Glyptotherium sp.
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publication ID |
https://doi.org/ 10.4202/app.00409.2017 |
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persistent identifier |
https://treatment.plazi.org/id/F8101767-FFB4-FFDD-FCA0-FF52FDBFFEB3 |
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treatment provided by |
Felipe |
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scientific name |
Glyptotherium sp. |
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Fig. 2 View Fig .
Material.—UNIRIO-PM 6231, osteoderms of dorsal carapace and caudal armor.
Description.— External morphology: The material analyzed consists of 118 isolated osteoderms belonging to one individual, from which 86 (72.9%) correspond to the dorsal carapace, while the others belong to the caudal armor. Except for some particular morphological features, most characters are shared with juvenile Glyptodon , as previously postulated (see Zurita et al. 2011b; Luna and Krapovickas 2011). The dorsal carapace osteoderms are mainly hexagonal, followed in frequency by the pentagonal shape, and others are approximately rectangular ( Fig. 2A–H View Fig ). The osteoderm diameter ranges 13.5–25.4 mm, with thickness 7.6–17.1 mm. The ratio between these two variables (diameter/thickness) ranges 1.31–2.46 ( Fig. 3 View Fig ), being in most of the osteoderms larger than those of juvenile Glyptodon (1.00–1.88). The external surface of each osteoderm is uniformly punctuated by small foramina that define a rough appearance. In some osteoderms, these foramina have the morphology of sinuous grooves. The central figure is circular and prominent, more elevated than the general surface and occupying from 20% in those from dorsal region (as those observed in morphotype 1 of the juvenile Glyptodon described by Luna and Krapovickas 2011) to the almost complete external surface in some osteoderms of the lateral regions. The central area of the central figure shows a clear depression in approximately 60% of the osteoderms; however, in those osteoderms where the central figure occupies most of the
10 15 20 25 30 35 40
45 50 55 60 65 70 Diameter (mm)
osteoderm, the surface is flat. Peripheral figures are absent or poorly defined in most of the osteoderms, except in those in which the radial and annular sulci are well defined; in these cases up to eight peripheral figures can be observed. In general, compared to juvenile Glyptodon , both central and peripheral figures are less prominent. The annular and radial sulci have a variable morphology: they are broad and shallow in those osteoderms in which the peripheral figures are scarcely defined, and narrower and deeper in those where the figures are better defined, although always less than in juvenile Glyptodon . At the intersection between the annular and radial sulci, it is possible to observe up to seven piliferous foramina with a diameter of about 1 mm ( Fig. 2A–G View Fig ). The articular area between osteoderms has some bony projections, although most osteoderms are eroded. The basal surface shows a mostly spongy aspect with respect to the external surface, being mainly concave, with small neurovascular foramina measuring less than 0.5 mm in diameter ( Fig. 2A View Fig ). These foramina are generally located in the central region; however, in some osteoderms, they are distributed throughout the whole surface and they may also be connected. The osteoderms of the border of the dorsal carapace have a prominent conical shape and their surfaces have a rough appearance ( Fig. 2I View Fig ).
The preserved caudal osteoderms correspond to proximal and distal rings. The former are approximately hexagonal in shape and the antero-posterior diameter ranges 17.8– 30.4 mm, while thickness ranges 6.6–11.9 mm. The posterior margin presents a weakly developed projection ( Fig. 2J View Fig ). In turn, the osteoderms of the distal rings are larger, with an antero-posterior diameter ranging 22.5–42.4 mm; the thickness ranges 14.9–31.3 mm, increased by the development of the projection of the posterior margin, which is pronounced and conical ( Fig. 2K View Fig ), although less acute than in the juvenile Glyptodon . The external surfaces of osteoderms of both morphotypes are uniformly punctuated, whereas the basal surface is characterized by large neurovascular foramina with a diameter ranging 0.5–1.0 mm, like the osteoderms of the dorsal carapace.
Statistical analysis: The cluster analysis ( Fig. 4) performed on the osteoderms of dorsal carapace from different specimens of Glyptodon and Glyptotherium resulted in two main clusters, differentiated mainly by the ontogenetic stage (juveniles and young adults/adults). In the former case, the clustering between specimens from the same genus is remarkable, grouping even the samples with scarce osteoderms (e.g., MAMM-PV 036). Within the young adults/ adults group, the two taxa are not clearly distincted as in the juvenile group. The adult specimen of Glyptotherium ( G. texanum ) from North America, described by Gillette et juvenile Glyptotherium (UNIRIO-PM 6231)
baby-juvenile Glyptotherium (Gillete et al. 2016)
juvenile Glyptodon (MCNC-PV 246)
juvenile Glyptodon (MAMM-PV 036)
adult Glyptotherium (Gillete et al. 2016)
young adult Glyptotherium (Gillete et al. 2016)
adult Glyptotherium (DGEO-UFPE)
young adult Glyptodon (MDVS-PV 064)
young adult Glyptodon (MCA 2013)
adult Glyptodon (MCNC-PV 284)
juvenile adult – adult young
0.00 0.18 0.36 0.54 0.72
al. (2016), and one group including an adult Glyptodon and two other smaller clusters are differentiated. The first of the latter is formed by the osteoderms of adult specimens of Glyptotherium ( G. cylindricum ) from South America and the young adult specimen of G. texanum , and the second by the young adult Glyptodon . The cluster analyses showed a high level of fit (cophenetic correlation index = 0.887). The Multivariate analysis of variance (MANOVA) shows that the main groups obtained in the cluster analysis were recognized to be statistically different (P <0.0001).
Histological analysis.—In general terms, all the osteoderms of Glyptotherium analyzed are composed of a cancellous internal core surrounded by a compact bone cortex. Nevertheless, they present some differences in the bone microanatomy. In the osteoderm of the medial zone of the dorsal carapace ( Fig. 5A View Fig ), the external cortex is thicker than the basal cortex. The cancellous bone in the inner core occupies approximately 40% of the osteoderm thickness. The transition between the compact and the cancellous bone is distinctive and the inter-trabecular spaces are large and show irregular shapes. Different from the osteoderm from the medial zone of the dorsal caparace, elements from lateral regions ( Fig. 5B, C View Fig ) exhibit a more compact appearance cancellous bone occupies less than 25% of the total area).
Also, the transition between compact and cancellous bone is gradual and the inter-trabecular spaces are comparatively smaller than the spaces observed in the dorsal osteoderm.
Despite the microanatomical differences reported between the sampled osteoderms, they share most of the histological features: the predominant extracellular cortical matrix is woven-fibred bone with a haphazard spatial arrangement of the collagen fibers and randomly distributed osteocyte lacunae ( Fig. 6A–D View Fig ); osteocyte lacunae are abundant and they have irregular or elongated shape ( Fig. 6B–E View Fig ); vascular spaces are mostly simple, with only a few primary osteons; and large neurovascular canals passing through the entire osteoderm are visible in all the sampled elements.
However, in the different regions of the osteoderms there are some histological particularities. In osteoderm II ( Fig. 5B View Fig ), the external cortex is characterized by abundant vascular canals of small size (0.05–0.1 mm), which are organized in a reticular pattern. The most external region exhibits several radially oriented vascular spaces, most of them open to the surface ( Fig. 6A, B View Fig ). The extent of vascularization in the external cortex is notably higher in this osteoderm than in the others, which exhibit a more compact appearance. In the marginal cortex of osteoderms I and II, the intrinsic fibers of the woven-fibered matrix tend to be slightly ordered and oriented toward the marginal surface in some areas ( Fig. 6C View Fig ). Vascular spaces in this region are larger than in the external and basal cortices (0.1–0.3 mm), giving a more porous (finely cancellous) aspect to this area. On the other hand, in the osteoderm III, which presents a more compact aspect, the intrinsic fibers and vascular spaces do not show a particular orientation in the marginal area ( Fig. 6D View Fig ). The inner core of all osteoderms is composed of cancellous bone, which results from local processes of resorption. Bony trabeculae mainly consist of remains of woven-fibered bone tissue. Centripetally deposed secondary lamellar bone is mostly absent around the resorption cavities ( Fig. 6E View Fig ). Finally, the basal cortex is only well preserved in the osteoderm III. Here, as occurs in the external cortex, the compact bone is composed of woven-fibered tissue ( Fig. 6F View Fig ). Bone cell lacunae are dense, have elongated or irregular shape, do not follow a particular orientation and show a rather convoluted organization. Vascular spaces are small and mostly longitudinally oriented.
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