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New Crassigyrinus-Like Fibula from the Tournaisian (Earliest Carboniferous) of Nova Scotia

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New Crassigyrinus-Like Fibula from the Tournaisian (Earliest Carboniferous) of Nova Scotia Canadian Journal of Earth Sciences New Crassigyrinus-like fibula from the Tournaisian (earliest Carboniferous) of Nova Scotia Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2019-0128.R3 Manuscript Type: Communication Date Submitted by the 27-Jan-2020 Author: Complete List of Authors: Lennie, Kendra; University of Calgary, Biological Sciences Mansky, Chris; Blue Beach Fossil Museum Anderson, Jason S.; University of Calgary, Comparative Biology and ExperimentalDraft Medicine Fin-to-Limb, Carboniferous, Vertebrate Evolution, Romer's Gap, Early Keyword: Tetrapod, Crassigyrinidae Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 16 Canadian Journal of Earth Sciences 1 New Crassigyrinus-like fibula from the Tournaisian (earliest 2 Carboniferous) of Nova Scotia 3 4 5 6 Kendra I. Lennie1,2 7 Chris F. Mansky3 8 Jason S. Anderson2,4 9 1. University of Calgary, Biological Sciences. 507 Campus Drive N.W. University of Calgary. Calgary, 10 Alberta. Canada, T2N 1N4. [email protected] 11 2. University of Calgary, McCaig Bone and Joint institute 12 3. Blue Beach Fossil Museum, 127 Blue Beach Road, Hantsport, Nova Scotia, B0P 1P0. 13 [email protected] 14 4. University of Calgary, Comparative Biology and Experimental Medicine. 3330 Hospital Dr. NW, 15 Calgary, Alberta. Canada, T2N 4N1. [email protected] 16 17 18 19 20 21 22 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 16 23 24 25 Abstract: 26 The transition between the Devonian and Carboniferous Periods is important for tetrapod vertebrates. 27 By the end of the Devonian the first limbs are present in aquatic animals, and by the mid Carboniferous 28 fully terrestrial tetrapods have diversified. 29 Knowledge of the fin-to-limb transition is sparse because few fossils from the earliest Carboniferous 30 (Tournaisian) are known. Blue Beach Nova Scotia, in addition to a small number of sites in Scotland and 31 Australia, is an exception to this global trend. Previous reports from Blue Beach identified fossils from a 32 variety of Devonian-like and Carboniferous-like tetrapod body forms, making it a valuable site for 33 studying the fin-to-limb transition. Here weDraft report on a new left fibula from Blue Beach, which we 34 attribute to the later occurring Visean-aged (Early Carboniferous) Crassigyrinidae. Recent investigations 35 of deposits in Scotland, similar in age to the Tournaisian exposed at Blue Beach, have found 36 Crassigyrinus-like elements as well, reinforcing this 20 million year lineage extension. 37 38 Keywords: 39 Fin-to-limb, Carboniferous, Crassigyrinidae, Early Tetrapod, Vertebrate Evolution, Romer’s Gap 40 41 42 43 44 45 46 https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 16 Canadian Journal of Earth Sciences 47 Introduction 48 Crassigyrinus scoticus is an unusual tetrapod first described from the Visean (Early 49 Carboniferous) and Namurian (Late Carboniferous; Panchen 1985; Panchen and Smithson 1990). The 50 holotype, described by Lydekker (1890), was not formally ascribed to Crassigyrinus scoticus until 51 a redescription by Panchen (1985), followed by Panchen and Smithson (1990). The material 52 is from the Visean-aged Gilmerton Ironstone in Scotland, and preserves only cranial material. Cranial, 53 pelvic girdle, and limb material also are known from the Namurian (Late Carboniferous) of the 54 Dora bone bed in Cowdenbeath, Scotland (Panchen 1985; Panchen and Smithson 1990). One reason for 55 its common description as an aberrant species is the minute size of the forelimbs, so small they were 56 originally thought to be part of the hyobranchial skeleton (Panchen 1985). As with many of the early 57 tetrapods, Crassigyrinus scoticus shows an Draftunusual range of “primitive” fish-like and “derived” 58 anthracosaur-like characteristics. The heavily reduced limbs, retention of fish-like foramina in the 59 humerus, torsion of hindlimb elements, and proportionately large, fish-like skull have led many 60 researchers to conclude that Crassigyrinus was an aquatic tetrapod (Panchen 1985; Panchen and 61 Smithson 1990; Herbst and Hutchinson 2019), with Carroll (1992) suggesting it may have had a 62 terrestrial ancestor and itself been secondarily aquatic. 63 Crassigyrinus is an unusual tetrapod in having a combination of features that suggest it is a very 64 derived form of an early tetrapod, and until recently no specimen from Tournaisian deposits, in which 65 most stem tetrapods are found, was known. Earlier reports from the earliest Tournaisian-aged Horton 66 Bluff Formation exposed at Blue Beach near Hantsport, Nova Scotia, suggested the presence of 67 Crassigyrinus-like fossils (Mansky and Lucas 2013), but these were briefly mentioned without detailed 68 description. Increased effort to sample the Tournaisian by Clack and colleagues (Clack, Porro, and 69 Bennett 2019), examining the Burnmouth Locality in Scotland, revealed a Crassigyrinus-like jaw 20 myr https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 16 70 older than the holotype Crassigyrinus scoticus (Clack, Porro, and Bennett 2019; Clack et al. 2019). Here 71 we report on a new Crassigyrinus-like element from Blue Beach, which increases our confidence in this 72 long range extension into antiquity for the family, and further supports the stem tetrapod placement of 73 the taxon. 74 Methods 75 The specimen NSM 005.GF.045.112 was collected by CM and prepared by KL using Paleotools 76 Microjacks 1-3 (Brigham, Utah) pin vice, carbowax, and PVA. Once fully prepared out of the matrix it was 77 Scanned in an Xradia Versa 510 (Carl Zeiss, Germany) at the University of Calgary with settings of 140kV, 78 72µA, no filter, and magnification 0.4x. The scan resulted in an image stack 1001 by 1024 pixels totaling 79 1823 images with a voxel size of 23.35µm. DraftThe resulting image stack was imported into Dragonfly 80 (Dragonfly 4.0. Object Research Systems (ORS) Inc, Montreal, Canada, 2018; software available at 81 http://www.theobjects.com/dragonfly) image intensity settings (look up tables or LUTs) were modified 82 to create high contrast images. 83 Locality 84 Blue Beach is one of a small number of localities worldwide that represent the Tournaisian Age 85 of the Early Carboniferous (Anderson et al. 2015). Blue Beach, along with Burnmouth in the Scottish 86 Borders Region, is one of the oldest localities within what was previously a global fossil hiatus known as 87 Romer’s Gap (Romer 1956; Coates and Clack 1995; Smithson et al. 2012). Disarticulated fish and 88 tetrapod elements are present at Blue Beach, but until recently little research has been done on the 89 elements. Sufficient numbers of more complete specimens have now been described, for interpretation 90 and identification of the isolated elements to be possible. Located between Hantsport and Avonport, 91 Nova Scotia, Blue Beach is near the mouth of the Avon River where it meets the Bay of Fundy. The Bay https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 16 Canadian Journal of Earth Sciences 92 of Fundy is known for record daily tides, and this tidal action exposes fossil material on a daily basis. 93 Whereas the tides aid in extracting material they also result in considerable wear, and potential that 94 material gets washed out with the tide. Wear from recent tidal action is not the only taphonomic factor 95 acting on these bones, as some show evidence of predepositional wear. This includes cracks and areas 96 of cortical erosion that are encased in matrix upon collection and are exposed after manual preparation. 97 The element comes from the Lighthouse Sandstone layer of the Hurd Creek Member of the 98 Horton Bluff formation (Anderson et al. 2015). It is mid to early late Tournaisian in age (late Tn2 to early 99 Tn3; Utting, et al. 1989; Martel, McGregor, and Utting 1993), probably slightly below the CM (claviger- 100 macra) palynozone of the Burnmouth specimen. However, the Tournaisian palynozonation of Scotland is 101 currently under review so the exact temporal relationship between the specimens remains 102 indeterminate (Anderson et al. 2015; Clack,Draft Porro, and Bennet 2018; Otoo et al. 2018). The depositional 103 environment of Horton Bluff is believed to be a high energy lagoonal site exhibiting marginal marine 104 conditions (Mansky and Lucas 2013). As such, the bones were disarticulated before or at the time of 105 deposition, when they were likely transported into the lagoonal environment at Blue Beach during 106 storms and under high energy conditions. It is unclear if the remains were originally from terrestrial or 107 aquatic environments. Most of the material from Blue Beach is preserved quite well in three 108 dimensions, and rugosity such as pitting and scarring often remains. 109 110 Systematic Paleontology 111 Osteichthyes Huxley, 1880 112 Sarcopterygii Romer, 1955 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 6 of 16 113 Tetrapodomorpha Ahlberg, 1991 114 Crassigyrinidae Huene, 1948 115 Referred specimen: NSM.005.GF.045.112. 116 Locality: Lighthouse Sandstone, Hurd Creek Member, Horton Bluff Formation, exposed below 117 the lighthouse (“Lighthouse Cove”) between Hantsport and Avonport, Nova Scotia. 118 Description 119 The element, a left fibula (Figure 1A and 2A-G), is 40mm in length from the middle of the 120 proximal surface to the middle of the distalDraft surface. The specimen appears to be dorsoventrally 121 flattened although what remains of the internal structure does not suggest crushing (Figure 1B-D). 122 Therefore the dorsoventral flattening appears to be a true morphological feature rather than an artifact 123 of taphonomy. The element is narrowest at the midshaft, and the distal end flares more than the 124 proximal end. There is no prominent scarring on either the flexor or extensor surface, although small 125 pits are visible on the extensor surface.
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