Darwin Day, as I thought they would, have become a permanent part of the signage for the main dinosaur exhibit.

Charles Darwin explains dinosaur evolution.
Charles Darwin explains dinosaur evolution. Note that the dinosaurs in the picture are the same colors as the Marx Toy Co. dinosaurs of the 1950s and 60s. I can’t imagine CD being wrong about something like that, so I guess the toy designers knew what they were doing back then.