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Leptorhynchos gaddisi

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Leptorhynchos
Temporal range:Late Cretaceous[1]
~80.5 to 72 Ma -Campanian
Life reconstruction ofL. gaddisiby one of the authors of its description
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Clade: †Oviraptorosauria
Superfamily: †Caenagnathoidea
Family: †Caenagnathidae
Genus: †Leptorhynchos
Longrichet al.,2013
Type species
†Leptorhynchos gaddisi
Longrichet al.,2013
Other species
Not to be confused withLeptorhynchos (plant).

Leptorhynchos(/ˌlɛptəuˈrɪŋkəus/) is an extinctgenusofcaenagnathidtheropodfrom theLate Cretaceousof what is now theUSstate ofTexas,although it has been suggested to also exist inAlbertaandSouth Dakota.The type species isL. gaddisi,and it is currently the only widely accepted valid species. The generic name ofLeptorhynchoscomes from the Greek"leptos"meaning "small" and"rhynchos"meaning "beak". Thespecificepithet is in honor of the Gaddis family, who owned the land on which the holotype was discovered.[2]

Discovery

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A picture of an outcrop of the Aguja Formation at Big Bend National Park

Leptorhynchoswas named in 2013 by Nick Longrich, Ken Barnes, Scott Clark, and Larry Millar. In their description, they conducted a specimen-level review ofNorth Americancaenagnathidsin an attempt to resolve the perennial taxonomic confusion surrounding the group. This included the type specimens ofCaenagnathus,Chirostenotes,andHagryphusas well as specimens of more ambiguous affinities such asROM781, which was previously named as a species ofOrnithomimus.Their analysis also included the specimenTMM 45920-1,which would later be designated as the holotype ofLeptorhynchos gaddisi.[2][3]

The results of Longrich and colleagues' analysis was the naming of the new genus,Leptorhynchos,and the assignment of"Ornithomimus" elegans(specimen ROM 781) as a second species in that genus. Several other specimens, such as MOR 1107, were referred to the genus but not assigned to a particular species. Their description contained an initial and then a revised diagnosis of the genus and both species.[2][3]Remains of other small caenagnathids fromLaramidiadiscovered in theHell CreekandScollardformations have variously been attributed to the genus, but without being assigned to either of the named species.

Description

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Species

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Leptorhynchos gaddisi

L. gaddisiwas named as the type species of the new genus by Longrich and colleagues. They based the diagnosis of this species on the anteriorly-projected beak tip, rounded ventral margin of thedentarysymphysis, and a spoon-shape to the beak tip in dorsal view.[3]Longrich and colleagues did not provide a mass estimate in their description but Rubén Molina-Pérez and Asier Larramendi suggested a length of 1.75 metres (5.7 ft) and a mass of roughly 19 kilograms (42 lb).[4]L. gaddisiis generally regarded as the only valid species ofLeptorhynchos.[5]

"Leptorhynchos" elegans
See also:Citipes
The holotype material ofCitipes(formerlyLeptorhycnhos elegans)

The fossil specimen ROM 781 was described in 1933 as a new species of the genusOrnithomimus.I was later reassigned to the genusMagrophalangia(now ajunior synonymofChirostenotes), then toElmisaurus,and then toChirostenotesbefore being named by Longrich and colleagues as the type specimen of the new speciesL. elegans.[5]They made this diagnosis based on the strongly upturned beak and straight anterior margin of the dentary symphysis and also referred the specimen TMP 1992.36.390 to the species. However, in their phylogenetic analysis which accompanied the description, the authors remarked that the two species form apolytomywith one another withinCaenagnathidaeand they may not represent the same genus.[2]In2020,Gregory Funston reassignedL. elegansto the new genus,Citipes.[5]Leptorhynchoshas not been included in any phylogenetic analyses withCitipessince the most recent referral, so the veracity of this reassignment has yet to be tested by new authors in order to affirm or contest it.[6]

Leptorhynchos sp.
Caenagnathid bones from the Frenchman Formation which may have belonged toLeptorhynchos

In their description of the genus, Longrich and colleagues referred the specimen MOR 1107 (part of amandible) toLeptorhynchos,but they did not assign it to either of the species they named. Although the bones are convex in profile, similar toChirostenotes,its smaller size led them to refer it toLeptorhynchos.[2]Other smallcaenagnathidremains have been variously referred to the genus since it was named, although none have been named as a their own species. Among these are caenagnathid remains from the lateMaastrichtianScollard Formation,[7]theFrenchman Formation,[8]and theHell Creek Formation.[9]Subsequent authors have disputed these referrals.[6]More caenagnathid remains have also recently been described from theAguja Formation,which have been speculated to belong toLeptorhynchos.[10]

Skeleton

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TheholotypeofLeptorhynchos gaddisi,given the designation TMM 45920-1, is a single fusedmandible.Additional specimens were also referred to the species in the paper describing it. These include acaudal vertebra,the partial third and fourthmetatarsals,and a single toe claw. These specimens were not associated with the holotype, but were referred toL. gaddisibased on their size and discovery in the same geologic layer.[2]Later authors have questioned this referral[5]andLeptorhynchoshas not been included in some recent analyses.[5][6]

The dentaries of the holotype were fully fused with no visible sutures, which suggest that the animal was fully mature when it died and the small size of the specimen is not the result ofontogeny.This was one of the primary reasons thatLeptorhynchoswas named as a new species instead of an immatureChirostenotes,which it closely resembled in shape but which was much larger. The interior surface of the jaw had several furrows and a lingual shelf with a ridge along its margin. The mandible itself was much more elongated than members ofoviraptoridae,but was proportionally relatively short for acaenagnathid.[2]

The referred specimens from the Aguja Formation are tentatively assigned to this taxon. They include a single partial vertebra, two partial metatarsals, and a pedal ungual. The vertebra is unremarkable with twinpleurocoelson each side of thevertebral centrum.The metatarsals strongly resemble those ofCitipes,which was part of the basis for the initial referral of that taxon to the genusLeptorhynchos.The metatarsals are also fused to thetarsal bones,which is the condition seen in bothCitipesandElmisaurus.[2]

Classification

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Diagram of most known caenagnathid remains

In their description of the holotype, Longrich and colleagues conducted a phylogenetic analysis. Their analysis used the dataset of Longrich's earlier publication in 2010 with several new taxa added for a total of 28 taxa coded for 205 characters. Their data set also included recent information aboutNemegtomaiaandNomingiawhich had been published since the analysis in 2010. Themonophylyof caenagnathidae was supported in their analysis based on the following diagnostic characters: fused dentaries, a ventrally bowed process on the underside of thedentary,the lack of contact between the dentary and themandibular fenestra,and a shallowsurangular bone.The analysis did resolve several taxa at the base of caenagnathidae includingGigantoraptorandMicrovenator,but there was less resolution in the more derived area of the tree. In particular, their strict consensus tree did not support the unambiguous monophyly of the genusLeptorhynchos;the two species they assigned to the genus were in apolytomywithHagryphusand a clade containingCaenagnathus,Chirostenotes,and the specimen BMNH 2033 (which is from theHell Creek Formationand was coded as a distinct taxon). The authors remark that they referred ROM 781 toLeptorhynchosbecause of the similar size of the two species, but noted that they may belong to separate genera, pending further research.[2]

Longrich and colleagues broadly determined that mostcaenagnathidgenera are diagnosed by characteristics of themandibleandmanus,which allows researchers to diagnose genera and species based on very incomplete remains, but which also means that more complete remains are undiagnostic if they do not preserve the mandible or manus. However, the authors note that the shape of the beak in modernbirdsis an important diagnostic trait, as well as in some dinosaurs likeTriceratopsandEdmontosaurus,so they argue that it is not unreasonable to assume that this may be sufficient in naming new genera or species. Furthermore, the degree of fusion exhibited by the jaw bones, as well as their surface texture, can be indicative of ontogenetic age in manyoviraptorosaurs,which can be used to determine if an individual specimen is a new taxon or simply a different life stage of an existing taxon.[2]

For specimens which do not contain the relevant diagnostic characters or any indication of their ontogenetic age, they have been assigned to existing taxa according to size and locality. Longrich and colleagues note that this approach has shortcomings, but they argue that the ecological abundance of adult animals in any ecosystem means that most fossilized animals will be adults anyways, which they suggest is sufficient for the purposes of their analysis. A consensus of the 116 most parsimonious trees in their analysis is shown below.[2]

Oviraptorosauria

The most recentphylogeneticanalysis includingLeptorhynchoswas the one conducted by Sungjin Lee, Yuong-Nam Lee, Anusuya Chinsamy, Junchang Lü,Rinchen Barsbold,and Khishigjav Tsogtbaatar in their description of the new genusGobiraptor.[11]Their analysis used the data set from an earlier study which included several of the same authors when they describedHuanansaurus.[12]Lee and colleagues were primarily interested inoviraptoridae,but they included most knowncaenagnathidgenera in their analysis. They recoveredLeptorhynchosandCitipes(thenL. elegans) in apolytomywith thegeneraElmisaurusandApatoraptorwithin a monophyletic "elmisaurinae". They do not comment any further on the implications of this analysis on caenagnathid phylogeny.[11]Subsequent analyses which have not includedLeptorhynchoshave not recovered these taxa as being closely related.[5]

Caenagnathoidea

Paleoecology

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A map of known caenagnathid remains from North America
A reconstruction of a hadrosaur from theKirtland Formation,which would have been climatically similar to the Aguja Formation

Paleoenvironment

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The only definite remains ofLeptorhynchoshave been recovered from the Upper Shale Member of theAguja Formationnear the town ofTerlingua, Texas.[13]The Upper Shale Member is made up ofmudstone,carbonaceousshale,lignite,andsandstone.During theCretaceous Period,this area would have been a freshwater or brackishcoastal marshand afloodplainthat was part of ariver delta.[14]The sediments also record the presence ofoxbow lakesand some coastal marine deposits.[15]

Contemporary fauna

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A wide variety ofvertebrateshave been unearthed from other outcrops of theAguja Formationin bothTexasandCoahuila,Mexico.The rocks preserve bothlittoralandmarine environmentsin which the fossils ofsharks,bony fish,ammonites,andtetrapodshave all been found. However,Leptorhynchosis only known from the Upper Shale Member of the formation, which preserves a different faunal assemblage from the older deposits. The Upper Shale Member, whereLeptorhynchoswas found, preserves afreshwaterecosystem with very few marine animals.[16]

A wide variety ofturtleshave been found from this period includingAdocus,Basilemys,andChupacabrachelys,the latter of which is only known from the Aguja Formation. Remains of numerous other turtles have been discovered includingtrionychids,baenids,andkinsternoids,but these have not been referred to any existing species.[16]A wide variety ofsquamateshave also been found in these areas includinganguids,scincomorphs,varanoids,andsnakes.[17]The giantalligatoridDeinosuchus riograndensishas also been found in the Aguja Formation, but is not known from the Upper Shale Member.[18]

Dinosaurs are the largest animals found in the Aguja Formation, and the taxa found in these rocks is broadly similar to contemporaneous faunal assemblages in theKaiparowits,Dinosaur Park,andJudith Riverformations.[19]Hadrosaursare diverse in the Upper Shale Member and includeAngulomasticator,[19]Maleficia,[20]and possiblyKritosaurus.Ceratopsidsare also present.Chasmosaurinesare also represented by two species ofAgujaceratops[21]and thecentrosaurinesare represented by thenasutoceratopsinYehuecauhceratops.[22]At least onepachycephalosaur,Texacephaleis known from cranial remains.[23]Both major groups ofankylosaurswere also present in the Upper Shale Member, although the precise identification of these specimens remains uncertain. Most ankylosaur remains from the Aguja Formation consist only ofosteodermsandvertebrae.[24]These have been referred to the generaEdmontonia,Euoplocephalus,andPanoplosaurus.[14]

Saurischiansare also present in large numbers in the Upper Shale Member. These consist exclusively oftheropodsbecausesauropodsappear to be completely absent inNorth Americauntil later in theCretaceous.[25]Leptorhynchosis the only theropod from the Upper Shale Member that has been named.[26]The rest of the theropod remains have been referred to existinggenera.Teeth and other fragmentary remains indicate thatornithomimosaurs,dromaeosaurids,troodontids,tyrannosaurids,andcaenagnathidswere present in the region during the Late Cretaceous. A few specimens have been referred to the generaChirostenotes,Saurornitholestes,Dromaeosaurus,Troodon,and the enigmaticRichardoestesia,but these referrals remain uncertain.[14][27]

See also

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References

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  1. ^Fowler, Denver Warwick (2017-11-22)."Revised geochronology, correlation, and dinosaur stratigraphic ranges of the Santonian-Maastrichtian (Late Cretaceous) formations of the Western Interior of North America".PLOS ONE.12(11): e0188426.Bibcode:2017PLoSO..1288426F.doi:10.1371/journal.pone.0188426.ISSN1932-6203.PMC5699823.PMID29166406.
  2. ^abcdefghijkLongrich, N. R.; Barnes, K.; Clark, S.; Millar, L. (2013)."Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a Revision of the Caenagnathinae".Bulletin of the Peabody Museum of Natural History.54:23–49.doi:10.3374/014.054.0102.S2CID128444961.
  3. ^abcLongrich, Nicholas R.; Barnes, Ken; Clark, Scott; Millar, Larry (2013). "Correction to" Caenagnathidae from the Upper Campanian Aguja Formation of West Texas, and a Revision of the Caenagnathinae "".Bulletin of the Peabody Museum of Natural History.54(2):263–264.doi:10.3374/014.054.0204.S2CID128898931.
  4. ^Molina-Pérez, Rubén; Larramendi, Asier (2019).Dinosaur Facts and Figures: The Theropods and Other Dinosauriformes.Translated by Connolly, David; Ramírez Cruz, Gonzalo Ángel. Illustrated by Andrey Atuchin and Sante Mazzei. Princeton University Press.ISBN978-0691180311.
  5. ^abcdefFunston, Gregory (July 27, 2020)."Caenagnathids of the Dinosaur Park Formation (Campanian) of Alberta, Canada: anatomy, osteohistology, taxonomy, and evolution".Vertebrate Anatomy Morphology Palaeontology.8:105–153.doi:10.18435/vamp29362.ISSN2292-1389.
  6. ^abcAtkins-Weltman, K. L.; Simon, D. J.; Woodward, H. N.; Funston, G. F.; Snively, E. (2024)."A new oviraptorosaur (Dinosauria: Theropoda) from the end-Maastrichtian Hell Creek Formation of North America".PLOS ONE.19(1). e0294901.doi:10.1371/journal.pone.0294901.PMC10807829.
  7. ^Voris, Jared T.; Zelenitsky, Darla K.; Therrien, François (2023-09-11). "Caenagnathids (Theropoda, Oviraptorosauria) from the uppermost Maastrichtian of the Scollard Formation of Alberta, Canada".Cretaceous Research.153:105708.doi:10.1016/j.cretres.2023.105708.ISSN0195-6671.S2CID261779584.
  8. ^Funston, Gregory; Currie, Philip; Burns, Michael (2015)."New elmisaurine specimens from North America and their relationship to the Mongolian Elmisaurus rarus".Acta Palaeontologica Polonica.doi:10.4202/app.00129.2014.S2CID73689603.
  9. ^Stein, Walter W. (2019)."TAKING COUNT: A Census of Dinosaur Fossils Recovered From the Hell Creek and Lance Formations (Maastrichtian)"(PDF).The Journal of Paleontological Sciences.8:1–42.
  10. ^Wick, Steven L.; Lehman, Thomas M.; Fortner, John D. (2023). "New caenagnathid (Theropoda: Oviraptorosauria) dinosaur specimens from middle and upper Campanian strata of West Texas".Geobios.doi:10.1016/j.geobios.2023.08.002.
  11. ^abLee, Sungjin; Lee, Yuong-Nam; Chinsamy, Anusuya; Lü, Junchang; Barsbold, Rinchen; Tsogtbaatar, Khishigjav (2019)."A new baby oviraptorid dinosaur (Dinosauria: Theropoda) from the Upper Cretaceous Nemegt Formation of Mongolia".PLOS ONE.14(2): e0210867.Bibcode:2019PLoSO..1410867L.doi:10.1371/journal.pone.0210867.PMC6364893.PMID30726228.
  12. ^Lü, Junchang; Pu, Hanyong; Kobayashi, Yoshitsugu; Xu, Li; Chang, Huali; Shang, Yuhua; Liu, Di; Lee, Yuong-Nam; Kundrát, Martin; Shen, Caizhi (2015)."A New Oviraptorid Dinosaur (Dinosauria: Oviraptorosauria) from the Late Cretaceous of Southern China and Its Paleobiogeographical Implications".Scientific Reports.5:11490.Bibcode:2015NatSR...511490L.doi:10.1038/srep11490.PMC4489096.
  13. ^Mannion, Philip (2013)."Terlingua area (Cretaceous of the United States); Also known as TMM 45920".The Paleobiology Database.Where: Brewster County, Texas
  14. ^abcRowe, Timothy; Cifelli, Richard L.; Lehman, Thomas M.; Weil, Anne (1992). "The Campanian Terlingua local fauna, with a summary of other vertebrates from the Aguja Formation, Trans-Pecos Texas".Journal of Vertebrate Paleontology.12(4):472–493.Bibcode:1992JVPal..12..472R.doi:10.1080/02724634.1992.10011475.
  15. ^Rivera-Sylva, H.E.; Frey, E.; Stinnesbeck, W.; Guzman-Gutirrez, J.R.; Gonzalez-Gonzalez (2017). "Mexican ceratopsids: Considerations on their diversity and evolution".Journal of South American Earth Sciences.75:66–73.doi:10.1016/j.jsames.2017.01.008.
  16. ^abLongrich, N.R.; Sankey, J.; Tanke, D. (2010). "Texacephale langstoni,a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA ".Cretaceous Research.31(2):274–284.Bibcode:2010CrRes..31..274L.doi:10.1016/j.cretres.2009.12.002.
  17. ^Nydam, Randall L.; Rowe, Timothy B.; Cifelli, Richard L. (2013)."Lizards and Snakes of the Terlingua Local Fauna (late Campanian), Aguja Formation, Texas, with Comments on the Distribution of Paracontemporaneous Squamates Throughout the Western Interior of North America".Journal of Vertebrate Paleontology.33(5):1081–1099.Bibcode:2013JVPal..33.1081N.doi:10.1080/02724634.2013.760467.ISSN0272-4634.JSTOR42568627.S2CID86519841.
  18. ^Anglen, John J.; Lehman, Thomas M. (2000). "Habitat of the giant crocodilianDeinosuchus,Aguja Formation (Upper Cretaceous), Big Bend National Park, Texas ".Journal of Vertebrate Paleontology.20(Supplement to 3): 26A.doi:10.1080/02724634.2000.10010765.S2CID220412294.
  19. ^abWagner, Jonathan R.; Lehman, Thomas M. (2009-06-12)."An enigmatic new lambeosaurine hadrosaur (Reptilia: Dinosauria) from the Upper Shale member of the Campanian Aguja Formation of Trans-Pecos Texas".Journal of Vertebrate Paleontology.29(2):605–611.Bibcode:2009JVPal..29..605W.doi:10.1671/039.029.0208.ISSN0272-4634.S2CID128555861.
  20. ^Prieto-Márquez, Albert; Wagner, Jonathan R. (2022-11-10)."A new 'duck-billed' dinosaur (Ornithischia: Hadrosauridae) from the upper Campanian of Texas points to a greater diversity of early hadrosaurid offshoots".Cretaceous Research.143:105416.doi:10.1016/j.cretres.2022.105416.ISSN0195-6671.S2CID253470207.
  21. ^Lehman, Thomas M.; Wick, Steven L.; Barnes, Kenneth R. (2017-08-03)."New specimens of horned dinosaurs from the Aguja Formation of West Texas, and a revision of Agujaceratops".Journal of Systematic Palaeontology.15(8):641–674.doi:10.1080/14772019.2016.1210683.ISSN1477-2019.S2CID88907183.
  22. ^Rivera-Sylva, H.E.; Hendrick, B.P.; Dodson, P. (2016)."A Centrosaurine (Dinosauria: Ceratopsia) from the Aguja Formation (Late Campanian) of Northern Coahuila, Mexico".PLOS ONE.11(4): e0150529.Bibcode:2016PLoSO..1150529R.doi:10.1371/journal.pone.0150529.PMC4830452.PMID27073969.
  23. ^Longrich, N. R.; Sankey, J.; Tanke, D. (2010). "Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA".Cretaceous Research.31(2): 274.Bibcode:2010CrRes..31..274L.doi:10.1016/j.cretres.2009.12.002.
  24. ^West, Bryanna (2020).Campanian-Maastrictian Ankylosaurs of West Texas(PDF)(Thesis). Texas Tech University.
  25. ^Lehman, Thomas M. (2001). "Late Cretaceous dinosaur provinciality". In Tanke, Darren H.; Carpenter, Kenneth (eds.).Mesozoic Vertebrate Life.Life of the past. Bloomington & Indianapolis: Indiana University Press. pp.310–328.ISBN0-253-33907-3.
  26. ^Sullivan, R.M., and Lucas, S.G. 2006. "The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America[permanent dead link‍]."New Mexico Museum of Natural History and Science, Bulletin 35:7-29.
  27. ^Sankey, Julia T. (2001)."Late Campanian Southern Dinosaurs, Aguja Formation, Big Bend, Texas".Journal of Paleontology.75(1):208–215.doi:10.1666/0022-3360(2001)075<0208:LCSDAF>2.0.CO;2.ISSN0022-3360.JSTOR1306931.
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