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New Embolomerous Tetrapod Material and a Faunal Overview of the Mississippian-Aged Point Edward Locality, Nova Scotia, Canada

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New Embolomerous Tetrapod Material and a Faunal Overview of the Mississippian-Aged Point Edward Locality, Nova Scotia, Canada Canadian Journal of Earth Sciences NEW EMBOLOMEROUS TETRAPOD MATERIAL AND A FAUNAL OVERVIEW OF THE MISSISSIPPIAN-AGED POINT EDWARD LOCALITY, NOVA SCOTIA, CANADA. Journal: Canadian Journal of Earth Sciences Manuscript ID cjes-2018-0326.R2 Manuscript Type: Article Date Submitted by the 07-Jun-2019 Author: Complete List of Authors: Adams, Gabrielle; Carleton University, Mann, Arjan; Carleton University, Earth Sciences; University of Toronto Faculty of Arts and Science, Earth Sciences Maddin, HillaryDraft C.; Carleton University, Mississippian, Carboniferous, tetrapod, embolomere, Point Edward Keyword: Formation Is the invited manuscript for consideration in a Special Not applicable (regular submission) Issue? : https://mc06.manuscriptcentral.com/cjes-pubs Page 1 of 38 Canadian Journal of Earth Sciences 1 2 3 4 Formatted for Canadian Journal of Earth Sciences 5 6 NEW EMBOLOMEROUS TETRAPOD MATERIAL AND A FAUNAL OVERVIEW OF THE 7 MISSISSIPPIAN-AGED POINT EDWARD LOCALITY, NOVA SCOTIA, CANADA. 8 9 10 11 Draft 12 13 14 Gabrielle R. Adams, Arjan Mann1, Hillary C. Maddin2. Department of Earth Sciences, 15 Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6 16 17 Corresponding author: Gabrielle R. Adams ([email protected]) 18 19 Keywords: Mississippian, Carboniferous, tetrapod, embolomere, Nova Scotia, Point Edward 20 Formation 21 1 [email protected] 2 [email protected] 1 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 2 of 38 22 23 NEW EMBOLOMEROUS TETRAPOD MATERIAL AND A FAUNAL OVERVIEW OF THE 24 MISSISSIPPIAN-AGED POINT EDWARD LOCALITY, NOVA SCOTIA, CANADA. 25 26 Gabrielle R. Adams, Arjan Mann, Hillary C. Maddin. 27 Abstract: Embolomerous tetrapods, mid-to-large aquatic predators, form a major faunal 28 constituent of Permo-Carboniferous tetrapod communities. Embolomeres are recognized by their 29 distinct circular, bipartite vertebrae. Although traditionally classified as stem amniotes, the 30 inclusion of embolomeres within the tetrapod crown group has recently been challenged. Despite 31 the group’s phylogenetic uncertainty, embolomeres provide an important record of a long-lived 32 tetrapod lineage, spanning ‘Romer’s Gap’Draft through to the Early Permian. Here we describe 33 embolomerous tetrapod material that was collected in 1915 by W. A. Bell (CMN 10015, herein 34 divided into CMN 10015A, B and C). The material, composed of numerous disarticulated cranial 35 and postcranial elements, was discovered near Sydney, Nova Scotia, as ex situ beach-float 36 pertaining to a horizon within the Mississippian-aged Point Edward Formation. Of this material, 37 a single left lower jaw of a proterogyrinid is identified, differing from previous embolomere 38 remains from this site identified as Pholiderpeton (?) bretonensis Romer, 1958. We also identify 39 an anterior jaw fragment as a separate taxon from the proterogyrinid, indicating the presence of 40 at least two embolomerous tetrapods in Bell’s collection. Other cranial and postcranial material 41 cannot be directly associated with either jaw and are not diagnostic enough to assign to a specific 42 taxon. Thus, the remaining material is referred to ‘Embolomeri indet.’ until more information is 43 available. Additionally, we summarize the fauna of the Point Edward locality revealing a diverse 2 https://mc06.manuscriptcentral.com/cjes-pubs Page 3 of 38 Canadian Journal of Earth Sciences 44 aquatic Late Mississippian ecosystem. Finally, the extensive embolomere material described here 45 presents new data that can broadly address embolomere diversity throughout the Carboniferous. 46 INTRODUCTION 47 48 Embolomeres are large aquatic tetrapods that occur in the fossil record from the 49 Early Carboniferous through to the Early Permian (Holmes 1989; Anderson et al. 2015). These 50 animals superficially resemble modern-day crocodilians and were among the largest predators of 51 their time. They are recognized in the fossil record by their bipartite vertebral centra, each 52 consisting of discrete, disc-shaped intercentrum and pleurocentrum (Holmes 1984). The latter is 53 often larger and anteroposteriorly wider than the intercentrum and supports the neural arch 54 (Panchen 1970), whereas the intercentrumDraft bears the articular facet for the capitulum of the rib. 55 This distinct vertebral morphology was named “embolomerous” by Cope (1884) and was once 56 thought to be diagnostic of the group. This has since been found not to be the case, leading to 57 confusion in both the taxonomic composition of the group, as well as the evolutionary 58 significance of this distinctive vertebral morphology (Panchen 1970). Watson (1926) later 59 suggested that because of their early occurrence in the fossil record and similarity to early 60 reptiles, embolomerous tetrapods might have been the link connecting osteolepiform 61 tetrapodomorph fish to later tetrapod descendants. However, since then embolomeres have more 62 widely been regarded as stem amniotes (Clack et al. 2017). Interestingly, Clack’s (2011) 63 description of an embolomere tail from the Middle Pennsylvanian-aged Five Points locality in 64 Ohio, indicated the presence of supraneural radials ⎼ a trait shared with taxa as primitive as 65 Devonian tetrapodomorph fish. This evidence, along with other studies (e.g., Laurin and Reisz 66 1997; 1999) questioned whether embolomeres occupy a such a derived position or should instead 67 be placed in a more basal position on the tetrapod lineage. This alternative hypothesis is also 3 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 4 of 38 68 supported by a more recent analysis by Pardo et al. (2017), who suggested embolomeres should 69 be classified as stem tetrapods alongside colostieds and baphetids. Despite the uncertainty 70 surrounding their interrelationships, the long evolutionary history of embolomeres makes them 71 an important group for studying early phases of tetrapod evolution (Clack 2002, 2012). 72 73 Tetrapod discoveries at the Mississippian-aged Point Edward locality 74 The Point Edward locality is located on a peninsula opposite Sydney Harbour, on Cape 75 Breton Island, Nova Scotia, Canada (Fig. 1A and B). The locality exposes a section of the Point 76 Edward Formation, which pertains to the Upper Mississippian of the Carboniferous (Allen et al., 77 2014). The first tetrapod remains described from the Point Edward locality, and of the Draft 78 formation in general, were collected in 1956 by a team led by Alfred Romer of the Museum of 79 Comparative Zoology, Harvard University (Sues et al. 2013). The impression of a tetrapod jaw, 80 MCZ 2772, was provisionally assigned to a new embolomerous tetrapod taxon, Pholiderpeton 81 (?) bretonensis Romer 1958. Some 15 years later, Donald Baird of Princeton University also 82 collected a lower jaw from the Point Edward locality. He was able to recognize it as the 83 counterpart to MCZ 2772 and the two pieces were reunited in the MCZ collections (Sues et al. 84 2013). In 1962, Baird described another skull fragment from the Point Edward locality, 85 attributing it to the stem tetrapod Spathicephalus pereger Baird 1962 (YPM-PU 17182). In 1968, 86 Baird further collected the articulated pectoral girdle and trunk region of a tetrapod (YPM VPPU 87 020100) deemed similar to Greererpeton burkemorani Romer 1969 (Sues et al. 2013) and a 88 clavicle of an embolomere (YPM-PU 17190; A. Mann pers. obs.), which Panchen (1970) 89 referred to Pholiderpeton (?) bretonensis; however, this material remains undescribed. 4 https://mc06.manuscriptcentral.com/cjes-pubs Page 5 of 38 Canadian Journal of Earth Sciences 90 Housed in the Canadian Museum of Nature, Aylmer, Quebec, Canada, is another 91 collection of disarticulated tetrapod remains found at the Point Edward locality by W. A. Bell of 92 the Geological Survey of Canada in 1915, CMN 10015. The exact location of this discovery is 93 unknown, although relocation attempts have been made by a team led by Hillary Maddin of 94 Carleton University. Despite being the first tetrapod material to be collected from Point Edward, 95 Bell’s collection has remained largely unstudied. It consists of disarticulated cranial and 96 postcranial elements preserved among over 110 separate pieces of matrix and isolated elements, 97 making it currently the most extensive collection of tetrapod remains known from Point Edward. 98 Although the matrix is all the same lithology, the separation of the blocks eliminates any 99 possibility of confidently associating the elements. The collection was prepared and illustrated in 100 1971 by the late Gary Bernacsek, but if Draftany manuscript on the material was written then, it could 101 not be found. The CMN collections card notes that the specimen was referred to ?Pholiderpeton 102 bretonense by Wann Langston, though no formal description to this effect could be found in the 103 literature. Holmes (1984) briefly suggested that because the specimen is of Mississippian age, it 104 is more likely to be a proterogyrinid embolomere than Pholiderpeton. No further analysis of this 105 material has taken place since. 106 Here we provide the first thorough description of Bell’s material. It is hoped that this 107 work will contribute to our understanding of Carboniferous tetrapod diversity in Nova Scotia, 108 and farther abroad, as information from new and previously collected material is compiled and 109 analyzed. 110 111 GEOLOGICAL CONTEXT 112 5 https://mc06.manuscriptcentral.com/cjes-pubs Canadian Journal of Earth Sciences Page 6 of 38 113 The bones examined here were found in an eroded, ex situ horizon of freshwater 114 limestone from the Point Edward Formation of the Lower Mabou Group (Bell 1938). 115 Temporally, this pertains to the Arnsbergian of the Late Mississippian (Allen et al. 2014; 116 Waldron et al. 2017) (see Fig. 1C). The Point Edward Formation has been described previously 117 (e.g. Belt 1965; Belt 1968), but a detailed measured section of the formation has yet to be 118 published; however, a description was provided in a report by Mather et al. (1944), which was 119 also reproduced in a Nova Scotia field guide by Carroll et al.
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