A new fossil Hardistiella montanensis lamprey from the Lower Carboniferous of Bear Gulch, Montana (USA) with some remarks on its lifestyle and the palaeoecology of the Bear Gulch embayment.

A new fossil Hardistiella montanensis lamprey from the Lower Carboniferous of Bear Gulch, Montana (USA) with some remarks on its lifestyle and the palaeoecology of the Bear Gulch embayment.

Introduction:  

Back in the year 2007, I took a trip to Bear Gulch, which is located south of the community of Forest Grove east of Lewistown in Fergus County, Montana.  The purpose of the trip was twofold – one aspect was to see the Native American Pictographs that are found on the west wall of Bear Gulch.  The secondary purpose of the trip was to hopefully do some fossil hunting in the Bear Gulch limestone formation.  After receiving a guided tour of the Pictographs, the landowner graciously allowed me to do some fossil hunting in a designated area of the property.

Bear Gulch has been the subject of an extensive amount of paleontological research into a large variety of very well preserved fossil fishes, sharks and invertebrates that have been found in the formation.  The results of the investigations have been published in the scientific literature.  Much of the published research is available online.  

During my fossil hunting activity at the site, I came across a small impression fossil in one of the limestone plates that I uncovered.  At the time of the discovery, I really did not know what I had.  But, after returning home, viewing the fossil under the microscope and photographing it followed by an extensive amount of research on the find, I came to the conclusion that I likely had discovered a fossil lamprey. I compiled the results of my find into a scientific paper that I would like to have published in the scientific literature.  However, such is not really possible for a private scientist who is not affiliated in some way with a recognized university or scientific institution.  I have published research articles in the past when I was affiliated with Cornell University doing research on animal waste odor control and more recently when I collaborated with a fellow researcher at a university in Germany when we published some of my research on ant sperm bundles in an open source online journal called PLOS ONE.  Now  that I am retired and no longer affiliated with any university, the process of publication in a peer reviewed scientific publication is hindered. 

So, I have decided to publish my work on this fossil in the form of this blog entry.  Hopefully the reader will find the information of interest. 

             

Background:   It has taken a relatively long time for palaeontologists searching the fossil record to find a Palaeozoic lamprey.  When the first specimen of the enigmatic Palaeospondylus gunni, Traquair was uncovered from the Devonian red sandstone of Achanarras Quarry in Caithness, Scotland and announced to the world in 1890, some scientists immediately hailed it as the first fossil lamprey to make its presence known from ancient rocks¹.  However, it was soon proved to be otherwise due to the presence of an ossified backbone – clearly not a lamprey-like feature².  A controversy still rages on to the present day as to exactly where to place this enigmatic chordate organism^{3, 4}.  

 

Finally in the year 1968, there came the announcement of the discovery of the first unambiguous fossil lamprey, Mayomyzon pieckoensis, from the Middle Pennsylvanian Francis Creek Shale of Illinois, USA⁵.  Since then several other lamprey fossils have come to light from far ranging parts of the world.  These include Hardistiella montanensis from the Lower Carboniferous Bear Gulch Limestone in Central Montana, USA^{6, 7, 8}, Mesomyzon mengae from the Lower Cretaceous Yixian Formation in Inner Mongolia, China⁹, and, most recently, Priscomyzon riniensis from Late Devonian Whitpoort Formation in South Africa¹⁰.   In addition to these four (4) different, but generally recognized unambiguous fossil lamprey species, one other lesser known and somewhat dubious lamprey species has been identified from the Francis Creek Shale of Illinois, USA – Pipiscius zangerli^{11, 12, 13, 14}.  All of these relatively recent discoveries have tended to show that Palaeozoic lampreys are surprisingly similar to modern lampreys in many respects¹⁵.   In fact, it has been quietly mentioned in some scientific circles that this jawless chordate group has somehow “missed out on” the process of evolution. 

Described here is a new fossil specimen of Hardistiella montanensis from the Bear Gulch limestone plattenkalk formation in Central Montana.  Preserved as a definitive impression fossil, this specimen is the first of this genus to display evidence of cartilaginous plates or oral fimbriae at the margin of the oral hood.  This new fossil material advances our understanding of the anatomy of ancient lampreys and provides additional clues regarding the palaeoecology of the Bear Gulch embayment.  However, it also raises questions about the lifestyle of this Paleozoic lamprey  – was it free-living or was it parasitic?

Stratigraphy and locality:  The author collected the fossil specimen that is described here from the Bear Gulch formation exposed in the east wall of Bear Gulch Canyon (Figures 1 & 2) south of Forest Grove, Fergus County, Montana in Section 22, T13N, R21E.  The fossil was found between 2 layers (plates) of a highly mineralized indurated, grey, silty limestone (Figure 3).  It was discovered in what Williams¹⁶ aptly describes as a “sled runner slump” or a large isolated bed of sedimentary limestone rock, which had detached from the parent formation in the canyon wall and slid down slope at some time in the geologic past (Figure 4).   As a result, this isolated segment

 

    Figure 1: Overview of the east wall of Bear Gulch.  The view is to the east.

    Figure 2:  A closer view of a portion of the east wall of Bear Gulch. The view is to the south.

    Figure 3:  A close-up view of the Bear Gulch limestone showing its plate like structure.

   Figure 4:  View of the “sled runner slump” of Bear Gulch limestone in which the fossil lamprey was discovered. Note the   

   angle of tilt of this formation with respect to the land surface.  The view is looking north. 

of the formation is tilted about 30 to 35 degrees to the horizontal allowing moisture to “wick” between the deposited plates of the limestone contributing to a higher than normal degree of mineralization on the bedding planes.  This situation impacts the fossils located between the layers obscuring some anatomical details that otherwise might be identified.  

  

The specimen was retrieved from the Marginal Basin Facies of the western portion of the Bear Gulch formation as initially described by Williams¹⁶ and later refined by Grogan and Lund¹⁷.  Many of the limestone plates extracted from the collection location showed the presence of oval-shaped concretions that were flattened parallel to the bedding planes.  When the rock was split at the bedding plane, these concretions would often pop out of the surrounding plate and a distinct organic odor was often detected.  Fossil material was often found within the oval depression vacated by the concretion.          

Preservation:  The specimen (WEB-3-081907-1; Figure 5) is preserved principally as a whole body impression in the rock along with dark organic stains on the grey-colored matrix.  It appears to have been pressed laterally into the matrix during fossilization

thereby showing quite accurately the actual body shape of the living animal similar to the fossilized orientation of the holotype specimen of Hardistiella montanensis (MV 7696)⁶.  This new specimen was preserved with a longitudinal twist into the matrix such that the dorsal side is recessed at a depth of about 0.252 mm (about 0.01”) into the rock while the ventral side is even with the surface of the matrix at the bedding plane.  Only the bottom part was retrieved from the formation.  Unfortunately, the upper counterpart was lost during extraction (tossed down the slope to the left of the formation shown in Figure 7) before the limestone plate containing the part was recognized as containing a fossil worthy of more than just casual attention.

The specimen was examined under a Zeiss stereomicroscope and has been photographed both dry (Figure 6.) and under ethyl alcohol (Figure 7.) in order to more clearly reveal salient features.  The specimen is currently in the author’s private collection.  However, if requested, I would consider donating the specimen in the University of Montana, Missoula, Montana Bear Gulch Fossil Collection for other interested researches to examine.  This is the same collection that currently houses the holotype of the species. 

                                      Figure 5:  View of the lamprey fossil in its limestone matrix.

     Figure 6: Close up view of Hardistiella montanensis, photographed dry under ambient light conditions.  Horizontal bar 

    represents 2mm.

 

   Figure 7:  Close up view of Hardistiella montanensis, photographed under ethyl alcohol and under ambient light conditions.   

   Horizontal bar represents 2mm.

Description:  The first significant feature of note in this new specimen is its relatively small size compared to other adult fossil and existing lamprey.  In fact, this specimen is so small that it was almost overlooked during the author’s exploration of the formation for fossil fish and sharks.  The specimen is 22.5 mm long and with a body depth of 5 mm, making for a length (L) to body depth (BD) ratio of 4.5:1.   It is shorter than specimens of Mayomyzon (33-61mm) from Illinois⁵, much shorter than Mesomyzon (84mm) from China⁹, Priscomyzon (42mm) from South Africa¹⁰ and the one complete adult specimen of Hadistiella (~100mm) from Montana.  However, it is similar in length to the type specimen of Pipiscius zangerli, which is 34 mm long (Figure 2 in Reference 11).   

This body size and L/BD ratio of this new specimen compares favourably with the second Hardistiella montanensis fossil described by Lund and Janvier⁷.  Their specimen had an overall length of 16mm and a body depth of 2.5mm for a length to body depth ratio of 6.4:1 (inferred from Figure 1A in Reference 7).  These investigators concluded that their specimen was likely a larval individual based on some internal body characteristics (traces of tectal cartilages and an olfactory capsule) shared by modern lampreys coupled with its very small size.  This may also be the case with the current specimen, based mainly on its small size (see discussion).   Note:  Please refer to the interpretive drawing in Figure 8 as the other features of this specimen are described.

 

Figure 8:  Interpretive drawing of Hardistiella montanensis showing key features:   b.a., brancial arch; b.c., buccal cavity; c.f., caudal fin; l.e.s., left eye stain; n.d. nasal discharge?; n.p., nasal papilla; o.f, oral fimbriae; o.h., oral hood; p.s, pineal spot; r.e.s., right eye stain; x-1, enigmatic organ # 1 (sensory projection?); x-2, enigmatic organ #2 (sensory projection or artefact of fossilization?).  Horizontal bar represents 2mm.  

 

This new Bear Gulch specimen shows an enlarged anterior lobe, which nicely corresponds with the oral hood of modern lampreys.  It also shows what appears to be a set of cartilaginous plates or oral fimbriae at the basal margin of the oral hood (Note: best visible in Figure 6).  From the fossil imprint, these plates appear to be rectangular in shape with the narrow dimension angled toward the edge of the hood, which conforms closely in relative size and orientation to those found in modern lampreys^{18, 19, 20}.  Due to the fact that the specimen is preserved in the lateral aspect, the view of the oral fimbriae is from the side of the oral hood, which was evidently compressed or flattened into the matrix during fossilization.   Traces of the soft tissue of the oral hood were not preserved, but the impressions of the individual oral fimbriae or plates were, making them stand out in the fossil impression in the matrix.  This is the first specimen (larval, transitional or adult) of Hardistiella montanensis to show this key modern lamprey-like anatomical feature.

Shown dorsally to the basal edge of the oral hood and near its mid point as viewed edge-on is what appears to be an organ variously known as the pharyngeal chamber, buccal cavity or buccal funnel in modern lamprey.  This feature is preserved as a lighter impression in the matrix.  At the posterior-dorsal apex of this chamber are four (4) closely spaced rod-shaped impressions that may be fossil remnants of support cartilage or muscle tissue at the entrance to the pharynx.  These impressions may be similar to what Maskell describes as “supra-oral lamina or cusps” in modern New Zealand lamprey²⁰.   They also appear to be quite similar in form and body location to a series of ridges and grooves found in the pharangeal tube and pouch of Pipiscius zangerli as described by Bardack and Richardson (See Figure 2 in Reference 11).  Their interpretation of these structures in their specimens was that they were fossil traces of muscles capable of pumping nutritive material into the animal.     

Evident in this specimen are two (2) eye stains one located slightly above and anterior-dorsal to the other (Figure 6.).  Based on the fact that this lamprey was evidently twisted dorsally into the matrix during the process of the fossilization, the left eye stain is slightly above that of the right eye stain.  This is consistent with the fact that when the specimen is photographed under ethyl alcohol (Figure 7), only the right eye socket appears as a definite impression in the matrix. 

Also visible in this specimen is a light-colored oval area posterior-dorsal to the eye stains.  This appears to be the pineal spot or light sensitive organ, which is also found in modern lampreys.  In addition, posterior to the eye stains is another light-colored oval feature, which in this case may be the otic capsule, a vibration sensitive organ found in modern lamprey.  

A cylindrically shaped nasal papilla is evident located anterior-dorsal to the eye stains with what appears to be a faint imprint of the nasal capsule below it.   Beyond the limit of the head but close to the dorsal edge of the body impression is a half oval discoloration in the matrix.  This may represent organic matter expelled from the nasohypophyseal opening that is located at the top of the nasal papilla.  The nasal papilla in this fossil is well anterior-dorsal of the eye.  This location is somewhat more distant in the anterior direction from the eye than in modern lampreys.   However, this location may simply be due to distortion (twisting and stretching) of this portion of the head during the process of fossilization.

The only fin evident in this specimen is the caudal fin, which is visible at the posterior end of the specimen.  There is no evidence of fin rays in this specimen.  It is possible that the body continues beyond the end of the caudal fin as this segment of the fossil is obscured by extensive mineralization of the matrix. 

Dorsal to the eye stains, there is a thin distinct, carbonaceous projection beyond the limit of the head.   This curious feature, or one just like it, was also noted by Janvier, Lund & Grogan, in the third specimen of Hardistiella montanensis that they described⁸.   They called it “an enigmatic imprint,” which they attributed to possible organic matter expelled from the nasohypophyseal opening or, alternately, to an artefact of fossilization.  

Because this curious feature now appears in two specimens of this fossil species from the same locale and in the same general location on the fossilized body, it is this investigator’s opinion that it is most likely not an artefact of fossilization.   Neither does it appear to be expelled organic matter from the nasal opening, as this opening is clearly anterior-dorsal and not dorsal of the eyes in this specimen and in modern lampreys.  This author suspects that it is an antenna or similar projection that had some special sensory function (see discussion).   

On the other hand, this new specimen has a curious or enigmatic imprint or feature of its own – one not seen in previously described lamprey specimens from Bear Gulch.  Projecting from the leading edge of the oral hood is a second relatively thin, distinct, carbonaceous projection that turns ventrally and then appears to divide into three branches.   Under the microscope, this projection appears to be segmented.  The nature of this projection is problematic.  This author suspects that it may be another sensory organ (a barbell?) similar to that found in several fossil and extant species of fish (see discussion).  Or, it may simply be an algae branch entrained in mucus from the oral hood that was buried with and co-fossilized with the lamprey.

Unlike previously described specimens of this genus, this specimen shows only one (1) or possibly two (2) gill pouches well posterior-ventral of the eyes.  Most of the branchial region of this specimen is obscured by clay mineral deposits that eclipse the ventral area of the body posterior-ventral of the eye stains thereby making a clear determination of the total number of gill pouches impossible.  

Discussion:  The size of this new fossil lamprey compares quite favourably with the ammocetes or larval forms of modern lampreys.  In his exhaustive study of the New Zealand Lamprey, Geotria australis Gray, Maskell²⁰ found ammocetes (larval) lampreys in rivers as small as 11 to 16 mm long and in relative abundance.  Another more recent investigation of larval sea lampreys, Petromyzon marinus, in Lake Superior (USA), showed body lengths on the order of 13mm after one year of growth²¹.  This new fossil specimen also conforms closely in length and body form to a previous specimen of this genus, which was presumed to be a larval or transitional form⁷ based in part on its relatively small size.

However, the presence of cartilaginous plates or oral fimbriae at the basal margin of the oral hood in this new fossil specimen is of considerable interest.  Not normally found in modern ammocoetes lamprey, this anatomical feature may be indicative of the fact that this specimen of Hardistiella montanensis was parasitic.  In fact, a parasitic lifestyle was recently attributed to the oldest of the fossil lamprey uncovered in South Africa¹⁰ due to the presence of an oral disk with oral fimbriae in that specimen. 

So, it is of interest to this investigator to ponder the point that the relatively small size of this lamprey specimen seems to match the relatively small size of the majority of the fossil adult fish and primitive sharks in the Bear Gulch embayment.  Of the hundreds of new species of fossil fish and sharks uncovered in Bear Gulch in the last 40 years, the majority are only at most a few inches in length and only two (2) primitive shark species are longer than a baseball bat²².   So, could this specimen, which is equipped with oral fimbriae and a suction disc be a parasitic lamprey?  Yet to be uncovered future specimens of this genus, hopefully preserved in the matrix in a full ventral orientation that will reveal a full face-on view of the oral disc, or, ideally, even preserved attached to a primitive adult fish or shark, may provide more clues on the lifestyle - free living versus parasitic - of Paleozoic lamprey in the Bear Gulch embayment.       

On the other hand, there are anatomical features associated with this new fossil specimen that could also lead one to postulate that it was possibly a free-living individual.  

  

Modern lampreys are known to go through several developmental stages in their life cycle, whether they are totally free-living or parasitic forms.   The life forms progress from fertilized egg, to larva (ammocoetes), to several transition forms (sometimes called “transformers” for the UK lamprey²³, the “Velasia stage” for Chile and New Zealand lampreys²⁰, or “macropthalmia” for pre-adult north Pacific lamprey ²⁴) and finally to an adult.  In the case of modern lampreys, the ammocoetes have poorly developed eyes to the point of being blind.  They also do not have any oral fimbriae at the edge of the oral hood.  However, they do have a well-developed pineal spot above the rudimentary eyes.  

The ammocoetes are known to burrow into the benthic substrate of rivers where they live in U-shaped burrows and are filter feeders for up to several years of their life^{20, 25}.  Given this situation, the larval lamprey has to rely on its electro-chemical senses, sensory organs associated with its nasal opening, and the pineal spot in order to receive information from and about its surroundings and to successfully feed²⁶.  

Recent research on modern lampreys has revealed that the pineal spot or organ appears to function as an oscillator for the circadian locomotor rhythm of lampreys such that they tend to be active in the early half of the dark period and inactive in the light period²⁷.  Due to the fact that this specimen and fossil lampreys in general have been shown to have this organ, its function would serve to define the daily rhythm of the fossil lamprey’s activity and feeding cycle within the environment of the Bear Gulch embayment.           

If this specimen is indeed a larval or early transitional form of Hardistiella montanensis and if it followed the life pattern of modern lampreys, it could be expected to burrow partly in the benthic substrate and engage in filter feeding – entraining detritus in mucus excreted from the oral hood.  If it was blind or lacked fully functional eyes at this stage, like modern lamprey ammocetes, then it would need some way of telling where it was located within the substrate burrow and it would need to electro-chemically detect the presence of food in the water column.  The presumed sensory projection anterior-dorsal to the eyes in this specimen could possibly assist the organism to position itself in the substrate burrow for optimal feeding activities and to insure optimal gill respiration. 

The presumed sensory organ on the leading edge of the oral disc could help the lamprey to sense electro-chemical conditions in the water column, the presence or absence of a current, the location of nearby objects, etc.  So these presumed sensory organs could possibly function as positional, as well as electro-chemical sensory devices similar to sensory barbells found in many modern (and fossil) bottom dwelling fishes such as sturgeon, loaches and catfish, among others.  

Obviously there is no way to test this hypothesis regarding the possible function(s) of these enigmatic appendages due to the fact that there are no direct counterparts to these structures in modern lampreys.  Other fossil lamprey specimens, yet to be uncovered and now resting quietly in the rocks of the Bear Gulch formation may shed more light on the exact nature and function of these enigmatic structures.   

Modern ammocoetes lampreys spend part or all of their life cycle in fresh water rivers where they burrow into the substrate to filter feed.  The parasitic forms migrate to the ocean where they find a host fish, but return to the rivers of their birth to spawn.  Based again on our current understanding of the life cycle of modern lampreys, the presence of this fossil ammocoetes lamprey in the western segment of the ancient Bear Gulch embayment lends further credence to the fact that this portion of the bay may have been, periodically at least, a fresh water environment resulting from flood inputs from rivers emptying into the shallow bay from the west.  Did this fossil lamprey actually live in the benthos of this area of the ancient bay during its larval stage?  Was it perhaps quickly buried in a sediment laden flood event originating in a river to the west?  Or, alternately, was it washed into the area from a fresh water river habitat along with a flood event and then quickly buried in the sediment?  We obviously may never know the definite answers to these questions. 

However, if the free-living lifestyle was in place when fossilization occurred, one might expect the burrow in which the organism was encased would also be fossilized.  For example, remnants of benthic worm borrows do occur in the fossil record^{28, 29}.  Also, Bear Gulch does have a reputation for exceptional preservation of fossil material³⁰.   So, the absence of a co-fossilized encasing burrow might lead one to suspect that this specimen was washed into the embayment by a sediment loaded river flood event.

In any case, it appears that the fossil extraction location may have been a near shore nursery area similar in nature and ecology to modern upper estuarine bays with fresh water inputs from a river or rivers and with saltwater inputs from a distant connection to the ocean.  Further excavation of lamprey fossils in this segment of the Bear Gulch formation will likely provide further information on both the life style of Hardistiella montanensis and of the paleoecology of the western margin of the Bear Gulch embayment.         

References Cited:

1.  Traquair, R. H. A further description of Palaeospondylus gunni, Traquair.  Proceedings of the Royal Physical Society of Edinburgh XII, 87-94 (1894).

2.  Jordan, D. S.  A Guide To The Study Of Fishes, Vol. 1.  Henry Holt and Company, N.Y. (1905).

3.  Thomson, K. S. A palaeontological puzzle solved? American Scientist 92, 209 (2004)

4.  Newman, D. B. Palaeospondylus: to be or not to be a larval lungfish? http://www.landforms.eu/orkney/Fossils/Palaeospondylus1.htm (2007)

5.  Bardack, D. & Zangerl, R. First fossil lamprey:  A record from the Pennsylvanian of Illinois. Science 162, 1265-1267 (1968).

6.  Janvier, P. & Lund, R. Hardistiella montanensis n. gen. et. sp. (Petromyzontida) from the Lower Carboniferous of Montana, with remarks on the affinities of the lampreys. J. Vertebrate Paleontology 2, 407-413 (1983).

7.  Lund, R. & Janvier, P. A second lamprey from the Lower Carboniferous (Namurian) of Bear Gulch, Montana (U.S.A.). Geobios 19, 647-652 (1986).

8.  Janvier, P., Lund, R. & Grogan, E. Further consideration of the earliest known lamprey Hardistiella montanensis, Janvier and Lund, 1983, from the Carboniferous of the Bear Gulch, Montana, U.S.A. J. Vertebrate Paleontology 24, 742-743 (2004).

9.  Chang, M., Zhang, J. & Miao, D. A lamprey from the Cretaceous Jehol biota of China. Nature 441, 972-974 (2006).

10.  Gess, R. W., Coates, M. I. & Rubidge, B.S. A lamprey from the Devonian period of South Africa. Nature 443, 981-984 (2006).

11.  Bardak, D. & Richardson, E. S. Jr. New agnathous fishes from the Pennsylvanian of Illinois.  Fieldiana Geology 33, 489-510 (1971).

12.  Janvier, P.  Hyperoartia. Lampreys. in The Tree of Life Web Project, http://tolweb.org/Hyperoartia (1997).

13.  Gill, H. S., Renaud, C. B, Chaopleau, F., Mayden, R. L., & Potter, I.C.  Phylogeny of living parasitic lampreys (Petromysontiformes) based on morphological data. Copeia 4, 687-703 (2003).

14.  Shu, D. et. al. A pipiscid-like fossil from the lower Cambrian of south China.   Nature 400, 746-749 (1999).

15.  Janvier, P. Modern look for ancient lamprey. Nature 443, 921-924 (2006).

16.  Williams, L. A. Deposition of the Bear Gulch Limestone:  a carboniferous plattenkalk from central Montana. Sedimentology 30, 843-860 (1983).

17.  Grogan, E. D. and Lund, R. The geological and biological environment of the Bear Gulch Limestone (Mississippian of Montana, USA) and a model for its deposition. Geodiversitas 24, 295-315 (2002).

18.  Khidir, K. T. and Renaud, C. B. Oral fimbriae and papillae in parasitic lampreys (Petromysontiformes).  Environmental Biology of Fishes 66, 271-278 (2003).

19.  Kobelkowsky, A. Skeleton and dentition of the lamprey of Chapala, Lampetra spadicea (Petromyzontidae).  Hidrobiologica 15, 151-159 (2005).

20.  Maskell, F. G. On the New Zealand lamprey, Geotria australis, Gray.  Part 1. – Biology and life history.  Transactions and Proceedings Of The Royal Society of New Zealand 60, 167-201 (1930).

21.  Manion, P. J. and McLain, A. L.  Biology of larval sea lampreys (Petromyzon marinus) of the 1960 year class, isolated in the Big Garlic River, Michigan, 1960-1965. Great Lakes Fish Commission Technical Report 16, 1-35 (1971).

22.  Musick, J. A. and Mcmillan, B. The Shark Chronicles – A Scientist Tracks The Consummate Predator, Henry Holt and Company, 27 (2002).

23.  Gardiner, R. Identifying lamprey.  A field key for sea, river and brook lamprey. Conserving Natura 2000 Rivers Conservation Techniques Series No. 4.  English Nature, Peterborough, UK.

24.  Graham, J. and Brun, C. Determining lamprey species composition, larval distribution, and adult abundance in the Deschutes River, Oregon, Subbasin.  2004-2005 Annual Report, Project No. 200201600, Bonneville Power Administration Report DOE/BP-00009553-3, Portland, Oregon (2005). 

25.  Hansen, M.J., Madenjian, C.P., Slade, J.W. et al. Population ecology of the sea lamprey (Petromyzon marinus) as an invasive species in the Laurentian Great Lakes and an imperiled species in Europe . Rev Fish Biol Fisheries (2016) 26: 509.

26.  Bullock, T. H., Hopkins, C. D., Popper, A.N. and Fay, R. R. Electroreception. In, Jorgensen, J. M.  Morphology of Electroreceptive Sensory Organs. Springer Handbook of Auditory Research 21, 47-67 (2006).

27.  Morita, Y., Tabata, M., Uchida, K. and Samejima, M.  Pineal-dependent locomotor activity of lamprey, Lampetra japonica, measured in relation to LD cycle and circadian rhythmicity. Journal of Comparative Physiology A:  Neuroethology, Neural, and Behavioral Physiology 171, 555-562  (1992)

28.  Jones, D. J. Some asteraform fossils from the Francis Formation of Oklahoma.  American Midland Naturalist 16, 427-428 (1935).

29.  Twitchett, R. J. The resting trace of an acorn-worm (Class: Enteropneusta) from the lower Triassic. Journal of Paleontology 70, 128-131 (1996).

30.  Hagadorn, J. W. Bear Gulch:  An exceptional upper Carboniferous plattenkalk.  In, Bottjer, D. J., ed. al., editors Exceptional Fossil Preservation:  A Unique View On The Evolution of Marine Life.  Columbia University Press, 167-183 (2002).

Acknowledgements:  The author wishes to thank local rancher and landowner, Macie Lundin Ahlgren, Grass Range, Montana for access to her land for the purposes of fossil collection.   

DINOSAUR EGG & NEST DIG IN THE TWO MEDICINE FORMATION OF MONTANA

DINOSAUR EGG & NEST DIG IN THE TWO MEDICINE FORMATION OF MONTANA (July 15th to 19th, 2015):

I recently participated in a dinosaur egg & nest excavation conducted by the Two Medicine Dinosaur Center (TMDC) based in Bynum, Montana.

Bynum is a small agriculturally based community located in Teton County in northwestern Montana east of the Rocky Mountain Front.   Bynum is about 13 miles north of Choteau, the Teton County seat. Situated on the western edge of the Great Plains where the Rocky Mountains literally jump up out of the plains and reach for the sky, this area represents a very stark, dramatic, and ever-changing landscape.  This is epitome of Big-Sky Country for sure.  Being there you are always aware of the fact that you are at the mercy of the weather.   You cannot escape it!

In the not to distant past, this area was the realm of the American Bison or Buffalo and home to the Blackfoot Indians who relied on the Buffalo for food and all their basic needs.  Eons ago, during what scientists have named the Cretaceous Period, this area was a tropical upland adjacent to an inland sea located further to the east that supported a large variety of dinosaurs.  The Bison and the dinosaurs are long gone, but their bones remain waiting to be discovered.  

    A squall drops rain on the Great Plains east of the Rocky Mountain Front south of Choteau, MT

 THE TWO MEDICINE DINOSAUR CENTER: 

    View of the Two Medicine Dinosaur Center, Bynum, Montana.

This rural Montana museum has some interesting dinosaur exhibits.  However, it is unique in that it provides a large variety of half-day, full-day and multi-day scientific dinosaur dig programs for the general public. Participants range in age from children to senior citizens without discrimination as to background or experience.  Available dig programs vary from a relatively short 3-hour site visit to a more extensive 10-day volunteer training program.   I should mention that it is very difficult if not almost impossible for the general public to gain access to sites containing significant dinosaur remains and then to participate in excavation programs under proper supervision. The TMDC nicely opens the door of opportunity to that unique experience.  Fees to participate in their programs are very reasonable and are really only designed to cover costs.  For more detailed information on the TMDC and their public programs, please visit their website.

Programs at the TMDC are supervised by David Trexler, Paleontologist, along with the assistance of several able and knowledgeable staff members.  Dave is not your customary egotistical academic egghead scientist who likes to do his research out of the public view, perhaps teach a select few graduate students, and then to publish his results in scientific journals to gain fame and recognition amongst his scientific peers.  That is Academia in general, but that is not Dave Trexler. Rather, I found Dave to be a very friendly, humble, yet very knowledgeable individual who is openly willing to share his special knowledge and practical expertise in paleontology with a broad spectrum of the public that participates in his field programs.  I was pleased to see how he treats all of his participants equally, always willing to answer even the very basic of questions.  He is especially great with kids - never bored with their floods of questions about various dinosaur species.  In fact, he will often ask kids, "what is your favorite dinosaur?"  And then, he really listens to what they have to say in response to that question.  He never talks down to anyone, but always tries to meet people at their level and to engage them in meaningful conversation.  You don't find folks like Dave Trexler too often in the scientific world. 

                                          Dave Trexler, Paleontologist

THE BACK STORY:

My interest in dinosaurs goes way back to my teen age years living in New Jersey.  Periodic visits to the American Museum of Natural History in New York City would stimulate that interest.  I would always bypass all the other exhibits in the museum and head for the dinosaur exhibits on the 4th floor for my dinosaur fix.  But, my ultimate career choice to be a microbiologist / environmental scientist would take me away from dinosaurs, but not permanently away from a latent interest in them, in geology and in the past history of the earth in general.

Living in Montana provides me with some unique opportunities to satisfy my curiosity about the past history of the earth and what life was like here in the very distant past.   My most recent interest in paleo history and dinosaurs was stimulated in part by this Geologic Road Sign (see below) found on Montana Highway 287 between Choteau and Augusta.  I invite you to read the text in detail and you will understand more why I decided to see if there was any way that I could participate in a dinosaur dig that would help to satisfy my curiosity regarding the paleo history of Montana.

             Montana Department of Transportation Geologic Road Sign "Egg Mountain."

Turns out that Marion Brandvold was Dave Trexler's mom.  In his youth growing up on a ranch in Bynam, Montana, Dave and his mom used to hop onto his Kawasaki motorcycle and go on fossil and mineral hunting trips in the Choteau and Bynum area.  With the permission of local ranchers they covered a wide area visiting badland outcrops all over the area looking for dinosaur bones and minerals.  One day his mom discovered a set of baby dinosaur bones (as noted on the sign) and, as they say, the rest is history.

    Bones of the first baby Maiasaura dinosaur found by Marion Brandvold now on exhibit at the Two Medicine Dinosaur Center in Bynum, MT.

Marion Brandvold's unique find ultimately got the attention of Jack Horner from the Museum of the Rockies in Bozeman, MT.  Horner visited the site of the find with Mrs. Brandvold with Dave Trexler present as well.  Mrs. Brandvold told Horner that she thought the adult dinosaurs took care of their young.  Horner was not immediately convinced of this as the conventional assumption at the time was that dinosaurs behaved like overgrown modern reptiles, who did not stick around to care for their young.  Later, after several expeditions to the site began to uncover dinosaur nests, eggs, and more skeletons of hatchlings and baby, as well as, adult dinosaurs, the conventional assumptions began to change.  These proved to be the first dinosaur nests found in the western hemisphere and the first dinosaur embryos ever discovered in the world.  Further research revealed that these dinosaurs were likely "warm blooded" like modern birds.  They lived in large herds like the more modern Buffalo, nested colonially, and cared for their young in the nest.  Many publications followed and the scientific world was amazed at what was found at "Egg Mountain" in Montana. As it turned out Mrs. Brandvold proved to be correct, as the scientific evidence accumulated that some species of dinosaurs apparently cared for their young.  The original "Egg Mountain" site is now owned by the Museum of the Rockies and is essentially "off-limits" to others.

The Two Medicine Geologic Formation is found in numerous other outcrops throughout the area.  It is in that formation that evidence of dinosaur nesting activity can be found.  Dave Trexler has obtained permission from local ranchers to visit these areas and to conduct  investigations and excavations to add to the body of information on dinosaur nest construction and nesting activity.  Most of the current research by others has concentrated on the eggs in the nest and on the skeletal remains of the young dinosaurs, but not on the entire nest structure.  Dave Trexler hopes to find and excavate a complete dinosaur nest and this is the focus of one of his current public field investigation programs - a program that I had an opportunity in which to participate.

SOME BACKGROUND INFORMATION ON DINOSAURS THAT CARED FOR THEIR YOUNG:

Maiasaura peeblesorum is a species of Duckbill dinosaur that inhabited the Choteau area during the Cretaceous period.  After emerging from their eggs, Maiasaura babies were helpless and vulverable. About a foot in length, newborn Maiasaura babies could not walk and had to stay in their nests until their legs were strong enough to support them.  While in the nest, the Maiasaura hatchlings were cared for by their parents.

    This diorama in the Old Trail Museum in Choteau shows an artist's impression of a mama Maiasarua caring for her newly hatched youngsters in the nest shown in the right background.

    This complete skeleton of a young Maiasaura is on display at the Old Trail Museum in Choteau

PREVIOUS AND CURRENT FIELD INVESTIGATIONS:

Based on his previous research and field investigations, Dave Trexler believes that the adult Maiasaura constructed their nests of individual mud balls arranged in a circle or oval.  The nests would serve to contain the eggs and to "corral" the young hatchlings until they were able to move around on their own.

In 2012, Trexler found what appeared to be a prospective nest site located on the top of a mound that was associated with an outcrop of the Two Medicine Formation located several miles west of Bynam on a private ranch.  He named the site "The Eyrie" and gave it the site inventory designation "TA2012.2."   The site name means "a large nest of a bird of prey, especially an eagle, typically built high in a tree or on a cliff."   Turns out that the selected site name fits the site conditions almost precisely, but not for an eagle nest, but for a dinosaur nest.  Preliminary investigations at the site in 2012 showed the slope leading up to the mound littered with bits of dinosaur egg shell with a circular area at the top that resembles the faint outline of a what may well be a nest.  Some concentrations of egg shell were found and were stabilized with plaster of Paris covers.  Then most of the area was covered with a cloth mesh to protect it until such time that the site could be revisited for further study and excavations.

    Overall view of the prospective nest site.  The individuals in the middle of the image are standing atop the nest site, which is found at the lower edge of an outcrop of the Two Medicine Formation.

    The prospective nest site showing conditions prior to the start of the 2015 excavations. The white "stone" shown in the middle of the image is an area of concentrated eggshell that was protected with a plaster cap.  Also visible in this image are remnants of protective cloth placed over the site in 2012.
 
Fast forward to July 2015.  On July 15, 2015, David Trexler along with several volunteers including myself, visited the site.  The first step was to remove the protective cloth over the area, much of which had deteriorated due to exposure to the weather and UV light and to clear the prospective excavation area of some mineral detritus that littered the site.   Then over the next several days the task was to slowly and deliberately remove layers from the prospective nest area to try to ascertain the configuration of the nest structure.  The soil layers on top of the nest were slowly excavated using dental picks and brushes so as not to miss any items within the nest area.  Items found included some minor amounts of egg shell and a variety of microfossils (mainly gastropods).  Structurally, what appeared to be a loaf of bread shaped solidified mudball was uncovered along with evidence of several soil faults in the nest area.  So far, no eggs or bones were uncovered.  The location's GPS coordinates and the elevations associated with selected features within the nest area were determined using a Topcon Total Station and tied to known benchmarks.   In addition, a site sketch was prepared, notes prepared each day and site photographs were taken to fully document the results of the site investigations.         

    The black specks visible in this image consist of egg shell fragments eroding out of the formation.

    Image shows a typical set of egg shell fragments found on the site.

    Group of volunteers working on the nest site excavation.  Dave Trexler is on the right.

    Nest site location and features are recorded using a Topcon Total Station.  

    View of the prospective nest site after 3 1/2 days of excavation.  A possible mudball is shown in the middle of the excavation.  The exact nature of the nest structure is yet to be determined.

The interior and exterior of a typical egg shell fragment collected from the excavation site was imaged using macro imaging techniques with a Canon 5D Mark II DSLR equipped with a B&L Micro Tessar lens set at f/8 and under ambient light conditions.  The typical shell fragment exterior has a rough bumpy outer surface.  On the other hand, the interior surface of the fragment is relatively smooth and shows a definite concave radius or curvature.

Additional excavations at this site scheduled for mid-August will hopefully begin to reveal more details of the nest structure and hopefully some eggs and possibly juvenile dinosaur bones or embryos.  Stay tuned for updates.

2016/2017/2018 UPDATE:

Additional continuing excavations at the Eyrie site west of Bynam, MT during the summers of 2016 to 2018 finally yielded several dinosaur eggs.  However, all were found in a crushed state with no embryonic remains inside.  To date a total of 14 plaster-jacketed eggs (includes 3 partial eggs) have been recovered from the site, with 9 of the eggs believed to be from a discrete clutch.  Laboratory investigations on the nature of the eggshell material is ongoing. 

Details on the results of the ongoing investigations are found in the following papers that can be accessed via the Research Gate website:

Przybyszewski, Eric & D Germano, Paul & Varricchio, David & Trexler, David. (August 2017). Filling a Data Gap with Analysis of Fossil Eggshell from the Late Cretaceous Upper Two Medicine Formation of Montana. 

Przybyszewski, Eric & D Germano, Paul & Varricchio, David & Trexler, David. (October 2018). New Insights on a Unique Eggshell Locality within the Late Cretaceous Upper Two Medicine Formation of Montana.