diff --git a/data/03/FD/87/03FD87F90B2FFB6EFCA6F8B5FADDF974.xml b/data/03/FD/87/03FD87F90B2FFB6EFCA6F8B5FADDF974.xml new file mode 100644 index 00000000000..fb4aa92dbb5 --- /dev/null +++ b/data/03/FD/87/03FD87F90B2FFB6EFCA6F8B5FADDF974.xml @@ -0,0 +1,725 @@ + + + +Caudal autotomy in Mesosaurus tenuidens Gervais, 1865 under scrutiny and a surprising new pattern of vertebral organization in the mesosaur tail + + + +Author + +Piñeiro, Graciela +Departamento de Paleontología, Facultad de Ciencias, Iguá 4225, CP 11400, Montevideo (Uruguay) +fossil@fcien.edu.uy + + + +Author + +Ferigolo, Jorge +Seção de Paleontologia, Museu de Ciências Naturais, Secretaria do Meio Ambiente e Infraestrutura do Rio Grande do Sul (SEMA), Rua Salvador França, 1427 - 90 690 - 000, Porto Alegre, RS (Brazil) +jorgeferigolo@gmail.com + + + +Author + +Farias, Brodsky Dantas Macedo de +Programa de Pós-Graduação em Zoologia, Universidade Federal do Rio de Janeiro, Museu Nacional, Parque Quinta da Boa Vista, 20940040, Rio de Janeiro, RJ (Brazil) +brodskymacedo@gmail.com + + + +Author + +Demarco, Pablo Núñez +Instituto de Ciencias Geológicas, Facultad de Ciencias. Universidad de la República, Iguá 4225, CP 11400 Montevideo (Uruguay) +pnunez@fcien.edu.uy + + + +Author + +Laurin, Michel +Centre de Recherche en Paléontologie (CR 2 P), CNRS, MNHN, Sorbonne Université, Muséum national d’Histoire naturelle, Département Origines & Évolution, CP 38, 57 rue Cuvier, F- 75231 Paris cedex 05 (France) +michel.laurin@mnhn.fr + +text + + +Geodiversitas + + +2025 + +2025-01-23 + + +47 + + +2 + + +17 +38 + + + + +https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/geodiversitas2025v47a2.pdf + +journal article +10.5252/geodiversitas2025v47a2 +1638-9395 +urn:lsid:zoobank.org:pub:5A325306-2A4B-4655-8563-2365659051CF + + + + + +The “pygal” caudal segment of +Mesosaurus + + + + + +The first seven to ten caudal vertebrae (observed intraspecific numerical variations may reflect sexual dimorphism; see + +Shine +et al. +1999 + +) constitute a specialized string characterized by the presence of ribs firmly attached to the short transverse processes, the lack of haemal arches (chevrons) and also the absence of “fracture/suture planes”. However, in mesosaurs the last vertebrae of the pygal segment can carry an haemal arch. + + + +FIG +. 2. — + +Mesosaurus tenuidens +Gervais, 1865 + +from the Mangrullo Formation of Uruguay. Morphology of the last caudal vertebrae of the pygal-like segment: +A +, +B +, +FC-DPV +2206; +C +, +FC-DPV +2467; +D +, +FC-DPV +2231. These specimens show the presence of transverse processes and associated ribs ( +yellow arrowheads +), as well as a haemal arch ( +red arrowheads +) in the preserved vertebrae. They must consequently be part of the last of the “pygal-like” series because the anterior portion of that segment lack chevrons, whereas in the postpygal vertebrae, transverse processes are very poorly developed, if at all. Scale bars: 10 mm. + + + + +TABLE +1. — List of studied specimens in this work. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
+SMF-R +391 +GP/2E 444 +FC-DPV +1467 +
+SMF-R +387 +GP/2E 449 +FC-DPV +1461 +
+SMF-R +396 +GP/2E 480 +FC-DPV +2534 +
+SMF-R +397 +GP/2E 486 +FC-DPV +2037 +
+SMF-R +402 +GP/2E 5423 +FC-DPV +2061 +
+SMF-R +4470 +GP/2E 5603 +FC-DPV +2116 +
+SMF-R +4473 +GP/2E 5610 +FC-DPV +2242 +
+SMF-R +4476 +GP/2E 5633 +FC-DPV +2280 +
+SMF-R +4477 +GP/2E 5637 +FC-DPV +2318 +
+SMF-R +4478 +GP/2E 5647 +FC-DPV +2481 +
+SMF-R +4479 +GP/2E 5714 +FC-DPV +2506 +
+SMF-R +4480 +GP/2E 5740 +FC-DPV +2504 +
+SMF-R +4482 +GP/2E 5764 +FC-DPV +1006 +
+SMF-R +4484 +GP/2E 5796 +FC-DPV +1100 +
+SMF-R +4485 +GP/2E 5812a +FC-DPV +1441 +
+SMF-R +4488 +GP/2E 5862 +FC-DPV +2231 +
+SMF-R +4490 +GP/2E 596 +FC-DPV +2232 +
+SMF-R +4493 +GP/2E 62 +FC-DPV +S/N +
+SMF-R +4496 +GP/2E 63 big +FC-DPV +S/N +
+SMF-R +4497 +GP/2E 63 little +FC-DPV +S/N +
+SMF-R +4512 +GP/2E 639 +FC-DPV +S/N +
+SMF-R +4513 +1 adult +GP/2E 644 +FC-DPV +2483 +
+SMF-R +4513 1 young +GP/2E 646 +FC-DPV +2489 +
+SMF-R +4528 +GP/2E 65 +FC-DPV +1219 +
+SMF-R +4710 +GP/2E 653a +FC-DPV +2074 +
+SMF-R +4712 +GP/2E 657b +FC-DPV +1742 +
+SMF-R +4921 +GP/2E 660 +FC-DPV +1745 +
+SMF-R +5040c +GP/2E 666 +FC-DPV +2414 +
SMF-R-4934GP/2E 664 +FC-DPV +2526 +
SMF-R-4935GP/2E 669a, b, c +FC-DPV +2307 +
+AMNH +23794 +GP/2E 670 +FC-DPV +2046 +
+AMNH +23795 +GP/2E 674a +FC-DPV +2035 +
+AMNH +23796 +GP/2E 674b +FC-DPV +2282 +
+AMNH +23799 +GP/2E 675 +FC-DPV +2281 +
+PIMUZ +A-III 192 +GP/2E 680 +FC-DPV +2480 +
+PIMUZ +A-III 513 +GP/2E 683 +FC-DPV +2517 +
+PIMUZ +A-III 591 +GP/2E exhibition S/N A +FC-DPV +3622 +
+PIMUZ +A-III 801 +GP/2E exhibition S/N B +FC-DPV +3623 +
MN 4741GP/2E exhibition S/N C +FC-DPV +3620 +
+MCN-PV +0048 +GP/2E exhibition S/N D +FC-DPV +1427 +
+MCN-PV +0049 +GP/2E exhibition S/N E +FC-DPV +2397 +
+MCN-PV +2158 +GP/2E exhibition S/N F +FC-DPV +3621 +
+MCN-PV +2214 +GP/2E exhibition S/N G +FC-DPV +2396 +
+MCN-PV +S/N +GP/2E exhibition S/N H +FC-DPV +1061 +
+DNPM +4816 +GP/2E S/N +FC-DPV +1347 +
GP/2E 114aGP/2E S/NFAGRO 0004
GP/2E 232GP/2E S/NFAGRO 0002
GP/2E 26639MG 9639FAGRO 0005
GP/2E 272PF 3530FAGRO 0006
GP/2E 284PF IPL 220011/04 770FAGRO 0007
GP/2E 296PF (0407)-3528
GP/2E 3579PF_3529
+ + +This configuration follows the previously documented trait of basal stegocephalians, in which all presacral vertebrae, as well as the first caudals, bear ribs ( +Romer 1947 +). + + +The ribs of the first five caudal vertebrae are long, stout and bent posteriorly, as is also observed for instance in captorhinids ( +Heaton & Reisz 1980 +; +Berman & Reisz 1986 +), diadectids ( +Berman & Henrici 2003 +) and seymouriamophs ( + +Berman +et al. +1987 + +). From the sixth to the ninth or tenth vertebrae, the ribs abruptly decrease in size with the last three either bent anteriorly or pointing laterally ( +Fig. 1 +). These anteriormost nine to ten caudal vertebrae may be considered as the “pygal-like” segment, which in extant squamates possessing intravertebral autotomy, is associated with the insertion of the caudofemoralis longus muscle, and thus autotomy cannot occur in vertebrae of this segment which is typically characterized by the absence of fracture planes ( + +Ritzman +et al. +2012 + +). + + +Due to the presence of long and firmly fused ribs, a condition which is morphologically similar to that observed in the posterior dorsal vertebrae ( +Fig. 1 +), the ribs of the first ten caudal vertebrae of mesosaurs are often preserved parallel to the stratification, and thus, the vertebrae are mostly exposed in ventral or dorsal view, or in a frontal or antero/posterolateral view on rare occasions. This makes it challenging to confirm the existence of potential “fracture planes” (from now on referred to as “fracture/suture planes”) within these anteriomost caudal vertebrae. However, some fortuitous isolated vertebrae recognized as part of the “pygal segment” because they bear short transverse processes carrying a rib, show that there are no central fractures in these vertebrae at the midcentrum area. The presence of haemal arches in the last vertebrae of the “pygal-like” segment can also be confirmed by examining these isolated vertebrae ( +Fig. 2C, D +). + + + +The postpygal caudal segment of +Mesosaurus + + + +The putative “fracture/suture planes” described byMacDougall +et al. +(2020) as evidence for autotomy in mesosaurs are present in vertebrae placed posterior to the last vertebra of the pygal segment. This vertebral segment will be known as the postpygal string and is characterized by vertebrae with diminutive transverse processes in the cranialmost segments (or none whatsoever, farther caudally), and are predominantly preserved in lateral view ( +Fig. 3 +). + + +The mesosaurid “postpygal” segment is formed by at least 56 vertebrae, some of which articulate with short ribs, if at all, but this condition is gradually lost in caudal direction. Most of them also bear haemal arches (chevrons); and only the last five or six vertebrae near to the tip of the tail are simplified and lack neural spines or haemal arches ( +Fig. 3B, C +). + + +This distribution indicates that + +Mesosaurus + +possessed a long tail consisting of more than 60 vertebrae, a length similar to what has been suggested for + +Captorhinus +Cope, 1895 + +and all the basalmost stegocephalians ( +Romer 1947 +). Moreover, based on the described general pattern for mesosaur caudal vertebrae, it is possible to identify the relative position of isolated caudal vertebrae in the tail, and also determine if it is part of the “pygal-like” or the “post-pygal” series through the orientation of the transverse processes and ribs and by the presence/absence of haemal arches ( +Fig. 3 +). + + + + \ No newline at end of file diff --git a/data/03/FD/87/03FD87F90B38FB7AFF0FFEB3FD3AF974.xml b/data/03/FD/87/03FD87F90B38FB7AFF0FFEB3FD3AF974.xml new file mode 100644 index 00000000000..aec759417f4 --- /dev/null +++ b/data/03/FD/87/03FD87F90B38FB7AFF0FFEB3FD3AF974.xml @@ -0,0 +1,382 @@ + + + +Caudal autotomy in Mesosaurus tenuidens Gervais, 1865 under scrutiny and a surprising new pattern of vertebral organization in the mesosaur tail + + + +Author + +Piñeiro, Graciela +Departamento de Paleontología, Facultad de Ciencias, Iguá 4225, CP 11400, Montevideo (Uruguay) +fossil@fcien.edu.uy + + + +Author + +Ferigolo, Jorge +Seção de Paleontologia, Museu de Ciências Naturais, Secretaria do Meio Ambiente e Infraestrutura do Rio Grande do Sul (SEMA), Rua Salvador França, 1427 - 90 690 - 000, Porto Alegre, RS (Brazil) +jorgeferigolo@gmail.com + + + +Author + +Farias, Brodsky Dantas Macedo de +Programa de Pós-Graduação em Zoologia, Universidade Federal do Rio de Janeiro, Museu Nacional, Parque Quinta da Boa Vista, 20940040, Rio de Janeiro, RJ (Brazil) +brodskymacedo@gmail.com + + + +Author + +Demarco, Pablo Núñez +Instituto de Ciencias Geológicas, Facultad de Ciencias. Universidad de la República, Iguá 4225, CP 11400 Montevideo (Uruguay) +pnunez@fcien.edu.uy + + + +Author + +Laurin, Michel +Centre de Recherche en Paléontologie (CR 2 P), CNRS, MNHN, Sorbonne Université, Muséum national d’Histoire naturelle, Département Origines & Évolution, CP 38, 57 rue Cuvier, F- 75231 Paris cedex 05 (France) +michel.laurin@mnhn.fr + +text + + +Geodiversitas + + +2025 + +2025-01-23 + + +47 + + +2 + + +17 +38 + + + + +https://sciencepress.mnhn.fr/sites/default/files/articles/pdf/geodiversitas2025v47a2.pdf + +journal article +10.5252/geodiversitas2025v47a2 +1638-9395 +urn:lsid:zoobank.org:pub:5A325306-2A4B-4655-8563-2365659051CF + + + + + +COULD +THE +REVERSED +EMBOLOMEROUS +CONDITION +HAVE BEEN PRESENT (ALTHOUGH MASKED) IN OTHER EARLY AMNIOTES THAN + +MESOSAURUS + +? + + + + + +Despite the reverse embolomerous condition described herein for the mesosaur caudal vertebrae, the architectural con - struction of the tail does not differ substantially from that observed in most groups of early amniote taxa. For instance, the caudal region, when preserved, is composed of vertebrae possessing an intercentrum positioned anterior to the pleurocentrum, as also occurs in the dorsal vertebral segment. Moreover, the intercentrum of vertebrae positioned posterior to the proximal string (pygal) with a variable number of elements, carries the haemal arches even near the tip of the tail ( +Heaton & Reisz 1980 +). However, a rapid revision of the available previous literature (old and more recent) shows that the mesosaur configuration could have been present in the caudal vertebrae of other basal tetrapod taxa. Starting with the study of Everett +Olson (1936) +on the axial musculature in early tetrapods, we can see some clues: caudal vertebrae assigned to + +Diadectes +Cope, 1878 + +and + +Dimetrodon +Cope, 1878 + +are drawn in figure 8 of +Olson (1936: 280) +and their haemal arches are fused to the posterior end of the centrum. The same condition is apparently present in the synapsid + +Varanosaurus acutirostris +Broili, 1904 + +, according to +Sumida (1989: 155 +, fig. 4) and could have been developed in earlier taxa such as the seymouriamorphs, as documented by +Laurin (1996: 658 +, fig. 5) for + +Ariekanerpeton sigalovi +( +Tatarinov, 1968 +) + +, where four haemal arches are positioned (although not articulated) close to the posterior end of the respective centra. The fact that all four arches display the exactly same position with respect to the centra, makes it improbable that it results from a taphonomic process. + + +In basal diapsids, there seems to be an anterior “pygal segment”, although it is shorter than that observed in + +Mesosaurus + +. In + +Petrolacosaurus +Lane, 1945 + +, however, intercentra are described in this anteriormost caudal segment, as well as the corresponding haemal arches associated to the third or fourth vertebrae ( +Peabody 1952 +; +Reisz 1981 +). Furthermore, the possibility of development of autotomy was suggested for + +Araeoscelis +Williston, 1910 + +, although it was only based on the presence of an isolated ossified, roughly conical structure of uncertain identity, bearing strongly marked ribs as a kind of superficial ornamentation, a morphology very similar to what is observed in regenerated tails of some squamates (see +Vaughn 1955 +: pl. 2). + + +Another interesting case is that of + +Dolabrosaurus aquatilis +Berman & Reisz, 1992 + +, a drepanosaurid diapsid from the Upper Triassic of North America, where the haemal arches can be fused to both the posterior and the anterior end of the caudal vertebrae ( +Berman & Reisz 1992 +), This suggests a reverse embolomerous condition in the more anterior vertebrae, but a return to the normal configuration at the posterior region. More recently, + +Hypuronector limnaios +Colbert & Olsen, 2001 + +, another related drepanosaurid, was shown to display the reverse embolomerous condition. In this last taxon, the fusion of the haemal arches to a trapezoid-like intercentrum is more evident, and a putative fracture plane can be also observed at the middle of the centrum in some of the preserved caudal vertebrae (see +Colbert & Olsen 2001 +: fig. 9C). The hypothesis of autotomy suggested for captorhinids (i.e., + +LeBlanc +et al. +2018 + +) is difficult to ascertain because of the fragmentary nature of the analyzed specimens, as explained above. But taking into account the obvious presence of fracture-suture lines in most of the caudal vertebrae shown by + +LeBlanc +et al. +2018 + +) and the articulation of the haemal arches to the posterior end of the centrum observed in the string of caudal vertebrae belonging to a juvenile individual shown ( + +LeBlanc +et al. +2018 + +: fig. 4b), it may be not surprising that capthorinids, diadectids, seymouriamorphs and some synapsids may have had the reverse embolomerous condition, but it was not previously detected. + + +THE +INTENSE +CONTROVERSY +ABOUT +MESOSAUR +RELATIONSHIPS +IS +NOT +OVER + + +Although mesosaurs are most frequently considered to be specialized aquatic amniotes ( +Araújo 1977 +; +Oelofsen 1981 +; +Modesto 1996 +, +1999 +; among others), they display a combination of primitive and derived characters, perhaps associated to a progressive although incomplete adaptation of an aquatic lifestyle ( + +Núñez Demarco +et al. +2018 + +). However, the extent of such an adaptation in mesosaurs is not completely clear. It is true that some of the mesosaur features reveal limited capability for terrestrial locomotion, a trait also observed in numerous Carboniferous stegocephalians, such as + +Gephyrostegus +Jaekel, 1903 + +and + +Westlothiana +Smithson & Rolfe, 1990 + +( +Smithson 1989 +; + +Piñeiro +et al. +2016 + +; +Herbst & Hutchinson 2018 +). The last two taxa, despite being outside Amniota, exhibit terrestrial specializations like the development of an amniotic tarsus with precursor bones arranged in the normal position of the astragalus and calcaneum but showing different stages of fusion with the intermedium and the fibulare (see figure +10 in + +Piñeiro +et al. +2016 + +). But mesosaurs may not have developed capabilities to an exclusively fully aquatic lifestyle, and they presumably inhabited shallow, plausibly hypersaline water. This is suggested by the the presence of pachyosteosteosclerosis in this taxon, a condition which was suggested to be developed in animals adapted to shallow aquatic environments ( +Houssaye 2009 +; +Canoville & Laurin 2010 +). This hypothesis could be linked to the progressive draught of the Mangrullo and Irati seas, as was suggested in previous papers based on solid evidence suggesting an increasing of the water salinity and the deposition of evaporitic gypsum crystals ( + +Piñeiro +et al. +2012b + +, +2025 +; + +Petri +et al. +2022 + +). + + +Transitional features in mesosaurs have been interpreted as suggestive of possible affinities with other aquatic to semiaquatic taxa, such as the recumbitrostran microsaur lepospondyls ( + +Piñeiro +et al. +2016 + +; + +Núñez Demarco +et al. +2022 + +), which were recently considered by some authors as being part of the stem of Amniota ( + +Pardo +et al. +2017 + +). However, affinities between mesosaurs and recumbirostran microsaurs may be unlikely given that extensive phylogenetic analyses recovered the former as amniotes, close to the base of +Sauropsida +or at the base of Parareptilia. Furthermore, the position of recumbirostran microsaurs has been far more controversial; they are stem-amphibians according toMarjanović & Laurin (2019), but crown-amniotes according to + +Pardo +et al. +(2017) + +and + +Mann +et al. +(2023) + +, among others. + + +However, mesosaurs have retained many ancestral characters, including: 1) the presence of five phalanges in the fifth pedal toe, whereas just four or three are observed in most tetrapods and basal amniotes ( + +Hylonomus +Dawson, 1860 + +pes, for instance, is reconstructed with three phalanges at the V toe; + +Clack +et al. +2022 + +); 2) a longer metatarsal V. Among basal stegocephalians, a long toe V, which is the longest of the pedal series, is a condition only present in the anthracosaur + +Silvanerpeton miripedes +Clack, 1994 + +( +Clack 1994 +; +Ruta & Clack 2006 +) and the embolomerous + +Archeria +Case 1915 + +(see + +Clack +et al. +2022 + +). While this character can be autapomorphic for mesosaurs or it can be an adaptation to an aquatic (or semi-aquatic) lifestyle, it is only shared with basal taxa; and 3) mesosaurs displayed an isometric growth pattern, a condition that could be considered of uncertain polarity, given that it is documented in few taxa, but that currently is only observed in basal or stem amniote taxa. The isometry is particularly marked at the level of limbs, as observed in microsaurs and other lepospondyls, sharply contrasting with the allometric pattern characterizing other early amniotes ( + +Núñez Demarco +et al. +2022 + +). + + +According to a recent taxonomic review of +Mesosauridae +, + +Mesosaurus tenuidens + +is the only valid species ( + +Piñeiro +et al. +2021 + +; but see also +Verrière & Fröbisch 2022 +), reducing even more the already low diversity in early tetrapods observed during the lifespan of mesosaurs in Southern Gondwana. Whereas mesosaur phylogenetic affinities remain controversial, a putative relationship between mesosaurs and the basalmost amniote groups seems possible, even at the level of the amniote stem group ( + +Piñeiro +et al. +2016 + +; + +Núñez Demarco +et al. +2022 + +, but see also + +Pardo +et al. +2017 + +). + + +Other hypotheses have suggested a position on the reptilian stem ( +Laurin & Reisz 1995 +; +Laurin & Piñeiro 2017 +) or at the base of Parareptilia ( +Modesto 2006 +), but they would have to be revised by including recently published new data about mesosaur anatomy, ontogeny, taxonomy and physiology. + +Indeed, mesosaurs have always appeared as a very basal group in the main known phylogenetic trees on amniote relationships, either as basal sauropsids or as basal parareptiles (regarding that the later are also basal sauropsids), and that signal should be taken into account in future studies. + + + \ No newline at end of file