Waukeshaaspisis an extinct genus oftrilobite(a diverse group of marine arthropods) known from the lowerSilurianagedWaukesha Biota.A single species is currently known,Waukeshaaspis eatonae,which is known fromstratabelonging to theTelychianagedBrandon Bridge FormationinWisconsin.Originally discovered alongside the Waukesha Biota in 1985, this genus wouldn't be properly described until 2024. Currently, this genus is placed within the familyDalmanitidae,within the largerPhacopida,which lasted from the LowerOrdovicianto the UpperDevonian.
| Waukeshaaspis Temporal range:
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| Fossil specimen ofW. eatonae | |
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| World map of the lower Silurian (435 mya), roughly the same age as the Waukesha Biota | |
Scientific classification
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | †Trilobita |
| Order: | †Phacopida |
| Family: | †Dalmanitidae |
| Genus: | †Waukeshaaspis Randolfe & Gass, 2024 |
| Species: | †W. eatonae
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| Binomial name | |
| †Waukeshaaspis eatonae Randolfe & Gass, 2024
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This genus is rather unique, as it is the only common trilobite found within the Waukesha Biota, and is usually preserved in a more complete state compared to other contemporary genera. Its abundance is also notable, with around 200 or so specimens having been recorded, making it one of the most abundant organisms at the site. This arthropod is so common, that entire planes of rock have been found with dozens of preservedexoskeletons.Its sheer abundance suggests that this trilobite was well adapted to the conditions present in the region. This contrasts with the knowntaphonomicbias that the Waukesha biota has, where hard shelled organisms are either poorly preserved, or absent entirely. Unlike other members of the dalmanitid family, thepygidium(posterior section) of this genus lacks a terminal spine, instead possessing an embayment which may have helped withrespirationwhen the arthropod was enrolled.
Background
editThe Brandon Bridge Formation is a geologic formation within the state of Wisconsin that dates to the Lower Silurian (more specifically the Telychian andSheinwoodianstages).[1]Within the formation exists the smaller Waukesha Biota, aKonservat-Lagerstättenfossil site known for its exceptional preservation of soft-bodied and lightlysclerotizedorganisms that are not normally found in Silurian strata.[2]The biota itself is found within a 12 cm (4.7 in) layer of thinly-laminated, fine-grained, shallow marine sediments consisting ofmudstoneanddolomitedeposited within a sedimentary trap at the end of an erosional scarp over the eroded dolomites of theSchoolcraftand Burnt Bluff Formations.[1]The site itself is known from two quarries; one inWaukesha county,and the other in the city ofFranklin,inMilwaukee County.[2]The two faunas are almost identical to one another, with the exception being that the Franklin quarry lacks any fossils of trilobites.[2][3]A unique trait of the biota is its taphonomy, being that the majority of hard-shelled organisms (which are normally found in Silurian strata), are poorly preserved, or entirely absent.[2]With the exceptions to this being the various trilobites andconulariids(a group ofcnidarianswith pyramidaltheca) from the site.[2]The exceptional preservation of non-biomineralized and lightly sclerotized remains of the Waukesha Biota is generally attributed to a combination of favorable conditions, including the transportation of organisms to a sediment trap that helped to protect from scavengers, and promoted the build up of organic films that coated the surfaces of the dead organisms, which inhibited decay, sometimes enhanced by promoting precipitation of a thinphosphaticcoating, which is observed on many of the fossils.[4][5]However, some of the fossils are also coated with other materials, includingpyriteandcalcium carbonate.[2][3]
Discovery and naming
editWaukeshaaspiswas first discovered alongside the Waukesha Biota in 1985, due to quarrying activity conducted by Waukesha Lime And Stone Company, which revealed theLagerstätten.[6][1]Fossils of this genus are only known from the Waukesha quarry, along with the entirety of the other trilobite fossils from the locality.[2]Before it was named,Waukeshaaspiswas recognized as one of the most common organisms within the Waukesha Biota, only behind several unnamed members of theLeperditicopida(a group ofbivalvedarthropods sometimes associated with theostracods).[1][3]It was also recognized as a new species due to the unique differences between it and other dalmanitids.[7]Despite its recognition, it would take multiple decades before this genus would receive a proper description, which was published by Randolfe & Gass, 2024.[3]Theholotypespecimen ofWaukeshaaspis,UWGM 7447, and most of the known recorded fossils are currently housed within theUW–Madison Geology Museum,along with the majority of the Waukesha fossils.[3][6][5][2]
This arthropods genus name,Waukeshaaspis,is derived from the city ofWaukesha,and theGreekwordaspís,meaning "round shield".[3][8]Thespecific name,eatonae,is in honour of Carrie Eaton, who is the curator of the UWGM, and has helped to catalogue the Waukesha fossils.[3]
Description
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Waukeshaaspiswas a modest sized trilobite, with a average length of around 60 mm (6 cm) long, with sizes going down to at least 9 mm (0.9 cm).[3]Thecephalonof the trilobite was semi-circular, and possessed very long genal spines that extended down to the beginning of the pygidium.[3]The cephalon also posessed afacial suturethat was anterior to the trilobitesglabellarregion, which would have assisted duringecdysis(or molting), as the librigenal area of the cephalon would split along the suture, exposing the other areas of the trilobites head.[9][3]The glabella was roughly the same size, in terms of length and width, and would housed the trilobitescrop.[3]The trilobites pair of eyes, which wereschizochroalin appearance, sat on the posterior margin of the cephalon, and were composed of around 32 files, which bore eight distinct lenses.[3][10]The eyes themselves were notably large, and sat on an elevated area of the preocular region of the cephalon.[3]Thethoraxwas composed of around 11 distinct segments, which gradually increased in both length and width before gradually experiencing a decrease in width.[3]The animals pygidium was roughly triangular in shape, and possessed a distinct embayment towards the terminal end, but lacked a terminal spine as seen in most other dalmanitids.[3]The pygidium also possessed around 10 pairs of axial segments and pleurae, but also a smaller, more elongated piece just in front of the embayment.[3]The embayment itself sat towards the posterior-medial area of pygidium, and possessed a gradual curve and narrow shape.[3]Despite the abundance of both dorsal and ventral oriented specimens, no fossils are known which preserve the various appendages, including theantennae,gills, andbiramous limbs.[3]The animalshypostome(a hard mouthpart which sat ventral side of the cephalon) is also unknown.[3][11]Despite this, several fossils ofWaukeshaaspis,including UWGM 7460 and UWGM 7461, have been found with perseveredgastrointestinal tracts.[3]
Classification
editSince its initial discovery, this trilobite has always been referred to the dalmanitidae, but it wasn't until Randolfe & Gass, 2024 when a more in depth review of this species taxonomy was preformed.[3][1][2][7]The study found ample evidence for this trilobites placement into the dalmanitid family, due to the number of characteristics shared between it, and other dalmanitid genera.[3][2]The 2024 study further placedWaukeshaaspisinto theDalmanitinaesubfamily,but expressed caution due to the dubious validity of the subfamily.[3]The dalmanitidae as a whole are classified within the largerdalmanitoidea,which also includes theDiaphanometopidaeandProsopiscidaefamilies.[12]
Paleoecology
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Waukeshaaspisrepresents an anomaly among the other Waukesha trilobites, as many of the other genera known, includingDistyrax,Meroperix,andArctinurusare comparatively more rare, and not as well preserved.[3][2]This contrasts withWaukeshaaspis,with some specimens, including UWGM 2576 and UWGM 5581, preserving dozens of exoskeletons in close association with one another.[3][2]These types of specimens have been theorized to represent either mating or molting events for the trilobites.[3]The sheer abundance suggests that this dalmanitid was more tolerant of the conditions in the area, however the lack of trackways, and common mode of preservation suggests that this trilobite did not inhabit the preservational area of the Waukesha Biota, but was potentially carried by currents after death.[3]Interestingly, all of the known specimens ofWaukeshaaspisrepresent trilobites in the holapsid stage of life (mature adults), and the lack of juvenile specimens is most likely a case of preservational bias.[3]Although the preferred diet ofWaukeshaaspisis unclear, it can be inferred from other dalmanitids that it was a specialized predator or scavenger.[11][10]The most notable feature ofWaukeshaaspiswas the distinct embayment on its pygidium, which contrasts with the terminal spines usually found in dalmanitids.[3]These spines are thought to have aided the trilobites during the enrolling process, as well as during the act of burrowing.[3]Because of this, it was originally hypothesized thatWaukeshaaspiswas incapable of this action, however, Randolfe & Gass, 2024 suggest that the exceptionally long genal spines of this genus may have filled that role, citing that other dalmanitids with long genal spines, such asOdontochileandNeedmorella,either lack or have a reduced terminal spine.[3]The embayment on the pygidium may have filled a number of roles, including aiding respiration, allowing the antennae to protrude out, and for the release offecal matter.[3]
During the lower Silurian, the area that would become the Waukesha Biota was a shallow,peritidalenvironment.[2][7][3]The benthic area of the region was most likely anoxic, and in combination with oceanic currents, helped to preserve the organisms from the ecosystem.[2][3][7]Some notable contemporary organisms include various arthropods (phyllocarids,thylacocephalans,marrellomorphs,etc)paleoscolecids,lobopodians,poriferans,conodonts,and various other groups.[2][7][1][13]
References
edit- ^abcdefMikulic, Donald G.; Briggs, D.E.G.; Kluessendorf, Joanne (1985)."A new exceptionally preserved biota from the Lower Silurian of Wisconsin, U.S.A."Philosophical Transactions of the Royal Society of London B.311(1148): 75–85.Bibcode:1985RSPTB.311...75M.doi:10.1098/rstb.1985.0140.JSTOR2396972.
- ^abcdefghijklmnoWendruff, Andrew J.; Babcock, Loren E.; Kluessendorf, Joanne; Mikulic, Donald G. (2020)."Paleobiology and Taphonomy of exceptionally preserved organisms from the Waukesha Biota (Silurian), Wisconsin, USA".Palaeogeography, Palaeoclimatology, Palaeoecology.546:109631.Bibcode:2020PPP...54609631W.doi:10.1016/j.palaeo.2020.109631.S2CID212824469.
- ^abcdefghijklmnopqrstuvwxyzaaabacadaeafagahRandolfe, E. A.; Gass, K. C. (2024)."Waukeshaaspis eatonaen. gen. n. sp.: a specialized dalmanitid (Trilobita) from the Telychian of southeastern Wisconsin ".Journal of Paleontology:1–9.doi:10.1017/jpa.2024.32.
- ^Wendruff, Andrew J.; Babcock, Loren E.; Wirkner, Christian S.; Kluessendorf, Joanne; Mikulic, Donald G. (2020)."A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation".Scientific Reports.10(14): 14.Bibcode:2020NatSR..10...14W.doi:10.1038/s41598-019-56010-z.PMC6965631.PMID31949185.
- ^abJones, Wade T.; Feldman, Rodney M.; Schweitzer, Carrie E. (2015)."Ceratiocarisfrom the Silurian Waukesha Biota, Wisconsin ".Journal of Paleontology.89(6): 1007–1021.Bibcode:2015JPal...89.1007J.doi:10.1017/jpa.2016.22.S2CID131127241.
- ^abPulsipher, M. A.; Anderson, E. P.; Wright, L. S.; Kluessendorf, J.; Mikulic, D. G.; Schiffbauer, J. D. (2022). "Description ofAcheronautagen. nov., a possible mandibulate from the Silurian Waukesha Lagerstätte, Wisconsin, USA ".Journal of Systematic Palaeontology.20(1). 2109216.doi:10.1080/14772019.2022.2109216.S2CID252839113.
- ^abcdeGass, Kenneth C.; Braddy, Simon J. (2023)."The Waukesha Biota: a wonderful window into early Silurian life".Geology Today.39(5): 169–176.Bibcode:2023GeolT..39..169G.doi:10.1111/gto.12447.ISSN0266-6979.
- ^"Definition of ASPIS".merriam-webster.Retrieved2024-11-17.
- ^Riccardo Levi-Setti (1995),Trilobites,University of Chicago Press,ISBN978-0-226-47452-6
- ^abSiveter, Derek J.; Fortey, Richard A.; Briggs, Derek E. G.; Siveter, David J.; Sutton, Mark D. (November 2021). Zhang, Xi-Guang (ed.)."The first Silurian trilobite with three-dimensionally preserved soft parts reveals novel appendage morphology".Papers in Palaeontology.7(4): 2245–2253.Bibcode:2021PPal....7.2245S.doi:10.1002/spp2.1401.ISSN2056-2799.S2CID239718706.
- ^abFortey, R. A.; Owens, R. M. (1999), "Feeding habits in trilobites",Palaeontology,42(3): 429–65,Bibcode:1999Palgy..42..429F,doi:10.1111/1475-4983.00080,S2CID129576413
- ^S. M. Gon III."Order Phacopida".RetrievedJanuary 11,2011.
- ^"Abstract: The First Post-Cambrian Marrellomorph Arthropod from North America (2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015))".gsa.confex.Retrieved2024-11-20.